Reef Fish Assemblages Research Articles

Loss of Coral Trait Diversity and Impacts on Reef Fish Assemblages on Recovering Reefs.

Understanding patterns of biodiversity change is essential as coral reefs experience recurrent cycles of disturbance and recovery. Shifts in the total cover and species composition of habitat-forming corals can have far-reaching consequences, including shifts in coral functional traits and impacts on local fish assemblages. We surveyed coral and fish assemblages along the southern coast of Hainan Island near Sanya, China, in 2006, 2010, and 2018, during a period with repeated mass bleaching events. We showed that coral biodiversity in this region is in a state of flux, with losses and gains in coral cover and an increase in species richness over time. Despite increasing species diversity, the region suffered a loss of coral trait diversity by 2010, with an incomplete recovery by 2018, owing to declines in species with key habitat-forming traits (e.g., high surface areas and fractal structure) such as corymbose corals. Concurrently, there was an increase in functional redundancy due to the proliferation of the dominant encrusting and massive corals. Coral cover was positively associated with the abundance of reef fish, indicating that the changes observed in coral abundance can impact reef-associated species. These results demonstrate that the slow recovery of coral biodiversity in southern Hainan Island has been hampered by the loss of specific coral traits and highlight the importance of protecting vulnerable coral traits in conservation and management strategies.

Regional-scale disturbances drive long-term decline of inshore coral reef fish assemblages in the Great Barrier Reef Marine Park.

Anthropogenic pressure is increasing the variety and frequency of environmental disturbance events, limiting recovery and leading to long-term declines in wild plant and animal populations. Coral reefs and associated fish assemblages are inherently dynamic due to their susceptibility to a host of disturbances, but regional-scale nuances in the drivers of long-term change frequently remain poorly resolved. Here, we examine the effects of multiple potential drivers of change in coral reef fish assemblages across 4 inshore regions of the Great Barrier Reef Marine Park (GBRMP), Australia, over 12-14 years (2007-2021). Each region had a unique disturbance history, in conjunction with long-term changes in physical and habitat variables. Phases of recovery were apparent in the years between disturbance events at all locations, but these were not long enough to prevent substantial declines in reef fish density (by 33%-72%) and species richness (by 41%-75%) throughout the study period. The main drivers of change in fish assemblages varied among regions; however, the most rapid changes followed cyclone and flood events. Limited recovery periods resulted in temporal shifts in fish species composition from typically coral-associated to algae-associated. Most trophic groups declined in density except farmers, grazers, omnivores and parrotfish. No-take marine reserves (NTMRs) had small and inconsistent effects on total fish assemblages, but delivered benefits for fishery-targeted piscivores. Our findings suggest that coral reef responses to local stressors and cumulative escalating climate change impacts are highly variable at regional scales, and that small NTMRs are unlikely to mitigate the impacts of increasingly frequent climatic disturbances. Nearshore coral reefs worldwide are high-value habitats that are either already degraded or vulnerable to degradation and the loss of important fish groups. Global efforts to reduce greenhouse gas emissions must be coupled with effective local management that can support the functioning and adaptive capacity of coral reefs.

Managing nutrition-biodiversity trade-offs on coral reefs

Coral reefs support an incredible abundance and diversity of fish species, with reef-associated fisheries providing important sources of income, food, and dietary micronutrients to millions of people across the tropics. However, the rapid degradation of the world's coral reefs and the decline in their biodiversity may limit their capacity to supply nutritious and affordable seafood while meeting conservation goals for sustainability. Here, we conduct a global-scale analysis of how the nutritional quality of reef fish assemblages (nutritional contribution to the recommended daily intake of calcium, iron, and zinc contained in an average 100g fish on the reef) relates to key environmental, socioeconomic, and ecological conditions, including two key metrics of fish biodiversity. Our global analysis of more than 1,600 tropical reefs reveals that fish trophic composition is a more important driver of micronutrient concentrations than socioeconomic and environmental conditions. Specifically, micronutrient density increases as the relative biomass of herbivores and detritivores increases at lower overall biomass or under high human pressure. This suggests that the provision of essential micronutrients can be maintained or even increase where fish biomass decreases, reinforcing the need for policies that ensure sustainable fishing, and that these micronutrients are retained locally for nutrition. Furthermore, we found a negative association between micronutrient density and two metrics of fish biodiversity, revealing an important nutrition-biodiversity trade-off. Protecting reefs with high levels of biodiversity maintains key ecosystem functions, whereas sustainable fisheries management in locations with high micronutrient density could sustain the essential supply of micronutrients to coastal human communities.

