Coral Reefs最新文献

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.

A habitat’s structural complexity is a key determinant of the recruitment and composition of associated communities. While the influence of the physical structure of corals on coral reef fish recruitment is well studied, the significance of other benthic components, like macroalgae, remains unclear. We used experimental patches of the canopy-forming macroalga Sargassum to assess the influence of macroalgal complexity, which was manipulated by altering thallus density and biomass, on coral reef fish recruitment. We established twenty-five 75 × 75 cm patches on the reef flat of Orpheus Island, (inshore, central Great Barrier Reef) during austral summer. Patches were randomly divided into five treatments of varying Sargassum thallus density (3–9 thalli) and/or biomass (177–779 g per patch) and surveyed daily for recruiting fishes for 18 d. We recorded 35 fish species recruiting to our patches, with Sargassum biomass having the greatest influence on fish recruits’ abundance and species richness. Comparisons between treatments with equal thallus density but varying biomass revealed a positive association between Sargassum biomass and fish species richness and abundance (up to ~ 2.5-fold differences). Additionally, treatments with similar total Sargassum biomass but different density revealed a negative relationship between density and fish species richness and abundance (20–30% reduction). These positive associations with Sargassum thallus biomass suggest that recruiting fishes favour the fine-scale complexity of intra-thallus spaces, rather than the larger, inter-thallus gaps. This study highlights that fine-scales of complexity within tropical macroalgal beds may influence the reef fish recruitment value of these often-underappreciated areas.

The impacts of ocean acidification on coral reef macroalgal community composition and metabolism have implications for the habitat supporting capacity of future reefs. In this pilot study, we use co-located semi-hourly measurements of total dissolved inorganic carbon (DIC), total alkalinity, and the stable carbon isotope composition of DIC (δ¹³C_DIC) over a 27 + h period from Tetiaroa Atoll, French Polynesia, to investigate the potential for reef carbonate chemistry to record information related to benthic photosynthetic community composition and response to natural gradients in ambient acidity and dissolved carbon dioxide. The results of this preliminary sampling and modeling exercise suggest that Tetiaroa’s macroalgal communities express plastic carbon-concentrating mechanisms (CCMs) over daily cycles of productivity but may potentially vary this expression as a function of ambient CO₂ and acidity within the ecosystem. Additional studies are, therefore, underway to investigate the implications of these observations for reef macroalgal compositional differences under rapidly acidifying oceans.

Black corals are important components of mesophotic and deep-water marine habitats. Their presence at great depths (e.g., 50 to 200 m) makes accessibility difficult, limiting our understanding of the associated biodiversity. Amphipods dominate vagile epifauna in marine habitats around the world, fulfilling important ecosystem functions. However, there are no studies on amphipods exclusively associated with black corals, including relationships between their ecological patterns (e.g., abundances) and the size of coral colonies. We investigated the epifaunal composition and abundance associated with black coral colonies of Antipathella wollastoni in the subtropical eastern Atlantic Ocean. In total, 1,736 epifaunal individuals were identified, of which 1,706 (98.27%) were amphipods, belonging to 6 taxa. We identified and described a new amphipod genus and species within the Stenothoidae family, Wollastenothoe minuta gen. nov., sp. nov., which outnumbered the amphipod assemblage (86.15%) and provided a complete taxonomic key of Stenothoidae family including this new finding. For the first time, the association between an amphipod species and a black coral was described, including a strong correlation between coral colony size and amphipod abundances. This study demonstrates that epifauna associated with mesophotic black corals remains largely undescribed.

