Reef Sites Research Articles

Relationship of biological communities to habitat structure on the largest remnant flat oyster reef (Ostrea angasi) in Australia

Oyster reef restoration is a growing field in Australia, yet formal descriptions of associated biological communities for reefs created by native flat oysters (Ostrea angasi) do not currently exist. Native flat oysters once formed extensive and complex three-dimensional habitats in bays and estuaries across southern Australia until indiscriminate fishing, sedimentation and disease led to their near disappearance. To determine the diversity and abundance on naturally occurring oyster reefs, we sampled four sites on the last known naturally occurring oyster reef ecosystem, which resides in north-eastern Tasmania, and compared them to the surrounding soft sediment regions. Assemblages were related to environmental variables to determine whether consistent patterns were present. Oyster reef sites contained three times the faunal abundance of the surrounding soft sediment regions. Abundance among echinoderms, arthropods, molluscs and fish was much elevated, whereas annelids showed similar levels of abundance but differed in terms of species composition. These results show that oyster reefs do support abundant and diverse assemblages, emphasising the probable loss of community-level biodiversity associated with their historical decline around southern Australia.

Using baited remote underwater videos (BRUVs) to characterize chondrichthyan communities in a global biodiversity hotspot.

Threatened chondrichthyan diversity is high in developing countries where scarce resources, limited data, and minimal stakeholder support often render conservation efforts challenging. As such, data on many species, including many evolutionarily distinct endemics, is poor in these countries and their conservation status and habitat needs remain uncertain. Here, we used baited remote underwater videos (BRUVs; n = 419) conducted at 167 sites over two years to assess the frequency of occurrence (FO), relative abundance, diversity, and structure of chondrichthyan assemblages in one of the world’s chondrichthyan biodiversity and endemism hotspots, South Africa. We compared chondrichthyan assemblages across three habitat types, and between unprotected and protected areas (a small marine protected area [MPA] and a larger, seasonal whale sanctuary). Although in total we observed 18 chondrichthyan species (11 families), over half of all observations were of just two species from the same family of mesopredatory endemic catsharks; only 8.8% were larger shark species. These mesopredatory species do not appear to be threatened, but some skates and larger shark species, including some endemics, were much rarer. Overall chondrichthyan FO was high (81% of all BRUVs); FO was higher in kelp (100% of BRUVS) and reef (93%) sites than at sites in sandy habitat (63%), which had a distinct chondrichthyan community. Independent of habitat, the chondrichthyan community did not relate strongly to protection. Because sites with kelp and reef habitat were rare in the whale sanctuary, this protected area had a lower chondrichthyan FO (67% of BRUVs) than either unprotected sites (81%) or those in the small MPA (98%), as well as having lower chondrichthyan relative abundance and species richness. Our study provides evidence of the importance of distinct habitat types to different chondrichthyan species, and suggests that even small MPAs can protect critical habitats, such that they may provide safe refuge for endemic species as anthropogenic pressures increase.

Uptake of groundwater nitrogen by a near-shore coral reef community on Bermuda

Nutrient enrichment can slow growth, enhance bioerosion rates, and intensify algal competition for reef-building corals. In areas of high human population density and/or limited waste management, submarine groundwater discharge can transfer anthropogenic nutrients from polluted groundwater to coastal reefs. In this case study, we investigate the impact of submarine groundwater discharge on a near-shore reef in Bermuda, where over 60% of sewage generated by the island’s 64,000 residents enters the groundwater through untreated cesspits. Temperature, salinity, pH, and alkalinity were monitored at a groundwater discharge vent, three locations across the adjacent coral reef (0–30 m from shore), and a comparison patch reef site 2 km from shore. Groundwater discharge was characterized by low salinity, low aragonite saturation state (Ωar), high alkalinity, elevated nitrate + nitrite (NO3– + NO2–; hereafter, “NO3–”) concentrations (> 400 µM), and an elevated 15N/14N ratio of NO3– (δ15N = 10.9 ± 0.02‰ vs. air, mean ± SD). Rainfall and tidal cycles strongly impacted groundwater discharge, with maximum discharge during low tide. NO3– concentrations on the near-shore reef averaged 4 µM, ten times higher than that found at the control site 2 km away, and elevated NO3– δ15N at the near-shore reef indicated sewage-contaminated groundwater as a significant nitrogen source. Tissue δ15N of Porites astreoides, a dominant reef-building coral, was elevated by ~ 3‰ on the near-shore reef compared to the control site, indicating that corals across the near-shore reef were assimilating groundwater-derived nitrogen. In addition, coral skeletal density and calcification rates across the near-shore reef were inversely correlated with NO3– concentration and δ15N, indicating a negative coral health response to groundwater-borne nutrient inputs. P. astreoides bioerosion rates, in contrast, did not show an effect from the groundwater input.