Structure of Reef Fish Families (Butterflyfishes and Angelfishes) at Isolated Oceanic Reefs in the Indian Ocean: Christmas Island and the Cocos (Keeling) Islands

There has been substantial research on the factors that structure reef fish assemblages, but this has mostly focused on nearshore or continental reefs. This study examines patterns of abundance and species composition for two iconic groups of coral reef fishes, angelfishes (family Pomacanthidae) and butterflyfishes (family Chaetodontidae) at two isolated, oceanic reefs in the Indian Ocean: Christmas Island and the Cocos (Keeling) Islands. Six explanatory variables were investigated to determine whether large-scale physical factors are more important than fine-scale biotic factors in structuring reef fish communities on oceanic islands. For angelfishes, depth was the factor that most explained patterns in abundance (explaining 46.5% of the variation), species richness (44.8%) and composition (15.3%), with both abundance and species richness being greater at 20 m than at 5 m. Differences in species composition were greater between depths than between islands. For butterflyfishes, variation in abundance and species richness was best explained by the difference in aspect or exposure among sites, though abundance and composition also differed significantly between Christmas Island and the Cocos (Keeling) Islands. Large-scale variation in the structure of these reef fish assemblages could not be explained based on differences in habitat diversity, or coral and algal cover. This study indicates that large-scale physical factors (island location, exposure, depth) are more important than fine-scale biotic factors in structuring reef fish assemblages on oceanic islands.

Can niche plasticity mediate species persistence under ocean acidification?

Global change stressors can modify ecological niches of species, thereby altering ecological interactions within communities and food webs. Yet, some species might take advantage of a fast-changing environment, allowing species with high niche plasticity to thrive under climate change. We used natural CO2 vents to test the effects of ocean acidification on niche modifications of a temperate rocky reef fish assemblage. We quantified three ecological niche traits (overlap, shift and breadth) across three key niche dimensions (trophic, habitat and behavioural). Only one species increased its niche width along multiple niche dimensions (trophic and behavioural), shifted its niche in the remaining (habitat) was the only species to experience a highly increased density (i.e. doubling) at vents. The other three species that showed slightly increased or declining densities at vents only displayed a niche width increase in one (habitat niche) out of seven niche metrics considered. This niche modification was likely in response to habitat simplification (transition to a system dominated by turf algae) under ocean acidification. We further showed that, at the vents, the less abundant fishes had a negligible competitive impact on the most abundant and common species. This species appeared to expand its niche space, overlapping with other species, which likely led to lower abundances of the latter under elevated CO2. We conclude that niche plasticity across multiple dimensions could be a potential adaptation in fishes to benefit from a changing environment in a high-CO2 world.

Study on the relationship between economic input growth in Marine protected areas and environmental governance in the North Pacific Coast of Costa Rica: Based on reef fish assemblages

Reef fish communities under fishing pressure often experience reduced biomass, abundance, and altered size structure. The establishment of marine protected areas (MPAs) can help mitigate these declines. However, the success of MPAs, especially in developing countries with financial and socioeconomic challenges, largely hinges on effective enforcement. This study utilized underwater visual surveys (UVS) and baited remote underwater video stations (BRUVS) to evaluate population density, size distribution, and biomass of both economically valuable (e.g., target and ornamental species) and ecologically important (e.g., small/large predators and herbivores) fish groups within and outside a no-take MPA on the northern Pacific coast of Costa Rica.The results indicated that protective measures did not significantly affect the biomass of economically valuable fish species. However, there were notable differences in fish abundance and size distribution between no-take zones (where fishing is prohibited) and open-fishing zones. This suggests that, despite potential illegal fishing activities within the MPA, certain fish community components benefit from the protective measures.Specifically, herbivores and ornamental fish, which are often targeted by artisanal compressor fishing and the aquarium trade, exhibited higher biomass and abundance levels within the MPA. Additionally, significant shark species such as Galeocerdo cuvier, Carcharhinus leucas, and Carcharhinus limbatus were exclusively found within the MPA.The study also highlighted the crucial role of habitat quality, particularly high coral cover, in enhancing the biomass of ornamental fish.This research contributes to the growing body of evidence that MPAs, even with limited enforcement, consistently offer ecological benefits for reef fish communities

Out of shape: Ocean acidification simplifies coral reef architecture and reshuffles fish assemblages.