Variable temperature regimes that expose corals to sublethal heat stress have been recognized as a mechanism to increase coral thermal tolerance and lessen coral bleaching. However, there is a need to better understand which thermal regimes maximize coral stress hardening. Here, standardized thermal stress assays were used to determine the relative thermal tolerance of three divergent genera of corals (Acropora, Pocillopora, Porites) originating from six reef sites representing an increasing gradient of annual mean diel temperature fluctuations of 1–3 °C day⁻¹. Bleaching severity and dark-acclimated photochemical yield (i.e., F_v/F_m) were quantified following exposure to five temperature treatments ranging from 23.0 to 36.3 °C. The greatest thermal tolerance (i.e., F_v/F_m effective dose 50) was found at the site with intermediate mean diel temperature variability (2.2 °C day⁻¹), suggesting there is an optimal priming exposure that leads to maximal thermal tolerance. Interestingly, Acropora and Pocillopora originating from the least thermally variable regimes (< 1.3 °C day⁻¹) had lower thermal tolerance than corals from the most variable sites (> 2.8 °C day⁻¹), whereas the opposite was true for Porites, suggesting divergent responses across taxa. Remarkably, comparisons across global studies revealed that the range in coral thermal tolerance uncovered in this study across a single reef (< 5 km) were as large as differences observed across vast latitudinal gradients (300–900 km). This finding indicates that local gene flow could improve thermal tolerance between habitats. However, as climate change continues, exposure to intensifying marine heatwaves is already compromising thermal priming as a mechanism to enhance coral thermal tolerance and bleaching resistance.

Predicting the potential distribution of a non-native species can assist management efforts to mitigate impacts on recipient ecosystems. However, such predictions are lacking for marine species, such as the non-native regal demoiselle, Neopomacentrus cyanomos, that is currently expanding its distribution in the western Atlantic. We used correlative species distribution models with three common algorithms to predict suitable habitat for N. cyanomos in the region. We compared models developed using native, non-native, and global occurrences to differentiate drivers across separate ranges using a suite of 12 environmental characteristics. While final models included an ensemble of variables, the majority ranked the combined effect of temperature variables as a key predictor correlated with the distribution of N. cyanomos. Habitat suitability increased as water temperatures increased beyond 16 °C and where annual thermal ranges were greater than 10 °C at the shallowest depth with substrate within a study cell (~ 9.2 km² resolution). Habitat suitability also increased where maximum surface temperatures were greater than 27 °C. In the non-native range, the proportion of reef available in each cell was another important variable increasing the suitable habitat for N. cyanomos. Our models predicted high habitat suitability for N. cyanomos throughout the Greater Caribbean, in higher latitudes along North and South American Atlantic coasts, in the eastern Pacific Ocean, and highlights key areas where managers can monitor and target potential removal efforts. The distribution of this non-native species is likely to continue expanding throughout the region with little known about potential implications on native communities.

Increasingly frequent and severe bleaching events driven by climate change are decreasing coral populations worldwide. Recovery of these populations relies on reproduction by the survivors of such events including local and upstream larval sources. Yet, corals that survive bleaching may be impaired by sublethal effects that suppress reproduction, reducing larval input to reefs, and consequently impeding recovery. We investigated the impact of the 2020 mass-bleaching event on Acropora millepora reproduction on inshore, turbid reefs in Woppaburra sea Country (the Keppel Islands), to improve our understanding of the effects of bleaching on coral populations. A. millepora experienced high bleaching incidence but low mortality across the island group during this event and thus constituted an ideal population to investigate potential sublethal effects on reproductive output. Six months after the heat wave, and just prior to spawning, we collected, decalcified, and dissected samples from 94 tagged A. millepora colonies with a known 2020 bleaching response, to investigate the relationships between stress severity and reproduction. Despite having regained their pigmentation, we detected a significant reduction in fecundity in colonies that had bleached severely. Considering the impact of the bleaching event on the coral population sampled (i.e., mortality, bleaching severity and colony size), coupled with reductions in fecundity, we estimated a total decrease in population-level reproductive output of 21%. These results suggest that reduced reproductive output may impact recovery of coral populations following bleaching and should be considered alongside traditional estimates of coral mortality.

