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Article

Assessing the Motile Fauna of Eastern Mediterranean Marine Caves

by
Markos Digenis
1,*,
Michail Ragkousis
2,
Charalampos Dimitriadis
3,
Stelios Katsanevakis
2 and
Vasilis Gerovasileiou
1,4,*
1
Department of Environment, Faculty of Environment, Ionian University, 29100 Zakynthos, Greece
2
Department of Marine Sciences, University of the Aegean, University Hill, 81100 Mytilene, Greece
3
National Marine Park of Zakynthos, Eleftheriou Venizelou 1, 29100 Zakynthos, Greece
4
Institute of Marine Biology, Biotechnology and Aquaculture (IMBBC), Hellenic Centre for Marine Research (HCMR), 71500 Heraklion, Greece
*
Authors to whom correspondence should be addressed.
Fishes 2025, 10(8), 383; https://doi.org/10.3390/fishes10080383
Submission received: 11 May 2025 / Revised: 14 July 2025 / Accepted: 24 July 2025 / Published: 5 August 2025
(This article belongs to the Section Biology and Ecology)
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Abstract

Although marine caves are among the most species-diverse habitats in the Mediterranean Sea, most available studies have focused on their sessile fauna. This study provides the first quantitative assessment of motile fauna in 27 marine caves across four geographical subareas of the Aegean and Ionian Seas, using a rapid assessment visual census protocol, applied through 3 min time transects in each ecological cave zone. Multivariate analysis revealed that the motile community structure of the cave entrance was differentiated from that of the semidark and dark zones. Deeper caves were distinct from shallower ones while caves of the east Aegean differed from those around Crete Island. A total of 163 taxa were recorded, 27 of which are reported herein for the first time in marine caves of the eastern Mediterranean Sea, while three species (two native and one introduced) are recorded in Greek waters for the first time, enriching our knowledge on the permanent and occasional cave residents. Seventeen species were introduced, comprising more than half of the total fish abundance in the southeasternmost cave. Our limited knowledge of the motile fauna of Mediterranean marine caves coupled with the continued spread of introduced species highlights the urgent need for monitoring and conservation actions, especially within marine protected areas.
Keywords:
motile species; introduced species; visual census; sea caves; ecological zone; Aegean Sea; Ionian Sea; Greece
Key Contribution: A visual census protocol can be applied to rapidly assess the motile community structure of eastern Mediterranean marine caves, a species-diverse habitat differentiated depending on the depth and geographic area.

1. Introduction

The rocky coasts of the Mediterranean Sea are characterized by the presence of numerous marine caves, which can be either semi-submerged or entirely submerged [1]. Marine caves rank among the richest habitats in terms of biodiversity in the Mediterranean Sea, with approximately 2400 taxa reported from 350 caves (mostly semi-submerged and/or shallow) documented to date [2].
Most studies on marine cave fauna have focused on sessile communities, e.g., [3,4,5,6,7,8]. Although efforts to study motile fauna in Mediterranean marine caves date back to the 1960s [9,10], most available studies are either qualitative or limited to specific taxonomic groups [11,12,13,14,15,16,17,18,19]. Recent reviews on marine cave fishes and crustaceans point to a rich diversity of motile species that find refuge in these habitats [20,21,22]. In addition, the exploration of marine caves in previously under-studied areas has led to several new records of rarely observed species [23,24,25], suggesting that marine cave biodiversity is greater than previously estimated.
However, most studies on motile cave fauna have been conducted in the western and central Mediterranean [13,26,27,28,29,30], leaving significant knowledge gaps in the eastern and southern sectors of the basin. These areas are experiencing rapid ecological shifts as they have been impacted by mass mortality events and biological invasions over the past decades [31,32]. Marine caves are threatened by multiple global and local pressures [33], such as the effects of climate change, coastal infrastructure development, unregulated tourism, and marine pollution [1,2,34,35]. Recent studies have highlighted the growing numbers of introduced species in marine caves of the eastern and southern Mediterranean [36,37,38], with the term “introduced species” being used to include non-indigenous, cryptogenic (species with unclear native or introduced origin), crypto-expanding (species with unclear natural or human-mediated expansion), and species with questionable status [37]. Specifically, within only eight years, the number of introduced species inhabiting Mediterranean marine caves has more than doubled [37]. Approximately half of these species (60 species or 47.6%) are motile, with the majority recorded in the eastern basin (50), particularly in the Levantine (45) and Aegean (20) ecoregions. Most of these introduced species originate from the Indo-Pacific and have entered the Mediterranean Sea through the Suez Canal [37]. In light of such abrupt ecological changes, there is an urgent need to obtain quantitative data on the population structure of motile fauna in eastern Mediterranean caves, to better understand the potential responses of native biodiversity to cumulative pressures [20]. Systematic sampling in such environments is particularly challenging due to sharp ecological gradients, limited visibility, and time and space constraints of cave habitats [34,39]. Marine caves are characterized by steep environmental gradients, such as the decrease in light levels and hydrodynamism, accompanied by increased oligotrophy towards the inner zones, caused by their unique topographic and morphological features [40,41]. These gradients structure the cave biota into three distinct ecological zones: the well-lit entrance zone (CE), dominated by macroalgae (mostly rhodophytes); the intermediate semidark zone (SD), dominated by sciaphilic animals; and the inner dark zone (D), where both diversity and biotic cover diminish [2]. While such environmental gradients are primarily known to influence sessile communities, increasing evidence indicates notable spatial variability among motile taxa, particularly fish assemblages. Most fish species tend to occur in the entrance and semidark zones of caves, whereas only a limited number of larger or hyperbenthic species, along with small epibenthic and cryptobenthic fishes, are typically found in the innermost dark sections ([22] and references therein).
Beyond this small-scale heterogeneity, cave assemblages significantly differ among Mediterranean biogeographic regions, supporting the view that caves are highly fragmented habitats, functioning as isolated “islands” that host unique and often isolated populations [42].
In this study, a novel visual census protocol was developed and applied to rapidly and quantitatively assess the motile faunal community in 27 marine caves of the eastern Mediterranean Sea. Specifically, we tested whether motile community structure (i) shows high similarity between equivalent ecological zones across different caves; (ii) differs significantly among geographic subareas and among caves within each subarea; and (iii) exhibits similar patterns for species with high (e.g., fish) and low mobility (e.g., crustaceans, mollusks). Given the high numbers of introduced fishes observed in the studied caves, we also investigated whether the ratios of introduced to native fishes (in terms of both species richness and abundance) correspond with the known southeast-to-northwest gradient observed in the Mediterranean Sea [31]. In addition, a broader assessment of motile biodiversity in the studied caves is presented, combining visual census data with qualitative sampling, being the first large-scale study of this kind in the most vulnerable sector of the Mediterranean basin.

2. Materials and Methods

2.1. Study Area

Twenty-seven marine caves in the eastern Mediterranean, distributed across ten islands and spanning four geographical subareas of Greece (east Aegean, central Aegean, Ionian Sea and Crete), were surveyed for their motile fauna during different sampling periods between May and December of the years 2020 and 2022 (Figure 1, Table 1) by a single observer during a single dive per cave. Eleven of these caves had fully submerged entrances, whereas sixteen had semi-submerged entrances. The maximum entrance depth ranged from 3.5 to 32 m for submerged caves and from 3.5 to 20 m for semi-submerged ones; cave lengths ranged from 11 to 163 m (Table 1). All studied caves had an entrance and a semidark zone, while eleven also featured a dark zone. Most of the studied caves (20) are located within national parks (National Marine Park of Zakynthos and National Park of Samaria) and/or protected areas of the European Union’s Natura 2000 network (Table 1), including nineteen designated as Habitats Directive Sites and two as Birds Directive Sites.

2.2. Sampling

A visual census protocol was developed and applied to rapidly and efficiently assess the motile faunal communities in marine caves. According to this protocol, a single scientist/scientific diver recorded both species richness and abundance of all observed motile taxa within a 3 min visual survey transect conducted in each of the three ecological cave zones (i.e., entrance, semidark, and dark) while SCUBA diving. Motile species were recorded on cave walls, crevices, overhangs, the cave bed, and ceiling (when present in submerged caves) within each zone. Basic topographic and morphological features of each cave (e.g., submersion level, depth) were also recorded after the visual census. This protocol was designed for non-decompression single-dive surveys in marine caves up to a depth of 30 m, considering the logistical constraints of diving time at such depths (16 to 20 min maximum). This approach allowed for a safe exit from inner cave zones under a precautionary approach and standardized research effort across caves with different topographic features (i.e., depth and varying extent of ecological zones). Overall, a maximum time of nine minutes (three minutes per ecological zone) is required for each survey, with less time needed in caves lacking a dark zone. For deeper caves or those with complex morphology, supplemental diving rules need to be considered.
In the present study, the visual census protocol was consistently applied once in each cave, by the same scientific diver (M.D.), who always entered first, during morning to mid-day hours, to minimize disturbance to the motile fauna and ensure consistency across observations. A second diver accompanied the lead, being responsible for maintaining time intervals between zones and ensuring diving safety. Following the visual census, the team of diving scientists recorded the presence and abundance of motile taxa observed outside the time transects. They also collected qualitative samples for morphological identification (approximately 76 specimens) and close-up photos when in situ identification was not feasible (e.g., for small-sized taxa), to produce a biodiversity inventory for the studied caves. Conspicuous taxa (mostly fishes) were identified during the dives, while small-sized taxa (e.g., mollusks) were mainly identified from collected samples.

2.3. Statistical Analyses

Data on the abundance of all motile taxa recorded within time transects were square-root transformed, and a triangular similarity matrix was generated using the Bray–Curtis similarity index [44]. A two-way non-parametric multivariate analysis of variance (PERMANOVA) [45] was performed, with the factor ‘Cave’ (random, 27 levels—see Table 1 for site names) nested within the factor ‘Subarea’ (fixed, 4 levels—Ionian, Crete, east Aegean, central Aegean). To visualize multivariate patterns, non-metric multidimensional scaling (nMDS) and cluster analysis were applied. The SIMPROF test was used to examine the null hypothesis of no meaningful clustering among samples (significance level: 5%, confidence level: 95%) [44,46]. A Spearman rank order correlation was used to investigate the monotonic relationship of species abundance with the resulting multivariate community patterns. Species that exhibited correlation values greater than 0.6 (and p < 0.05) were overlaid onto the nMDS plot as vectors [47,48]. Similarity percentages (SIMPER) analysis was performed to estimate the contribution of individual taxa to dissimilarity patterns [47]. PERMANOVA, nMDS, and SIMPER analyses were also independently conducted for fish and invertebrate taxa, following the above-mentioned design. If there was no significant variation in community structure among caves within the same geographic subarea, a one-way PERMANOVA was applied, based on pooled abundance data from caves within each subarea to examine potential differences in community structure across the three cave ecological zones. Multivariate, non-parametric resemblance analysis was performed using the software PRIMER-6 [48] with the PERMANOVA+ add-on package [49].

