Coral Reefs最新文献

The degradation of tropical coral reefs continues unabated as global climate change causes mass “coral bleaching” events. At the organismal level, there is significant evidence that the production of reactive oxygen (ROS) and nitrogen (RNS) species, followed by programmed cell death, causes coral bleaching. Additionally, in tropical marine environments exposure to high irradiances of solar radiation contributes to the photooxidative production of ROS in corals. But most thermal stress experiments on corals have not manipulated and tested the direct and interactive effects of solar radiation on coral bleaching, which is further compounded by the ecologically unrealistic low irradiances used in many experiments. Using published data, a direct relationship between excitation pressure (Q_m) on photosystem II for the photosymbionts of corals with irradiance, when exposed to thermal stress, is demonstrated here. Using these results, the photoinhibition model of oxidative stress and coral bleaching is refined for shallow coral reefs; high irradiances increase Q_m and when exposed to thermal stress result in an increase in ROS and coral bleaching, but under low irradiances the production of ROS decreases while the production of RNS increases, leading to coral bleaching. This suggests that irradiance-dependent effector molecules of coral bleaching (i.e., ROS versus RNS) may dominant the oxidative stress landscape in the coral holobiont. Incorporating measurements of irradiance, tissue oxygen concentrations and ROS/RNS levels, in addition to temperature, into experiments and predictive models is required in order to better understand the full range of environmental conditions that cause coral bleaching.

Phenotypic variability is the ability of the same species to express different phenotypes under different environmental conditions. Several coral species that exist along a broad depth distribution have been shown to differ in skeletal morphology and nutrient acquisition at different depths, which has been attributed to variability in response to differing levels of light availability. This study examined the phenotypic variability of two common depth generalist corals, Montastraea cavernosa and Porites astreoides, along a gradient from 10 to 50 m in the Cayman Islands, by examining changes in skeletal morphology, photophysiology, symbiont cell density, and chlorophyll concentration. Skeletal features of M. cavernosa were found to increase in size from 10 to 30 m, but returned to smaller sizes from 30 to 50 m, while P. astreoides skeletal features continued to increase in size from 10 to 40 m. No differences were observed in either symbiont density or chlorophyll concentration across depths for either species. However, all photophysiological parameters exhibited significant depth-dependent variations in both species, revealing adaptive strategies to different light environments. These results suggest that both species have high variability in response to depth. Patterns of skeletal morphology and photophysiology, however, suggest that M. cavernosa may be more variable in regulating photosynthetic efficiency compared to P. astreoides, which likely facilitates the broader depth distribution of this species.

Densities of juvenile corals (≤ 50 mm diameter) are expected to vary between geographically isolated and more spatially proximate reefs, and may constrain local recovery potential. This study compared juvenile coral densities and their relationships with local abundance of adult congenerics at geographically isolated reefs within Australia’s Coral Sea Marine Park (CSMP) versus highly connected reefs within the Great Barrier Reef Marine Park (GBRMP). Three latitudinal regions and two habitats (reef crest and slope) were examined within both marine parks to test for spatial variation. Densities of juvenile corals in the CSMP (13.99 ± 0.72 juveniles 10 m⁻²) were significantly lower compared to those in the GBRMP (23.72 ± 1.86 juveniles 10 m⁻²). Specifically, there were significantly less Acropora and Pocillopora juveniles on the reef crest in the central CSMP compared to the GBRMP. Relationships between juvenile abundance and percent coral cover were greatest for Acropora and Pocillopora in the GBRMP. This may be due to the low range of coral cover estimates recorded in the CSMP, especially for Acropora (0–15%). Low juvenile coral abundance, and in particular, the lack of fast-growing juvenile corals (e.g., Acropora) in the Central CSMP, in combination with low cover of broodstock (particularly Acropora) on CSMP reefs, poses a significant constraint on post-disturbance recovery capacity, possibly attributable to isolation and limited connectivity among reefs in this region.

