Reef Species Research Articles

Chemical fractionations and mobilization potentials for some trace metals in reef sediments and corals of Qeshm Island, the Persian Gulf

The bioavailability of trace metals in coral skeletons and sediment samples from Larak and Qeshm Islands in the Persian Gulf was investigated using the sequential extraction technique (SET), bioaccumulation measurement and risk assessment indices. The fractionation results and risk assessment indices indicated that Pb at the Qeshm Station and Cd and Zn at both Stations could have adverse biological effects due to high bioavailability. The bioaccumulation rate of metals in different reef species and at different Stations was not significant. The studied coral reefs showed a high tendency for Pb adsorption, so they could be an efficient bioindicator of Pb contamination. Statistical analysis showed that Pb and Zn were mainly from anthropogenic contamination sources, while the other metals were primarily of natural origin. The results indicated that further studies are needed to make a realistic assessment of the discharge of trace metals to the Persian Gulf.

Sensitivity of the Indo-Pacific coral Acropora millepora to aromatic hydrocarbons

The risks posed by petroleum spills to coral reefs are poorly understood and quantifying acute toxicity thresholds for aromatic hydrocarbons to reef-building corals is required to assess their sensitivity relative to other taxa. In this study, we exposed Acropora millepora to toluene, naphthalene and 1-methylnaphthalene (1-MN) in a flow-through system and assessed survivorship and sublethal responses including growth, colour and the photosynthetic performance of symbionts. Median 50% lethal concentrations (LC50s) decreased over the 7-d exposure period, reaching asymptotic values of 22,921, 5,268, 1167 μg L−1 for toluene, naphthalene and 1-MN, respectively. Corresponding toxicokinetic parameters (εLC50) defining the time progression of toxicity were 0.830, 0.692, and 0.256 d−1, respectively. Latent effects after an additional 7-d recovery in uncontaminated seawater were not observed. Effect concentrations (EC50s) for 50% growth inhibition were 1.9- to 3.6-fold lower than the LC50s for each aromatic hydrocarbon. There were no observed effects of aromatic hydrocarbon exposure on colour score (a proxy for bleaching) or photosynthetic efficiency. Acute and chronic critical target lipid body burdens (CTLBBs) of 70.3 ± 16.3 and 13.6 ± 18.4 μmol g−1 octanol (± standard error) were calculated for survival and growth inhibition based on 7-d LC50 and EC10 values, respectively. These species-specific constants indicate adult A. millepora is more sensitive than other corals reported so far but is of average sensitivity in comparison with other aquatic taxa in the target lipid model database. These results advance our understanding of acute hazards of petroleum contaminants to key habitat-building tropical coral reef species.

Multi-proxy assessment of coral reef formation and biotic-abiotic diversity in an urban coastal reef ecosystem in northeastern Brazil

Coral reefs are habitats with high animal and mineral diversity and are subject to both climate change and anthropogenic impacts. This article presents novel and relevant data on the Seixas coral reef environment's geological, sedimentological, mineralogical, and biotic aspects in Paraíba State, northeastern Brazil. The aim of this study is to evaluate the processes of reef formation and the diversity of coral reef species in urban coastal environments in northeastern Brazil using a multi-proxy approach. Materials and methods employed to analyze the formation and diversity of biotic and abiotic species include (a) bathymetric survey, (b) collection of sedimentological, mineralogical, and granulometric data, (c) geological and stratigraphic determination, and (d) identification of biotic and abiotic species. Mineralogical slide results reveal that the Seixas Reef is a recent biogenic coral-algal carbonate formation associated with coastline evolution, high coastal sedimentation, and changes that occurred alongside sea-level rise (Holocene-Quaternary period). The diversity results indicate that benthic organism settlement occurred on a consolidated arenite base, with the fauna undergoing continuous succession processes. It can be concluded that this coral reef is highly vulnerable due to the material of its formation and comprises subsectors with high diversity (fore reef) and others with low diversity (reef top), which are affected by both anthropogenic and natural factors. Studies of this nature can contribute to understanding the evolution of coastal reefs, as their proximity to the continent makes them more vulnerable, and they experience direct physical impacts from fishing and tourist activities.