The Rarity of Depth Refugia from Coral Bleaching Heat Stress in the Western and Central Pacific Islands

Some researchers have suggested that corals living in deeper reefs may escape heat stress experienced by shallow corals. We evaluated the potential of deep coral reef refugia from bleaching stress by leveraging a long record of satellite-derived sea surface temperature data with a temporal, spatial, and depth precision of in situ temperature records. We calculated an in situ stress metric using a depth bias-adjusted threshold for 457 coral reef sites among 49 islands in the western and central Pacific Ocean over the period 2001–2017. Analysis of 1,453 heating events found no meaningful depth refuge from heat stress down to 38 m, and no significant association between depth and subsurface heat stress. Further, the surface metric underestimated subsurface stress by an average of 39.3%, across all depths. Combining satellite and in situ temperature data can provide bleaching-relevant heat stress results to avoid misrepresentation of heat stress exposure at shallow reefs.

Small-Scale Variability Dominates Benthic Coverage and Diversity Across the Jardines de La Reina, Cuba Coral Reef System

Coral reefs are complex and biodiverse ecosystems that are undergoing significant change. Understanding reef composition and biodiversity at multiple spatial scales is necessary to track both large-scale and more subtle ecosystem changes. The Jardines de la Reina (JR) archipelago, located offshore of the island of Cuba, contains the largest marine protected area (MPA) in the Caribbean Sea but lacks multi-scale studies. In this contribution, we documented the diversity of scleractinian corals, octocorals, algae, and sponges across nested spatial scales spanning four orders of magnitude (101–105 m). In addition, we tested the hypothesis that species diversity followed a gradient along the ca. 200 km of reef tract. Across the archipelago, we examined benthic cover and species diversity within 255 photo-quadrats (25 × 25 cm) at 13 fore reef sites (two sampling locations per site, and 10 photo-quadrats per location). Small-scale (101 m) variability between photo-quadrats characterized the coral reef community structure in JR compared with local- (102 m) and mesoscale (104–105 m) variability. This finding suggests that biological processes (e.g. recruitment, competition) had primacy over hydrodynamics for driving the differences in reef community composition. However, the dominance of algae and low cover and diversity of scleractinian corals suggests the pervasive effects of global change on coral communities despite potential benefits provided by the MPA (e.g. oligotrophy and abundance of herbivores). There was not a gradient of benthic community structure along the fore reef tract of JR; instead, a patchy distribution occurred in response to more subtle drivers acting at local scales. Overall, our multi-scale comparison was useful for differentiating the impacts of processes potentially impacting the JR reefs, thus providing important information to understand how reef communities are impacted by different environmental and anthropogenic stressors, and the potential benefits of MPAs.

Tissue-Specific Microbiomes of the Red Sea Giant Clam Tridacna maxima Highlight Differential Abundance of Endozoicomonadaceae.