Coral skeletons are composites of aragonite and biomolecules. We report the concentrations of 11 amino acids in massive Porites spp. coral skeletons cultured at two temperatures (25 °C and 28 °C) and 3 seawater pCO₂ (180, 400 and 750 µatm). Coral skeletal aspartic acid/asparagine (Asx), glutamic acid/glutamine (Glx), glycine, serine and total amino acid concentrations are significantly higher at 28 °C than at 25 °C. Skeletal Asx, Glx, Gly, Ser, Ala, L-Thr and total amino acid are significantly lower at 180 µatm seawater pCO₂ compared to 400 µatm, and Ser is reduced at 180 µatm compared to 750 µatm. Concentrations of all skeletal amino acids are significantly inversely related to coral calcification rate but not to calcification media pH. Raman spectroscopy of these and additional specimens indicates that CO₃ disorder in the skeletal aragonite lattice is not affected by seawater pCO₂ but decreases at the higher temperature. This is contrary to observations in synthetic aragonite where disorder is positively related to the aragonite precipitation rate mediated by either increasing temperature (this study) or increasing Ω (this study and a previous report) and to the concentration of amino acid in the precipitation media (a previous report). We observe no significant relationship between structural disorder and coral calcification rate or skeletal [amino acid]. Both temperature and seawater pCO₂ can significantly affect skeletal amino acid composition, and further work is required to clarify how environmental change mediates disorder.

In this study, we delved into the interaction between corallivorous marine gastropods, the muricid Coralliophilinae Chenu, 1859, and their cnidarian food targets. Coralliophilinae is a subfamily of specialised corallivorous caenogastropods that feed by browsing on octocorals or hexacorals. Only sparse information is available on the phylogenetic relationships and the degree of specificity of the trophic relationships within this corallivorous lineage. To address these gaps, we generated the largest molecular dataset to date, comprising two mitochondrial (cox1 and 16S rDNA) and one nuclear gene (ITS2 rDNA) from 586 specimens collected worldwide. The coral hosts of coralliophilines were identified through an integrative approach, combining literature data with new records, employing morphological and/or molecular markers, and incorporating data from DNA barcoding of the snail stomach content. Our comprehensive approach unveiled the existence of numerous cryptic species in Coralliophilinae, while the phylogeny showed that most of the currently accepted genera are not monophyletic. The molecular dating confirmed the origin of the Coralliophilinae in Middle Eocene, with diversification of most lineages during the Miocene. Our results indicate that the subfamily’s ancestor evolved in shallow waters in association with Scleractinia. Through the evolutionary history of Coralliophilinae, multiple host shifts to other cnidarian orders were observed, not correlated with changes in the depth range. The results of diversification analyses within the subfamily further suggest that the association with the host has influenced the evolutionary patterns of Coralliophilinae, but not vice versa.

High sea surface temperatures recorded in summer 2021 introduced a unique opportunity for ‘real-time’ assessment of Exmouth Gulf turbid reef’s resilience to a marine heatwave event. Four sites along a turbidity and temperature gradient were surveyed during (March 2021) and after (October 2021) the event to assess bleaching rates (Bleaching Index = BI), differences in coral morphological responses to the heat wave, and post-event changes in benthic and coral community structure. Despite experiencing higher temperatures (> 30 °C) and Degree Heating Weeks (DHW = 8), the most turbid reef site, Somerville, displayed greater resilience to heat stress (BI = 14) compared to the “clear water” site, Bundegi (BI = 19.3), where temperatures never exceeded 30 °C (3 DHW). Our results also reveal that encrusting and massive corals, often considered more resilient to bleaching, displayed increased bleaching susceptibility at the turbid sites, potentially due to the synergistic effects of sedimentation and heat stress. In contrast, branching and foliose corals showed greater resilience to the heat wave in turbid water settings, while encrusting and branching corals exhibited lower resilience in the clearwater site. These findings highlight complex interactions between heat and reduced UV stress on turbid reefs potentially increasing resilience to bleaching but likely only for those coral morphologies that are not heavily impacted by sedimentation.

In February 2010, the cargo vessel M/V Vogetrader ran aground on a forereef in Oahu, Hawaii. Baseline surveys documented considerable damage to coral communities. Several restoration actions were implemented in 2013, including active restoration (rubble removal, coral outplanting) and passive restoration (natural recovery), with the goal of returning corals to their pre-disturbance state. In 2022, repeated surveys were conducted across three injury zones that varied in the severity of impact and the restoration actions employed to provide a rare assessment of restoration outcomes a decade post-grounding. We found coral recovery to be contingent on the severity of impact and the quality of the impacted habitat, not the amount of active restoration. Despite rubble removal efforts, present-day rubble cover was significantly higher at the impact sites compared to the reference sites and appeared to constrain recovery in the injury zone where grounding impacts destabilized the reef framework. Outplant efforts did not increase coral density or mean size relative to natural recovery sites, though this may be the result of an ineffective outplant design rather than failed outplanting as a whole. The sites closest to returning to a pre-disturbance state were the passive restoration sites. This, however, likely reflects the low severity of grounding impacts and the marginal (e.g., small and sparse) population of corals at these sites. These findings suggest that the extent of active restoration actions should be carefully and intentionally scaled to the severity and spatial extent of impact (with greater impacted areas receiving greater amounts of restoration), and that with sufficient time, marginal reef habitats with a low impact severity can likely recover from passive restoration alone.