Biology and status of Epinephelus fuscoguttatus (Forsskål, 1775) stocks on the Kenyan coast

AbstractGroupers are apex predators that are believed to play crucial roles in ecosystems, so any loss or decline of these species in coral reefs can adversely affect ecosystem stability. Epinephelus fuscoguttatus is currently categorized as vulnerable (VU) from its previous near threatened (NT) category. Information about their biological and ecological status is limited to assist in formulating management plans for the species in Kenya. Therefore, we aimed to provide baseline scientific information on the biology of E. fuscoguttatus, to enable formulation of sustainable management strategies. Sampling was conducted for 1 year at two fish landing sites along the Kenyan coast: Shimoni and Mayungu. Exploitation rate, size at maturity (L50), GSI, and fecundity were estimated. We found that E. fuscoguttatus was currently exploited above an optimum level, (E = 0.9). Length at maturity L50 was 59.50 cm for males and 48.2 cm for females, and mean fecundity was 509,121 eggs/female/year. The gonadosomatic index was highest in June and December, but ripe females were identified in several months to suggest a protracted spawning period. The exploitation rate of E. fuscoguttatus was not sustainable. Consequently, we recommend reducing fishing effort to biologically sustainable levels to enhance recovery.

Importance of coastal vegetated habitats for tropical marine fishes in the Red Sea

Marine vegetated habitats such as seagrass, mangroves, and macroalgae are common along tropical coastlines globally and provide habitats for a diversity of fishes, including juvenile fish and species found on coral reefs. Understanding the use of these habitats by different fish species and life stages is fundamental to spatial planning, fisheries management, and conservation. While previous studies have focused on the habitat potential of seagrass, macroalgae, or mangroves for coral reef fish independently, it is important to consider their combined roles, as tropical seascapes are often mosaics of such habitats. In this study, we evaluated habitat associations across life stages for fish species in coral reefs, seagrasses, macroalgae, and mangroves in Saudi Arabia’s central Red Sea. Through in situ visual surveys, we documented 36% of local coral reef fish species in one or more vegetated habitats, with the fraction of coral reef species utilizing macroalgae or seagrass much greater than that of mangroves (29%, 18%, and 6%, respectively). Mangroves hosted mainly juvenile fish (83% of observed population) and macroalgae hosted the largest proportion of herbivores (39% of observed population), suggesting that each environment offers different combinations of resources (food and shelter), and a mix of these habitats could support biological connectivity across a seascape. Species targeted by local fisheries made up 37% of the species documented in vegetated habitats. The use of multiple habitat types by juvenile and commercially important fishes in the Red Sea underscores the need for a holistic approach to habitat protection.Graphical abstract

Applying Transfer Learning ResNet-50 for Tracking and Classification of A Coral Reef in Development The Mobile Application with Scrum Framework

A Coral Reef has an important role in keeping a balanced ecosystem in the ocean. This research aims to develop a mobile application to track and classify to identify Coral Reefs with a presentation of information names of species, the type of classification of coral (hard or soft coral), accuracy, and area distribution that has been recorded before in certain areas. This research, utilized Flutter for deploying a mobile application, Deep Learning of Transfer Learning (TL) ResNet-50 for the classification of Coral Reefs, and the Google Cloud Platform used to deploy Rest API and deploy model TL ResNet-50 has been created, then the MongoDB database for storing data of the Coral Reef. A species of Coral Reef that could be classified to identify i.e. Acropora Clathrata, Acropora Florida, Cyphastrea Microphthalma, Diploastrea Heliopora, and Pachyseris Speciosa. A total dataset of a Coral Reef has 2197 images and is trained with TL ResNet-50 and it has resulted in an accuracy of 0.9594 or 96% for the classification of Corel Reef. We used the Scrum framework to produce a product in a short time and assist to manage process application development.

