Coral Reefs最新文献

Cycles of disturbance and recovery govern the temporal dynamics of living coral cover on coral reefs. Monitoring the state of the Great Barrier Reef at regional and individual reef scales has been ongoing by the Long-Term Monitoring Program at the Australian Institute of Marine Science since 1986. After a period of relative stability between 1986 and 2010, the latest decade of surveys recorded increased frequency of intense, large-scale disturbance events and coral cover has reached unprecedented lows and highs in each region. Following the consecutive bleaching events in 2016 and 2017, widespread recovery occurred on the northern and central Great Barrier Reef between 2017 and 2022, which was halted in 2023. An examination of the effects of the 2022 bleaching event revealed that the direct and indirect impacts of this event, along with ongoing crown-of-thorns starfish outbreaks, notable incidences of coral disease, and the passage of a tropical cyclone all contributed to the most recent coral cover changes across the Great Barrier Reef. The prognosis for future disturbances suggests increasing and longer-lasting marine heatwaves, continuing severe tropical cyclones and the ongoing risk of outbreaks of crown-of-thorns starfish. Although the observed capacity for recovery is a cause for cautious optimism for the overall state of the Great Barrier Reef, there is increasing concern for its ability to continue to bounce back in the face of escalating climatic pressure.

Heat stress-induced bleaching has been shown to lower the photosynthetic and physiological performances and even causes mortality in giant clams. However, there is a lack of information on the responses of sub-tropical giant clams to bleaching stress as well as their recovery from bleaching. Here we exposed the giant clams Tridacna crocea from sub-tropical Okinawa to different temperature conditions for 21 days and then examined their recovery at control temperatures (28–29 °C) within 42 days. T. crocea in control and in 30–31 °C retained their colors, whereas bleaching was observed in 32–33 °C and in the increasing temperatures (29–33 °C, 1 °C change every 5 days). The F_v/F_m decreased at 32–33 °C and in the increasing temperatures (29–33 °C), even before the onset of bleaching, but the F_v/F_m returned to baseline values at day 9 of recovery period. Zooxanthellae density and chlorophyll a + c concentrations were decreased, whereas the zooxanthellae cell size was increased in all elevated temperatures at day 21 of exposure period. Respiration (R) in all temperature conditions was not affected during exposure period, whereas gross photosynthesis (P_g) and P_g/R were reduced at 32–33 °C. At day 42 of recovery period, most bleached individuals regained their colors, phototrophic potential, and zooxanthellae population. No giant clams died within 21 days of exposure period, but mortalities were observed at 32–33 °C and at increasing temperatures (29–33 °C) during recovery period. This study shows that the sub-tropical giant clams are vulnerable to heat stress, but their ability to recover may suggest their persistence in a warming ocean.

Antipathes galapagensis is a prevalent habitat-forming black coral in subtidal ecosystems of the Galápagos Marine Reserve (GMR). Despite their ecological importance and status as a CITES-regulated order, little is known about their depth distribution, population structure and ecology in the GMR. Surveys were conducted in 2021 and 2022 at 9 sites in the central Galápagos Archipelago to investigate how black coral densities, occupancy, size, habitat utilization, and epizoan overgrowth varied between 2.0 and 20.0 m depth. The shallowest black corals occurred at 3.4 m depth, one of the shallowest occurrences of an Antipathes spp. in the world. Coral density increased with depth, with a maximum density of 5.2 colonies per m² observed across the depth range surveyed. Occupancy modeling also yielded curves with increasing probabilities of black coral presence with depth at all sites. Colony height increased with depth at 8 out of 9 sites and was positively correlated with coral density at 6 of 9 sites. Overall, 47% of colonies surveyed occupied cryptic habitats and 53% were attached to exposed substrate, but black coral habitat usage patterns varied with depth at 5 of 9 sites. At these sites, colonies on shallower transects (5.0, 10.0 m depth) more frequently displayed cryptic habitat usage while colonies along the deeper transects (15.0, 20.0 m) were more often exposed. In general, coral density, probability of occupancy, height, and exposed habitat utilization increased with depth, while the average degree of overgrowth and number of epibiont taxa were unrelated to depth. Five hypotheses regarding factors potentially limiting the shallow (upper) depth distribution of A. galapagensis—ranging from negative impacts of the physical environment to high predation on exposed substrates—are presented for future testing. These results provide a comprehensive ecological characterization of Galápagos black coral populations that can be used to assess the impact of future environmental change and applied to management decisions for this key marine foundation species in the GMR.