Giant clams (subfamily Tridacninae) are prevalent members of coral reef communities and engage in symbioses with algal photosymbionts of the family Symbiodiniaceae, similar to their scleractinian coral counterparts. However, we know little about their associated bacterial microbiome members. Here, we explored bacterial community diversity of digestive system, gill, and mantle tissues associated with the giant clam Tridacna maxima across a cross-shelf gradient (inshore, midshore, and offshore reef sites) in the central Red Sea using 16S rRNA gene amplicon sequencing. Different tissues harbor spatially stable and distinct microbial communities. Notably, diverse assemblages of bacteria affiliated to the family Endozoicomonadaceae were prevalent in all tissues, but particularly abundant in gills and to a lesser extent in digestive tissues. Besides Endozoicomonadaceae, bacteria in the families Pasteurellaceae, Alteromonadaceae, and Comamonadaceae were common associates, depending on the tissue queried. Taxonomy-based functional inference identified processes related to nitrogen cycling (among others) to be enriched in giant clam tissues and contributed by Endozoicomonadaceae. Our study highlights the tissue-specificity and broad taxonomic range of Endozoicomonadaceae associates, similar to other marine invertebrates, and suggests their contribution to nitrogen-related pathways. The investigation of bivalve-associated microbiome communities provides an important addition to the pathogen-focused studies for commercially important bivalves (e.g., oysters).

A rapid spread of the stony coral tissue loss disease outbreak in the Mexican Caribbean.

Caribbean reef corals have experienced unprecedented declines from climate change, anthropogenic stressors and infectious diseases in recent decades. Since 2014, a highly lethal, new disease, called stony coral tissue loss disease, has impacted many reef-coral species in Florida. During the summer of 2018, we noticed an anomalously high disease prevalence affecting different coral species in the northern portion of the Mexican Caribbean. We assessed the severity of this outbreak in 2018/2019 using the AGRRA coral protocol to survey 82 reef sites across the Mexican Caribbean. Then, using a subset of 14 sites, we detailed information from before the outbreak (2016/2017) to explore the consequences of the disease on the condition and composition of coral communities. Our findings show that the disease outbreak has already spread across the entire region by affecting similar species (with similar disease patterns) to those previously described for Florida. However, we observed a great variability in prevalence and tissue mortality that was not attributable to any geographical gradient. Using long-term data, we determined that there is no evidence of such high coral disease prevalence anywhere in the region before 2018, which suggests that the entire Mexican Caribbean was afflicted by the disease within a few months. The analysis of sites that contained pre-outbreak information showed that this event considerably increased coral mortality and severely changed the structure of coral communities in the region. Given the high prevalence and lethality of this disease, and the high number of susceptible species, we encourage reef researchers, managers and stakeholders across the Western Atlantic to accord it the highest priority for the near future.

Impact of the tropical cyclone Ockhi on ecological and geomorphological structures of the small low-lying Islands in the Central Indian Ocean

Ockhi, was an intense tropical cyclone that devastated parts of Sri Lanka and India in 2017 and was the most intense tropical cyclone in the Arabian Sea, Central Indian Ocean, since Cyclone Megh in 2015. The ninth depression, and the third and strongest named storm during 2017, North Indian Ocean cyclone season, Ockhi, originated from an area of low pressure that formed in the eastern Andaman Sea on November 21, 2017. Here we describe the impacts of Ockhi on benthic coral reef assemblages of an atoll island directly in the path of the cyclone. We assessed the effect of the cyclone in the reefs around Kavaratti Island, by comparing the data from recent pre-Ockhi documentation with its present status. The study provided a unique opportunity to identify and describe the impacts of an intense tropical cyclone on reefs of a small low lying island in the Central Indian Ocean, which is often assumed to be vulnerable to physical disturbance due to their poorly lithified framework. For the present study, the entire Kavaratti atoll was demarcated into three zones (lagoon, western outer reef, and eastern outer reef), and data was gathered from 29 pre-fixed stations. Observed impacts of Ockhi were site-specific and spatially highly heterogeneous, but appeared to have been strongly influenced by the level of exposure, the site received, and the biological make-up of individual reefs sites. Live coral cover on western reefs had a considerably lower impact due to the shelter provided by the land and the trends in the substrate composition before and after Ockhi is almost similar. However, drastic devastation was observed in the eastern reef system, after the Ockhi event. The combination of repeated, intense cyclonic activities and mass bleaching events will act together to significantly hamper the rapid recovery of these reefs and also adversely affect the livelihood of the community.