Climate change stressors are progressively simplifying biogenic habitats in the terrestrial and marine realms, and consequently altering the structure of associated species communities. Here, we used a volcanic CO2 seep in Papua New Guinea to test insitu if altered reef architecture due to ocean acidification reshuffles associated fish assemblages. We observed replacement of branching corals by massive corals at the seep, with simplified coral architectural complexity driving abundance declines between 60% and 86% for an assemblage of damselfishes associated with branching corals. An experimental test of habitat preference for a focal species indicated that acidification does not directly affect habitat selection behaviour, with changes in habitat structural complexity consequently appearing to be the stronger driver of assemblage reshuffling. Habitat health affected anti-predator behaviour, with P. moluccensis becoming less bold on dead branching corals relative to live branching corals, irrespective of ocean acidification. We conclude that coral reef fish assemblages are likely to be more sensitive to changes in habitat structure induced by increasing pCO2 than any direct effects on behaviour, indicating that changes in coral architecture and live cover may act as important mediators of reef fish community structures in a future ocean.

Reef fish assemblages differ both compositionally and functionally on artificial and natural reefs in the eastern Gulf of Mexico

Reef fish assemblages differ both compositionally and functionally on artificial and natural reefs in the eastern Gulf of Mexico

Multiple events determine the distribution of fishes’ early life stages in the Abrolhos Bank, Southwestern Atlantic

Fluctuations in reef fish settlement and recruitment significantly impact local population dynamics and adult population size. We use light traps to evaluate reef fish settlement in inshore and offshore reefs in the Abrolhos Bank, in addition to the spatio-temporal distribution patterns, and environmental variables' influence. Data were collected from inshore and offshore reefs, and statistical analyses, including GLMs, PERMANOVA and nMDS, aimed to understand spatial-temporal species distribution patterns and the relationship between environmental variables. Results indicate greater species abundance and diversity offshore, influenced by winds, tides, and distance from shore, explaining 50% of larval patterns and highlighting the importance of spatial-temporal variations in early-life reef fish assemblages. However, several factors, including habitat type, quality, complexity, seascape configuration, and MPA location, may influence these patterns. Additionally, we provide evidence that commercially important species like Lutjanids use Abrolhos reef areas as nursery grounds.

Red snapper excavate sediments around artificial reefs: observations of ecosystem-engineering behavior by a widely distributed lutjanid

Hard substrate and vertical relief are limited habitat resources for reef-associated species in many regions. On the West Florida Shelf (WFS) of the Gulf of Mexico, red grouper Epinephelus morio act as ecosystem engineers by excavating sediments to expose limestone bedrock. Excavations can exceed 25 m in diameter and 2 m in depth and are among the most abundant WFS seafloor features at depths between 40 and 110 m. As part of a survey of hard-bottom habitats and associated reef fish assemblages, 1203 excavations were identified in WFS waters along the Florida Panhandle between 2014 and 2019. These excavations often contained subsided artificial reef material within their interior and infrequently included E. morio among observed fishes. We video-identified red snapper Lutjanus campechanus excavating sediments around 2 subsided artificial reefs in 2015 and 2017 for a total of approximately 56 min of excavation activity. A total of 24 excavation events were documented around a tire pile in 2015, and 5 were documented around a pyramid-shaped reef module in 2017. These observations help to explain the subsidence of artificial reefs and apparent excavation around their bases despite the scarcity of previously known excavating species. This suggests that L. campechanus might be ecosystem engineers on the WFS.

Vertical structure of reef fish assemblages and light penetration reveal new boundaries of mesophotic ecosystems in the subtropical Southwestern Atlantic

In the Southwest Atlantic, fisheries and in situ observations suggest that mesophotic reefs occur further south than has been reported in the literature, and a description of these subtropical regions is still lacking. We used Baited Remote Underwater stereo-Videos to explore unrevealed patterns in the vertical structure of fish assemblages on subtropical Atlantic reefs, contrasting shallow and mesophotic habitats. Our data on species turnover and light penetration reveal that in the subtropical Atlantic, the boundaries between shallow and mesophotic habitats occur at depths of 18 m, which is shallower than most previous studies have shown. Generalized additive mixed models identified different environmental and management factors as important predictor variables that explain distribution of fish assemblages’ attributes. Besides adding new evidence about mesophotic limits, we described variations in the vertical structure of fish assemblages, providing important information for the description and conservation of mesophotic environments in subtropical regions.

