Coral Reefs最新文献

Parasites represent a critically understudied component of reef communities—a knowledge gap that has become more evident as infectious diseases emerge. Here, we test the roles of competing ecological and evolutionary factors in driving infections by an emerging infectious phenomenon: Black spot syndrome (BSS) in Caribbean reef fishes. BSS, a condition associated with localized hyperpigmentation in the dermis and fins of fishes, has recently been linked to infection by trematode parasites in the genus Scaphanocephalus. Using phylogenetic generalized linear mixed models, we evaluated the influence of host phylogeny, habitat preference, body size, and trophic position on infection abundance. Metacercariae of Scaphanocephalus were recorded in 29 of 41 fish species, including 21 new host species records, and within 306 fish (62.3% prevalence). Among species, infection load increased significantly with host body size and decreased with host trophic level, such that large-bodied herbivores tended to support the most infection. There was no significant effect of host phylogeny on infection load. These results suggest the parasite is a generalist in its use of fish intermediate hosts and emphasize the influence of local variation in parasite exposure risk. Overall, the count of visible spots per fish was a positive predictor of Scaphanocephalus abundance among species and individuals, although not all fish species exhibited spots, even when infection loads were high. Findings from this study indicate that Scaphanocephalus infections are far more prevalent in reef fishes than previously recognized and highlight the importance of investigating infection patterns beyond the external symptoms of BSS.

Several remote sensing projects have produced coral reef habitat maps globally. This includes the Allen Coral Atlas (ACA) project. The present study focuses on assessing the accuracy of the ACA 6-class benthic habitat products available for New Caledonia in the 0–10-m depth range. The assessment involves using independent control data collected through thousands of in situ photographs of the benthic environment during sea cucumber stock assessments on multiple sites around New Caledonia. The overall accuracy of the ACA benthic product ranked from 20 to 67% depending on the sites and evaluation method. These results are generally lower than those achieved by other global and local coral reef mapping and products which can be primarily explained by the lack of local ground-truth data to train the classifications. In addition, we discuss other significant misclassifications immediately detectable through historical knowledge, and the limited relevance of the classification scheme to represent the actual diversity of New Caledonia coral reef habitats, a key criteria to guide conservation with habitat maps. Overall, the study highlights the limitations of the ACA benthic product that users should be aware of and offer some recommendations and caveats for both potential users and map producers in other areas.

Site-attached fish that form social groups may face a trade-off between the advantages of group living and the disadvantages related to intra-group competition for food. A possible solution for the latter is space partitioning among group members. Technological limitations related to individual tagging and underwater tracking hindered such spatial studies in grouping fishes. Here, using underwater video cameras and recent developments in deep learning tools, we successfully tracked the 3D movements of individually tagged fish in 4 groups of the damselfish Dascyllus marginatus in the coral reef of Eilat, Red Sea. Our findings, based on tracking sessions lasting 3–11 min that were recorded during a period of > 1 month, show that the individual fish kept separate foraging spaces with minimal overlap and that this separation was stable in time. When the tidally driven current reversed, the separation was kept, and a corresponding reversal was found in the positions of each fish relative to the coral and its neighbors. We propose that the stable spatial partitioning observed in our study is a primary mechanism through which site-attached species can organize themselves in order to reduce intra-group competition.

Oxygen depletion is well recognized for its role in the degradation of tropical coral reefs. Extreme acute hypoxic events that lead to localized mass mortality and the formation of ‘dead zones’ (a region where few or no organisms can survive due to a lack of oxygen) are particularly concerning as they can result in wide-ranging losses of biodiversity, ecosystem productivity and functioning, economic prosperity, and wellbeing. In March of 2022, the annual coral spawning event at Bills Bay (Coral Bay, Ningaloo Reef, Western Australia) coincided with elevated seawater temperature, calm weather conditions and a flood tide resulting in coral spawn becoming trapped in Bills Bay. Immediately after, there was a mass fish kill, which is believed to have been caused by local eutrophication resulting in severe oxygen depletion. The impact the deoxygenation and thermal stress event had on benthic communities has not yet been quantified; hence, the principal aim of this study is to document the extent of change that occurred in the benthic communities before and after the 2022 coral spawning event over a spatial gradient from the nearshore to mid-reef. Percent coral cover in the Bay decreased from 55.62 ± 2.26% in 2016–2018 and 70.44 ± 5.24% in 2021 to 1.16 ± 0.51% in 2022. Over the same period, the percent cover of turf algae increased from 27.40 ± 2.00% in 2016–2018 and 24.66 ± 6.67% in 2021 to 78.80 ± 3.06% in 2022, indicating a dramatic phase shift occurred at Bills Bay. The abundance of healthy coral colonies recorded on replicated belt transects at nine sites declined from 3452 healthy individuals in 2018 to 153 individuals in 2022 and coral generic richness decreased by 84.61%, dropping from 26 genera in 2018 to 4 genera in 2022. Previously dominant genera such as Acropora, Montipora and Echinopora, were extirpated from survey sites. Isolated colonies of massive Porites spp. and encrusting Cyphastrea sp. survived the event and understanding the mechanisms underpinning their greater survivorship is an important area of future research. Long-term monitoring is recommended to track the community recovery process and improve our understanding of the longer-term implications of this acute mortality event on the ecological, socio-economic and cultural values of Ningaloo Reef.