Crustacean symbiosis with Caribbean sea anemones Bartholomea annulata: occupancy modeling, habitat partitioning, and persistence

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 631:99-116 (2019) - DOI: https://doi.org/10.3354/meps13160 Crustacean symbiosis with Caribbean sea anemones Bartholomea annulata: occupancy modeling, habitat partitioning, and persistence Lindsay K. Huebner1,2,*, Colin P. Shea2, Paul M. Schueller3, Ashley D. Terrell1, Stephen G. Ratchford4, Nanette E. Chadwick1 1Department of Biological Sciences, Auburn University, Auburn, Alabama 36849, USA 2Fish & Wildlife Research Institute, Florida Fish & Wildlife Conservation Commission, St. Petersburg, Florida 33701, USA 3Fish & Wildlife Research Institute, Florida Fish & Wildlife Conservation Commission, Gainesville, Florida 32653, USA 4College of Science and Math, University of the Virgin Islands, St. Thomas, US Virgin Islands 00802, USA *Corresponding author: lindsay.huebner@myfwc.com ABSTRACT: Coral reef cnidarians often host crustaceans in multi-level symbioses that may cause reef-wide impacts, especially through anemoneshrimp cleaner interactions with fish clients. Despite the ubiquity and importance of these interactions, patterns of temporal and spatial variation in crustacean association with sea anemones remain largely unknown. We censused corkscrew sea anemones Bartholomea annulata and crustacean associates (5 shrimp and 1 crab species) every 3-6 mo for 2.5 yr at 2 reef sites in St. Thomas, US Virgin Islands. Crustacean abundance per anemone varied with species and census period. Occupancy rates increased with anemone body size, more so offshore where anemones were smaller and less abundant than inshore. Four species of obligate anemoneshrimps partitioned space among 5 microhabitat zones on the host anemone body. Dynamic multi-state models revealed that anemone persistence was enhanced primarily by anemone body size, with variable secondary effects of site and anemoneshrimp species. The presence of the snapping shrimp Alpheus armatus did not enhance the persistence of host anemones. However, the presence of the dedicated cleaner shrimp Ancylomenes pedersoni enhanced the persistence of small host anemones at the inshore site but reduced the persistence of the occasional cleaner shrimp Periclimenes yucatanicus on host anemones, indicating mutualistic and competitive interactions among some partners in this system. Patterns of association among anemones and crustaceans varied significantly at both temporal (seasonal and annual) and spatial scales (among anemones and reef sites), with implications for the ecology of client fishes that visit these Caribbean anemones to receive cleaning services from anemoneshrimps. KEY WORDS: Multi-state occupancy model · Anemoneshrimp · Alpheus armatus · Ancylomenes pedersoni · Periclimenes yucatanicus · Heteromysis actiniae · Mutualism · Coral reef Full text in pdf format Supplementary material PreviousNextCite this article as: Huebner LK, Shea CP, Schueller PM, Terrell AD, Ratchford SG, Chadwick NE (2019) Crustacean symbiosis with Caribbean sea anemones Bartholomea annulata: occupancy modeling, habitat partitioning, and persistence. Mar Ecol Prog Ser 631:99-116. https://doi.org/10.3354/meps13160 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 631. Online publication date: November 21, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Do oyster breakwater reefs facilitate benthic and fish fauna in a dynamic subtropical environment?