3. Results

3.1. Species Richness

Within the time transects, 70 motile taxa belonging to seven phyla were identified: Chordata (37), Arthropoda (14), Echinodermata (11), Mollusca (4), Annelida (2), Platyhelminthes (1), and Cnidaria (1). These were identified to the species (55), genus (9), family (4), and class (2) levels by a single observer during a single dive per cave (Table 2).
The taxa recorded within transects comprised 77.8% of the total motile fauna recorded in situ; an additional 20 taxa were observed out of time transects (Table 2). Osteichthyes represented more than half (52.8%) of the taxa which were recorded within transects. At a cave level, the number of motile taxa recorded in transects ranged from 6 to 18, representing 33.3% to 91.7% of the total in situ observed fauna (Figure S1), with a mean of 61.2% ± 2.8 (SE).
The highest number of taxa was recorded in the semidark zone (45), followed by the cave entrance (42), and the dark zone (30). Osteichthyes were the most frequently observed group in all three zones, representing 73.8% of the motile fauna in the cave entrance, 55.5% in the semidark, and 36.6% in the dark zone. The most common taxa were the cardinal fish Apogon imberbis (present in all caves), followed by the polychaete Hermodice carunculata (in 22 caves), the sea urchin Arbacia lixula and holothurians (each recorded in 21 caves).
Species richness per zone (recorded within transects) ranged from 2 to 12 taxa, comprising 16.7% to 100% of the total taxa observed in situ in each respective zone (mean 65.1% ± 3.3 SE, Figure S2). The lowest percentage values (16.7%) were observed in the semidark zones of Blue 2 and Polyaigos caves, while the highest values (100%) were observed in the entrance zones of six caves (Sulfur 1, Sulfur 2, Marathia, Achata 2, Seal’s 2 and Polyaigos), the semidark zone of one cave (Alikes), and the dark zone of two caves (Sulfur 2 and Cathedral) (Table 3). On average, the proportion of motile taxa recorded within transects to the total recorded taxa was highest in the entrance zone (75.1%), followed by the dark (64.4%) and the semidark zone (49.7%) (Table 3).

3.2. Abundance

The abundance of motile taxa recorded within transects per cave ranged from 14 to 2411 individuals, comprising between 35.5% and 99.5% of all individuals observed in situ (mean 76.6% ± 4.1 SE, Figure S3). Osteichthyes were the most abundant group comprising 64.2% of all individuals recorded, followed by Arthropoda (32.3%), Echinodermata (2.1%), and Annelida (1.2%). The remaining groups (Mollusca, Cnidaria, and Platyhelminthes) comprised 0.2% of the total abundance. Apogon imberbis was the most abundant fish in most caves (19), followed by atherinids (6) and Anthias anthias, which dominated in the two deepest caves (Shrimp and Neptune’s cave). The semidark zone often presented the highest transect abundance (in 15 caves). In total, the highest transect abundance in a single cave was observed in the dark zone (up to 1311 individuals of mostly Plesionika narval), followed by the semidark zone (1054 individuals of mostly Atherina spp.) and the cave entrance (324 individuals of mostly Anthias anthias). The proportion of transect-recorded abundance relative to the total abundance was highest in the dark zone (81.6%), followed by the entrance (77.9%) and the semidark zone (72.6%) (Table 3, Figure S4).

3.3. Resemblance Patterns

Two-way PERMANOVA analysis results indicated that motile community structure significantly differed among the geographic subareas (pseudo-F = 1.622; df = 3; p = 0.021); no significant differences were evident among individual caves within subareas (pseudo-F = 1.154; df = 23; p = 0.083). Pairwise comparisons showed significant differentiation between the east Aegean and Crete (t = 1.428, p = 0.032), with Apogon imberbis, Atherina spp., Chromis chromis, Plesionika narval, Hermodice carunculata, and Arbacia lixula contributing 52.2% to this differentiation (Tables S1–S3). The average similarity within each area ranged from 20.3% for the east Aegean to 27.3% for the central Aegean. Within all geographic areas, significant differences in community structure were detected between the cave entrance and the inner semidark and dark zones (see Tables S4–S7) (Ionian: pseudo-F = 2.682, df = 2, p = 0.001; Crete: pseudo-F = 2.690, df = 2, p = 0.002; east Aegean: pseudo-F = 1.699, df = 2, p = 0.041; central Aegean: pseudo-F = 2.192, df = 2, p = 0.038). Apogon imberbis and Plesionika narval showed the strongest positive associations with the semidark and dark cave zones, while Coris julis, Chromis chromis, Thalassoma pavo, and Arbacia lixula were more closely associated with the cave entrance (Figure 2).
Cluster analysis indicated that the species composition of the deepest caves with fully submerged entrance (Neptune’s and Shrimp cave) was significantly different from all other caves (Figure 3), with an average dissimilarity of 80.3% (SIMPER and SIMPROF analyses). This differentiation was primarily driven by the shrimp Plesionika narval (45.4%) and the fish Anthias anthias (10.5%).
SIMPER analysis also showed that Neptune’s and Shrimp caves had an average similarity of 64.8%, mainly due to P. narval (72.1% contribution), while all other caves clustered with an average similarity of 31.9%, primarily due to A. imberbis (52.3% contribution). When fish and motile invertebrate taxa were analyzed separately, two-way PERMANOVA indicated no differentiation among the four subareas or between the caves within the same geographic subarea. However, for fish species alone, PERMANOVA detected significant differences in community structure between the entrance and inner zones across all subareas: Ionian: pseudo-F = 3.139, df = 2, p = 0.001; Crete: pseudo-F = 3.314, df = 2, p = 0.004; central Aegean: pseudo-F = 2.941, df = 2, p = 0.034; east Aegean: pseudo-F = 2.101, df = 2, p = 0.030 (see Tables S8–S13). Apogon imberbis was predominantly associated with inner zones, whereas Coris julis, Chromis chromis, and Thalassoma pavo were mostly related to the cave entrance (Figure 4).

