Search Results (21)

We adapt previously developed conceptual and numerical models of ciguateric food chains on the Great Barrier Reef, Australia, to model the bioaccumulation of ciguatoxins (CTXs) in parrotfish, the simplest food chain with only two trophic levels. Our model indicates that relatively low (1 cell/cm²) densities of Gambierdiscus/Fukuyoa species (hereafter collectively referred to as Gambierdiscus) producing known concentrations of CTX are unlikely to be a risk of producing ciguateric fishes on the Great Barrier Reef unless CTX can accumulate and be retained in parrotfish over many months. Cell densities on turf algae equivalent to 10 Gambierdiscus/cm² producing known maximum concentrations of Pacific-CTX-4 (0.6 pg P-CTX-4/cell) are more difficult to assess but could be a risk. This cell density may be a higher risk for parrotfish than we previously suggested for production of ciguateric groupers (third-trophic-level predators) since second-trophic-level fishes can accumulate CTX loads without the subsequent losses that occur between trophic levels. Our analysis suggests that the ratios of parrotfish length-to-area grazed and weight-to-area grazed scale differently (allometrically), where the area grazed is a proxy for the number of Gambierdiscus consumed and hence proportional to toxin accumulation. Such scaling can help explain fish size–toxicity relationships within and between trophic levels for ciguateric fishes. Our modelling reveals that CTX bioaccumulates but does not necessarily biomagnify in food chains, with the relative enrichment and depletion rates of CTX varying with fish size and/or trophic level through an interplay of local and regional food chain influences. Our numerical model for the bioaccumulation and transfer of CTX across food chains helps conceptualize the development of ciguateric fishes by comparing scenarios that reveal limiting steps in producing ciguateric fish and focuses attention on the relative contributions from each part of the food chain rather than only on single components, such as CTX production. Full article

The hypothesis that disturbance to coral reefs creates new surfaces that increase the risk of ciguatera is premised upon the increased algal substrates that develop on these surfaces being colonised by high ciguatoxin (CTX)-producing Gambierdiscus species that proliferate and enter the ciguatera food chain. Current evidence indicates that new algal substrates are indeed rapidly colonised by Gambierdiscus. However, the requirement that these Gambierdiscus species include at least one that is a significant (high) CTX-producer is more likely a limiting step. While ambient environmental conditions impact the capacity of Gambierdiscus to bloom, factors that limit the growth of the bloom could influence (typically increase) the flux of CTX entering marine food chains. Additionally, new algal substrates on damaged reefs can be preferentially grazed to funnel ciguatoxins from Gambierdiscus to herbivores in disturbed reef areas. In societies consuming second trophic level species (herbivores, grazers, and detritivores), such funnelling of CTX would increase the risk of ciguatera, although such risk would be partially offset over time by growth (toxin-dilution) and depuration. Here, we review evidence for six potential mechanisms to increase ciguatera risk from disturbance to coral reefs and suggest a hypothesis where ecosystem changes could increase the flux of CTX to groupers through a shift in predation from predominately feeding on planktonic-feeding prey to mostly feeding on benthic-feeding prey, increasing the potential for CTX to accumulate. Evidence for this hypothesis is stronger for the Pacific and Indian Oceans, and it may not apply to the Caribbean Sea/Atlantic Ocean. Full article

Outbreaks of crown-of-thorn starfish (COTS) have caused dramatic declines in reefs through predation on corals, but the post-bloom effects of COTS may still potentially threaten the environment and living organisms due to massive organic decomposition. This stimulation experiment showed that the decomposition of COTS debris triggered an extra mineralization process and resulted in acidifying, hypoxic, and eutrophic seawater. Consequently, the photosynthetic efficiency of coral symbionts decreased by 83%, and coral bleached after removing the stress within two days, then the coral skeleton dissolved at rates of 0.02–0.05 mg cm⁻² day⁻¹. Within two weeks, the photosynthesis and growth of benthic algae were suppressed by 27–86% and 1.5–16%, respectively. The mortality of turf algae and coralline algae indicated compromised primary productivity and limited coral recruitment, respectively. However, macroalgae, as coral competitors, became the only survivors, with increasing chlorophyll content. This study suggests a continuing decline of reefs during the collapse phase of COTS outbreaks and highlights the need for improving control strategies for the COTS population. Full article

