Search Results (164)

To determine the factors influencing juvenile recruitment of the kelp Eisenia bicyclis, a seven-year monitoring survey was conducted in an area affected by seismic subsidence caused by the 2011 earthquake and subsequent breakwater restoration. Juvenile recruitment was high in September 2011 and in May to June of 2013–2015, but low in 2012, 2016 and 2017. Analysis of the relationship between environmental factors and juvenile recruitment revealed that recruitment was associated with light intensity, with lower water temperature two months prior, and an increase in nutrients four months prior. The seasonal increase in nutrient concentrations during winter may have been influenced by the seasonal northwestward coastal current. In contrast, despite elevated nutrient concentrations, recruitment was relatively poor in 2016–2017. This might be attributed to the unstable seabed environment associated with the breakwater construction. Our monthly monitoring of both the number of E. bicyclis juvenile recruitments and environmental factors at the same site demonstrated that a time-lagged increase in nutrient concentrations and a decrease in water temperature are associated with Eisenia bicyclis juvenile recruitment. This study provides fundamental information on kelp recruitment that will contribute to predicting the recovery of kelp communities following disturbances and recruitment dynamics under environmental change. Full article

The amphi-atlantic rafting crab Plagusia depressa (Brachyura: Plagusiidae) has been recorded for the first time in European continental waters. Three specimens were captured manually in a rocky shore intertidal/subtidal of a beach located in the Gulf of Cádiz (Spain). These specimens were identified using morphological and molecular techniques (DNA barcoding of the 16S and COI genes). The 16S sequence suggests that these specimens are more closely related to African specimens than to those from the Caribbean. However, given the rafting behavior of this species, the specimens recorded in the Gulf of Cádiz may have originated from more distant regions within its distribution range for which molecular data are not available. We present a detailed morphological identification of these specimens and compare them with Plagusia squamosa, which occurs in the nearby Mediterranean Sea. This comparison contributes to clarifying the morphological traits that distinguish the two species. This finding highlights the role of southern Iberian waters in facilitating the introduction and establishment of non-native species. Full article

Four new species of Chromadorea (Nematoda) from marine benthic habitats in Chinese sea areas are described and illustrated. Halichoanolaimus parvulus sp. nov. is characterized by a comparatively smaller body; amphideal fovea comprising 4.5–5 turns; spicules arched, middle portion broad, progressively attenuating distally; gubernaculum slender, comprising two detached lateral elements becoming narrower toward the distal end; a short precloacal seta present; tail conico-cylindrical with three-fifths cylindrical portion in males. Cobbionema sinica sp. nov. is characterized by a pharynx with a distinct anterior bulb and an enlarged posterior portion; cephalic setae measuring 6 µm in length; amphideal fovea consisting of 4–4.5 turns; spicules 2.1–2.5 cloacal body diameters long, arrow-shaped; gubernaculum rod-like, parallel to the distal part of spicules, tail conico-cylindrical, terminating in an enlarged end and a distinct spinneret; precloacal supplement absent. Linhystera longispicula sp. nov. is characterized by cuticle with subtle transverse striations; six lateral labial sensory setae and four cephalic sensory setae are setiform, collectively forming a single circle; buccal cavity minute and slit-like, amphideal fovea circular far from the anterior end; curved, stout spicules reach a length exceeding two times the cloacal body diameter; gubernaculum is absent; conico-cylindrical tail without terminal setae. Linhystera nanhaiensis sp. nov. also has the common characteristics of the genus. It has relatively large body size with long conico-cylindrical tail; three terminal setae present; spicules resembling ox horns, reaching 1.2 times the cloacal body diameter, gubernaculum absent. This work contributes to the study of nematode diversity in China. Full article