3.4. Biodiversity Inventory

A total of 163 motile taxa belonging to seven phyla were identified: Chordata (57), Mollusca (51), Arthropoda (30), Echinodermata (18), Platyhelminthes (4), Annelida (2), and Cnidaria (1). These were identified to the species (142), genus (9), family (9), superfamily (1), class (1), and order (1) levels, and included 12 protected and 17 introduced species (Table 4). These taxa were identified visually during the time transects and through out-of-transect in situ observations (1–3 dives per cave and 1–3 observers per dive), and by examining the supplementary collected material (photos and samples).
The total number of motile species recorded per cave ranged from 9 to 54 taxa. The Lithistid cave in southern Crete and Seal’s 3 cave on Samos Island (eastern Aegean) were the most species-rich sites, with 54 and 49 taxa recorded, respectively.
Table 4. Complete list of all motile taxa recorded in the studied caves by major taxonomic group (in bold). *: Introduced species; ǂ: Protected species; °: species morphologically identified with collected specimens; f: species recorded for the first time in eastern Mediterranean marine caves (black colored) and in Mediterranean marine caves (orange colored). Colored circles indicate the presence of taxa in different ecological zones (white: entrance zone; gray: semidark zone; black: dark zone); numbers in brackets indicate the number of caves where each taxon was recorded; blue triangles in squares indicate the geographical subarea each taxon was recorded (left: Ionian; bottom: Crete; right: east Aegean; top: central Aegean).
Table 4. Complete list of all motile taxa recorded in the studied caves by major taxonomic group (in bold). *: Introduced species; ǂ: Protected species; °: species morphologically identified with collected specimens; f: species recorded for the first time in eastern Mediterranean marine caves (black colored) and in Mediterranean marine caves (orange colored). Colored circles indicate the presence of taxa in different ecological zones (white: entrance zone; gray: semidark zone; black: dark zone); numbers in brackets indicate the number of caves where each taxon was recorded; blue triangles in squares indicate the geographical subarea each taxon was recorded (left: Ionian; bottom: Crete; right: east Aegean; top: central Aegean).
Phylum CnidariaGastropoda (cont.)
ScyphozoaPolycera quadrilineata (O. F. Müller, 1776) f Fishes 10 00383 i001 (1) Fishes 10 00383 i002
Pelagia noctiluca (Forsskål, 1775) f Fishes 10 00383 i003 (7) Fishes 10 00383 i004Pseudofusus rolani (Buzzurro & Ovalis, 2005) ° f Fishes 10 00383 i005 (1) Fishes 10 00383 i006
Phylum PlatyhelminthesSimiliphora similior (Bouchet & Guillemot, 1978) Fishes 10 00383 i007 (1) Fishes 10 00383 i008
Planocera sp. ° Fishes 10 00383 i009 (1) Fishes 10 00383 i010Spurilla neapolitana Bergh, 1889 f Fishes 10 00383 i011 (1) Fishes 10 00383 i012
Prostheceraeus moseleyi Lang, 1884 f Fishes 10 00383 i013 (2) Fishes 10 00383 i014Steromphala rarilineata (Michaud, 1829) ° f Fishes 10 00383 i015 (1) Fishes 10 00383 i016
Monobiceros langi Faubel, 1984 ° f Fishes 10 00383 i017 (5) Fishes 10 00383 i018Tarantinaea lignaria (Linnaeus, 1758) f Fishes 10 00383 i019 (2) Fishes 10 00383 i020
Thysanozoon brocchii (Risso, 1818) Fishes 10 00383 i021 (1) Fishes 10 00383 i022Trapania lineata Haefelfinger, 1960 ° Fishes 10 00383 i023 (1) Fishes 10 00383 i024
Phylum MolluscaTritia incrassata (Strøm, 1768) f Fishes 10 00383 i025 (1) Fishes 10 00383 i026
CephalopodaTylodina perversa (Gmelin, 1791) ° Fishes 10 00383 i027 (1) Fishes 10 00383 i028
Octopus vulgaris Cuvier, 1797 f Fishes 10 00383 i029 (2) Fishes 10 00383 i030Umbraculum umbraculum ([Lightfoot], 1786) Fishes 10 00383 i031 (7) Fishes 10 00383 i032
Sepia officinalis Linnaeus, 1758 f Fishes 10 00383 i033 (3) Fishes 10 00383 i034Bivalvia
GastropodaPectinidae sp. Fishes 10 00383 i035 (1) Fishes 10 00383 i036
Aplus gaillardoti (Puton, 1856) ° f Fishes 10 00383 i037 (2) Fishes 10 00383 i038Phylum Annelida
Aplus scacchianus (R. A. Philippi, 1844) ° Fishes 10 00383 i039 (1) Fishes 10 00383 i040Polychaeta
Berthella aurantiaca (Risso, 1818) ° f Fishes 10 00383 i041 (1) Fishes 10 00383 i042Bonellia viridis Rolando, 1822 Fishes 10 00383 i043 (10) Fishes 10 00383 i044
Berthella ocellata (Delle Chiaje, 1830) f Fishes 10 00383 i045 (2) Fishes 10 00383 i046Hermodice carunculata (Pallas, 1766) Fishes 10 00383 i047 (22) Fishes 10 00383 i048
Berthellina edwardsii (Vayssière, 1897) ° f Fishes 10 00383 i049 (1) Fishes 10 00383 i050Phylum Arthropoda
Bittium sp. Fishes 10 00383 i051 (5) Fishes 10 00383 i052Malacostraca
Bittium latreillii (Payraudeau, 1826) ° Fishes 10 00383 i053 (2)Fishes 10 00383 i054Brachycarpus biunguiculatus (Lucas, 1846) Fishes 10 00383 i055 (15) Fishes 10 00383 i056
Calliostoma laugieri (Payraudeau, 1826) ° Fishes 10 00383 i057 (2) Fishes 10 00383 i058Calcinus tubularis (Linnaeus, 1767) Fishes 10 00383 i059 (1) Fishes 10 00383 i060
Caloria elegans (Alder & Hancock, 1845) f Fishes 10 00383 i061 (3) Fishes 10 00383 i062Carupa tenuipes Dana, 1852 * ° Fishes 10 00383 i063 (5) Fishes 10 00383 i064
Cerithium scabridum R. A. Philippi, 1848 * ° Fishes 10 00383 i065 (2) Fishes 10 00383 i066Dardanus calidus (Risso, 1827) Fishes 10 00383 i067 (5) Fishes 10 00383 i068
Cerithiidae sp. Fishes 10 00383 i069 (5) Fishes 10 00383 i070Dromia personata (Linnaeus, 1758) ° Fishes 10 00383 i071 (11) Fishes 10 00383 i072
Charonia seguenzae (Aradas & Benoit, 1871) ǂ Fishes 10 00383 i073 (2) Fishes 10 00383 i074Galathea strigosa (Linnaeus, 1761) Fishes 10 00383 i075 (1) Fishes 10 00383 i076
Clanculus corallinus (Gmelin, 1791) ° Fishes 10 00383 i077 (4) Fishes 10 00383 i078Gonioinfradens giardi (Nobili, 1905) * f Fishes 10 00383 i079 (2) Fishes 10 00383 i080
Clanculus cruciatus (Linnaeus, 1758) ° Fishes 10 00383 i081 (2) Fishes 10 00383 i082Herbstia condyliata (Fabricius, 1787) ° Fishes 10 00383 i083 (1) Fishes 10 00383 i084
Conomurex persicus (Swainson, 1821) * Fishes 10 00383 i085 (1) Fishes 10 00383 i086Herbstia spp. Fishes 10 00383 i087 (7) Fishes 10 00383 i088
Cratena peregrina (Gmelin, 1791) f Fishes 10 00383 i089 (1) Fishes 10 00383 i090Hemimysis spp. ° Fishes 10 00383 i091 (8) Fishes 10 00383 i092
Dendrodoris grandiflora (Rapp, 1827) f Fishes 10 00383 i093 (1) Fishes 10 00383 i094Lysmata nilita Dohrn & Holthuis, 1950 Fishes 10 00383 i095 (2) Fishes 10 00383 i096
Diaphorodoris papillata Portmann & Sandmeier, 1960 f Fishes 10 00383 i097 (1) Fishes 10 00383 i098Lysmata seticaudata (Risso, 1816) Fishes 10 00383 i099 (3) Fishes 10 00383 i100
Episcomitra cornicula (Linnaeus, 1758) ° Fishes 10 00383 i101 (2) Fishes 10 00383 i102Maja sp. Fishes 10 00383 i103 (1) Fishes 10 00383 i104
Ergalatax junionae Houart, 2008 * ° Fishes 10 00383 i105 (1) Fishes 10 00383 i106Mysida spp. Fishes 10 00383 i107 (21) Fishes 10 00383 i108
Euthria cornea (Linnaeus, 1758) ° Fishes 10 00383 i109 (2) Fishes 10 00383 i110Pagurus anachoretus Risso, 1827 Fishes 10 00383 i111 (5) Fishes 10 00383 i112
Facelina annulicornis (Chamisso & Eysenhardt, 1821) ° f Fishes 10 00383 i113 (1) Fishes 10 00383 i114Pagurus chevreuxi (Bouvier, 1896) ° Fishes 10 00383 i115 (1) Fishes 10 00383 i116
Facelina rubrovittata (A. Costa, 1866) f Fishes 10 00383 i117 (1) Fishes 10 00383 i118Paguroidea spp. Fishes 10 00383 i119 (10) Fishes 10 00383 i120
Felimare gasconi (Ortea, 1996) ° f Fishes 10 00383 i121 (1) Fishes 10 00383 i122Palaemon serratus (Pennant, 1777) Fishes 10 00383 i123 (9) Fishes 10 00383 i124
Felimida krohni (Vérany, 1846) f Fishes 10 00383 i125 (1) Fishes 10 00383 i126Palinurus elephas (Fabricius, 1787) ǂ Fishes 10 00383 i127 (1) Fishes 10 00383 i128
Fissurellidae sp. Fishes 10 00383 i129 (1) Fishes 10 00383 i130Paractaea monodi Guinot, 1969 ° f Fishes 10 00383 i131 (2) Fishes 10 00383 i132