Oyster breakwater reefs used for coastal protection have shown to enhance local biodiversity. Particularly, macro-invertebrate and fish assemblages can benefit directly from reefs providing structurally complex habitats and indirectly through alteration of soft-sediment environment near the reef areas. To test this hypothesis, a manipulative field experiment was carried out on an eroding intertidal flat in the southeastern coast of Bangladesh by deploying replicate units of each 20 m long oyster breakwater reefs specially designed to protect adjacent shorelines. Transient fishes and resident intertidal macro-invertebrate communities were assessed monthly for a period of 18 months. On the intertidal flat, five transects were setup for faunal and environmental data collection, three crossing the breakwater reefs and two along the control areas without reefs. Prior to the deployment of the reefs, both the macro-invertebrate and fish assemblage were not significantly different among the five transects, indicating a rather uniform distribution of species in all tidal flats. Data collected post-reef deployment revealed that oyster breakwater reefs supported a greater biomass as well as abundance of benthic macro-invertebrates on the landward mudflat behind the reefs than the mudflat of control sites. The community structure, and seasonal variation of the macrobenthic community were associated with the variations in the sediment accumulation, as influenced by the breakwater reefs. Additionally, higher abundance of transient finfish and mobile macro-invertebrates at the reef sites suggest that the faunal communities were attracted by the higher abundance of prey resources (i.e. polychaetes, small crustaceans, juvenile gastropods and bivalves) as supported by the reefs. Thus, the reef areas served as shelter, nursery, and foraging grounds for different species. Though the ecological benefits of using oyster breakwater reefs only span adjacent to the reefs, this study confirms the importance of reef structure in facilitating local coastal biodiversity in a subtropical region.

Structural Complexity and Benthic Cover Explain Reef-Scale Variability of Fish Assemblages in Los Roques National Park, Venezuela

Global and local stressors are causing the worldwide loss of coral cover and structural complexity at an unprecedented pace on reefs. In consequence the habitat of coral reef fish has suffered a profound degradation affecting the abundance, biodiversity and species composition of this taxonomic group. Thus, understanding the link between coral reef fish assemblages and their habitats is paramount to predict their responses to increasing human threats. Herein, we implemented Structure from Motion (SfM) techniques and digital mosaics to characterize the habitat of reef fish in terms of structural complexity and cover of benthic organisms, and we examined the relationships between these metrics and the variation in fish assemblages among sites using a multivariate approach. We found that fish assemblage attributes varied across reef sites in Los Roques, depending on the highly specific features of the benthic habitat. Results indicate that 69% of the variation in species-specific abundance of fish (i.e., reef fish assemblage structure) was explained by cover of massive coral and turf algae, the number and sizes of holes, and the site. Furthermore, when fish biomass per species was utilized as a response variable, 64% of the variation in assemblage structures was explained by a model that included: cover of crustose coralline algae (CCA), variation and the maximum height of reef structures along the transect, the number of holes and the site. All these variables together also explained > 60% of variation of total abundance, biomass and species richness. When data were sorted by trophic groups, CCA cover explained 70% of the variation in forager biomass, whereas the number of holes explained up to 60% of variation in carnivore biomass. These results suggest that each trophic group relates differently to the benthic habitat. We conclude that variation in fish assemblages among sites can be explained by features of the benthic habitat, but more importantly the absence of specific attributes may impact fish trophic groups differently.

Assessment of Elkhorn Coral Populations and Associated Herbivores in Akumal, Mexico

Coral decline in the Caribbean is marked by the loss of habitat-forming corals, such as elkhorn coral (Acropora palmata). Elkhorn coral recovery has been isolated and patchy, but recently a “re-sheeting” phenomenon, in which elkhorn tissue grows over standing dead coral skeletons, was observed along the reefs in the Mexican Yucatan peninsula. Little is known about the ecological factors contributing to “re-sheeting”, but it is hypothesized that grazing from herbivores provides top-down control of algal growth and promotes coral recovery. The purpose of this study was to evaluate the status of elkhorn populations in Akumal, Mexico and determine if Diadema urchins or parrotfish populations are associated with higher elkhorn abundance and lower algal cover. To achieve this objective, we surveyed 12 spur and groove reef sites in Akumal, where re-sheeting was recently observed, and measured elkhorn coral and herbivore population metrics. We found that both herbivore groups are associated with increasing elkhorn coral presence and cover, and lower macroalgal cover. Additionally, we tested for sampling bias in counting Diadema urchins and found that a significant difference in urchins counts between paired day and night transects on shallow, high complexity reefs Our results suggest that historically important herbivore groups may be contributing to the recovery of elkhorn coral in Akumal by facilitating tissue re-sheeting.