Evaluating the bathymetric distribution of phytobenthic communities is essential for understanding the factors affecting habitat heterogeneity along a depth gradient. In the present study, we investigated the composition and vertical zonation patterns of phytobenthic communities across different bottom types (rocky and sedimentary) along the Turkish Aegean coasts. Dominant habitat types were identified in 175 depths and classified into 18 categories (Posidonia oceanica, Cymodocea nodosa, Halophila stipulacea, Halopteris spp., Stypopodium schimperi, Ericaria crinita, coralligenous, coralligenous/Mesophyllum spp., Jania spp./Halopteris spp., Ulva spp., rocky, rocky-turf, sandy, sandy-Caulerpa taxifolia var. distichophylla, sandy-Gongolaria montagnei var. compressa, silt, muddy, slime). Among the study sites, P. oceanica meadows (41%) were the dominant habitat in 70 depths, followed by sandy (30%), and rocky bottoms (11%). Total coverage of P. oceanica meadows was recorded as 28%, 80%, 76%, and 56% at 5 m, 10 m, 15 m, and 20 m depths, respectively. Seagrass meadows have started to be replaced by sandy bottoms at 30 m (52%) and 40 m (72%). Considering the bathymetrical divergence in phytobenthic community composition and abundance particularly in urban sites, reflected the influence of intense anthropogenic stressors. Here, non-destructive and cost-effective visual sampling technique based on in situ observations of phytobenthic community assemblages, proved to be an effective approach for the assessment of subtidal habitats. Full article

In terrestrial environments, nest site selection by birds and mammals is often related to the physical attributes of surrounding vegetation. Similarly, some elasmobranchs use different habitats, including kelps, as oviposition sites. However, habitat features that drive oviposition site selection remain poorly understood. We examined the relationship between kelp morphology (holdfast diameter, number of stripes, and total length) and kelp forest configuration (density, size structure, predator density) with egg presence to identify the factors influencing oviposition choice in the redspotted catshark (Schroederichthys chilensis). We conducted surveys over a latitudinal gradient (19° S to 39° S), encompassing much of the overlap between the kelp, Lessonia trabeculata and S. chilensis in Chile. Eggs were exclusively attached between the upper stipe and basal fronds of Lessonia trabeculata in all sites. At the individual scale, S. chilensis selected larger kelps within a patch, independent of the general population size structure. The number of eggs and clutches was positively associated with stipe length and holdfast diameter. Across all sites, egg-bearing kelps were consistently clustered at a similar depth in the kelp forest rather than being randomly distributed. At the site scale, egg number had a negative correlation with their main predator abundance, Taliepus dentatus, and juvenile kelp density. These results suggest that S. chilensis shows low plasticity in substrate use, as evidenced by non-random, consistent oviposition in kelp morphology along a latitudinal gradient. Our results underscore the need to incorporate kelp size thresholds and the protection of egg-bearing aggregations into harvesting regulations, as overexploitation of L. trabeculata directly threatens the reproductive viability of S. chilensis. Full article

The kelp genus Eisenia Areschoug is represented by two species in the Southeast Pacific: Eisenia cokeri, distributed in Peru and Chile, and E. gracilis, endemic to Peru. However, the taxonomic distinction between these species has long been questioned, and it remains unclear whether E. cokeri is conspecific with the Northeast Pacific species E. arborea. To address these issues, we conducted an integrative taxonomic assessment combining morphological analyses, molecular phylogenetics, and molecular species delimitation approaches. Sampling for morphological and molecular analyses was carried out in subtidal zones at five localities along the Peruvian coast, and an additional locality in Chile was included for molecular analyses where E. cokeri was documented. Peruvian Eisenia species exhibited consistent morphological differentiation, including differences in thallus size, holdfast diameter, stipe modifications (e.g., longitudinal division and pseudostipe formation), frond division, frond margins, and surface roughness, as supported by morphometric analyses. Phylogenetic reconstructions based on mitochondrial and chloroplast markers, together with concordant results from multiple species delimitation methods (ABGD, GMYC, and bPTP), consistently recovered three independent evolutionary lineages corresponding to E. cokeri, E. gracilis, and a distinct lineage of Eisenia from the Desventuradas Islands (Chile). Our results confirm the taxonomic distinctiveness of E. cokeri and E. gracilis, demonstrate that E. cokeri is genetically distinct from E. arborea, and reveal the presence of a previously unrecognized lineage of Eisenia in the Southeast Pacific. These findings refine species boundaries within the genus and provide a robust framework for the management and conservation of these endemic, foundation, habitat-forming species. Full article