This study was carried out to determine the levels of resistance and resilience of kelp forests to large-scale physical disturbances. Our study site, Seongsan, Jeju Island, was impacted by super typhoon ‘Hinnamnor’. Before the typhoon, Seongsan had shown high ecosystem stability. Our results indicated that the ecological stability of a kelp forest facing a severe typhoon is strongly linked to the prevailing environmental conditions. Although typhoon impact resulted in a significant loss of brown macroalgae canopy, Ecklonia cava remained dominant within the kelp forest community. Resistance and resilience levels strongly depended on water temperature and movement and presence of turf-forming algae. Hence, hydrodynamic and biological factors strongly influence the overall stability of a kelp forest. We also report the first occurrences of a scleractinian coral species (i.e., Montipora millepora) at Seongsan, which became visible after canopy loss following the typhoon. Our findings provide valuable ecological information about the benthic community of kelp-dominated ecosystems and are essential to mitigate the impacts of expected climate change-driven rises in seawater temperature and the frequency of super typhoons. Full article

Published data were used to model the transfer of ciguatoxins (CTX) across three trophic levels of a marine food chain on the Great Barrier Reef (GBR), Australia, to produce a mildly toxic common coral trout (Plectropomus leopardus), one of the most targeted food fishes on the GBR. Our model generated a 1.6 kg grouper with a flesh concentration of 0.1 µg/kg of Pacific-ciguatoxin-1 (P-CTX-1 = CTX1B) from 1.1 to 4.3 µg of P-CTX-1 equivalents (eq.) entering the food chain from 0.7 to 2.7 million benthic dinoflagellates (Gambierdiscus sp.) producing 1.6 pg/cell of the P-CTX-1 precursor, P-CTX-4B (CTX4B). We simulated the food chain transfer of ciguatoxins via surgeonfishes by modelling Ctenochaetus striatus feeding on turf algae. A C. striatus feeding on ≥1000 Gambierdiscus/cm² of turf algae accumulates sufficient toxin in <2 days that when preyed on, produces a 1.6 kg common coral trout with a flesh concentration of 0.1 µg/kg P-CTX-1. Our model shows that even transient blooms of highly ciguatoxic Gambierdiscus can generate ciguateric fishes. In contrast, sparse cell densities of ≤10 Gambierdiscus/cm² are unlikely to pose a significant risk, at least in areas where the P-CTX-1 family of ciguatoxins predominate. The ciguatera risk from intermediate Gambierdiscus densities (~100 cells/cm²) is more difficult to assess, as it requires feeding times for surgeonfish (~4–14 days) that overlap with turnover rates of turf algae that are grazed by herbivorous fishes, at least in regions such as the GBR, where stocks of herbivorous fishes are not impacted by fishing. We use our model to explore how the duration of ciguatoxic Gambierdiscus blooms, the type of ciguatoxins they produce, and fish feeding behaviours can produce differences in relative toxicities between trophic levels. Our simple model indicates thresholds for the design of risk and mitigation strategies for ciguatera and the variables that can be manipulated to explore alternate scenarios for the accumulation and transfer of P-CTX-1 analogues through marine food chains and, potentially, for other ciguatoxins in other regions, as more data become available. Full article