Assessing the Resilience Potential of Inshore and Offshore Coral Communities in the Western Gulf of Thailand

Coral reefs in the Gulf of Thailand have experienced severe coral bleaching events and anthropogenic disturbances during the last two decades. This study assessed the resilience potential of coral communities at Ko Losin offshore reef sites and Mu Ko Chumphon nearshore coral reefs, in the south of Thailand, by conducting field surveys on the live coral cover, hard substratum composition and diversity and density of juvenile corals. Most study sites had higher percentages of live coral cover compared to dead coral cover. Some inshore and offshore reef sites showed low resilience to coral bleaching events. The total densities of juvenile corals at the study sites were in the range of 0.89–3.73 colonies/m2. The density of the juvenile corals at most reef sites was not dependent on the live coral cover of adult colonies in a reef, particularly for the Acropora communities. We suggest that Ko Losin should be established as a marine protected area, and Mu Ko Chumphon National Park should implement its management plans properly to enhance coral recovery and promote marine ecotourism. Other measures, such as shading, should be also applied at some coral reefs during bleaching periods.

Coral Records of Variable Stress Impacts and Possible Acclimatization to Recent Marine Heat Wave Events on the Northwest Shelf of Australia

AbstractThe ability of massive corals to record the impacts of marine heat wave events provides a unique perspective into the variable responses of corals to anthropogenic climate change. In this study, coral cores (Porites spp.) were collected from seven reef sites across the inner‐, mid‐, and outer‐NW shelf of Australia, to examine seasonal patterns of trace element (TE), Sr/Ca and Li/Mg ratios, and extension rate signatures associated with past marine heat waves in the region. TE anomalies and declines in linear extension rate were observed in the records during the late 1990s (two of five records) and more recently during the summers of 2011 (three of seven records) and 2013 (five of seven records), indicating the impacts of marine heat waves have become increasingly widespread in the region. However, for the summers of 2011 and 2013, no significant relationships were observed between the magnitude of these TE ratio anomalies in the core records and maximum thermal stresses predicted at the reef sites from high‐resolution satellite records. We show that the strongest individual reductions in linear extension rates and associated TE ratio anomalies occurred during the 2011 heat wave, rather than during the subsequent and more intense (~1 °C warmer) 2013 event. Together, these observations suggest that at the local reef scale, Porites spp. colonies and their symbionts exhibit differential responses to heat wave events, with the prior exposure to less intense events probably playing an important role in acclimatization.

Effect of reef morphology and depth on fish community and trophic structure in the northcentral Gulf of Mexico

Reef fish resources provide numerous ecosystem services in the northern Gulf of Mexico (nGOM) large marine ecosystem. Artificial reefs (ARs) have been distributed across the nGOM in attempts to enhance reef fish habitat and increase fishery productivity, but few data exist to distinguish ecological from fishery functions of ARs compared to natural reefs (NRs), particularly at the regional scale. Therefore, we conducted remotely operated vehicle surveys of reef fish communities at 47 reef sites within a ~20,000 km2 area of the nGOM shelf and tested the effect of reef type (NR versus AR), depth (≤35 or >35 m), relief (≤2 m or >2 m), and complexity (low or high) on fish diversity and community structure as well as trophic guild- and species-specific densities. Twenty-one species were present at >20%, nine at >50%, and three at >75% of study reefs. Fishery species (i.e., Lutjanus campechanus, Seriola dumerili, and Rhomboplites aurorubens) and invasive Pterois volitans were frequently observed (>50% of sites) or numerically dominant, especially at ARs. Main effects did not significantly affect the presence of specific species or trophic guilds, but interactions among factors significantly affected species- and trophic guild-specific densities. Our results indicate that effects of habitat characteristics on fish communities are more nuanced than previously described. Fish communities are moderately similar at the majority of sites but specific habitat characteristics can interact to dramatically affect densities of some species, particularly those that depend on complex structures for refuge. Simple ARs tend to concentrate high densities of a few important fishery species with low densities of other small demersal reef fishes. Complex NRs with high relief also support high densities of planktivorous fishery species but greatly increase densities of small, demersal, non-fishery species that directly utilize complex reef structure for refuge.