Variously shaped corals, such as branching and massive corals, exhibit divergent environmental susceptibility properties. The susceptibility potential of these corals may be regulated by specific symbiotic Symbiodiniaceae and bacteria. In this study, we investigated seawater characteristics between the north and south zones at the Wuzhizhou Island (WZZ), sampled branching coral Acropora hyacinthus, lamellar coral Montipora informis, and massive coral (Galaxea fascicularis and Porites lutea). Physiological characteristics were measured, and amplicon sequencing was performed to Symbiodiniaceae and bacterial community structure analysis. Corals experienced severe anthropogenic disturbance, with more than 1.4-fold increase in DIN, including ({{text{NH}}}_{4}^{+}), ({{text{NO}}}_{3}^{-}), and ({{text{NO}}}_{2}^{-}) in the north of the WZZ Island compared to the southern region. However, massive corals (G. fascicularis and P. lutea) showed relatively less disruption in both their symbiont composition and physiological responses. Notably, M. informis displayed distinct variations, with disturbances in the northern region resulted in a decline in the density of symbiotic micro-algae associated with Cladocopium sp. C26 due to elevated concentrations of ammonium and nitrate. The four coral species hosted different symbionts within the same area. P. lutea hosted Cladocopium sp. C15 with the lowest density of symbiotic micro-algae, along with the lowest Fv/Fm and YII values compared to other corals in the southern zone. G. fascicularis exhibited high abundance of Durusdinium sp. D1 and D4, which showed strong correlation with Fv/Fm. In southern M. informis, Cladocopium sp. C26 was identified as the predominant symbiotic micro-algae that displayed a significant positive correlation with YII. The bacterial community composition and metabolism functional attribution predicted by PICRUSt differed between A. hyacinthus, M. informis, and massive corals (G. fascicularis, P. lutea). Comprehensive analysis revealed different susceptibility properties among branching, lamellar, and massive corals under anthropogenic disturbance associated with changes in Symbiodiniaceae and bacterial community.

Abstract

Organismal symbioses are fundamental to biodiversity, evolution, and ecosystem functioning. On coral reefs, many decapod species have formed distinct epibiotic symbioses through decoration tendencies that enhance diet, camouflage, and defence. The red decorator crab, Schizophrys aspera (Majidae: Decapoda), has a broad Indo-Pacific distribution and is a successful predator of juvenile crown-of-thorns seastars (CoTS; Acanthaster sp.). However, little is known of the biology and decorating symbioses of S. aspera on the Great Barrier Reef (GBR), where CoTS pose ongoing management challenges. We characterised S. aspera and its epibiont community collected in coral rubble patches on the southern GBR. S. aspera predominantly used sponges (94 ± 1%; mean ± SE) in its decoration, with greater proportions of the carapace covered for juveniles (58 ± 5%) and females (46 ± 4%) compared to males (24 ± 4%). In short-term (8-d) experiments, S. aspera substantially reduced sponge (31%) and algal (47%) cover on rubble pieces, demonstrating its potential to alter sessile communities. The close association of S. aspera with sponges and algae likely reflects its diet and enhances camouflage and chemical defence in its coral rubble niche on the GBR. As sessile taxa are often noxious, we postulate that these symbioses may confer resilience of S. aspera to plancitoxins in its consumption of CoTS. Evaluating how epibiont diversity and biochemistry shape the habitat associations, distribution, and role of S. aspera as predator and prey may be important to understanding its ability to mediate CoTS densities on the GBR and elsewhere.