Cosmopolitan species are rare in red algae, which have a low-dispersal capacity unless they are dispersed by human-mediated introductions. Gelidium crinale, a turf-forming red alga, has a widespread distribution in tropical and temperate waters. To decipher the genetic diversity and phylogeography of G. crinale, we analyzed mitochondrial COI-5P and plastid rbcL sequences from collections in the Atlantic, Indian, and Pacific Oceans. Phylogenies of both markers statistically supported the monophyly of G. crinale, with a close relationship to G. americanum and G. calidum from the Western Atlantic. Based on the molecular analysis from these materials, Pterocladia heteroplatos from India is here merged with G. crinale. Phylogeny and TCS networks of COI-5P haplotypes revealed a geographic structure of five groups: (i) Atlantic-Mediterranean, (ii) Ionian, (iii) Asian, (iv) Adriatic-Ionian, and (v) Australasia-India-Tanzania-Easter Island. The most common ancestor of G. crinale likely diverged during the Pleistocene. The Bayesian Skyline Plots suggested the pre-LGM population expansion. Based on geographical structure, lineage-specific private haplotypes, the absence of shared haplotypes between lineages, and AMOVA, we propose that the cosmopolitan distribution of G. crinale has been shaped by Pleistocene relicts. The survival of the turf species under environmental stresses is briefly discussed. Full article

Reef degradation and algae-farming fish alter the structures and compositions of coral-algal-microbial communities. We collected epilithic macroalgae in different reef conditions and damselfish territories. The microbial communities were characterized by subjecting the V3-V4 hypervariable region of the 16S rRNA gene to amplicon sequencing. Metagenomic analysis revealed 2 domains, 51 phyla, 112 orders, and 238 families and the dominance of Proteobacteria and Bacteroidota in both fair and degraded reefs inside and outside territories. Chloroflexi on the degraded reef was dominant and its proportion was almost two and a half times compared to the fair reef, whereas Cyanobacteria was low on the degraded reef. Bacteroidota was dominant on the fair reef, whereas Actinobacteriota was scarce on this reef. For the damselfish territories, Chloroflexi was dominant inside the territory, whereas Bacteroidetes were found outside the territory. Differences in the microbial species diversity and richness were not apparent between all sites; however, species evenness was higher on the degraded reef condition and lower outside the territory. Important potential pathogens of reef organisms, such as Vibrio, Photobacterium, and Phormidium, were found on the degraded reef areas inside the damselfish territory. The farming behaviors of damselfish influenced microbial communities by changing the epilithic algal matrix that harbors many microbial communities. This study provides useful information on microbial biota in coral reef habitats which is further applicable to reef conservation and coastal management. Full article

Environmental and human factors are inducing a drastic decline in many marine algae in regions with a high floristic richness as in the Canary Islands. Simultaneously, undescribed algal species continue to be discovered, suggesting a probable loss in diversity, before being properly identified and catalogued. Turf-forming Gelidiales occur in marine littoral communities from tropical to warm temperate regions and are challenging to identify correctly because of their small size and simple morphology. In the present study, we combined morphological and molecular phylogenetics methods to study a turf-forming species of the genus Pterocladiella from the Canary Islands (NE Atlantic). Both cox1 and rbcL gene analyses revealed a novel species described here, Pterocladiella canariensis sp. nov. The new species has no single unique morphological feature, but it is different by a distinctive combination of attributes, namely, minute size less than 18 mm in height, ribbon-like erect axes, small polygonal cortical cells, cystocarp circular in outline with placental tissue attached to the floor, spermatangial sori with sterile margins with spermatangia simultaneously formed on both sides of the blade, and tetrasporangia arranged in V-shaped rows. Phylogenies inferred from cox1 and concatenated genes (cox1 + rbcL) suggest a link to only two Pterocladiella species endemic to South Africa and Madagascar; nevertheless, the rbcL gene establishes P. canariensis as the earliest divergent lineage of the genus. Full article