Effects of sponge-to-sponge contact on the microbiomes of three spatially competing Caribbean coral reef species.

Sponges perform important ecosystem functions, host diverse microbial symbiont communities (microbiomes), and have been increasing in density on Caribbean coral reefs over the last decade. Sponges compete for space in coral reef communities through both morphological and allelopathic strategies, but no studies of microbiome impacts during these interactions have been conducted. Microbiome alterations mediate spatial competition in other coral reef invertebrates and may similarly impact competitive outcomes for sponges. In this study, we characterized the microbiomes of three common Caribbean sponges (Agelas tubulata, Iotrochota birotulata, and Xestospongia muta) observed to naturally interact spatially in Key Largo, Florida (USA). For each species, replicate samples were collected from sponges in contact with neighbors at the site of contact (contact) and distant from the site of contact (no contact), and from sponges spatially isolated from neighbors (control). Next-generation amplicon sequencing (V4 region of 16S rRNA) revealed significant differences in microbial community structure and diversity among sponge species, but no significant effects were observed within sponge species across all contact states and competitor pairings, indicating no large community shifts in response to direct contact. At a finer scale, particular symbiont taxa (operational taxonomic units at 97% sequence identity, OTUs) were shown to decrease significantly in some interaction pairings, suggesting localized effects for specific sponge competitors. Overall, these results revealed that direct contact during spatial competition does not significantly alter microbial community composition or structure of interacting sponges, suggesting that allelopathic interactions and competitive outcomes are not mediated by microbiome damage or destabilization.

Coral persistence despite marginal conditions in the Port of Miami

Coral cover has declined worldwide due to anthropogenic stressors that manifest on both global and local scales. Coral communities that exist in extreme conditions can provide information on how these stressors influence ecosystem structure, with implications for their persistence under future conditions. The Port of Miami is located within an urbanized environment, with active coastal development, as well as commercial shipping and recreational boating activity. Monitoring of sites throughout the Port since 2018 has revealed periodic extremes in temperature, seawater pH, and salinity, far in excess of what have been measured in most coral reef environments. Despite conditions that would kill many reef species, we have documented diverse coral communities growing on artificial substrates at these sites—reflecting remarkable tolerance to environmental stressors. Furthermore, many of the more prevalent species within these communities are now conspicuously absent or in low abundance on nearby reefs, owing to their susceptibility and exposure to stony coral tissue loss disease. Natural reef frameworks, however, are largely absent at the urban sites and while diverse fish communities are documented, it is unlikely that these communities provide the same goods and services as natural reef habitats. Regardless, the existence of these communities indicates unlikely persistence and highlights the potential for coexistence of threatened species in anthropogenic environments, provided that suitable stewardship strategies are in place.

Continent-wide declines in shallow reef life over a decade of ocean warming.

Human society is dependent on nature1,2, but whether our ecological foundations are at risk remains unknownin the absence of systematic monitoring of species' populations3. Knowledge of species fluctuations is particularly inadequate in the marine realm4. Here we assess the population trends of 1,057 common shallow reef species from multiple phyla at 1,636 sites around Australia over the past decade. Most populations decreased over this period, including many tropical fishes, temperate invertebrates (particularly echinoderms) and southwestern Australian macroalgae, whereas coral populations remained relatively stable. Population declines typically followed heatwave years, when local water temperatures were more than 0.5 °C above temperatures in 2008. Following heatwaves5,6, species abundances generally tended to decline near warm range edges, and increase near cool range edges. More than 30% of shallow invertebrate species in cool latitudes exhibited high extinction risk, with rapidly declining populations trapped by deep ocean barriers, preventing poleward retreat as temperatures rise. Greater conservation effort is needed to safeguard temperate marine ecosystems, which are disproportionately threatened and include species with deep evolutionary roots. Fundamental among such efforts, and broader societal needs to efficiently adapt to interacting anthropogenic and natural pressures, is greatly expanded monitoring of species'population trends7,8.