Flabellina affinis (Gmelin, 1791) Fishes 10 00383 i133 (2) Fishes 10 00383 i134Paragalene longicrura (Nardo, 1869) Fishes 10 00383 i135 (1) Fishes 10 00383 i136
Flabellinidae sp. Fishes 10 00383 i137 (1) Fishes 10 00383 i138Percnon gibbesi (H. Milne Edwards, 1853) * Fishes 10 00383 i139 (1) Fishes 10 00383 i140
Fusinus sp. ° Fishes 10 00383 i141 (2) Fishes 10 00383 i142Plesionika narval (Fabricius, 1787) Fishes 10 00383 i143 (8) Fishes 10 00383 i144
Hexaplex trunculus (Linnaeus, 1758) Fishes 10 00383 i145 (1) Fishes 10 00383 i146Scyllarides latus (Latreille, 1803) ǂ Fishes 10 00383 i147 (6) Fishes 10 00383 i148
Homalopoma sanguineum (Linnaeus, 1758) ° Fishes 10 00383 i149 (5) Fishes 10 00383 i150Scyllarus pygmaeus (Spence Bate, 1888) ǂ Fishes 10 00383 i151 (2) Fishes 10 00383 i152
Luria lurida (Linnaeus, 1758) ǂ Fishes 10 00383 i153 (8) Fishes 10 00383 i154Siriella gracilipes Nouvel, 1942 ° Fishes 10 00383 i155 (5) Fishes 10 00383 i156
Muricopsis cristata (Brocchi, 1814) ° Fishes 10 00383 i157 (11) Fishes 10 00383 i158Stenopus spinosus Risso, 1827 Fishes 10 00383 i159 (17) Fishes 10 00383 i160
Naria spurca (Linnaeus, 1758) ǂ Fishes 10 00383 i161 (3) Fishes 10 00383 i162Urocaridella pulchella Yokes & Galil, 2006 * ° Fishes 10 00383 i163 (5) Fishes 10 00383 i164
Peltodoris atromaculata Bergh, 1880 Fishes 10 00383 i165 (5) Fishes 10 00383 i166Xantho pilipes A. Milne-Edwards, 1867 ° Fishes 10 00383 i167 (1) Fishes 10 00383 i168
Phyllidia flava Aradas, 1847 ° f Fishes 10 00383 i169 (2) Fishes 10 00383 i170Pycnogonida
Pisania striata (Gmelin, 1791) Fishes 10 00383 i171 (1) Fishes 10 00383 i172Pantopoda sp. ° Fishes 10 00383 i173 (1) Fishes 10 00383 i174
Plocamopherus ocellatus Rüppell & Leuckart, 1828 * Fishes 10 00383 i175 (1) Fishes 10 00383 i176 
Phylum EchinodermataOsteichthyes (cont.)
CrinoideaGammogobius steinitzi Bath, 1971 Fishes 10 00383 i177 (10) Fishes 10 00383 i178
Antedon mediterranea (Lamarck, 1816) ° Fishes 10 00383 i179 (4) Fishes 10 00383 i180Gobiidae sp. Fishes 10 00383 i181 (2) Fishes 10 00383 i182
AsteroideaGobius bucchichi Steindachner, 1870 Fishes 10 00383 i183 (1) Fishes 10 00383 i184
Coscinasterias tenuispina (Lamarck, 1816) Fishes 10 00383 i185 (5) Fishes 10 00383 i186Gobius vittatus Vinciguerra, 1883 Fishes 10 00383 i187 (1) Fishes 10 00383 i188
Hacelia attenuata Gray, 1840 Fishes 10 00383 i189 (1) Fishes 10 00383 i190Grammonus ater (Risso, 1810) Fishes 10 00383 i191 (5) Fishes 10 00383 i192
Marthasterias glacialis (Linnaeus, 1758) Fishes 10 00383 i193 (4) Fishes 10 00383 i194Lepadogaster candolii Risso, 1810 Fishes 10 00383 i195 (1) Fishes 10 00383 i196
Ophidiaster ophidianus (Lamarck, 1816) ǂ Fishes 10 00383 i197 (9) Fishes 10 00383 i198Lepadogaster lepadogaster (Bonnaterre, 1788) Fishes 10 00383 i199 (2) Fishes 10 00383 i200
OphiuroideaMarcelogobius splechtnai (Ahnelt & Patzner, 1995) Fishes 10 00383 i201 (6) Fishes 10 00383 i202
Ophiactis sp. ° Fishes 10 00383 i203 (1) Fishes 10 00383 i204Microlipophrys nigriceps (Vinciguerra, 1883) Fishes 10 00383 i205 (11) Fishes 10 00383 i206
Ophioderma longicaudum (Bruzelius, 1805) f Fishes 10 00383 i207 (3) Fishes 10 00383 i208Mugilidae spp. Fishes 10 00383 i209 (3) Fishes 10 00383 i210
Ophiopsila aranea Forbes, 1843 ° f Fishes 10 00383 i211 (1) Fishes 10 00383 i212Mullus surmuletus Linnaeus, 1758 Fishes 10 00383 i213 (3) Fishes 10 00383 i214
Ophiothrix fragilis (Abildgaard in O.F. Müller, 1789) Fishes 10 00383 i215 (10) Fishes 10 00383 i216Muraena helena Linnaeus, 1758 Fishes 10 00383 i217 (2) Fishes 10 00383 i218
Ophiuroidea sp. Fishes 10 00383 i219 (13) Fishes 10 00383 i220Oblada melanurus (Linnaeus, 1758) Fishes 10 00383 i221 (7) Fishes 10 00383 i222
EchinoideaParablennius gattorugine (Linnaeus, 1758) Fishes 10 00383 i223 (1) Fishes 10 00383 i224
Arbacia lixula (Linnaeus, 1758) ° Fishes 10 00383 i225 (21) Fishes 10 00383 i226Parablennius rouxi (Cocco, 1833) Fishes 10 00383 i227 (1) Fishes 10 00383 i228
Centrostephanus longispinus (Philippi, 1845) ǂ Fishes 10 00383 i229 (2) Fishes 10 00383 i230Parupeneus forsskali (Fourmanoir & Guézé, 1976) * Fishes 10 00383 i231 (3) Fishes 10 00383 i232
Diadema setosum (Leske, 1778) * Fishes 10 00383 i233 (4) Fishes 10 00383 i234Pempheris rhomboidea Kossmann & Räuber, 1877 * Fishes 10 00383 i235 (4) Fishes 10 00383 i236
Paracentrotus lividus (Lamarck, 1816) ǂ Fishes 10 00383 i237 (2) Fishes 10 00383 i238Phycis phycis (Linnaeus, 1766) Fishes 10 00383 i239 (5) Fishes 10 00383 i240
Sphaerechinus granularis (Lamarck, 1816) Fishes 10 00383 i241 (7) Fishes 10 00383 i242Pterois miles (Bennett, 1828) * Fishes 10 00383 i243 (10) Fishes 10 00383 i244
Stylocidaris affinis (Philippi, 1845) Fishes 10 00383 i245 (2) Fishes 10 00383 i246Sargocentron rubrum (Forsskål, 1775) * Fishes 10 00383 i247 (6) Fishes 10 00383 i248
HolothuroideaSciaena umbra Linnaeus, 1758 ǂ Fishes 10 00383 i249(1) Fishes 10 00383 i250
Holothuria (Platyperona) sanctori Delle Chiaje, 1823 Fishes 10 00383 i251 (13) Fishes 10 00383 i252Scorpaena maderensis Valenciennes, 1833 Fishes 10 00383 i253 (19) Fishes 10 00383 i254
Holothuria spp. Fishes 10 00383 i255 (21) Fishes 10 00383 i256Scorpaena notata Rafinesque, 1810 Fishes 10 00383 i257 (1) Fishes 10 00383 i258
Phylum ChordataScorpaena porcus Linnaeus, 1758 Fishes 10 00383 i259 (1) Fishes 10 00383 i260
OsteichthyesScorpaena scrofa Linnaeus, 1758 Fishes 10 00383 i261 (2) Fishes 10 00383 i262
Anthias anthias (Linnaeus, 1758) Fishes 10 00383 i263 (2) Fishes 10 00383 i264Scorpaenodes arenai Torchio, 1962 Fishes 10 00383 i265 (1) Fishes 10 00383 i266
Apogon imberbis (Linnaeus, 1758) Fishes 10 00383 i267 (27) Fishes 10 00383 i268Serranus cabrilla (Linnaeus, 1758) Fishes 10 00383 i269 (8) Fishes 10 00383 i270
Atherina spp. Fishes 10 00383 i271 (8) Fishes 10 00383 i272Serranus scriba (Linnaeus, 1758) Fishes 10 00383 i273 (9) Fishes 10 00383 i274
Blenniidae spp. Fishes 10 00383 i275 (3) Fishes 10 00383 i276Siganus luridus (Rüppell, 1829) * Fishes 10 00383 i277 (5) Fishes 10 00383 i278
Boops boops (Linnaeus, 1758) Fishes 10 00383 i279 (3) Fishes 10 00383 i280Siganus rivulatus Forsskål & Niebuhr, 1775 * Fishes 10 00383 i281 (1) Fishes 10 00383 i282
Chromis chromis (Linnaeus, 1758) Fishes 10 00383 i283 (20) Fishes 10 00383 i284Sparisoma cretense (Linnaeus, 1758) Fishes 10 00383 i285 (8) Fishes 10 00383 i286
Conger conger (Linnaeus, 1758) Fishes 10 00383 i287 (3) Fishes 10 00383 i288Spicara smaris (Linnaeus, 1758) Fishes 10 00383 i289 (1) Fishes 10 00383 i290
Corcyrogobius liechtensteini (Kolombatovic, 1891) Fishes 10 00383 i291 (5) Fishes 10 00383 i292Symphodus mediterraneus (Linnaeus, 1758) Fishes 10 00383 i293 (3) Fishes 10 00383 i294
Coris julis (Linnaeus, 1758) Fishes 10 00383 i295 (19) Fishes 10 00383 i296Symphodus sp. Fishes 10 00383 i297 (1) Fishes 10 00383 i298
Diplodus annularis (Linnaeus, 1758) Fishes 10 00383 i299 (5) Fishes 10 00383 i300Synodus saurus (Linnaeus, 1758) f Fishes 10 00383 i301 (2) Fishes 10 00383 i302
Diplodus puntazzo (Walbaum, 1792) Fishes 10 00383 i303 (1) Fishes 10 00383 i304Thalassoma pavo (Linnaeus, 1758) Fishes 10 00383 i305 (16) Fishes 10 00383 i306
Diplodus sargus (Linnaeus, 1758) Fishes 10 00383 i307 (7) Fishes 10 00383 i308Thorogobius ephippiatus (Lowe, 1839) Fishes 10 00383 i309 (6) Fishes 10 00383 i310
Diplodus vulgaris (Geoffroy Saint-Hilaire, 1817) Fishes 10 00383 i311 (7) Fishes 10 00383 i312Torquigener flavimaculosus Hardy & Randall, 1983 * Fishes 10 00383 i313 (3) Fishes 10 00383 i314
Enchelycore anatina (Lowe, 1838) * Fishes 10 00383 i315 (4) Fishes 10 00383 i316Tripterygion delaisi Cadenat & Blache, 1970 Fishes 10 00383 i317 (1) Fishes 10 00383 i318
Epinephelus costae (Steindachner, 1878) Fishes 10 00383 i319 (4) Fishes 10 00383 i320Tripterygion melanurus Guichenot, 1850 Fishes 10 00383 i321 (18) Fishes 10 00383 i322
Epinephelus marginatus (Lowe, 1834) ǂ Fishes 10 00383 i323 (6) Fishes 10 00383 i324Tripterygion tripteronotum (Risso, 1810) Fishes 10 00383 i325 (3) Fishes 10 00383 i326