Bioerosion on inshore reefs is expected to increase with global climate change reducing reef stability and accretionary potential. Most studies investigating bioerosion have focused on external grazers, such as parrotfish and urchins, whose biomass is more easily measured. Yet, cryptic endolithic bioeroders such as macroboring (worms, sponges and bivalves) and microboring taxa (fungus and algae) have the potential to be the dominant source of reef erosion, especially among inshore reef systems exposed to increased nutrient supply. We measured bioerosion rates of bioeroder functional groups (microborers, macroborers, and grazers), and their response to environmental parameters (temperature, light, turbidity, chlorophyll a), as well as habitat variables (coral cover, turfing algae, macroalgae) across two inshore turbid reefs of north Western Australia. Total bioerosion rates were low (0.163 ± 0.012 kg m⁻² year⁻¹) likely due to low light and nutrient levels. Macroborers were the dominant source of bioerosion and were positively correlated with turfing algae cover, highlighting the role of turf-grazing fish on endolithic bioerosion rates. Overall low bioerosion rates suggest that despite the reduced coral cover and carbonate production, these reefs may still maintain positive reef accretion rates, at least under current environmental conditions. However, an improved understanding of relationships between environmental drivers, habitat and grazing pressure with bioeroding communities is needed to improve predictions of reef carbonate loss with future climate change. Full article

Our goal was to understand the mechanisms behind the impact of nutrient enrichment at intermediate distances from aquaculture on the interactions of a subtidal macroalgae community with its main grazer, the sea urchin Paracentrotus lividus. We assessed the diversity and cover of the macroalgal community, the abundance and biometrics of the sea urchins, the carbon and nitrogen elemental and isotopic compositions, and their metabolome in two stations, at an intermediate distance (station A) and away (station B) from a fish cage facility in the Aegean Sea (Greece), during the warm and cold seasons. The nutrient input at station A favored a shift to a macroalgal assemblage dominated by turf-forming species, depleted of native-erected species and with a higher abundance of invasive algae. A stable isotope analysis showed fish-farm-associated nitrogen enrichment of the macroalgae and trophic transfer to P. lividus. A decrease in metabolites related to grazing, reproduction, and energy reserves was found in P. lividus at station A. Furthermore, the metabolomic analysis was able to pinpoint stress in P. lividus at an intermediate distance from aquaculture. The chosen combination of traditional ecology with omics technology could be used to uncover not only the sublethal effects of nutrient loading but also the pathways for species interactions. Full article

The persistence and resilience of marginal shallow coral reefs at their limits of environmental tolerance have declined due to chronic environmental degradation and climate change. However, the consequences for the natural recovery ability of reefs of disturbance remain poorly understood. This study considered the potential for natural recovery through coral recruitment on fringing reefs across different geographic regions under contrasting environmental conditions in Puerto Rico. Reefs in areas with significant water quality degradation and more severe physical impacts of hurricanes were expected to have lower coral recruit density and diversity, and therefore less potential for recovery. Sixteen reefs were assessed across three geographic regions. Degraded reefs sustained a lower percentage of live coral cover and had higher macroalgae and turf algae abundance. Locations affected by high PO₄, NH₃⁺ and optical brightness concentrations, high turbidity, and high sea surface temperature anomalies, chlorophyll-a concentration and light attenuation Kd₄₉₀ evidenced significantly lower coral recruit density and diversity. Hurricane-decimated reefs also exhibited impoverished coral recruit assemblages. Low coral recruitment could have important long-term implications under projected climate change and sea level rise, particularly in coastal urban habitats. There is a need to implement effective environmental conservation, ecological restoration and community participation strategies that facilitate enhanced coral recruitment success and assisted recovery processes. Full article

While studies show that nutrient pollution shifts reef trophic interactions between fish, macroalgae, and corals, we know less about how the microbiomes associated with these organisms react to such disturbances. To investigate how microbiome dynamics are affected during nutrient pollution, we exposed replicate Porites lobata corals colonized by the fish Stegastes nigricans, which farm an algal matrix on the coral, to a pulse of nutrient enrichment over a two-month period and examined the microbiome of each partner using 16S amplicon analysis. We found 51 amplicon sequence variants (ASVs) shared among the three hosts. Coral microbiomes had the lowest diversity with over 98% of the microbiome dominated by a single genus, Endozoicomonas. Fish and algal matrix microbiomes were ~20 to 70× more diverse and had higher evenness compared to the corals. The addition of nutrients significantly increased species richness and community variability between samples of coral microbiomes but not the fish or algal matrix microbiomes, demonstrating that coral microbiomes are less resistant to nutrient pollution than their trophic partners. Furthermore, the 51 common ASVs within the 3 hosts indicate microbes that may be shared or transmitted between these closely associated organisms, including Vibrionaceae bacteria, many of which can be pathogenic to corals. Full article