Endemic to the Brazilian fauna, the brain coral Mussismilia hispida is the second most widespread zooxanthellate coral of the South-west Atlantic and, most importantly, is within the main reef-building species of the region. Counterintuitively, M. hispida has one of its most abundant populations near its southernmost distributional limit, the Alcatrazes Archipelago off the coast of São Paulo State. On this archipelago, colonies thrive from 2 to over 20 m deep, and in some localities, M. hispida covers more than 50% of the rocky shore. Although more resistant to bleaching than other coral species, a capacity enhanced by colder water resurgence around the archipelago, signs of a coral disease affecting some colonies were recorded in 2019, simultaneously with a severe bleaching event. Diseased corals had tissue loss and a distinct white lesion on the corals’ tissue, suggesting that it may be a White Plague disease. Using 16S rRNA metabarcoding, we compared the microbial community associated with the part of the colonies presenting signs of disease to those apparently healthy. Results indicate that the microbiota genera from healthy and diseased colony portions are highly variable, suggesting community dysbiosis and alterations in the metabolic pathways of the microbiome. While it was not possible to identify a pathogen or a pathogenic consortium associated with the disease, the overall microbial signature, characterized by the presence of Roseimarinus, Carboxylicivirga, Tepidibacter, Vallitalea, and Halodesulfovibrio, is similar to that found in diseased Caribbean massive corals.

Life history characteristics of cryptobenthic reef fishes (CRFs), such as their fast growth and reproductive rates, near-shore larval retention and high turnover, predispose these species to rapid diversification and cryptic speciation. This may be particularly true for isolated CRF populations. The sailfin blenny, Emblemaria pandionis, is widespread throughout the Caribbean and is found on the reefs of the Flower Garden Banks, an isolated reef system in the NW Gulf of Mexico. Using DNA barcoding and multi-locus delimitation, we show that E. pandionis is a species complex comprised of at least four distinct taxonomic units in the Caribbean, one at the Flower Garden Banks, a second in eastern Florida, a third in the central Caribbean and a fourth in Curaçao. The phylogenetic relationships within the E. pandionis species complex are defined by well-established phylogeographic barriers to gene flow in the Caribbean. Populations of E. pandionis from eastern Florida are genetically distinct from populations found in the Bahamas, highlighting the role of the Florida Strait as a strong barrier to gene flow and populations in Curaçao are deeply divergent from all other populations sampled in the Caribbean. Results from this study highlight the roles of isolated reefs and ocean currents in the speciation of cryptobenthic reef fishes.

Metabarcoding is revolutionising the analysis of biodiversity in marine ecosystems, especially as it provides a means of detecting and identifying cryptic life stages in field samples. The planktonic larval stage of many species underpins the abundance and distribution of adult populations but is challenging to characterise given the small size of larvae and diffuse distributions in pelagic waters. Yet, planktonic larval dynamics are key to understanding phenomena observed in adult populations, such as the boom-and-bust dynamics exhibited by some echinoderms. Rapid changes in echinoderm population density can have significant effects on local benthic ecosystems. For example, outbreaks of the crown-of-thorns sea star (CoTS) on the Great Barrier Reef (GBR) have led to considerable declines in coral cover. Here, we used a DNA metabarcoding approach to investigate the spatio-temporal distribution and diversity of echinoderm larvae on the GBR, including CoTS. Generalised linear mixed models revealed that echinoderm larval richness, was significantly correlated with temporal variables (i.e. season and year) which is consistent with expected fluctuations in larval output based on adult spawning periodicity. However, neither site-specific differences in echinoderm larval richness, nor correlations between larval composition and environmental, temporal, or spatial variables were found. This study validates the utility of metabarcoding approaches for detecting and characterising echinoderm larvae, including CoTS, which could prove useful to future monitoring efforts. Our findings suggest that metabarcoding can be used to better understand the life history of planktonic larvae, and analyses combining environmental (e.g., temperature, nutrients) and oceanographic (e.g., currents) data could deliver valuable information on the factors influencing their spatio-temporal distributions.