Peroxynitrite Generation and Increased Heterotrophic Capacity Are Linked to the Disruption of the Coral-Dinoflagellate Symbiosis in a Scleractinian and Hydrocoral Species.

Ocean warming is one of the greatest global threats to coral reef ecosystems; it leads to the disruption of the coral–dinoflagellate symbiosis (bleaching) and to nutrient starvation, because corals mostly rely on autotrophy (i.e., the supply of photosynthates from the dinoflagellate symbionts) for their energy requirements. Although coral bleaching has been well studied, the early warning signs of bleaching, as well as the capacity of corals to shift from autotrophy to heterotrophy, are still under investigation. In this study, we evaluated the bleaching occurrence of the scleractinian coral Mussismillia harttii and the hydrocoral Millepora alcicornis during a natural thermal stress event, under the 2015–2016 El Niño influence in three reef sites of the South Atlantic. We focused on the link between peroxynitrite (ONOO−) generation and coral bleaching, as ONOO− has been very poorly investigated in corals and never during a natural bleaching event. We also investigated the natural trophic plasticity of the two corals through the use of new lipid biomarkers. The results obtained first demonstrate that ONOO− is linked to the onset and intensity of bleaching in both scleractinian corals and hydrocorals. Indeed, ONOO− concentrations were correlated with bleaching intensity, with the highest levels preceding the highest bleaching intensity. The time lag between bleaching and ONOO− peak was, however, species-specific. In addition, we observed that elevated temperatures forced heterotrophy in scleractinian corals, as Mu. harttii presented high heterotrophic activity 15 to 30 days prior bleaching occurrence. On the contrary, a lower heterotrophic activity was monitored for the hydrocoral Mi. alicornis, which also experienced higher bleaching levels compared to Mu. hartii. Overall, we showed that the levels of ONOO− in coral tissue, combined to the heterotrophic capacity, are two good proxies explaining the intensity of coral bleaching.

Patterns of juvenile reef-fish recruitment in Kenya’s shallow fringing- lagoon reefs

Studies to understand local-scale patterns in the recruitment of juvenile coral-reef fishes within the western Indian Ocean (WIO) region are few, yet such knowledge is important in fisheries management. Underwater visual census surveys were conducted at five shallow fringing-lagoon reef sites along the Kenyan coast, between June 2012 and March 2016, to quantify patterns in the abundance of new recruits and juveniles. Recruitment was observed year-round, with a consistent pronounced seasonal peak in recruit densities and species richness during December to April of each year, which was strongly correlated with high sea temperatures. Annual variations in recruitment were also observed, with a higher recruitment peak in 2013 as compared with in other years. A total of 112 species belonging to 19 families were identified, dominated by species belonging to the Pomacentridae, Labridae and Apogonidae, which altogether represented 91% of the total number of recruits recorded. The species with the largest number of recruits (Chromis viridis, Thalassoma hebraicum and Gomphosus caeruleus) showed evidence of year-round recruitment, although the timing of recruitment peaks was not consistent. Multivariate analysis of the species composition separated mainland from offshore fringing-reef sites, and also revealed strong habitat associations, pointing towards increasing recruit abundance with increasing live hard-coral cover and rugosity. Live hard-coral cover, which constituted an average of 21%, was associated with 63% of the total number of recruits recorded. This study contributes new insight into local-scale patterns of juvenile reef-fish recruitment in Kenya and the WIO region, and demonstrates the important nursery function of shallow fringing-lagoon reefs.