3.5. Introduced Species

Seventeen introduced species were recorded, belonging to four phyla: Chordata (8), Arthropoda (4), Mollusca (4), and Echinodermata (1). The lionfish Pterois miles was the most frequently encountered introduced species, recorded in ten caves across the east Aegean, Crete, and the Ionian Sea, followed by Sargocentron rubrum in six caves of the east Aegean, and Pempheris rhomboidea in four caves of the east Aegean and Crete (Figure 5, Table 4). The highest number of introduced species was recorded in the easternmost caves of the east Aegean and Crete, with Blue 2 cave (Kastellorizo Island) hosting the most (ten species).
Fishes constituted the most abundant introduced group in most caves. Blue 2, the southeasternmost studied cave, presented the highest overall abundance of introduced species, with more than 200 individuals of P. rhomboidea in its semidark zone and over 200 juveniles in its entrance zone, comprising approximately 53% of the cave’s total fish abundance (Figure 6).

4. Discussion

This study provides the first large-scale biodiversity assessment of motile fauna in 27 marine caves across the eastern Mediterranean, using a standardized quantitative methodology based on a rapid visual census protocol, complemented by qualitative material (photos and specimens). These caves were surveyed for the first time for their motile fauna, revealing rich biodiversity, with 163 taxa identified. Motile community structure exhibited considerable variation at a large spatial scale (i.e., among the four surveyed geographic subareas). In contrast, the lack of significant differentiation among caves within the same subareas suggests a more homogenized pattern in motile communities, likely due to the high mobility of most taxa, possible differences at local species pools and environmental filters. This finding contrasts with the widely accepted concept of cave “individuality” for sessile communities [3,4,6,50]. Species with distinct ecological niches and traits had a significant effect on the community structure across ecological zones. Reef-associated species dominated the cave entrance (e.g., Coris julis, Chromis chromis, Thalassoma pavo, and Arbacia lixula), while nocturnal (Apogon imberbis) and deeper-water species (Anthias anthias and Plesionika narval) prevailed in darker cave zones and deeper caves.
Consistent with previous faunistic zonation schemes for sessile communities in Mediterranean marine caves [40,51,52], it was observed that species typical of darker cave zones tend to shift towards the cave entrance with increasing depth. Examples include Thorogobius ephippiatus, Stenopus spinosus, and Plesionika narval, which were encountered closer to the entrance in deeper caves.
Apogon imberbis was the most widespread and abundant fish in most caves, echoing findings from Italy and France [11,53], where it comprised around 75% of the total fish density in caves [54]. However, in deeper caves, A. imberbis was usually replaced by Anthias anthias, while atherinids dominated the entrance and semidark zones of some semi-submerged caves forming large schools close to the surface. Among decapods, Stenopus spinosus was the most common (in 17 caves), followed by Brachycarpus biunguiculatus (in 15 caves) and Dromia personata (in 11 caves), in contrast with earlier studies where Palaemon serratus and Herbstia condyliata were more prominent [13,20].
Based on our findings and prior faunal categorization schemes, e.g., [2,19,20,22,53,54,55], motile taxa in the studied marine caves of the eastern Mediterranean can be assigned into the following ecological groups in relation to their degree of association with the cave environment: (1) accidental visitors (e.g., Pelagia noctiluca), often carried by currents and trapped inside the cave; (2) diurnal reef-associated species (e.g., Diplodus sargus, Coris julis, and Chromis chromis), which can occasionally be found in caves, usually close to the entrance; (3) trophic associates dependent on prey (typically but not exclusively) found within caves (e.g., Peltodoris atromaculata feeding on sponges); (4) cryptic habitat dwellers or “cave within cave” species, i.e., species associated with cryptic cave-like “mesolithial habitats”, such as crevices, empty holes of endolithic bivalves, overhangs, and fissures (e.g., Gammogobius steinitzi, Scyllarus pygmaeus, and the introduced Urocaridella pulchella); (5) nocturnal shelter-seekers, i.e., species finding shelter inside caves during daytime (e.g., Apogon imberbis, mysids, and the introduced Pempheris rhomboidea, and Sargocentron rubrum); (6) deeper-water species (e.g., Grammonus ater, Scorpaenodes arenai, and Stylocidaris affinis); (7) speleophilic species (typically but not exclusively) inhabiting and reproducing in marine caves (e.g., Stenopus spinosus and Palaemon serratus); and (8) cave-exclusive species (stygobionts), not observed in other environments than caves. Species belonging to the latter category were not observed in the studied marine caves, but they are known from other studies, e.g., [56,57]. It should be noted that some taxa could be assigned to more than one category (e.g., Muraena helena is both cryptic habitat dweller and nocturnal shelter-seeker). Categories 4–7 include species considered to exhibit secondary stygobiosis, since they originate from external marine environments and only secondarily inhabit marine caves [2,58].
In this study, the biodiversity inventory from the 27 studied marine caves revealed several rarely reported, protected, and introduced species, including new records for the study area and the marine cave habitat, thereby filling biogeographical and ecological knowledge gaps.

4.1. Rarely Reported Species

Overall, 17.8% of the identified taxa (29 species) were recorded for the first time in marine caves of the eastern Mediterranean Sea (Table 2), while 9.8% (16 species) were recorded for the first time in Mediterranean marine caves [15,19,20,22,25,59]. Some notable examples are presented below along with photographic evidence (Figure 7).
One of the most striking examples of rarely reported species was the finding of the Messina rockfish Scorpaenodes arenai in the same cave where it was first recorded in 2015 (Shrimp cave, Zakynthos Island), representing the shallowest Mediterranean records of this deep-water species and the only site where it can be observed through SCUBA diving [60]. Two individuals were sighted in an upside-down position in the semidark and dark zones of the cave (Figure 7A,B). The rockfish was recorded for the first time as feeding on the shrimp Plesionika narval, shedding light on its trophic habits inside marine caves.
The shrimp Brachycarpus biunguiculatus was observed almost exclusively in the semidark and dark zones of 15 caves, with up to 14 individuals in a single shallow cave in southern Crete (Figure 7D). Due to its highly cryptic habits and its nocturnal behavior, this species seeks shelter in dark environments such as caves, where it is mostly recorded in the Mediterranean Sea [20,61]. The frequent presence of B. biunguiculatus in 55% of the herein studied caves indicates that the species is a lot more common than previously thought.
Two of the recorded species, the flatworm Prostheceraeus moseleyi and the nudibranch Felimare gasconi, are herein reported for the first time in Greek waters as well as in the cave environment increasing the known fauna of Mediterranean marine caves. The flatworm P. moseleyi was observed in the entrance and semidark zones of two caves on Karpathos Island (Achata 2 and Vronti cave), and more recently at the entrance of a cave on the nearby Saria Island (35.854402° N, 27.193404° E), during another expedition (authors’ personal observation). This flatworm is easily distinguished from other congeneric Mediterranean species by its unique color patterns [62] (Figure 7C). The nudibranch F. gasconi was collected from the dark zone of Lithistid cave in Crete (Table 2, Figure 7E). This dark blue dorid is characterized by a notum edged with a yellow line, white markings in front of the rhinophores and behind the gill tuft, and a prominent thick white longitudinal line running dorsally [63].
Among the identified motile taxa, twelve are protected under the Bern and Barcelona Conventions and the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) (Table 4). Protected taxa were recorded in most studied caves (25) across all geographical areas, with 1–3 protected species found per cave, highlighting the high conservation value of Mediterranean marine caves [2,64].

4.2. Introduced Species in Marine Caves

Approximately 10% of all motile species identified in the studied caves were introduced, with the highest richness and abundance in southeastern areas. This pattern is consistent with their known distribution in other marine habitats [31,65,66,67]. Several of these species were recorded for the first time in marine caves or in specific areas. The introduced portunid crab Carupa tenuipes, which can be distinguished by its pale orange coloration and fingers dark brown distally and along their inner margins [68] (Figure 8A), was recorded for the first time in the Ionian Sea, within the semidark zone of Keri 2 cave on Zakynthos Island. The decapod Gonioinfradens giardi and the gastropod Conomurex persicus are herein firstly reported from the marine cave habitat, raising the total number of introduced species in Mediterranean marine caves to 128 [37]. Two individuals of the portunid crab G. giardi, were recorded in the semidark zone of Neptune’s cave on Karpathos Island, as far as 70 m from its entrance (Figure 8B). This species can be distinguished by the shape of its frontal lobes with two spines medially on the upper surface of its palms set close apart, its distinctive body color pattern, the small ancillary teeth between four well-developed teeth at the anterolateral border of the carapace, and light-banded dark-tipped anterolateral spines [69,70,71]. Another interesting finding was the presence of the shrimp Urocaridella pulchella in five caves, with up to 40 individuals in caves on Crete and Karpathos Islands (Figure 8E), mostly on soft substrate. This decapod was recently reported from Aegean and Ionian marine caves [72,73].
Several of the introduced fish species had considerably high abundances in the studied caves. Large aggregations of the well-established sweeper fish Pempheris rhomboidea were observed in the Blue 2 cave (Kastellorizo Island), with up to 400 individuals, half of which were juveniles (Figure 8C). Large schools of Siganus spp. were observed near the entrance of a cave in southern Crete (Figure 8D). Pempheris rhomboidea as well as some other introduced fishes (Sargocentron rubrum), undertake diurnal migrations to feed in outer environments, possibly enriching the oligotrophic cave interior with organic matter, in a manner similar to that of native species such as Apogon imberbis [53,54,74,75]. In contrast, other introduced species, such as Pterois miles, may negatively affect the cave ecosystem through predation and competition with native predators, as observed in [76,77] and through personal observations.

4.3. Marine Caves as Nursery Grounds

During the surveys, some species were found to be more common than expected, displaying interesting and little-known behavioral traits related to the marine cave habitat. For instance, the sea urchin Arbacia lixula was recorded in 78% of the surveyed caves (21 caves), constituting the most frequently reported echinoderm (Table 4). Although commonly regarded as a diurnal herbivore feeding primarily on crustose algae, it is actually an omnivore with a strong tendency toward carnivory, occasionally reaching high densities in barren states such as dark caves, where it avoids competition with the more dominant sea urchin Paracentrotus lividus [78,79]. In addition, small and medium sized individuals of A. lixula, being more vulnerable to predation, compensate for their less-efficient morpho-functional defenses against predators by adopting cryptic behavior and seeking refuge in concealed microhabitats [78,80,81,82]. This behavior likely explains the presence of A. lixula in all ecological cave zones, with juveniles observed as far as 160 m away from the entrance in the Elephant cave (Crete).
Mediterranean marine caves seem to serve as nursery grounds for certain species, such as Antedon mediterranea, a crinoid only sporadically reported from caves [2,83]. In this study, although A. mediterranea was observed in low numbers (in only four caves), we recorded a remarkably high abundance with numerous juveniles in the semidark zone of a submerged cave with freshwater inflow in southern Crete (personal observation). This observation probably represents the first documented case of caves functioning as a breeding ground for this echinoderm species.
Additionally, the cave interior may serve as an egg-laying site for cuttlefish, as eggs of Sepia spp. were recorded in the semidark zone of three caves distributed from the east to the central Aegean and Crete. Although other cephalopods, such as octopuses, have previously been reported to lay eggs in caves [84], this appears to be the first documented observation of cuttlefish eggs in Mediterranean marine caves.

4.4. Limitations of the Applied Methodology

The applied methodology enabled the identification of a high number of motile species through a standardized quantitative protocol requiring only one observer and non-decompression single-dive surveys. Nevertheless, since the proposed rapid assessment protocol is time limited—due to the logistic constraints of diving in space-limited and dark environments—it does not allow for a complete assessment of motile cave biota. The in-transect/total species richness percentage ratio differed among zones likely due to the varying light level and spatial extent of each zone. Specifically, the highest percentage at the cave entrance was probably due to the better visibility and its smaller size while the lower percentages in the dark zone are attributed to the poorest visibility and low species richness. The semidark zone presented the lowest proportion of in-transect to total species richness and abundance due to its largest size and higher heterogeneity in terms of resources and micro-habitats [3,4,40,85]. Thus, lower ratios are expected to be recorded in caves with extensive semidark zones, lower visibility (e.g., caves with sulfur springs and microbial mats) or increased surface complexity with several micro-habitats (e.g., submerged ceilings, fissures, and overhangs). The high small-scale heterogeneity of the cave habitat affects species diversity and distribution, with different species occupying specific sections and micro-habitats within caves [22]. To better capture this variability, the use of modified transect methods and quadrat sampling across distinct ‘sub-habitats’ (e.g., walls, ceilings, and floor) has been suggested, although these approaches typically require multiple dives or extended dive times [22,53,55].
In this study, taxa that could not be reliably identified in situ at species level were recorded at higher taxonomic ranks (e.g., Atherina spp., Clanculus spp.). Cryptic and small sized species such as cryptic habitat dwellers (e.g., Microlipophrys nigriceps, Corcyrogobius liechtensteini, Marcelogobius splechtnai, Gammogobius steinitzi) are likely underrepresented, especially in less-studied caves, such as deeper caves or caves with complex morphology. The combined approach adopted in this work, which included photographic documentation and qualitative sampling, seems to mitigate the restrictions of the time-limited visual census, as evidenced by the high total number of species recorded. However, to accurately assess the distribution and abundance of cryptobenthic fishes in marine caves, more targeted methodologies should be considered, such as the use of anesthetic agents and quadrat sampling [55].
Annual, seasonal, and diurnal variations are also expected to influence the species richness and abundance of motile taxa, especially for occasional visitors and/or highly mobile species (e.g., Atherina spp. and mysids). Although our visual census protocol was applied across different years and periods (Table 1), the majority of surveys (63%, corresponding to 17 caves) were carried out during the warm season (typically April to September in the Mediterranean Sea) and cosistently during morning to midday hours.
Although having a single observer entering first in the cave is expected to reduce disturbance, some highly mobile species (e.g., fishes) may still relocate toward outer or inner cave sections or hide in micro-habitats before being noticed. Finally, the involvement of multiple observers can introduce variability in species detection and data collection [86]. Thus, to minimize such bias, the same diver consistently applied the visual census protocol in all surveyed caves.

