Coral Reefs最新文献

Scleractinian corals, the principal architects of coral reefs, face substantial threats from ongoing and anticipated climate change and other anthropogenic disturbances. This underscores the significance of investigating alternative reef-building organisms and their contribution to reefs’ resilience. Among these alternatives, colonial hydrozoans of the genus Millepora, commonly called ‘fire corals’, play substantial roles in contributing to coral reef structure and functionality by depositing calcareous exoskeletons. Despite the ecological importance of fire corals, fundamental knowledge gaps remain regarding their biology and reproductive ecology. Here, we present a comprehensive study on the population dynamics, reproductive ecology, phenology, and sex ratio of the three Red Sea fire corals—Millepora dichotoma, M. exaesa, and M. platyphylla—in the Gulf of Aqaba and Eilat. The abundance of M. dichotoma and M. exaesa seems to have remained consistent over the last 50 years across two of the three depth zones surveyed, indicating their potential resistance or resilience. However, at the third depth surveyed, their abundance appears to have decreased. Our extensive in-situ monitoring of breeding events over six consecutive years has revealed a previously undetected relationship between Millepora species breeding events and the lunar cycle. Histological analyses indicated remarkably short reproductive cycles of only 2–3 weeks, recurring multiple times within a single season, in both M. dichotoma and M. exaesa, which is a unique reproductive aspect compared to other reef-building corals. These results highlight the high reproductive and resilience potential of Millepora species. Consequently, fire corals could assume a more substantial role as keystone species in changing environments and future reefs, emphasizing their importance in reef conservation and management.

Climate-driven species range expansions are underway with more tropically affiliated species, including Scleractinian corals, becoming increasingly abundant at higher latitudes. However, uncertainty remains on how these range shifts will affect reef-scale ecosystem processes, which will ultimately depend on the traits of the taxa that dominate these assemblages. Here, we quantified spatiotemporal patterns in the taxonomic and trait structure of coral assemblages along the subtropical-temperate coast of Western Australia (27°–34°S). Coral abundance was generally low and coral cover < 5% across our study sites. Coral assemblages shared similarities in morphological trait structures across the latitudinal gradient, mostly characterised by taxa with simple morphologies; yet subtle differences were also observed across latitudes, with high-latitude corals characterised by slower growth rates and reduced maximum colony sizes. We found a 3.4-fold increase (from 1 to 3.4 individuals m⁻²) in coral abundance at one heavily disturbed location, where canopy-forming seaweeds were replaced by turfing algae, a pattern that was partly driven by an increase in the relative contribution of warm affinity taxa, such as Acropora spp. We predicted these changes would be reflected in different components of functional diversity; yet, despite a localised signal of tropicalisation, we only observed subtle changes in the functional identity, richness, evenness, and divergence. The spatially invariant trait structure of coral assemblages suggests that the nature of ecosystem functions will likely remain unchanged during early stages of tropicalisation, and hence their contribution to temperate reef-scale ecological processes will depend on dominance over other benthic foundational species.

Coral reefs are known to be one of the most diverse marine ecosystems on earth. However, these important ecosystems are heavily stressed by natural and anthropogenic activities. Environmental DNA (eDNA) metabarcoding is an innovative approach that can provide a greater diversity of taxonomic detections, non-invasive sampling, and a lower field component cost than traditional biomonitoring methods. Taiping Island (Itu Aba Island) is one of the major coral reef islands situated in the South China Sea where underwater visual surveys documented an outbreak of Crown-of-Thorns starfish (COTS) in 2021. In our study, we used eDNA metabarcoding to investigate whether there were shifts in coral communities by comparing pre- and post-COTS outbreak communities. One metabarcoding assay targeting the 18S gene and two assays targeting the ITS2 region (one of these assays specifically targeting Acroporid corals) were applied to 42 seawater samples collected in 2019 and 2021 from 12 sites around Taiping Island. Based on these three metabarcoding assays, 52 unique hard coral species were identified, corresponding to a total of 51 species in 2019 and 26 species in 2021. Our results indicated a significant decline in coral diversity but an increase in sponge diversity from the phylum porifera at Taiping Island in 2021. We suggest that these faunal shifts may be due to active feeding and disturbance of COTS at outbreak proportions that result in habitat changes. Our findings also suggest that eDNA can continue to serve as a promising tool to monitor the change in coral as well as reef-associated taxa during devastating outbreak events.