Can marine heatwaves affect the fatty acid composition and energy budget of the tropical fish Zebrasoma scopas?

Marine heatwaves (MHWs) are extreme weather events featuring abnormally high seawater temperature, and expected to increase in frequency, duration and severity over this century. The impacts of these phenomena on physiological performance of coral reef species require understanding. This study aimed to evaluate the effects of a simulated MHW (category IV; ΔT = +2 °C, 11 days) (after exposure and 10-day recovery period) on fatty acid (FA) composition (as a biochemical indicator) and energy budget (i.e., growth, G, excretion (faecal, F and nitrogenous losses, U), respiration, R and food consumption, C) of a juvenile tropical surgeonfish species (Zebrasoma scopas). Significant and different changes were found under MHW scenario for some of the most abundant FA and respective groups (i.e., an increase in the contents of 14:0, 18:1n-9, ΣMonounsaturated (ΣMUFA) and 18:2n-6; and a decrease in the levels of 16:0, ΣSaturated (ΣSFA), 18:1n-7, 22:5n-3 and ΣPolyunsaturated (ΣPUFA)). The contents of 16:0 and ΣSFA were also significantly lower after MHW exposure compared to control (CTRL). Additionally, lower feed efficiency (FE), relative growth rate (RGR) and specific growth rate in terms of wet weight (SGRw), as well as higher energy loss for respiration were observed under MHW exposure conditions in comparison with CTRL and MHW recovery period. The energy proportion channelled for faeces dominated the mode of energy allocation, followed by growth in both treatments (after exposure). After MHW recovery, this trend was reversed, and a higher percentage was spent for growth and a lower fraction for faeces than in the MHW exposure period. Overall, FA composition, growth rates and energy loss for respiration of Z. Scopas were the physiological parameters most influenced (mainly in a negative way) by an 11-day MHW event. The observed effects in this tropical species can be exacerbated with increasing intensity and frequency of these extreme events.

Effectiveness of Venting and Recompression for Increasing Postrelease Survival of Barotraumatized Black Sea Bass across a Range of Depths

AbstractThe effectiveness of venting and recompression for increasing postrelease survival for fish that experience barotrauma has rarely been tested across a range of depths. We conducted a field tag–recapture experiment to test how well venting and recompression each increased postrelease survival of Black Sea Bass Centropristis striata relative to untreated controls at three different depth ranges on the U.S. South Atlantic continental shelf: 24–26, 29–32, and 35–38 m. Venting and recompression were applied by researchers alongside untreated controls at all three depths, and venting by anglers who were inexperienced with this technique was an additional treatment at the intermediate depth. Tests of independence were used to evaluate the association between treatment type (venting versus controls) and postrelease submergence at each depth. Cox proportional hazards models were fit to the tag–recapture data that were collected at each depth to determine whether the experimental treatment influenced postrelease survival. Postrelease submergence was significantly higher in vented fish at the intermediate and deep depths but not at the shallow depth. The hazards rates were not significant for venting and recompression at the shallow and intermediate depths but were at the deepest depth, demonstrating that these techniques practiced at >35 m increased postrelease survival relative to untreated controls. Mean increases in absolute survival at the 35–38 m depth were calculated to be 6.8% and 8.1% relative to controls when using venting and recompression, respectively. The results further suggest that anglers who are unfamiliar with venting do not reduce postrelease survival compared with venting by experienced personnel. These results provide guidance to fishery managers who are tasked with seeking methods to reduce catch‐and‐release mortality for an important reef species. Taken together, the findings from submergence success and survival models suggest that both venting and recompression should be encouraged to increase the postrelease survival of Black Sea Bass that are caught from depths >29 m.