5. Conclusions

The assessment of motile cave fauna in a large number of marine caves in the eastern Mediterranean Sea enabled—for the first time—the quantitative characterization of their motile assemblages, employing a standardized rapid visual census protocol. Through the suggested methodology, more than 60% on average of the motile cave fauna observed in situ can be recorded, providing information on species richness and abundance. Such data are vital for assessing the ecological quality of marine caves [33,87] and for informing long-term monitoring initiatives, especially in marine protected areas.
The high number of new species records for marine caves in the eastern Mediterranean, and for cave habitats overall, demonstrates that our knowledge regarding cave biota is far from complete. In order to understand the distribution pathways of current and future cave inhabitants, it is important to examine the association between motile species assemblages in caves and nearby habitats such as rocky reefs. Given the unique biodiversity of marine caves, their low ecological resilience, and the increasing occurrence of several introduced species, this key habitat emerges as particularly vulnerable. Notably, six of the identified introduced species are listed among the worst Mediterranean invasives [88], and recent studies have highlighted the urgent need to investigate their potential ecological impacts on cave biota [38]. The population explosion of certain introduced species and their increasing abundance in caves of southeastern subareas, as seen in [36,37,72,89] and the present study, indicate a rapid shift in the cave ecosystem. Therefore, the protection of certain caves should be prioritized. Among these caves is the Shrimp cave of Zakynthos Island, a currently uninvaded cave within an otherwise invaded area, which represents the shallowest known Mediterranean habitat of the deep-water Messina rockfish S. arenai. Additionally, the Lithistid cave in southern Crete and Seal’s 3 cave on Samos Island stand out as the two most species-rich caves studied. In this context, the long-term monitoring of the motile cave communities through seasonal surveys is recommended, particularly within newly established high-priority protected areas. However, the absence of historical baseline restricts our understanding of change in cave communities. This study provides a baseline for future comparisons of cave communities between invaded and uninvaded caves [90], and for future monitoring areas that are still unaffected or only minimally impacted in view of the continuous expansion of thermophilic introduced species due to climate change.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/fishes10080383/s1. Figure S1: Number of motile taxa recorded within time transects compared with all taxa recorded in situ during a single dive survey in each studied cave. Figure S2: Number of motile taxa recorded within time transects in the cave entrance (CE), the semidark (SD), and the dark zone (D) compared with all taxa recorded in situ during a single dive survey in each studied cave. Figure S3: Abundance recorded within time transects compared with all taxa recorded in situ during a single dive survey in each studied cave. Figure S4: Abundance recorded within time transects in the cave entrance (CE), the semidark (SD), and the dark zone (D) compared with the total abundance recorded in situ during a single dive survey in each studied cave. Table S1: Dissimilarity percentage analysis (SIMPER) showing the contribution of motile taxa to the average dissimilarity (%) between the subareas east Aegean and Crete. Table S2: Pair-wise tests for the two-way PERMANOVA analysis conducted with the factor ‘Cave’ nested as random within the fixed factor ‘Subarea’ for the total of motile taxa recorded in transect. Table S3: Construction of pseudo-F ratio from mean squares from the two-way PERMANOVA analysis conducted with the factor ‘Cave’ nested as random within the fixed factor ‘Subarea’ for the total of motile taxa recorded in transect. Table S4: Construction of pseudo-F ratios from mean squares from the one-way PERMANOVA analysis conducted with the factor ‘Zone’ within each subarea for the total of motile taxa recorded in transect. Table S5: Dissimilarity percentage analysis (SIMPER) showing the contribution of motile taxa to the average dissimilarity (%) between the cave entrance (CE) and the semidark zone (SD). Table S6: Dissimilarity percentage analysis (SIMPER) showing the contribution of motile taxa to the average dissimilarity (%) between the cave entrance (CE) and the dark zone (D). Table S7: Dissimilarity percentage analysis (SIMPER) showing the contribution of motile taxa to the average dissimilarity (%) between the semidark zone (SD) and the dark zone (D). Table S8: Pair-wise tests for the two-way PERMANOVA analysis conducted with the factor ‘Cave’ nested as random within the fixed factor ‘Subarea’ for fishes recorded in transect. Table S9: Construction of pseudo-F ratio from mean squares from the two-way PERMANOVA analysis conducted with the factor ‘Cave’ nested as random within the fixed factor ‘Subarea’ for fishes recorded in transect. Table S10: Construction of pseudo-F ratios from mean squares from the one-way PERMANOVA analysis conducted with the factor ‘Zone’ within each subarea for fishes recorded in transect. Table S11: Dissimilarity percentage analysis (SIMPER) showing the contribution of fish species to the average dissimilarity (%) between the cave entrance (CE) and the semidark zone (SD). Table S12: Dissimilarity percentage analysis (SIMPER) showing the contribution of fish species to the average dissimilarity (%) between the cave entrance (CE) and the dark zone (D). Table S13: Dissimilarity percentage analysis (SIMPER) showing the contribution of fish species to the average dissimilarity (%) between the cave entrance (CE) and the dark zone (D).

Author Contributions

Conceptualization and methodology, M.D. and V.G.; sampling: M.D., M.R. and V.G.; identified samples, M.D. and V.G.; formal analysis, M.D., C.D. and V.G.; writing—original draft preparation, M.D.; writing—review and editing, V.G., M.R., C.D. and S.K.; funding acquisition, M.D., S.K. and V.G. All authors have read and agreed to the published version of the manuscript.

Funding

The research was supported by the Hellenic Foundation for Research and Innovation (HFRI) under the 4th Call for HFRI PhD Fellowships (Fellowship Number: 10597). Part of the sampling activities was funded through the projects “First Call for HFRI Research Projects to support faculty members and researchers and the procurement of high-cost research equipment grant” (Project ALAS—‘ALiens in the Aegean—a Sea under siege’, project number: HFRI-FM17-1597) (3/2020-3/2023), and the “STUDIOTOPIA—Art meets Science in the Anthropocene (2019–2022)” residency program, hosted by Onassis Stegi and co-funded by the Creative Europe programme of the European Union. Additional support for the 2021 sampling campaign was provided to V.G. by the project “Centre for the study and sustainable exploitation of Marine Biological Resources (CMBR)” (MIS 5002670), implemented under the Action “Reinforcement of the Research and Innovation Infrastructure”, funded by the Operational Programme “Competitiveness, Entrepreneurship and Innovation” (NSRF 2014–2020) and co-financed by Greece and the EU (European Regional Development Fund).

Institutional Review Board Statement

The research has been accepted for implementation by the Research Ethics and Deontology Committee of the Ionian University (Approval code: 1036, Approval date: 2023-04-06).

Informed Consent Statement

Not applicable.

Data Availability Statement

All relevant data are contained within the article and its Supplementary Materials.

Acknowledgments

The authors are grateful to Dimitris Podaras and Maria Naletaki for their assistance with the identification of echinoderm and decapod samples, respectively; Fabio Crocetta for his help with mollusk identification; and Pierre Chevaldonné for verifying the identification of mysid specimens. We also thank Thanos Dailianis for providing one of the photos presented (Figure 7C) and for his contribution to some of the sampling campaigns. We are grateful to the Management Units of the Southeastern Aegean Protected Areas, Samaria National Park, and the Protected Areas of Western Crete, and Zakynthos and Ainos National Parks and Protected Areas of the Ionian islands of the Natural Environment and Climate Change Agency (NECCA) for granting sampling permissions in marine caves within these protected areas. We also wish to thank Dennis Mohr and the staff of Nero Sport Diving Center (Limni Keriou, Zakynthos), Nikos Giannoulakis from the Chania Diving Center (Chania, Crete), and Dinos Protopapas from the Karpathos Diving Center (Pigadia, Karpathos) for their valuable expertise and support during fieldwork in Zakynthos, Crete and in Karpathos Islands, respectively. Finally, we warmly thank Carlos Navarro-Barranco, Juan Sempere-Valverde, Sahar Chebaane, Alfredo Marchiò, and Ioannis Rallis for their assistance during fieldwork.

Conflicts of Interest

The authors declare no conflicts of interest.