The family Capitellidae performs critical roles in bioturbation and sediment remediation within global marine benthic ecosystems. However, they are a taxonomically challenging group due to their simple morphology and a ‘morphological mosaic’, where traditional classificatory traits, such as thoracic chaetiger counts, appear convergently across genera. Previous multi-locus studies (using 18S, 28S, H3, and COI) first highlighted this conflict, revealing the polyphyly of major genera like Notomastus and even Leiochrides itself (based on unidentified specimens). More recently, mitogenomic studies uncovered massive gene order rearrangements and a conflicting topology but did not include Leiochrides. Critically, with no complete mitogenome reported for a formally identified Leiochrides species, its true phylogenetic position and the validity of its polyphyly remain unresolved. To address this critical gap, we sequenced and characterized the first complete mitochondrial genome from a formally identified species, Leiochrides yokjidoensis, recently described from Korean waters. The complete mitogenome was 17,933 bp in length and included the typical 13 protein-coding genes (PCGs), 2 ribosomal RNAs (rRNAs), and 22 transfer RNAs (tRNAs). Gene order (GO) analysis revealed the occurrence of gene rearrangements in Capitellidae and in its sister clade, Opheliidae. A phylogenomic analysis using the amino acid sequences of 13 PCGs from 30 species established the first robust systematic position for the genus Leiochrides (based on this formally identified species). Phylogenetic results recovered Leiochrides as a sister group to the clade comprising Mediomastus, Barantolla, Heteromastus, and Notomastus hemipodus (BS 99%). This distinct placement confirms that Leiochrides represents an independent evolutionary lineage, phylogenetically separate from the polyphyletic Notomastus complex, despite their morphological similarities. Furthermore, our analysis confirmed the polyphyly of Notomastus, with N. hemipodus clustering distinctly from other Notomastus species. Additionally, signatures of positive selection were detected in ND4, and ND5 genes, suggesting potential adaptive evolution to the subtidal environment. This placement provides a critical, high-confidence anchor point for the genus Leiochrides. It provides a reliable reference to investigate the unresolved polyphyly suggested by previous multi-locus studies and provides compelling evidence for the hypothesis that thoracic chaetiger counts are of limited value for inferring phylogenetic relationships. This study provides the foundational genomic cornerstone for Leiochrides, representing an essential first step toward resolving the systematics of this taxonomically challenging family. Full article

We describe a new species of Desmoscolex collected from subtidal muddy sediments off Jindo Island, on the southern margin of Korea’s west coast. Desmoscolex (Desmoscolex) curuvus sp. nov. is distinguished by 17 main rings, a 9/8 somatic setal arrangement, subdorsal setae with a slightly swollen and hollow distal end, an oval head with laterally extended foreign material, a rounded amphidial fovea confined within the head region, and broad cephalic setae bearing a fine central canal with lateral membranes. The terminal ring is strongly bent ventrally. Females exhibit pronounced sexual dimorphism, including a pair of dorsal setae on the thirteenth main ring and a thicker terminal ring (maximum width 25–26 μm in males and 24–31 μm in females). High-resolution scanning electron microscopy (SEM) observations revealed a distinctive lip-region ultrastructure composed of a tuberculate membrane and six fragment-like membranous elements, representing a rare configuration within the genus. By documenting a new species possessing membranous structures in the cephalic setae and providing detailed ultrastructural characterization of the lip region, this study offers important new evidence for refining species delimitations in Desmoscolex. These findings underscore the diagnostic value of lip-region morphology and highlight the need for targeted sampling and further ultrastructural analyses to better resolve the hidden morphological diversity of the genus, particularly in the underexplored northwestern Pacific. Full article

We describe two new species of Paradraconema from subtidal sediments of Korean waters: P. tamraense sp. nov. from Jeju Island and P. gangchii sp. nov. from Dokdo Island. Although the epithet tamraense had appeared previously in the literature, it was treated as a nomen nudum and therefore lacked nomenclatural availability under the ICZN. In this study, the species is newly and validly established based on a critical reassessment of the original material, supported by new line drawings and detailed observations using differential interference contrast (DIC) and scanning electron microscopy (SEM). Paradraconema amraense sp. nov. is characterized by a slender body; pharyngeal annules bearing weakly developed longitudinal bars with smooth margins; a narrow lateral field at midbody; abundant and relatively long somatic setae; a head capsule partially covered with vacuolated ornamentation; an amphidial fovea that is elongate loop-shaped in males and circular, unispiral in females; eleven cephalic adhesion tubes (CAT); and comparatively long sublateral adhesion tubes (SlAT) and subventral adhesion tubes (SvAT). Paradraconema gangchii sp. nov. is characterized by a slender body; cuticle ornamentation with numerous longitudinal bars bearing finely crenulated margins in the pharyngeal region; sparse and short somatic setae; a head capsule fully covered with vacuolar ornamentation (reticulate under SEM); an amphidial fovea that is elongate loop-shaped in males and circular, unispiral, slightly over one coil in females; relatively short spicules (36–46 µm); eleven CAT; and relatively short SlAT and SvAT. SEM revealed several fine morphological features not previously documented in the genus, including the precise number and arrangement of CAT and detailed structures of the cuticle ornamentation and lip region. This study provides comprehensive SEM-based documentation for Paradraconema, increases the number of valid species in the genus to thirteen, and enhances our understanding of draconematid diversity in the northwestern Pacific. Full article