Sea slugs (Gastropoda: Heterobranchia) associated with Autonomous Reef Monitoring Structures (ARMS) in southern Gulf of Mexico and Mexican Caribbean Sea

Abstract Cryptic species in coral reefs, such as sea slugs, represent an important portion of their biodiversity, which is usually underestimated. Autonomous Reef Monitoring Structures (ARMS) have been implemented to estimate cryptic diversity in coral reefs. Therefore, this research aimed to contribute to the southern Gulf of Mexico (GM) and the Caribbean Sea (CAR) coral reefs’ sea slugs’ diversity and distribution using ARMS as a collection method. Fifty-eight ARMS were placed at three coral reefs in the GM and CAR, recovered after 1–2 years and then, disassembled at the laboratory. Plates were individually placed in trays with seawater, where we searched for sea slugs. A total of 242 organisms were found belonging to 31 species; 20 of them were identified to the species level, while 11 were determined up to genus or family. More than half of the species (19) were found in Bajo de 10 (GM), while 15 species were found in the CAR localities. Unlike previous studies, we assessed sea slugs’ diversity exclusively by an indirect sampling method. In this work, we found 9.4% of the sea slug diversity recorded in the Caribbean, and we report four determined species for the first time in the country. New records of species, and even one family for the GM stress the gap of information that we still need to fulfil in the area. We recognize ARMS as a useful tool to find juvenile, cryptic and rare species of sea slugs, as well as to standardize their quantification and record their diversity.

Remotely operated vehicle reveals fish orientate to the substrate underneath marina floating pontoons

The modern day seascape is a mix of natural habitats (saltmarsh, mangroves, seagrass, unvegetated beaches), but increasingly is being replaced with hard engineering structures (e.g. floating pontoons) that have resulted in novel habitats available for flora and fauna. While these engineered structures provide new marine habitat resources, from the viewpoint of biodiversity, they effectively support a sub-set of species found in natural habitats. Unlike previous studies that have used divers for fish visual census, we used a remotely operated vessel with an underwater camera to examine the fish community using floating pontoons in a marina facility in tropical central Queensland, Australia. The camera filmed continuously the edge and underside of pontoons (both surveys covered similar pontoon linear distances – July (winter) 430m; November (summer) 485m; 2021). Fifteen fish species representing 14 families were recorded, with more species observed during summer compared to the winter survey. Remarkably, across both surveys of the 243 fishes individuals that were recorded, 166 (68%) appeared upside-down in videos (i.e., oriented to the underside of the pontoon). Engaging a behaviour of swimming upside-down has been acknowledged in natural habitats elsewhere; some coral reef species living in caves or reef ledges orientate themselves to the cave ceiling or overhanging ledge to increase prey capture rate. However, this is the first study to record fishes exhibiting the same behaviour. We conclude that our less invasive video survey approach provided the opportunity to observe fishes in a state of natural behaviour, orientating themselves towards the pontoon substrate, which is probably simply a response of adhering to basic characteristic modes, i.e., it is the orientation relative to the substrate that is important, rather than their orientation in space per se. Indeed marina pontoons provide an additional feature in already habitat complex estuaries; these data add to why we need to consider the ecosystem services offered by marine infrastructure, and the plasticity of fish to adapt to new environments in an expanding blue economy.

The reef fish assemblage of a coral reef system in the southwestern Gulf of Mexico

Reef fish species richness of the Veracruz Reef System National Park (VRSNP) in the SW Gulf of Mexico is well known. However, the knowledge of the assemblage structure and its spatial variability in the reef ecosystem is quite limited. For that purpose, 5 field surveys (2012-2015) were performed, using the stationary visual census method, at 10 selected reefs. The most important findings were: 116 reef species were recorded. Average total reef fish density (2.31 Ind/m2) is similar to the records for the Caribbean reefs in the 20th century. The top 5 most abundant species were: Chromis multilineata, Ocyurus chrysurus, Abudefduf saxatilis, Stegastes leucostictus, and Elacatinus jarocho. We found evidence of a spatial distribution pattern with 3 well-defined groups of reefs: (1) those near the city of Veracruz, (2) those near the outlet of the Jamapa River, and (3) those farther from the city. Higher fish densities are associated to both high hermatypic coral and low crustose coralline algae bottom covers. The assemblage structure of reef fishes is different at distinct geomorphological reef zones. As expected, with some differences in the species abundance order, the assemblage structure of reef fishes is similar at all coral reefs in the Gulf of Mexico.