Multi-Scale Coral Reef and Seascape Habitat Variables Combine to Influence Reef Fish Assemblages

While benthic characteristics of coral reef habitats are a major driver of the structure of coral reef fish assemblages, non-reef habitats adjacent to coral reefs (e.g., mangroves, seagrass beds, and macroalgal beds) can affect reef fish assemblages. Here, we investigate how reef fish assemblages respond to local-scale benthic habitats within a coral reef and larger-scale adjacent seascape features (habitats within 500 m of coral reefs) on Siquijor Island in the Philippines. We examined an abundance of species for the entire reef fish assemblage and within the assemblages of parrotfishes (subfamily Scarinae) and wrasses (family Labridae). Five distinct habitat types were identified in a cluster analysis, which incorporated benthic characteristics within coral reefs and habitats adjacent to coral reefs. We found that the diversity and structure of coral reef fish assemblages were affected by benthic characteristics within coral reefs and also by benthic habitat types adjacent to coral reefs. Individual species responses and juveniles of certain species demonstrated uniquely high abundances in habitat clusters characterized by the non-reef habitats surrounding coral reefs. Considering coral reef habitats and adjacent non-reef habitats as a holistic, interconnected seascape will provide better estimations of the drivers of the structures of coral reef fish assemblages.

A Comparison of Methods of Visual Census and Cryptobenthic Fish Collecting, an Integrative Approach to the Qualitative and Quantitative Composition of the Mediterranean Temperate Reef Fish Assemblages

The present research quantitatively compared the fish composition among two methods for non-cryptic benthic fish species and one method for cryptobenthic fish species for the first time for the Mediterranean temperate reef fish assemblage. A visual census of fishes was performed within a cylinder of 4 m radius and within a cylinder of 2 m radius, while the cryptobenthic fishes were collected using a square of 1 m2 with anesthetic. The data and material were collected at fifty sampling points. The visual census methods together recorded 31 species, and the square with anesthetic method recorded 18 species. The quantitative comparison of methods of visual census and cryptobenthic fish collecting showed significantly different species richness, total fish abundance, and fish assemblage structure among methods. The applied methods were highly complementary. The cylinder of 2 m radius is well suited for epibenthic fishes and the cylinder of 4 m radius is reliable for hyperbenthic and benthopelagic fishes. Therefore, each of the methods well covered one of three components of ichthyobenthos (hyperbenthic, epibenthic, and cryptobenthic fishes), and all three methods together provided a far more complete assessment of fish species composition than any individual census method for the Mediterranean littoral benthic fishes.

Regional reef fish assemblage maps provide baseline biogeography for tropicalization monitoring

The Anthropocene rise in global temperatures is facilitating the expansion of tropical species into historically non-native subtropical locales, including coral reef fish. This redistribution of species, known as tropicalization, has serious consequences for economic development, livelihoods, food security, human health, and culture. Measuring the tropicalization of subtropical reef fish assemblages is difficult due to expansive species ranges, temporal distribution shifts with the movement of isotherms, and many dynamic density-dependent factors affecting occurrence and density. Therefore, in locales where tropical and subtropical species co-occur, detecting tropicalization changes relies on regional analyses of the relative densities and occurrence of species. This study provides a baseline for monitoring reef fish tropicalization by utilizing extensive monitoring data from a pivotal location in southeast Florida along a known transition between tropical and subtropical ecotones to define regional reef fish assemblages and use benthic habitat maps to spatially represent their zoogeography. Assemblages varied significantly by ecoregion, habitat depth, habitat type, and topographic relief. Generally, the southern assemblages had higher occurrences and densities of tropical species, whereas the northern assemblages had a higher occurrence and density of subtropical species. A total of 108 species were exclusive to regions south of the Bahamas Fracture Zone (BFZ) (South Palm Beach, Deerfield, Broward-Miami) and 35 were exclusive to the north (North Palm Beach, Martin), supporting the BFZ as a pivotal location that affects the coastal biogeographic extent of tropical marine species in eastern North America. Future tropicalization of reef fish assemblages are expected to be evident in temporal deviance of percent occurrence and/or relative species densities between baseline assemblages, where the poleward expansion of tropical species is expected to show the homogenization of assemblage regions as adjacent regions become more similar or the regional boundaries expand poleward. Ecoregions, habitat depth, habitat type, and relief should be incorporated into the stratification and analyses of reef fish surveys to statistically determine assemblage differences across the seascape, including those from tropicalization.