This paper reports two newly discovered species of Tricoma (Tricoma)—T. (T.) discrepans sp. nov. and T. (T.) parasetosa sp. nov.—obtained from the subtidal sediments at a depth of 13 m around Jindo Island, Korea. Tricoma (T.) discrepans sp. nov. differs from its congeners in possessing 40–41 main rings, an uncovered first main ring, large vesicular amphidial fovea, and a distinctly thickened tail cuticle that is densely covered with secretions and adhering particles. Somatic setae in males exhibit pronounced sexual dimorphism, with the subventral setae more than twice as thick as the subdorsal setae, a morphological feature documented here for the first time within the subgenus Tricoma (Tricoma). Tricoma (T.) parasetosa sp. nov. can be recognized by 31 (rarely 32) main rings, two pairs of long, thick posterior somatic setae inserted on massive peduncles, a vesicular amphidial fovea extending to the second main ring, and a gubernaculum proximal end gently curved ventrally. Although the labial region is indistinct, the species bears two conspicuous lateral labial projections and a prominent cephalic concretion. Together, these results broaden the current understanding of Tricoma diversity in the northwestern Pacific and emphasize additional morphological variation within Desmoscolecida based on detailed Differential Interference Contrast (DIC) and Scanning Electron Microscope (SEM) analyses. Full article

Invasive species can alter community composition and ecosystem functioning. In the subtidal rocky shores of Arraial do Cabo Bay, southeastern Brazil, the invasive coral Tubastraea spp. has established populations, raising concerns about long-term impacts on native benthic communities. This study investigates temporal shifts in β-diversity across 44 fixed plots containing Tubastraea spp., monitored over 383 days. Underwater photographic surveys and multivariate analyses identified nine distinct benthic community types, each forming mosaic structures of sessile organisms. Temporal β-diversity analyses revealed that only the group characterized by Tubastraea, crustose calcareous algae and the zoantharian Palythoa caribaeorum showed significant differences between species gains and losses over time, suggesting temporal-scale dependency. Key contributors to community dissimilarity included P. caribaeorum, crustose calcareous algae, turf, the sponge genus Darwinella, and Tubastraea. This study highlights the importance of considering both spatial and temporal heterogeneity when assessing the ecological impact of marine invasive species. Our findings underscore the need for multi-scale monitoring to fully understand the dynamics of tropical subtidal ecosystems under biological invasion. While numerous studies report a correlation between Tubastraea abundance and shifts in ecological diversity, this relationship may be weak, as critical drivers such as the complexity of community organization are rarely accounted for. Full article

Although effects of heavy metals in sediments on macrobenthic organisms have been extensively studied, few investigations have simultaneously assessed the influence of heavy metals in seawater and sediments on macrobenthic communities. This study investigated subtidal macrobenthic communities of Asan Bay, a coastal area in South Korea subject to extensive anthropogenic disturbances. It aimed to assess sources of heavy metals in seawater and sediments and evaluate their influence on the structure and composition of macrobenthic communities. Our findings suggest that cadmium (Cd), chromium (Cr), arsenic (As), and mercury (Hg) in seawater mainly originate from terrestrial inputs. Although the concentrations of heavy metals in seawater and sediments at most sampling stations complied with the Korean Environmental Quality Standards, the results of redundancy analysis (RDA), Spearman correlation, distance-based linear models (DistLM), and distance-based redundancy analysis (dbRDA) indicated that these heavy metals still influenced the structure of macrobenthic communities. Heavy metals in seawater were found to have a greater impact than metals in sediments, with Cr in seawater exerting the most decisive influence on macrobenthos (RDA showed that Cr explained 47.6% of the constrained species–environment relationship). Thus, Cr concentrations in bay seawaters should receive attention. Existing seawater quality standards may need to be reconsidered to reflect their effects on macrobenthic communities better. Full article