Integrating larval connectivity into the marine conservation decision-making process across spatial scales.

Larval dispersal connectivity is typically integrated into spatial conservation decisions at regional or national scales, but implementing agencies struggle with translating these methods to local scales. We used larval dispersal connectivity at regional (hundreds of kilometers) and local (tens of kilometers) scales to aid in design of networks of no-take reserves in Southeast Sulawesi, Indonesia. We used Marxan with Connectivity informed by biophysical larval dispersal models and remotely sensed coral reef habitat data to design marine reserve networks for 4 commercially important reef species across the region. We complemented regional spatial prioritization with decision trees that combined network-based connectivity metrics and habitat quality to design reserve boundaries locally. Decision trees were used in consensus-based workshops with stakeholders to qualitatively assess site desirability, and Marxan was used to identify areas for subsequent network expansion. Priority areas for protection and expected benefits differed among species, with little overlap in reserve network solutions. Because reef quality varied considerably across reefs, we suggest reef degradation must inform the interpretation of larval dispersal patterns and the conservation benefits achievable from protecting reefs. Our methods can be readily applied by conservation practitioners, in this region and elsewhere, to integrate connectivity data across multiple spatial scales.

Cell wall organic matrix composition and biomineralization across reef-building coralline algae under global change.

Crustose coralline algae (CCA) are one of the most important benthic substrate consolidators on coral reefs through their ability to deposit calcium carbonate on an organic matrix in their cell walls. Discrete polysaccharides have been recognized for their role in biomineralization, yet little is known about the carbohydrate composition of organic matrices across CCA taxa and whether they have the capacity to modulate their organic matrix constituents amidst environmental change, particularly the threats of ocean acidification (OA) and warming. We simulated elevated pCO2 and temperature (IPCC RCP 8.5) and subjected four mid-shelf Great Barrier Reef species of CCA to 2months of experimentation. To assess the variability in surficial monosaccharide composition and biomineralization across species and treatments, we determined the monosaccharide composition of the polysaccharides present in the cell walls of surficial algal tissue and quantified calcification. Our results revealed dissimilarity among species' monosaccharide constituents, which suggests that organic matrices are composed of different polysaccharides across CCA taxa. We also observed that species differentially modulate composition in response to ocean acidification and warming. Our findings suggest that both variability in composition and ability to modulate monosaccharide abundance may play a crucial role in surficial biomineralization dynamics under the stress of OA and global warming.

Islands in the mud: The South Texas banks provide crucial mesophotic habitat for coral communities

On the continental shelf off the coast of South Texas lie a series of natural hard-bottom structures (rocky outcrops and relic coral-algal reefs) known as the South Texas Banks (STB), which provide critical habitat for benthic organisms and pelagic fish. The depth of the banks, a persistent nepheloid layer, and strong currents have resulted in few studies that provide quantitative biodiversity data on the STB. Using a remotely operated vehicle (ROV), video surveys were conducted to quantitatively describe the mesophotic coral communities and assess habitat suitability of five STB: North Hospital, Hospital, Southern, Big Adam, and Mysterious Banks. Each of these STB have significantly different benthic communites, with coral communities composed primarily of antipatharians and octocorals. Big Adam Bank had the lowest biodiversity and the least coral cover. Mysterious Bank had abundant antipatharians, specifically Stichopathes spp., but low biodiversity overall. Hospital Bank had low coral diversity that was offset by high diversity in sponges and other invertebrate species. North Hospital and Southern Banks had abundant and diverse populations of coral species, including scleractinians, and other benthic invertebrates. These data indicate that the STB are crucial islands of biodiversity in an area with few suitable areas for coral reef species. In addition, predictive modelling of habitat suitability provided valuable estimates on the potential distribution of key benthic community members, such as scleractinians and antipatharians, throughout the entire areas of the five banks assessed.

Sound stimulus effects on dusky damselfish behavior and cognition.