Local and global ecological stressors are leading to increased documentation of phase shifts in coral reefs from healthy stony corals to macrophytes. In more rare cases, phase shifts result in sponge, zoantharian or other dominant species. In Ulithi Atoll, Federated States of Micronesia, we have documented an unusual phase shift from reefs with a diverse stony coral assemblage to reefs dominated by a single species of stony coral: Montipora sp.—a coral-to-coral phase shift. This monospecific type of reef lowers fish diversity and biomass, impacting both ecological integrity, and livelihoods of reef-dependent human communities. In this study, we used a genomic approach to characterize such a reef. We assembled a de-novo reference genome and used RAD seq data with thousands of SNPs to determine if different reefs result from sexual or asexual reproduction, if weedy Montipora fragments are transported between islands by human activities, and if there is evidence of natural selection on specific genotypes, thus favoring spreading success. We found that sexual reproduction is predominant in the focal species, that there is no evidence of human-mediated spread, and that some genomic regions might be under selection. While such results eliminate a number of spreading hypotheses, more precise dispersal maps will be important to determine the tempo and mode of ‘invasion’ of Montipora in Ulithi Atoll. This study shows that selection and adaptation may be contributing to the success of a stony coral (e.g., Phase shift). While a stony coral may be successful in a disturbed environment, it does not necessarily provide the type of habitat that is conducive to high fish biomass and coral diversity. These results serve as a cautionary tale for restoration efforts that focus on single species coral resilience rather than ecosystem function.

Environmental conditions at different water depths on tropical atolls are substantially different, but few studies have investigated the depth distribution and adaptation in the microbiomes of juvenile and adult corals. We collected samples of juvenile and adult Pocillopora verrucosa from different depths on an atoll in the central South China Sea and analyzed their communities of symbiotic Symbiodiniaceae and associated bacteria. Results showed that the Symbiodiniaceae communities were significantly different at different depths in both juvenile and adult P. verrucosa. Symbiodiniaceae community changed with increasing depth and was dominated by Durusdinium and Cladocopium at 1-m and 20-m depth, respectively. Furthermore, the composition and diversity of Symbiodiniaceae in juvenile and adult corals were different at the same depths. The compositions of associated bacterial communities at different depths also differed significantly between juvenile and adult P. verrucosa. The relative abundance of Endozoicomonas in juvenile and adult P. verrucosa increased with increasing depth, while the Thermus decreased. Our study suggests that juvenile and adult P. verrucosa corals in shallow-water regions associate with high abundances of thermotolerant Symbiodiniaceae and bacteria in the shallow reef flats with high temperature and intense solar radiation, but associate with Symbiodiniaceae and associated bacteria with high photosynthetic efficiency at greater depths.

The speciose scarinine clade of coral reef parrotfishes display significant variation in trophic cranial morphology, yet are often described as generalist herbivores. The hypothesis that many parrotfishes target micro-photoautotrophs is a new framework within which to clarify parrotfish diets. Here, we investigate the dietary targets of Scarus rubroviolaceus using the feeding substrata extraction method and then compare the results to fourteen other syntopic parrotfish species. Scarus rubroviolaceus were followed on snorkel until repeated biting was observed. A 22 mm × 20 mm core was extracted around the bite. We identified and quantified the bite core biota by scraping the top 1 mm from bite cores for microscopy and 16S/18S small subunit rRNA metabarcoding. Filamentous cyanobacteria density on S. rubroviolaceus bite cores did not differ from the other fourteen parrotfish species, Calothrix (Nostocales) being the most frequently observed filamentous cyanobacteria for all fifteen parrotfish species. The 18S metabarcoding analysis detected the encrusting, endolithic sponge taxon Clionaida in the S. rubroviolaceus bite cores. We investigated the possibility of spongivory across all fifteen parrotfish species including an analysis of sponge-associated microbiota detected on the bite cores. This revealed a new axis of trophic partitioning with varying levels of spongivory amongst the fifteen Indo-Pacific parrotfish species. The bite cores of Cetoscarus ocellatus, Chlorurus spilurus, Chlorurus microrhinos, Scarus frenatus and S. rubroviolaceus particularly indicated spongivory. Our findings develop our understanding of parrotfish diet and provide further evidence that parrotfishes are specialized feeders and partition benthic trophic resources.