Change in the subtidal reef fish assemblage at Kuchierabu-jima Island, southern Japan, between 1972 and 2005

Change in the subtidal reef fish assemblage at Kuchierabu-jima Island, southern Japan, between 1972 and 2005

Upper mesophotic reef fish assemblages at Bahía de Banderas, Mexico.

There is no information on the species associated with the mesophotic reefs of Banderas Bay, located in the central Mexican Pacific. This study analysed the reef fish assemblage from three depths (50, 60 and 70 m) in three sampling sites of the southern submarine canyon of the Bay: Los Arcos, Bajo de Emirio and Majahuitas. Several analyses were performed to test the hypothesis that there are important differences in fish abundance and species composition between sites and depths. Twenty-two species of bony fishes grouped in 14 families were recorded. PERMANOVA results showed that there were no significant differences in fish diversity parameters between sites, indicating a certain uniformity in their distribution. However, nine species were exclusive to one site and depth (five singleton species with only one individual recorded and four unique species recorded only once). On the other hand, there were significant differences between depths, mainly between 50 and 70 m. Diversity decreases with depth and species composition changes. SIMPER, Shade Plot and NMDS analysis show the most representative species at each depth, with at least half of the species (11) recorded only at 50 m and four species at the deeper levels (60 - 70 m). The observed assemblage includes several of the most caught species in the shallow water artisanal fishery, which is the most traditional and common type of fishery in the Bay. In addition, the Pomacanthuszonipectus (Cortés angelfish) is of particular interest, as it has a special protection status in the official Mexican standard (NOM-059-SEMARNAT, 2010) due to its use as an ornamental species in aquaria. We hypothesised that the mesophotic zone may serve as a refuge for these fishes, so we propose that the information obtained is an important basis for new research aimed at the sustainable management of fisheries in the area.

Local habitat composition and complexity outweigh seascape effects on fish distributions across a tropical seascape

ContextThe distribution of animals is influenced by a complex interplay of landscape, environmental, habitat, and anthropogenic factors. While the effects of each of these forces on fish assemblages have been studied in isolation, the implications of their combined influence within a seascape remain equivocal.ObjectivesWe assessed the importance of local habitat composition, seascape configuration, and environmental conditions for determining the abundance, diversity, and functional composition of fish assemblages across a tropical seascape.MethodsWe quantified fish abundance in coral, macroalgal, mangrove, and sand habitats throughout the Dampier Archipelago, Western Australia. A full-subsets modelling approach was used that incorporated data from benthic habitat maps, a hydrodynamic model, in situ measures of habitat composition, and remotely sensed environmental data to evaluate the relative influence of biophysical drivers on fish assemblages.ResultsMeasures of habitat complexity were the strongest predictors of fish abundance, diversity, and assemblage composition in coral and macroalgal habitats, with seascape effects playing a secondary role for some functional groups. Proximity to potential nursery habitats appeared to have minimal influence on coral reef fish assemblages. Consequently, coral, macroalgal, and mangrove habitats contained distinct fish assemblages that contributed to the overall diversity of fish within the seascape.ConclusionsOur findings underscore the importance of structural complexity for supporting diverse and abundant fish populations and suggest that the value of structural connectivity between habitats depends on local environmental context. Our results support management approaches that prioritise the preservation of habitat complexity, and that incorporate the full range of habitats comprising tropical seascapes.

Is a recent large expansion of a no-take reserve sufficient to change the reef fish assemblage? A before-after assessment in Alcatrazes Wildlife Refuge, Southwestern Atlantic

Marine protected areas (MPAs) have been established with the aim of preserving and recovering marine environments, as well as managing fisheries activities. Some features of MPAs can enhance conservation goals, such as being completely no-take, well-enforced, large, old and isolated. The no-take area in the Alcatrazes Archipelago, southwestern Atlantic, was recently expanded from four separate small areas of 3 km2 (totalling 12.5 km2) established in 1987, to a large continuous no-take reserve (NTR) of 675 km2 established in August 2016, allowing tourism activities. In this study, the aim was to detect recent changes in the reef fish assemblage following the expansion of the NTR using visual census samples in specific sites around the main island. The surveys were conducted before (2015–2016; n = 230 censuses) and after (2019–2020; n = 320 censuses) the expansion of the NTR. Generalized additive mixed models were fitted to predict fish richness, functional richness, abundance and biomass, considering factors like depth, year and specific sites. The most parsimonious models for mean richness, functional richness, abundance and biomass all included a negative relationship with protection after the expansion, but with an increase of unique species and unique functional entities. Beta diversity values between sites decreased after the expansion with a smaller contribution of nestedness, which indicates a greater sharing of species among the reef areas around the main island. We raised the hypothesis that the decreases in fish fauna metrics could be attributed to several factors: (1) the recency of the NTR expansion, making it difficult to detect the benefits of protection in this short time frame (i.e., less than five years); (2) the type of habitat protected after the expansion, which included mostly sandy bottoms, possibly not promoting connectivity; and (3) the presence of recreational divers in the recently protected area hampering the detection of fish due to possible changes in fish behaviour (mainly for large species with commercial use). By studying one of the largest southwestern Atlantic no-take MPAs, we add evidence that area increment alone is not enough to optimize the protection of marine biodiversity within a short time scale and continuous ecological monitoring is essential for adaptive management, especially in the early stages of MPAs.