The Beibu Gulf’s ocean circulation system regulates regional marine ecosystems, sediment transport, and coastal geomorphology while also supporting vital economic activities. This study integrates one-year current observations from four in-situ current observation stations (B1−B4) with simulations using the Regional Ocean Modeling System (ROMS) to characterize circulation dynamics in the gulf. Observations show persistent northward subtidal currents west of Hainan Island year-round, primarily sustained by tidal-induced residual currents. These currents briefly reverse southward during strong northerly wind events, whereas subtidal currents in the northern Beibu Gulf are more wind-dependent, showing pronounced seasonal variations. Numerical results confirm that winter circulation is dominated by a basin-wide cyclonic gyre driven by northeasterly monsoons. In summer, circulation in the northern gulf is cyclonic under southeasterly winds, but turns anticyclonic when southwesterly winds prevail, indicating strong sensitivity to summer monsoon wind direction. By combining multi-station observations and numerical simulations, this study provides a systematic characterization of the seasonal circulation of the oceanic system in the Beibu Gulf, offering new insights into its dynamic mechanisms. Full article

The eastern North Pacific Ocean coastline (from the Salish Sea to the western Aleutian Islands) is highly glaciated with relic sediment deposits scattered throughout a highly contoured and variable bathymetry. Oceanographic conditions feature strong currents and tidal exchange. Sand wave fields are prominent features within these glaciated shorelines and provide critical habitat to sand lance (Ammodytes spp.). Despite an awareness of the importance of these benthic habitats, attributes related to their structure and characteristics remain undocumented. We explored the micro-bathymetric morphology of a subtidal sand wave field known to be a consistent habitat for sand lance. We calculated geomorphic attributes of the bedform habitat, analyzed sediment composition, and measured oceanographic properties of the associated water column. This feature has a streamlined teardrop form, tapered in the direction of the predominant tidal current. Consistent flow paths along the long axis contribute to well-defined and maintained bedform morphology and margin. Distinct patterns in amplitude and period of sand waves were documented. Strong tidal exchange has resulted in well-sorted medium-to-coarse-grained sediments with coarser sediments, including gravel and cobble, within wave troughs. Extensive mixing related to tidal currents results in a highly oxygenated water column, even to depths of 80 m. Our analysis provides unique insights into the physical characteristics that define high-quality habitat for these fish. Further work is needed to identify, enumerate, and map the presence and relative quality of these benthic habitats and to characterize the oceanographic properties that maintain these benthic habitats over time. Full article

Plastic debris is a pervasive and persistent threat to marine ecosystems. Microplastics (plastics < 5 mm) are increasing in a variety of marine habitats, including open water systems, shorelines, and benthic sediments. It remains unclear how microplastics distribute and accumulate in marine systems and the extent to which this pollutant is accessible to marine taxa. We examined subtidal benthic sediments and beach sediments in critical nearshore habitats for forage fish species—Pacific sand lance (Ammodytes personatus), Pacific herring (Clupea pallasi), and surf smelt (Hypomesus pretiosus)—to quantify microplastic concentrations in the spawning and deep-water habitats of these fish and better understand how microplastics accumulate and distribute in nearshore systems. In the San Juan Islands, we examined an offshore subtidal bedform in a high-flow channel and beach sites of protected and exposed shorelines. We also examined 12 beach sites proximate to urban areas in Puget Sound. Microplastics were found in all samples and at all sample sites. Microfibers were the most abundant, and flakes were present proximate to major shipyards and marinas. Microplastics were significantly elevated in Puget Sound compared to the San Juan Archipelago. Protected beaches had elevated concentrations relative to exposed beaches and subtidal sediments. Microplastics were in higher concentrations in sand and fine-grain sediments, poorly sorted sediments, and artificial sediments. Microplastics were also elevated at sites confirmed as spawning habitats for forage fish. The model results indicate that both current speed and proximate urban populations influence nearshore microplastic concentrations. Our research provides new insights into how microplastics are distributed, deposited, and retained in marine sediments and shorelines, as well as insight into potential exposure in benthic, demersal, and shoreline habitats. Further analyses are required to examine the relative influence of urban populations and shipping lanes and the effects of physical processes such as wave exposure, tidal currents, and shoreline geometry. Full article