Anthropogenic noises are widespread and affect marine wildlife. Despite the growing knowledge on noise pollution in the marine environment, its effects on fish cognition are scarce. Here, we investigated the effects of sound exposure on anxiety-like behavior and memory retention on dusky damselfish Stegastes fuscus. The animals were trained in a conditioned place aversion task, and exposed to two daily sessions of music at intensities of 60-70 dBA or 90-100 dBA, while the control group was kept at 42-46 dBA (no music) for five days. After that, fish were tested in the novel tank paradigm and tested for the memory of the aversive task. In the novel tank, animals exposed to sound spent more time still and decreased the distance from the bottom of the tank. Animals also spent more time on the aversive side of the conditioning tank. These results suggest that anthropogenic noise applied through high-intensity music can increase anxiety and decrease memory retention in S. fuscus, suggesting the deleterious potential of noise for reef species.

A Lagrangian model-based physical connectivity atlas of the Red Sea coral reefs

Connectivity, the exchange of individuals and genes among geographically separated marine populations, plays a key role in coral reef biodiversity and resilience. The Red Sea is a semi-enclosed basin with dynamic circulation and abundant coral reefs, making it a natural laboratory for coral reef connectivity research. Previous studies broadly investigated Red Sea connectivity, but were spatially restricted to regional or sparsely-distributed reef sites. Here, using hydrodynamic and particle tracking models, a high-resolution circulation-driven physical connectivity atlas covering every Red Sea coral reef, including seasonality, was simulated and further validated against availablein-situgenetic datasets. The simulation was conducted without incorporating larval traits to isolate and quantify the connectivity contributed by circulation. Our validation experiment suggests the importance of circulation in shaping the genetic structure of Red Sea reef species, supporting the Isolation By Circulation (IBC) theory in the Red Sea seascape genetics. The simulated atlas reveals that reefs in the northern Red Sea are better sources and destinations than those in the southern basin, regardless of season. The east-west connections between the southern reefs are identified to be weak. Complex circulation dynamics drive a regional-specific seasonality, e.g., the Farasan Islands reefs are better sources during summer while the nearby Bab-Al-Mandeb strait reefs are better sources during winter. The west-coast reefs are generally winter-intensified sources whereas the east-coast reefs are generally summer-intensified sources. The revealed seasonality of physical connectivity is important for larval dispersal processes as reef species may spawn in different seasons. This physical connectivity atlas provides a reference for designing marine conservation strategies from a circulation perspective and easy-to-access physical connectivity datasets for the future Red Sea seascape genetic studies.

Giant clam (Tridacna) distribution in the Gulf of Oman in relation to past and future climate

The Oman upwelling zone (OUZ) creates an unfavorable environment and a major biogeographic barrier for many coral reef species, such as giant clams, thus promoting and maintaining faunal differences among reefs on the east and west side of the Arabian Peninsula. We record the former existence of Tridacna in the Gulf of Oman and review its stratigraphic distribution in the Persian Gulf to provide new insights on the connectivity of coral reef habitats around southern Arabia under changing climate and ocean conditions. Fossil shells were carbon-14 dated and employed as sclerochronological proxy archives. This reveals that the Omani population represents a last glacial colonization event during the Marine Isotope Stage 3 interstadial under colder-than-present temperatures and variable upwelling intensity linked to Dansgaard-Oeschger climate oscillations. It was favored by temperatures just above the lower threshold for the habitat-forming reef coral communities and instability of the upwelling barrier. We conclude that the distribution of Tridacna in the northern Arabian Sea is generally limited by either strong upwelling or cool sea surface temperature under gradually changing climate conditions at the interglacial-glacial scale. Opportunities for dispersal and temporary colonization existed only when there was a simultaneous attenuation of both limiting factors due to high-frequency climate variability. The OUZ will unlikely become a future climate change refuge for giant clams because they will be exposed either to thermal stress by rapid anthropogenic Indian Ocean warming or to unfavorable upwelling conditions.