Most comparative studies assessing reef health focus on living hard coral cover as the key metric. In Indonesia, in situ monitoring of coral cover has been ongoing for over five decades. However, as monitoring data and research findings are predominantly published in the local language (Bahasa Indonesia), local data often escape global attention, resulting in Indonesian coral reefs receiving less scientific attention despite accounting for ~ 15% of all coral reef area globally. Here, we systematically compiled both globally and locally published data on coral cover across Indonesia to assess changes over recent decades. We analysed 7,614 data entries extracted from 621 publications and found that the majority (79.1%) of the publications were written in Bahasa Indonesia, constituting 63.4% of the total data entries. Our dataset revealed limited evidence of net declines in coral cover over the last three decades (1994–2022). There was also no clear relationship between coral cover and human density, as well as with the thirteen environmental/anthropogenic drivers examined. We discuss several factors that may contribute to this lack of detectable large-scale change including: recent data potentially representing a ‘shifted baseline’; the ‘averaging out’ of localised changes in coral cover dynamics at a broad scale; sampling biases; and/or the potential resilience of Indonesian coral reefs compared to other regions. This study highlights the wealth of accessible local coral reef data published in languages other than English and emphasises the importance of using such data to enhance our understanding of the long-term dynamics of coral reef ecosystems worldwide.

As one of the world’s most diverse ecosystems, coral reefs have been the focus of numerous biogeographic analyses. With strong biodiversity gradients across the Indo-Pacific, coral reefs have shed light on the effects of evolutionary history, isolation, and human exploitation on local assemblages. However, there are also strong environmentally driven local gradients in faunal assemblages. We ask, does reef fish community composition and trait space vary to a greater extent across small scales (i.e. along habitat gradients) or across large scales (i.e. across geographic regions separated by up to 12,000 km)? Using a standardized survey method that explicitly includes habitats (i.e. the slope, crest, and flat), we surveyed a highly diverse family of reef fishes (Labridae) in nine regions across the Indo-Pacific, from the Cocos (Keeling) Islands to French Polynesia. We demonstrate that small-scale habitat gradients represent a greater axis of variation, in both the taxonomic and trait composition of fish assemblages, than large-scale biogeographic gradients. Indeed, fish assemblages just 10 m apart, along a habitat gradient, appear to differ more than assemblages in the same habitats separated by over 12,000 km along the world’s largest biodiversity gradient. Essentially, fish assemblages cluster by habitat regardless of their biogeographic region, with habitat associations trumping biogeographic affiliations. This emphasizes the primacy of local environmental factors, such as hydrodynamics, in shaping the ecology of reef fishes. It also raises serious concerns over the use of combined datasets, where data from different habitats are used, without explicit recognition, in global-scale analyses.

Coral reefs are among the most biodiverse ecosystems on Earth, largely due to the structural complexity created by corals. Coral habitat is crucial refuge for numerous small animals, and competition for habitat can structure populations if in short supply. Reefs in Hawai‘i are largely dominated by the small branching coral Pocillopora meandrina, which supports diverse communities of fishes and invertebrates. Two species of nocturnal scorpionfishes, Sebastapistes coniorta and S. galactacma, are particularly common in P. meandrina, inhabiting the complex branching morphology of their host corals during the day and feeding in and around these corals at night. Surveys of scorpionfishes in 458 P. meandrina between 3 and 22 m deep along the south and west shores of O‘ahu revealed inverse depth distributions over which these species occurred in P. meandrina. Sebastapistes coniorta almost exclusively occurred in coral colonies between 5 and 10 m deep, while S. galactacma were found across all depths surveyed, though were far more common and abundant in deeper coral colonies (15–20 m) below the range of S. coniorta. Further, measurements of host colony morphometrics revealed that these species appeared to use microhabitat in subtly different ways. The larger-bodied species, S. coniorta, was more commonly found in P. meandrina with wider spaces between branches, while the smaller-bodied species was negatively associated with wider branch spacing. These patterns indicate habitat partitioning between S. coniorta and S. galactacma at both the reef and colony scale, which may explain how these species are able to coexist on reefs in Hawai‘i.