The spatial distribution of coral reef biodiversity is regulated by a series of natural variables and human-induced factors such as depth, habitat availability, spatial variation, and management policies. However, spatial distribution patterns and management zoning strategy outcomes of coral reefs biodiversity are still scarce in several areas, such as Southwestern Atlantic Ocean Marine Protected Areas (MPAs). It has been previously demonstrated that better management strategies worldwide could be supported by better species distribution data. In the present study, a total of 94 reefs spatially distributed around the MPA Costa dos Corais (Northeastern Brazil) under different zoning strategies and ranging from 1 to 30 m depth were sampled. Our study is the first one to characterize biodiversity spatial distribution of the largest Brazilian coastal MPA Costa dos Corais biodiversity and the importance of management zoning as a major coral reef conservation strategy in Brazil. Highest coral cover (48.33%) and coral richness (6.31 species/20 m) have been recorded for North of Alagoas (NAL), and highest fish abundance (75.22 individuals/100 m²), richness (11.45 species/100 m²) and biomass (395.60 g/100 m²) were recorded for South of Alagoas (SAL). Yet, only fish richness and biomass were significantly different compared with other regions. Compared to other management zones, no-take zones had the highest coral cover and richness, and fish abundance, richness and biomass. Additionally, our findings have shown that depth positively influences fish and negatively influences coral biodiversity. Hence, management and zoning strategies have influenced the structure of coral reef communities with a series of different ecological effects highlighting the importance of those strategies for Southwestern Atlantic Ocean MPAs.

Research on Mesophotic Coral Ecosystems (MCEs; 30–150 m) has grown exponentially in the last few decades, highlighting their rich diversity and extensive distribution. However, they are still largely underexplored compared to shallow-water coral reefs and frequently remain under-protected and under-represented in marine spatial planning. One reason for the imbalance between the high ecological value of MCEs and the limited levels of protection may be that baseline data on MCEs are largely missing to date, yet are crucial to provide evidence-based information for management actions. Here, we present data on the alpha and beta diversity of the benthic communities within MCEs in the Chagos Archipelago, Indian Ocean. Using imagery collected from Remotely Operated Vehicle surveys, benthic invertebrate megafauna were surveyed along the entire depth gradient from shallow to lower mesophotic depths (15–160 m). The diversity of the benthic communities decreased with increasing depth, from shallow water to the lower mesophotic zone. Nevertheless, the deepest parts of MCEs in the Archipelago displayed higher species richness values than several other shallow subtropical regions. In addition, the benthic communities showed high dissimilarity along the depth gradient, indicating that the key driver of community composition change with depth is species turnover (species replacement), revealing the uniqueness of MCEs. This study presents novel findings on MCEs in the central Indian Ocean, demonstrating that they host a high and unique benthic diversity, and highlighting the need to protect these ecosystems to preserve the overall biodiversity of coral reefs.

A mass coral bleaching event occurred in the summer of 2022 in subtropical Hong Kong, driven by two marine heatwaves (MHWs) with high intensities of 1.56 and 0.86 °C above a mean climate condition, both MHWs 7 days with a short gap of 4 days during the strong La Niña year. A transect survey was conducted at nine study sites in three regions, which revealed widespread coral bleaching with bleached coral cover ranging from 2.4 to 70.3%. In situ environmental data revealed the presence of a thermocline and halocline. Local conditions, including depth and wave exposure, significantly influenced the bleaching response. Shallow-water (2–4 m) corals were primarily affected, particularly in sheltered and moderately sheltered sites that exhibited higher levels of bleached coral cover (42.97 ± 15.4% and 44.93 ± 29.4%, respectively) compared to the exposed sites (31.8 ± 5.2%). Bleaching in deep waters (4–6 m) was minimal, with only a few colonies of Goniopora at two of the three sheltered sites exhibiting bleaching (1.7 ± 1.5%). Heat stress resistance differed between coral genera. Recovery rate for four common coral genera is low for Acropora tumida. Additionally, a minor hypoxia event was found to cause mortality of non-coral benthos at a sheltered site (Sharp Island). These findings highlight the alarming impact of extreme heatwaves on subtropical coral communities and underscore the importance of monitoring coral bleaching.