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Fishes 10 00383 g001
Figure 1. Location of the studied marine caves with fully submerged (circles) and semi-submerged (triangles) entrances and given reference numbers (RN) (see Table 1). Biogeographical subareas (Ionian Sea, central Aegean, east Aegean, and Crete) based on [43] and modified. The inset map (upper left) indicates the location of the surveyed area within the Mediterranean Sea.
Figure 1. Location of the studied marine caves with fully submerged (circles) and semi-submerged (triangles) entrances and given reference numbers (RN) (see Table 1). Biogeographical subareas (Ionian Sea, central Aegean, east Aegean, and Crete) based on [43] and modified. The inset map (upper left) indicates the location of the surveyed area within the Mediterranean Sea.
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Figure 2. Non-metric multidimensional scaling (nMDS) three-dimensional plot showing the dissimilarities among motile taxa recorded in transects at different ecological zones and the species contributing the most to this differentiation. CE: cave entrance; SD: semidark zone; D: dark zone.
Figure 2. Non-metric multidimensional scaling (nMDS) three-dimensional plot showing the dissimilarities among motile taxa recorded in transects at different ecological zones and the species contributing the most to this differentiation. CE: cave entrance; SD: semidark zone; D: dark zone.
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Figure 3. Cluster dendrogram with the percent similarity among all studied caves (NEP: Neptune’s; SHR: Shrimp; BUT: Butterfly; KER 2: Keri 2; ACH 2: Achata 2; LIT: Lithistid; SEAL 2: Seal’s 2; BLUE 2: Blue 2; BLUE 1: Blue 1; GLI: Glika Nera; ELE: Elephant; PANT: Pantieronisi; ALT: Altar; SEAL 3; Seal’s 3; KAL: Kalymnos; ACH 1: Achata 1; CATH: Cathedral; SUL 1: Sulfur 1; MAV: Mavros Kavos; ALI: Alikes; SUL 2: Sulfur 2; SEAL 1: Seal’s 1; VRO: Vronti; EFS: Efstathios; MAR: Marathia; POL: Polyaigos; SKO: Skotino). Red lines indicate non-significant differentiation; Black lines indicate significant differentiation.
Figure 3. Cluster dendrogram with the percent similarity among all studied caves (NEP: Neptune’s; SHR: Shrimp; BUT: Butterfly; KER 2: Keri 2; ACH 2: Achata 2; LIT: Lithistid; SEAL 2: Seal’s 2; BLUE 2: Blue 2; BLUE 1: Blue 1; GLI: Glika Nera; ELE: Elephant; PANT: Pantieronisi; ALT: Altar; SEAL 3; Seal’s 3; KAL: Kalymnos; ACH 1: Achata 1; CATH: Cathedral; SUL 1: Sulfur 1; MAV: Mavros Kavos; ALI: Alikes; SUL 2: Sulfur 2; SEAL 1: Seal’s 1; VRO: Vronti; EFS: Efstathios; MAR: Marathia; POL: Polyaigos; SKO: Skotino). Red lines indicate non-significant differentiation; Black lines indicate significant differentiation.
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Figure 4. Non-metric multidimensional scaling (nMDS) two-dimensional plot showing the dissimilarities among the fish taxa recorded in transects at different ecological zones and the fish species contributing the most to this differentiation. CE: cave entrance; SD: semidark zone; D: dark zone.
Figure 4. Non-metric multidimensional scaling (nMDS) two-dimensional plot showing the dissimilarities among the fish taxa recorded in transects at different ecological zones and the fish species contributing the most to this differentiation. CE: cave entrance; SD: semidark zone; D: dark zone.
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Figure 5. Introduced species recorded in the studied caves in and out of transects labelled with different colors (MAV: Mavros Kavos; SUL 1: Sulfur 1; SUL 2: Sulfur 2; ALT: Altar; KER 2: Keri 2; MAR: Marathia; SKO: Skotino; CATH: Cathedral; ALI: Alikes; GLI: Glika Nera; LIT: Lithistid; VRO: Vronti; NEP: Neptune’s; ACH 1: Achata 1; ACH 2: Achata 2; BLUE 2: Blue 2; SEAL 2: Seal’s 2; KAL: Kalymnos; SEAL 3: Seal’s 3; PANT: Pantieronisi; POL: Polyaigos; EFS: Efstathios). Caves with no introduced species are not presented.
Figure 5. Introduced species recorded in the studied caves in and out of transects labelled with different colors (MAV: Mavros Kavos; SUL 1: Sulfur 1; SUL 2: Sulfur 2; ALT: Altar; KER 2: Keri 2; MAR: Marathia; SKO: Skotino; CATH: Cathedral; ALI: Alikes; GLI: Glika Nera; LIT: Lithistid; VRO: Vronti; NEP: Neptune’s; ACH 1: Achata 1; ACH 2: Achata 2; BLUE 2: Blue 2; SEAL 2: Seal’s 2; KAL: Kalymnos; SEAL 3: Seal’s 3; PANT: Pantieronisi; POL: Polyaigos; EFS: Efstathios). Caves with no introduced species are not presented.
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Figure 6. Percent ratio of introduced to native fish species recorded in transect for the studied marine caves (SUL 1: Sulfur 1; SUL 2: Sulfur 2; ELE: Elephant; LIT: Lithistid; VRO: Vronti; NEP: Neptune’s; ACH 1: Achata 1; ACH 2: Achata 2; BLUE 2: Blue 2; SEAL 2: Seal’s 2; KAL: Kalymnos; SEAL 3: Seal’s 3). Caves with no introduced species are not presented.
Figure 6. Percent ratio of introduced to native fish species recorded in transect for the studied marine caves (SUL 1: Sulfur 1; SUL 2: Sulfur 2; ELE: Elephant; LIT: Lithistid; VRO: Vronti; NEP: Neptune’s; ACH 1: Achata 1; ACH 2: Achata 2; BLUE 2: Blue 2; SEAL 2: Seal’s 2; KAL: Kalymnos; SEAL 3: Seal’s 3). Caves with no introduced species are not presented.
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Figure 7. The Messina rockfish Scorpaenodes arenai eating the shrimp Plesionika narval in a deep marine cave of Zakynthos Island ((A): front view; (B): side view); the flatworm Prostheceraeus moseleyi photographed at the entrance of a cave in Saria Island (C); two individuals of the decapod Brachycarpus biunguiculatus (D) and the collected nudibranch Felimare gasconi from a shallow marine cave of Crete (E). Photos by M. Digenis (A,B,E), T. Dailianis (C), and M. Ragkousis (D).
Figure 7. The Messina rockfish Scorpaenodes arenai eating the shrimp Plesionika narval in a deep marine cave of Zakynthos Island ((A): front view; (B): side view); the flatworm Prostheceraeus moseleyi photographed at the entrance of a cave in Saria Island (C); two individuals of the decapod Brachycarpus biunguiculatus (D) and the collected nudibranch Felimare gasconi from a shallow marine cave of Crete (E). Photos by M. Digenis (A,B,E), T. Dailianis (C), and M. Ragkousis (D).
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Figure 8. The introduced crabs Carupa tenuipes (A) and Gonioinfradens giardi (B) from the dark zone in a cave of Rhodes (Seal 2) and Karpathos Islands (Neptune’s cave), respectively; juveniles of the sweeper fish Pempheris rhomboidea (C) from the cave entrance of Blue 2 cave in Kastellorizo Island; school of Siganus spp. passing in front of Glika Nera cave entrance in south Crete (D); the shrimp Urocaridella pulchella (E) from the semidark zone of a cave in south Crete. Photos by M. Ragkousis (A,E), M. Digenis (B,C), and V. Gerovasileiou (D).
Figure 8. The introduced crabs Carupa tenuipes (A) and Gonioinfradens giardi (B) from the dark zone in a cave of Rhodes (Seal 2) and Karpathos Islands (Neptune’s cave), respectively; juveniles of the sweeper fish Pempheris rhomboidea (C) from the cave entrance of Blue 2 cave in Kastellorizo Island; school of Siganus spp. passing in front of Glika Nera cave entrance in south Crete (D); the shrimp Urocaridella pulchella (E) from the semidark zone of a cave in south Crete. Photos by M. Ragkousis (A,E), M. Digenis (B,C), and V. Gerovasileiou (D).
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Table 1. Reference number (RN), location, depth, year of sampling, and protection status (Natura 2000 code; * for National Parks) of the 27 studied marine caves. Oct: October; Nov: November; Dec: December; Jun: June; Aug: August.
Table 1. Reference number (RN), location, depth, year of sampling, and protection status (Natura 2000 code; * for National Parks) of the 27 studied marine caves. Oct: October; Nov: November; Dec: December; Jun: June; Aug: August.
RNSite NameLocation
(Island)		Latitude (DD)Longitude (DD)Entrance Bottom Depth (m)Month–Year of SurveyProtection Status
1Butterfly caveZakynthos37.6452520.830139Nov-2022GR2210001 *
2Mavros Kavos caveZakynthos37.6457320.8325020Nov-2022GR2210001 *
3Sulfur 1 caveZakynthos37.6480020.8410813Nov-2022GR2210001 *
4Sulfur 2 caveZakynthos37.6479820.8412912Nov-2022GR2210001 *
5Altar caveZakynthos37.6471720.8453616.5Nov-2022GR2210001 *
6Shrimp caveZakynthos37.6470020.8460032Nov-2022GR2210001 *
7Keri 2 caveZakynthos37.6614620.858585.2Nov-2022*
8Marathia caveZakynthos37.6649620.858693.5Nov-2022GR2210002 *
9Seal’s 1 cave Crete35.5501724.0694213May-2021-