Intact shallow and mesophotic assemblages of large carnivorous reef fishes underscore the importance of large and remote protected areas in the Coral Triangle

Abstract Overfishing remains a threat to coral reef fishes worldwide, with large carnivores often disproportionately vulnerable. Marine protected areas (MPAs) can restore fish populations and biodiversity, but their effect has been understudied in mesophotic coral ecosystems (MCEs), particularly in the Coral Triangle. Videos were analysed from baited remote underwater video systems deployed in 2016 to investigate the assemblage structure of large carnivorous fishes at shallow (4–12 m) and mesophotic (45–96 m) depths in two of the largest and most isolated MPAs in the Philippines: an uninhabited, fully no‐take MPA enacted in 1988 (Tubbataha Reefs Natural Park) and an archipelagic municipality surrounded by an extensive but not fully no‐take MPA declared in 2016 (Cagayancillo). Taxa focused on were groupers (Serranidae), snappers (Lutjanidae), emperors (Lethrinidae), jacks (Carangidae) and the endangered Cheilinus undulatus (Labridae). Mean abundance and species richness were not greater in TRNP than in Cagayancillo regardless of depth despite long‐term protection in the former. Limited impacts of fishing in Cagayancillo may explain this result. Differentiation of fish assemblages was evident between TRNP and Cagayancillo but more obvious between depths at each location, probably due more to habitat than MPA effects. In Cagayancillo, overall carnivorous reef fish, grouper and jack mean abundance were 2, 2 and 10 times higher, respectively, at mesophotic depths, suggesting that MCEs can serve as deep refugia from fishing. These findings of differentiation between depths and higher abundance of certain taxa in mesophotic depths emphasize that MCEs are distinct from shallow reefs, serve as important habitat for species susceptible to overfishing and, thus, must be explicitly included in the design of MPAs. This study also highlights the value of maintaining strict protection of MPAs like TRNP for the Coral Triangle and an opportunity to safeguard intact fish assemblages in Cagayancillo by expanding its no‐take zones.

Low diversity and abundance of predatory fishes in a peripheral coral reef ecosystem.

Semi-enclosed seas are often associated with elevated local threats and distinct biogeographic patterns among marine fishes, but our understanding of how fish assemblage dynamics vary in relation to relatively small semi-enclosed seas (e.g., the Gulf of Aqaba) remains limited. Baited remote underwater video surveys (n = 111) were conducted across ~300 km of coral reef habitats in the Gulf of Aqaba and the northern Red Sea. A total of 55 predatory fish species were detected, with less than half of all species (n = 23) observed in both basins. Relative abundance patterns between the Gulf of Aqaba and the northern Red Sea were variable among taxa, but nearly twice as many predatory fish were observed per unit of effort in the northern Red Sea. In general, assemblages in both basins were dominated by three taxa (Epinephelinae, Carangidae, and Lethrinidae). Large-bodied and threatened species were recorded at very low abundances. Multivariate analysis revealed distinct assemblage structuring of coral reef predators between the Gulf of Aqaba and the northern Red Sea. Most of the species driving these differences were recorded in both basins, but occurred at varying levels of abundance. Environmental factors were largely unsuccessful in explaining variation in assemblage structuring. These findings indicate that biological assemblages in the Gulf of Aqaba are more distinct than previously reported and that reef fish assemblage structuring can occur even within a relatively small semi-enclosed sea. Despite inter-basin assemblage structuring, the overall low abundance of vulnerable fish species is suggestive of overexploitation in both the Gulf of Aqaba and the northern Red Sea of Saudi Arabia. As the region surveyed is currently undergoing large-scale coastal development, the results presented herein aim to guide spatial management and recovery plans for these coral reef systems in relation to this development.