Coral restoration efforts have rapidly increased worldwide, including the development of several programmes on the Great Barrier Reef (GBR) in recent years. While many restoration programmes utilise in-water nurseries to accelerate coral biomass yields, the impact of nursery environments on propagule quality has not been examined despite the importance of coral fitness for ensuring resistant populations. Here, we investigated two fitness indicators (lipid diversity and tissue protein abundance) of Acropora millepora adults and eggs grown on coral nurseries versus native reef on the GBR, with adults assessed at two sites (Blue Lagoon and Rayban) and eggs assessed at one site (Blue Lagoon). Lipid profiles of adult colonies varied by site and origin (nursery versus wild reef), with adult nursery corals exhibiting an elevated relative abundance of storage lipids (diacylglycerols and triacylglycerols) and lipid classes responsible for regulating membrane structure (phosphatidylcholines and sterol esters), while wild corals were characterised by a greater relative abundance of fatty acids and classes involved in immunoregulation. Comparing eggs from different origins, nursery offspring were richer in energy-storing triacylglycerols, as well as ceramides and phosphatidylcholines essential for membrane structure, while wild eggs had a greater relative abundance of wax ester species also important for energy storage. No differences were found in total protein abundance (adult or eggs) or egg physical characteristics (count and size) between nursery and wild origins. Variations in lipid profiles are consistent with differences in environmental conditions between reef sites and origin (nursery versus wild), highlighting the need to consider site selection and propagation conditions when planning restoration projects. Importantly, these findings demonstrate that the lipid classes with the highest relative abundance in A. millepora nursery and wild eggs differed from those in adults from the same origin, suggesting that propagation origin is more important for driving lipid profiles in coral eggs compared to parental effects.

In recent years, several studies have highlighted the high resilience of zoantharians to ocean warming. In particular, populations of Palythoa caribaeorum are proliferating and beginning to dominate the coastal ecosystems of the Canary Islands. This expansion has been associated with increasing sea surface temperatures (SSTs). Here, we provide new insights into the endosymbiont-P. caribaeorum associations during and after a heat stress experiment to understand the processes underlying their high resilience to elevated temperatures. For this purpose, 61 colonies collected in the Canary Islands were exposed to an increasing temperature gradient (from 24 to 32 °C) to assess their heat tolerance, and then transferred back to the control temperature (24 °C) to evaluate their resilience. Colonies performance was assessed by comparing host color changes (bleaching degree), analyzing their Symbiodiniaceae morphological condition, and determining the dominant lineage of Symbiodiniaceae using the psbA_ncr molecular marker. All colonies showed signs of bleaching during heat stress, evidenced by color loss and a decrease in healthy Symbiodiniaceae content. Nevertheless, P. caribaeorum showed high resistance to heat stress, as all colonies kept up to 30 °C were able to survive and significantly recover. Furthermore, as the experimental temperature increased, a new haplotype of the Cladocopium C1 lineage, not detected in the control and wild samples, emerged and dominated most of the colonies (59.09%). Our study demonstrates the resilience of P. caribaeorum to heat stress in the Canary Islands, raising important ecological concerns about the future of native macroalgae ecosystems in an ocean warming scenario.

The gametogenic cycle in broadcast spawning corals takes several months, with oogenesis culminating in synchronized maturation when seawater temperatures rise. Temperature is known for governing reproductive seasonality, yet little is known about how multiple stressors may affect spawning timing. The semi-enclosed lagoon of Bouraké in New Caledonia is subjected to high fluctuations in seawater temperature, pH, salinity, and oxygen, representing an ideal playground to explore possible effects of extreme environmental variability on coral gametogenesis. Here, the spawning window and fecundity metrics (i.e., colony- and polyp-level fecundity, and egg size) of Acropora tenuis, Montipora digitata, and M. stellata from Bouraké were compared with four reference sites located at variable distances from Bouraké. Results suggest that Bouraké and its nearby control site largely spawned synchronously, but there was a spawning asynchrony between Bouraké and the sites further south, in all three species. Interestingly, no reduction in the number of eggs per fecund polyp or number of fecund polyps was observed in Bouraké compared with the reference sites, in any species. However, A. tenuis and M. digitata had smaller eggs in Bouraké compared to reference sites, with possible repercussions for coral fitness. In conclusion, some reproductive traits are maintained in coral species inhabiting a highly variable environment, but smaller gametes may alter population recovery processes. Furthermore, since our data are limited to 2 yrs of observations, spawning synchronization between Bouraké and its surroundings warrant continued investigation to determine whether coral colonies from this area harbor traits that increase fitness under future climate scenarios.