We review and develop conceptual models for the bio-transfer of ciguatoxins in food chains for Platypus Bay and the Great Barrier Reef on the east coast of Australia. Platypus Bay is unique in repeatedly producing ciguateric fishes in Australia, with ciguatoxins produced by benthic dinoflagellates (Gambierdiscus spp.) growing epiphytically on free-living, benthic macroalgae. The Gambierdiscus are consumed by invertebrates living within the macroalgae, which are preyed upon by small carnivorous fishes, which are then preyed upon by Spanish mackerel (Scomberomorus commerson). We hypothesise that Gambierdiscus and/or Fukuyoa species growing on turf algae are the main source of ciguatoxins entering marine food chains to cause ciguatera on the Great Barrier Reef. The abundance of surgeonfish that feed on turf algae may act as a feedback mechanism controlling the flow of ciguatoxins through this marine food chain. If this hypothesis is broadly applicable, then a reduction in herbivory from overharvesting of herbivores could lead to increases in ciguatera by concentrating ciguatoxins through the remaining, smaller population of herbivores. Modelling the dilution of ciguatoxins by somatic growth in Spanish mackerel and coral trout (Plectropomus leopardus) revealed that growth could not significantly reduce the toxicity of fish flesh, except in young fast-growing fishes or legal-sized fishes contaminated with low levels of ciguatoxins. If Spanish mackerel along the east coast of Australia can depurate ciguatoxins, it is most likely with a half-life of ≤1-year. Our review and conceptual models can aid management and research of ciguatera in Australia, and globally. Full article

The role of habitat degradation on the spread of the alien green alga Caulerpa cylindracea is reported here by comparing observations achieved through a multi-year assessment on three Mediterraneans habitats, namely Posidonia oceanica meadows, Phyllophora crispa turf, and coralligenous reefs. Due to the peculiarity of the study site, both natural-reference and impacted conditions were investigated. C. cylindracea occurred in all the studied habitats under impacted conditions. High susceptibility to the invasion characterized impacted P. oceanica, where Caulerpa cover reached 70.0% in summer months. C. cylindracea cover did not differ significantly among conditions in P. crispa turf, where values never exceeded 5.0%. Conversely, the invasive green algae was low in abundance and patchily distributed in coralligenous reefs. Our results confirmed that habitat loss enhances the spread of C. cylindracea, although with different magnitudes among habitats. Dead matte areas of P. oceanica represented the most vulnerable habitat among those analyzed, whereas coralligenous reefs were less susceptible to the invasion under both the studied conditions. Full article

Presence of mollusk assemblages was studied within red coralligenous algae Corallina officinalis L. along the southern Istrian coast. C. officinalis turfs can be considered a biodiversity reservoir, as they shelter numerous invertebrate species. The aim of this study was to identify mollusk species within these settlements using DNA barcoding as a method for detailed identification of mollusks. Nine locations and 18 localities with algal coverage range above 90% were chosen at four research areas. From 54 collected samples of C. officinalis turfs, a total of 46 mollusk species were identified. Molecular methods helped identify 16 gastropod, 14 bivalve and one polyplacophoran species. COI sequences for two bivalve species (Musculus cf. costulatus (Risso, 1826) and Gregariella semigranata (Reeve, 1858)) and seven gastropod species (Megastomia winfriedi Peñas & Rolán, 1999, Eatonina sp. Thiele, 1912, Eatonina cossurae (Calcara, 1841), Crisilla cf. maculata (Monterosato, 1869), Alvania cf. carinata (da Costa, 1778), Vitreolina antiflexa (Monterosato, 1884) and Odostomia plicata (Montagu, 1803)) represent new BINs in BOLD database. This study contributes to new findings related to the high biodiversity of mollusks associated with widespread C. officinalis settlements along the southern coastal area of Istria. Full article