10Blue 1 caveCrete35.5505124.070117May-2021-
11Skotino caveCrete35.5513824.0699911May-2021-
12Cathedral caveCrete35.5518124.0705212May-2021-
13Elephant caveCrete35.4692124.2448410Dec-2022GR4340010
14Glika Nera caveCrete35.2012424.116338Jun-2021GR4340008 *
15Lithistid caveCrete35.2013424.119814Jun-2021GR4340008 *
16Alikes caveCrete35.4167624.9865716Oct-2021-
17Vronti caveKarpathos35.5373327.212554Aug-2020GR4210002
18Neptune’s caveKarpathos35.5557127.2096227Aug-2020GR4210002
19Achata 1 caveKarpathos35.5590627.2042010Aug-2020GR4210002
20Achata 2 caveKarpathos35.5591927.2045011.5Aug-2020GR4210002
21Blue 2 caveKastellorizo36.1257229.5788117Aug-2020GR4210004
22Seal’s 2 caveRhodes36.3261728.214524Aug-2020-
23Kalymnos caveKalymnos36.9258726.971934Aug-2020GR4210019
24Seal’s 3 caveSamos37.7723927.059832Aug-2020-
25Pantieronisi cavePantieronisi36.9685325.1214114Aug-2020GR4220025
26Polyaigos cavePolyaigos36.7861924.636508Aug-2020GR4220006
27Efstathios caveAgios Efstathios36.7738024.581076Aug-2020GR4220006
Table 2. List of all taxa recorded during the visual census in the studied caves by major taxonomic group (in bold). *: taxa recorded within time transects; ǂ: taxa recorded out of transect. Gammogobius/Corcyrogobius: refer to the species Gammogobius steinitzi Bath, 1971 and/or Corcyrogobius liechtensteini (Kolombatovic, 1891), two small-sized cryptobenthic fish with similar color patterns, often difficult to be distinguished visually by the observer within the time transects.
Table 2. List of all taxa recorded during the visual census in the studied caves by major taxonomic group (in bold). *: taxa recorded within time transects; ǂ: taxa recorded out of transect. Gammogobius/Corcyrogobius: refer to the species Gammogobius steinitzi Bath, 1971 and/or Corcyrogobius liechtensteini (Kolombatovic, 1891), two small-sized cryptobenthic fish with similar color patterns, often difficult to be distinguished visually by the observer within the time transects.
Phylum CnidariaEchinoidea
ScyphozoaArbacia lixula (Linnaeus, 1758) *
Pelagia noctiluca (Forsskål, 1775) *Centrostephanus longispinus (Philippi, 1845) *
Phylum PlatyhelminthesDiadema setosum (Leske, 1778) *
Monobiceros langi Faubel, 1984 *Paracentrotus lividus (Lamarck, 1816) *
Phylum MolluscaSphaerechinus granularis (Lamarck, 1816) *
CephalopodaStylocidaris affinis (Philippi, 1845) *
Octopus vulgaris Cuvier, 1797 ǂHolothuroidea
Sepia officinalis Linnaeus, 1758 *Holothuria spp. *
GastropodaPhylum Chordata
Berthella ocellata (Delle Chiaje, 1830) ǂOsteichthyes
Charonia seguenzae (Aradas & Benoit, 1871) ǂAnthias anthias (Linnaeus, 1758) *
Clanculus spp. ǂApogon imberbis (Linnaeus, 1758) *
Homalopoma sanguineum (Linnaeus, 1758) *Atherina spp. *
Luria lurida (Linnaeus, 1758) ǂBlenniidae spp. ǂ
Naria spurca (Linnaeus, 1758) *Boops boops (Linnaeus, 1758) *
Peltodoris atromaculata Bergh, 1880 *Chromis chromis (Linnaeus, 1758) *
Plocamopherus ocellatus Rüppell & Leuckart, 1828 ǂConger conger (Linnaeus, 1758) ǂ
Umbraculum umbraculum ([Lightfoot], 1786) ǂCoris julis (Linnaeus, 1758) *
Phylum AnnelidaDiplodus annularis (Linnaeus, 1758) *
PolychaetaDiplodus puntazzo (Walbaum, 1792) *
Bonellia viridis Rolando, 1822 *Diplodus sargus (Linnaeus, 1758) *
Hermodice carunculata (Pallas, 1766) *Diplodus vulgaris (Geoffroy Saint-Hilaire, 1817) *
Phylum ArthropodaEnchelycore anatina (Lowe, 1838) ǂ
MalacostracaEpinephelus costae (Steindachner, 1878) *
Brachycarpus biunguiculatus (Lucas, 1846) *Epinephelus marginatus (Lowe, 1834) *
Carupa tenuipes Dana, 1852 ǂGammogobius/Corcyrogobius spp. *
Dardanus calidus (Risso, 1827) * Gobiidae sp. ǂ
Dromia personata (Linnaeus, 1758) *Gobius vittatus Vinciguerra, 1883 *
Galathea strigosa (Linnaeus, 1761) ǂGrammonus ater (Risso, 1810) ǂ
Herbstia sp. *Marcelogobius splechtnai (Ahnelt & Patzner, 1995) *
Lysmata spp. *Microlipophrys nigriceps (Vinciguerra, 1883) *
Maja sp. *Mugilidae spp. *
Paguroidea spp. *Mullus surmuletus Linnaeus, 1758 *
Palaemon serratus (Pennant, 1777) * Muraena helena Linnaeus, 1758 ǂ
Palinurus elephas (Fabricius, 1787) *Oblada melanurus (Linnaeus, 1758) *
Paragalene longicrura (Nardo, 1869) *Parupeneus forsskali (Fourmanoir & Guézé, 1976) *
Plesionika narval (Fabricius, 1787) *Pempheris rhomboidea Kossmann & Räuber, 1877 *
Scyllarides latus (Latreille, 1803) *Phycis phycis (Linnaeus, 1766) *
Stenopus spinosus Risso, 1827 *Pterois miles (Bennett, 1828) *
Urocaridella pulchella Yokes & Galil, 2006Sargocentron rubrum (Forsskål, 1775) *
Xanthidae spp. ǂSciaena umbra Linnaeus, 1758 *
Phylum EchinodermataScorpaena scrofa Linnaeus, 1758 ǂ
CrinoideaScorpaena spp. *
Antedon mediterranea (Lamarck, 1816) ǂScorpaenodes arenai Torchio, 1962 *
AsteroideaSerranus cabrilla (Linnaeus, 1758) *
Coscinasterias tenuispina (Lamarck, 1816) ǂSerranus scriba (Linnaeus, 1758) *
Hacelia attenuata Gray, 1840 *Siganus luridus (Rüppell, 1829) *
Marthasterias glacialis (Linnaeus, 1758) *Siganus rivulatus Forsskål & Niebuhr, 1775 ǂ
Ophidiaster ophidianus (Lamarck, 1816) *Sparisoma cretense (Linnaeus, 1758) *
OphiuroideaSymphodus sp. *
Ophiuroidea spp. *Synodus saurus (Linnaeus, 1758) *
Osteichthyes (cont.)Torquigener flavimaculosus Hardy & Randall, 1983 *
Thalassoma pavo (Linnaeus, 1758) *Tripterygion spp. *
Thorogobius ephippiatus (Lowe, 1839) * 
Table 3. Species richness and abundance per ecological zone recorded in transect in the studied caves. The percentage of species richness and abundance recorded in transects in relation to the total (in and out of transects) is presented in brackets. CE: cave entrance; SD: semidark zone; D: dark zone; SE: standard error.
Table 3. Species richness and abundance per ecological zone recorded in transect in the studied caves. The percentage of species richness and abundance recorded in transects in relation to the total (in and out of transects) is presented in brackets. CE: cave entrance; SD: semidark zone; D: dark zone; SE: standard error.
 Species RichnessAbundance
CaveCE (%)SD (%)D (%)CE (%)SD (%)D (%)
Butterfly10 (71.4)9 (42.9)-55 (80.9)1054 (91.2)-
Mavros Kavos9 (90)8 (44.4)-20 (90.9)198 (76.5)-
Sulfur 14 (100)2 (25)5 (62.5)14 (100)51 (85)38 (90.5)
Sulfur 25 (100)7 (58.3)5 (100)8 (100)185 (96.4)42 (100)
Altar9 (75)10 (66.7)-35 (61.4)65 (65)-
Shrimp6 (60)6 (85.7)10 (90.9)324 (97.9)776 (99.6)1311 (99.5)
Keri 24 (75)5 (62.5)-110 (97.4)1010 (99.6)-
Marathia7 (100)6 (85.7)-18 (100)28 (87.5)-
Seal’s 14 (80)4 (30.8)-6 (60)8 (38.1)-
Blue 16 (75)6 (40)3 (37.5)15 (57.7)11 (21.2)7 (46.7)
Skotino5 (50)5 (55.6)-6 (50)25 (78.1)-
Cathedral6 (46.2)4 (44.4)3 (100)160 (94.7)54 (90)3 (100)
Alikes7 (77.8)3 (100)-27 (65.9)83 (100)-
Glika Nera6 (66.7)6 (54.6)-11 (34.4)31 (47)-
Lithistid10 (90.9)4 (33.3)5 (38.5)75 (98.7)110 (88.7)39 (61.9)
Elephant8 (61.5)8 (57.1)4 (57.1)132 (95.7)74 (87.1)21 (70)
Vronti3 (75)4 (57.1)-6 (85.7)32 (91.4)-
Neptune’s7 (87.5)2 (33.3)-110 (99.1)1105 (99.6)-
Achata 17 (87.5)3 (75)-65 (98.5)13 (92.9)-
Achata 23 (100)7 (53.9)-12 (100)206 (96.7)-
Blue 25 (45.5)2 (16.7)5 (71.4)160 (42.6)5 (20.8)266 (98.5)
Seal’s 210 (100)5 (55.6)5 (45.5)131 (98.5)33 (86.8)18 (69.2)
Kalymnos7 (46.7)6 (42.9)-91 (57.6)28 (45.2)-
Seal’s 38 (38.1)5 (22.7)-104 (57.5)33 (27.7)-
Pantieronisi8 (88.9)9 (45)4 (36.4)264 (45.5)36 (55.4)61 (83.6)
Polyaigos12 (100)2 (16.7)4 (57.1)27 (100)26 (59.1)10 (71.4)
Efstratios8 (47.1)5 (35.7)5 (83.3)21 (31.8)15 (33.3)28 (87.5)
Mean ± SE
(Mean % ± SE)		6.8 ± 0.4
(75.1 ± 3.9)		5.3 ± 0.4
(49.7 ± 4.2)		4.8 ± 0.6
(64.4 ± 6.9) 		74.3 ± 15.7
(77.9 ± 4.6)		196.1 ± 66.2
(72.6 ± 5.2)		153.7 ± 107.2
(81.6 ± 5.1)
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Digenis, M.; Ragkousis, M.; Dimitriadis, C.; Katsanevakis, S.; Gerovasileiou, V. Assessing the Motile Fauna of Eastern Mediterranean Marine Caves. Fishes 2025, 10, 383. https://doi.org/10.3390/fishes10080383

AMA Style

Digenis M, Ragkousis M, Dimitriadis C, Katsanevakis S, Gerovasileiou V. Assessing the Motile Fauna of Eastern Mediterranean Marine Caves. Fishes. 2025; 10(8):383. https://doi.org/10.3390/fishes10080383

Chicago/Turabian Style

Digenis, Markos, Michail Ragkousis, Charalampos Dimitriadis, Stelios Katsanevakis, and Vasilis Gerovasileiou. 2025. "Assessing the Motile Fauna of Eastern Mediterranean Marine Caves" Fishes 10, no. 8: 383. https://doi.org/10.3390/fishes10080383

APA Style

Digenis, M., Ragkousis, M., Dimitriadis, C., Katsanevakis, S., & Gerovasileiou, V. (2025). Assessing the Motile Fauna of Eastern Mediterranean Marine Caves. Fishes, 10(8), 383. https://doi.org/10.3390/fishes10080383

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