Fishes with high reproductive output potential on California offshore oil and gas platforms

Reproductive output can serve as an important metric to assess the value of a marine habitat as it combines fish densities, size at maturity, and the exponential increase of fecundity with body length. California may permit some portion of the structures of offshore oil and gas platforms to remain in place if a "net benefit to the marine environment" can be demonstrated. Here we assess habitats at 23 oil and gas platforms in terms of site- and species- specific estimates of potential reproductive output. We identified 17 fish species (15 rockfishes Sebastes spp.) that have potential reproductive output densities (no. eggs m–2) on individual platforms that were tens to hundreds of times their average on natural reefs in the study area, with the highest potential reproductive output values being observed on platforms for all but two of these species. These extreme values were typically observed in platform base habitats, and likely result from the combined effects of high levels of fish recruitment to midwater platform habitats, relatively low fishing activity on these structures, and ontogenetic habitat use (depth-specific) patterns that make some platforms better habitats for some species based on the seafloor depth where they are sited. However, spatial variability was also very high across both platform and natural reef sites, including reproductive potential for almost all focal species being zero at the majority of surveyed sites. The contribution of fish reproductive potential to the discussion of decommissioning alternatives should therefore be considered on a case-by-case basis for each platform in California.

The coral Platygyra verweyi exhibits local adaptation to long-term thermal stress through host-specific physiological and enzymatic response

Climate change threatens coral survival by causing coral bleaching, which occurs when the coral’s symbiotic relationship with algal symbionts (Symbiodiniaceae) breaks down. Studies on thermal adaptation focus on symbionts because they are accessible both in vitro and in hospite. However, there is little known about the physiological and biochemical response of adult corals (without Symbiodiniaceae) to thermal stress. Here we show acclimatization and/or adaptation potential of menthol-bleached aposymbiotic coral Platygyra verweyi in terms of respiration breakdown temperature (RBT) and malate dehydrogenase (MDH) enzyme activity in samples collected from two reef sites with contrasting temperature regimes: a site near a nuclear power plant outlet (NPP-OL, with long-term temperature perturbation) and Wanlitong (WLT) in southern Taiwan. Aposymbiotic P. verweyi from the NPP-OL site had a 3.1 °C higher threshold RBT than those from WLT. In addition, MDH activity in P. verweyi from NPP-OL showed higher thermal resistance than those from WLT by higher optimum temperatures and the activation energy required for inactivating the enzyme by heat. The MDH from NPP-OL also had two times higher residual activity than that from WLT after incubation at 50 °C for 1 h. The results of RBT and thermal properties of MDH in P. verweyi demonstrate potential physiological and enzymatic response to a long-term and regular thermal stress, independent of their Symbiodiniaceae partner.

Participatory reporting of the 2016 bleaching event in the Western Indian Ocean

Climate change, coupled with an El Nino, caused a devastating bleaching event in the Western Indian Ocean (WIO) in 1998. Similar extreme conditions at the end of 2015 meant that there was a very high risk of widespread bleaching in the WIO at the start of 2016. In anticipation of a regional bleaching event, a citizen-science online reporting tool was developed to collect data in broad categories of bleaching and mortality from various stakeholders across the region, e.g. general public, scientists, reef managers, divers. The main objectives were to (i) document in real-time the impacts of the 2016 coral bleaching event at a regional scale and (ii) demonstrate the value of basic data to illustrate and understand important trends. A total of 698 records from 55 organisations and over 80 observers were collected through the online reporting form and via email. Thermal stress across the WIO during the bleaching season (January–May) was high enough to cause widespread bleaching and significant mortality, with reef sites on average, experiencing a maximum of 5.4 Degree-Heating-Weeks (DHW), with some sites experiencing up to 15 DHW. During the peak-bleaching months, 37% of sites were affected by high or extreme bleaching, while 8.5% of sites showed no evidence of bleaching. Seychelles was the most affected by bleaching with 90% of reported sites showing high or extreme bleaching, followed by Tanzania, Comoros, Reunion and Mauritius. Sites in the Mozambique Channel (south and north) were the least affected by bleaching. Over 60% of sites experienced some level of bleaching-induced coral mortality from April onwards, but the impact was heterogeneous, with reefs in some areas showing substantial recovery from bleaching and others showing almost no recovery. As the first effort in the WIO to gather bleaching data at this scale during a major bleaching event, this study has shown that participatory data collection from various stakeholders, even at a basic level, can reveal important regional-scale, real-time trends and information about coral bleaching.