The increasing threat of ocean warming has led to the more frequent endangerment of coral reefs, including the heat-tolerant Pavona decussata. To shed light on the molecular mechanisms involved in the response of coral to ocean warming, we investigated the gene expression profiles of P. decussata after natural thermal stress. Using PacBio Sequel II sequencing technology, we obtained relatively complete transcriptome data for P. decussata and then analyzed its gene expression quantitatively with Illumina RNA-seq technology. We acquired information on gene function, structure, and expression profile from coral host and zooxanthellae. Analysis of Illumina sequencing data revealed that unbleached coral host might rely on the active utilization of amino acids to maintain a stable living condition based on the tricarboxylic acid cycle under high temperature stress, and that zooxanthellae might benefit from ammonium produced by coral host. Moreover, the downregulation of unbleached coral host gene expression in innate immune pathways centered on the transcription factors that heat shock factor and nuclear factor (NF)-κB, as well as the tyrosine kinase pathway, might be crucial for maintaining the equilibrium of the zooxanthellae under thermal stress. Thus, the differences in these molecular mechanisms could determine, to some extent, whether coral host can maintain a symbiotic relationship with algae under heat stress. This study elucidated the molecular mechanisms underlying differences in thermal tolerance within P. decussata species and supported further theoretical basis in coral molecular biology and ecological conservation, which enhance our comprehension of coral responses to future climate change.

The intensification of warming-induced mass-mortalities in invertebrate populations including in temperate regions is a critical global issue. Mesophotic zones (30–150 m depth) have been suggested as potential refuges from climate change for gorgonian populations, offering hope for reseeding damaged shallow populations. Using a proteomic approach, we investigated the responses and acclimatization ability of the yellow gorgonian Eunicella cavolini along an environmental gradient following reciprocal transplantations between shallow (20 m) and mesophotic (70 m) zones. Our findings indicate that yellow gorgonians from mesophotic waters exhibit a greater plasticity when transplanted to shallow waters, compared to shallow gorgonians transplanted to the mesophotic zone at 70 m. Transplanted colonies from mesophotic to shallow waters showed an increasing level of proteins involved in immune response but displayed no signs of necrosis or apoptosis, highlighting the acclimation potential of mesophotic populations. These results suggest that Eunicella cavolini populations may exhibit physiological plasticity in response to future climate change, allowing natural colonization from mesophotic populations. This analysis offers valuable insights into gorgonians' cellular and molecular responses to environmental changes.

Herbivorous fishes play important roles on coral reefs, acting as key trophic conduits of primary productivity. Whilst these roles are widely appreciated on tropical reefs, the relative contribution of fishes which inhabit marginal reefs, such as Prionurus surgeonfishes, is not well understood. Here, we examine the extent to which herbivorous fish productivity varies amongst global ecoregions, specifically considering the relative contribution of Prionurus. We also compare the productivity of Prionurus to that of other herbivorous fishes in relation to water temperatures. Our analysis revealed that the Eastern Galápagos Islands support the highest levels of herbivorous fish productivity recorded to date, with Prionurus laticlavius accounting for over 94% of that productivity. Moreover, Prionurus productivity peaked at relatively cool water temperatures (~ 22–25 °C), although patterns were driven by P. laticlavius. These results highlight the exceptional herbivorous fish productivity in the Eastern Galápagos Islands and the disproportionate contribution of P. laticlavius in this locality.

Establishment of the coral–algal symbiosis begins during early ontogeny when juveniles acquire a mix of algae from their environment that often differs from the adults’ algal assemblages. Despite the importance of the type of Symbiodiniaceae to this symbiosis, it is largely unknown how coral host identity and environment affect symbiosis establishment and is affected by the genetic composition of the symbionts. Here, we reciprocally transplanted planulae of the octocoral Rhytisma fulvum (Forskål, 1775) across depths and monitored the algal assemblages in the developing juveniles for 11 months. We then compared these to adult assemblages using ITS2 metabarcoding. Juveniles were consistently dominated by Symbiodinium, in addition to multiple Cladocopium species, which shifted in dominance with the juvenile age but maintained high similarity across depths. The type of Symbiodiniaceae environmentally available thus likely contributes to the algal symbionts that are initially acquired, while host identity may play a significant role in selecting for symbionts that are maintained during juvenile development.