Endosymbiotic dinoflagellates in the family Symbiodiniaceae are physiologically and ecologically important for reef-building corals. Certain symbiotic lineages may provide adaptive functions that aid corals in coping with and surviving rapid environmental and climate changes; and thus, there is a growing interest in exploring Symbiodiniaceae communities and their associated roles. Steroid biomarkers have been proposed as a means of identifying species-specific symbionts, but their reliability has yet to be examined through comparison of different coral species that harbor known Symbiodiniaceae. Here, steroid molecular and δ¹³C analyses are applied to four stony corals that host identified (Porites lobata and Galaxea fascicularis) or undescribed (Goniopora tenuidens and Goniastrea minuta) Symbiodiniaceae to address this issue. The 23-Me C₂₈Δ^5,22, 23,24-Me C₂₉Δ^5,22, and dinosterol are characteristic of P. lobata; while, C₂₉Δ⁵, gorgosterol, and 4α-methylgorgostanol are diagnostic for G. fascicularis, tracking the marked differences in their Symbiodiniaceae assemblages. These two steroid groups also exhibit largely similar (− 20.6 to − 17.0‰) and visibly variable (− 24.1 to − 17.3‰) δ¹³C signatures, following the low and high diversity of symbionts in P. lobata and G. fascicularis, respectively. Our present results, together with previous reports, clearly demonstrate the effectiveness of steroid molecular and δ¹³C features in depicting Symbiodiniaceae population, providing a useful complement to Symbiodiniaceae genetic analysis. A further comparison of steroid characteristics between unclear and known Symbiodiniaceae in our four corals reveals the almost identical symbiotic population between G. minuta and G. fascicularis and a restricted range of symbiotic composition in G. tenuidens that is shared with G. fascicularis (and G. minuta). Additionally, the occurrence of 5α-stanols suggestive of anaerobic conversion on Δ⁵-sterols implies complex steroid interactions within coral–algae–microbe holobionts.

Global warming causes functional shifts and reorganisation in marine communities through range shifts to high-latitude reefs and cnidarian bleaching mortality in the tropics. Such changes threaten the integrity and structure of marine communities, especially as foundational and associated species are reduced or lost. However, comparatively little is known about the extent of range shifts and their ecological consequences for the overlooked components of marine ecosystems, such as octocorals and zoantharians (O + Z) on shallow coral reefs. As these groups play a crucial part in building complexity and sustaining life in reef communities, functional shifts in these taxa may cascade through the entire ecosystem, but these processes have not been quantified. Here, we examined the environmental drivers and functional consequences of spatial variation in octocoral and zoantharian communities across 27 sites in southern Japan, spanning from tropical to warm-temperate waters. We collated a trait database for 42 entities (species, genus, and family level identifications) of octocorals and zoantharians and calculated functional diversity and functional richness to measure functional compositional change. We identified five functional groups according to their trait similarities and identified how their abundances respond to changing environmental factors with general additive models (GAMs). We found functional shifts among octocorals and zoantharians across the tropical to temperate thermal gradient, with the abundances of two functional groups best explained by gradients in minimum sea surface temperature. Non-linear relationships between the functional groups and thermal gradients imply a more intricate relationship than expected, suggesting other non-temperature-based drivers, e.g., nitrogen or pH levels might also play an important role. Only functional group richness and species richness showed significant correlations with latitude, whilst functional diversity and functional richness did not. Our results indicate that octocoral and zoantharian communities and functionality potentially undergo shifts with clear community compositional changes, influenced by climate change across environmental gradients. However, the taxonomy and identification of these taxa remain difficult, and information on functional traits is often sparse or not species-specific, indicating a clear need for further basic zoological and ecological work on octocorals and zoantharians.

Coral reef ecosystems are declining and may not recover under future climate scenarios without intervention. Seeding reefs with corals bred in aquaculture is a promising restoration intervention; however, early coral recruits (spat) are vulnerable to overgrowth by benthic algae and maximizing their survival is essential for the feasibility of large-scale breeding operations. This study investigated the optimal light quality and intensity for spat survival and growth in the presence of algal communities typically used in coral aquaculture to induce larval settlement, but which might also outcompete spat and reduce survival during the grow-out period. Spat were exposed to two light spectra (blue and a full spectrum) at four light intensities (5–160 µmol m⁻² s⁻¹) over 12-week post-settlement. Survival was reduced under the highest intensity by nearly 40% compared to the lowest intensity. Light spectrum only affected survival at 60 µmol m⁻² s⁻¹—where survival was higher under blue compared to full spectrum light. Light treatments did not affect final spat size but spat were 33% smaller at the highest light intensity in weeks 6 and 8 due to overgrowth by crustose coralline algae (CCA), which was most abundant under these conditions. Low light intensity, on the other hand, favored green and brown algae, potentially due to their respective physiologies or less competition from crustose coralline algae. These results indicate that low light intensity presents several advantages for maintaining spat in coral aquaculture, including maximizing survival without significantly affecting growth, as well as minimizing husbandry and operating expenses.