Shallow Reef Fish Research Articles

Towards process-oriented management of tropical reefs in the anthropocene

Tropical reefs and the fish relying on them are under increasing pressure. Shallow-reef fish provide important ecological information in addition to sustaining fisheries, tourism and more. Although empirical metrics of fish biomass are widely used in fisheries management, metrics of biomass production—how much new biomass is produced over time—are rarely estimated even though such production informs potential fisheries yields. Here we estimate fish standing biomass (B), biomass production (P, the rate of biomass accumulation) and biomass turnover (P/B ratio, the rate of biomass replacement) for 1,979 tropical reef sites spanning 39 tropical countries. On the basis of fish standing biomass and biomass turnover, we propose a conceptual framework that splits reefs into three classes to visualize ecological and socio-economic risk and help guide spatial management interventions (for example, marine protected areas) to optimize returns on conservation efforts. At large scales, high turnover was associated with high human pressure and low primary productivity, whereas high biomass was associated with low human pressure and high primary productivity. Going beyond standing fish biomass to consider dynamic ecological processes can better guide regional coral reef conservation and sustainable fisheries management.

Changes in reef fish assemblages in a cross-shelf euphotic-mesophotic gradient in tropical SW Atlantic

Despite a vast number of studies about shallow reef fish assemblages, and an increasing amount of studies about mesophotic ones, there are very few cross-shelf assessments including both, shallow and mesophotic depths. Herein, we analyze changes in reef fish assemblages in a cross-shelf euphotic-mesophotic (19–72.6 m) gradient in tropical SW Atlantic. Data was obtained using a novel low-cost 360° stationary video system. Sixty-four species from thirty families were identified. Depth, distance offshore and proportion of consolidated substrate were the main predictors of fish assemblages’ structure. Four distinct fish assemblages were identified across the depth gradient (20–30, 30–40, 40–50 and 50–75 m), with marked shifts in composition, abundance, and trophic structure. Abundance of invertebrate feeders and large roving herbivores declined across the shelf and with increasing depth, while abundance of planktivores and piscivores increased, particularly below 50 m. These changes were likely caused by changes in food availability and habitat suitability. Our low-cost video system yielded high-resolution images that enabled us to accurately survey reef fish assemblages, being therefore a useful method for studies focusing on both, euphotic and mesophotic reef ecosystems. Our results contribute to a better understanding of how reef fish assemblages change with increasing depth in SW Atlantic reefs and corroborate the idea that the breakpoint between euphotic and mesophotic fish assemblages is context-dependent rather than previously defined as 30 m depth.

Comparing mesophotic and shallow reef fish assemblages in the 'Au'au Channel, Hawaii: fish size, feeding guild composition, species richness, and endemism

Mesophotic (30–150 m) reef fish assemblages in the 'Au'au Channel, between the Hawaiian Islands of Maui and Lanai, were compared visually with neighboring shallow (<30 m depth) reef fish assemblages for differences in structure. Between 2007 and 2011, approximately 7000 mesophotic and 4000 shallow reef fishes were identified, sized (standard length), and assigned to seven foraging guilds. The shallow water zone had more species than the mesophotic zone (99 vs 80, respectively). Mesophotic planktivores and two herbivore species were significantly larger than their shallow reef counterparts. Shallow reef fish assemblages had a higher Chao1 estimated species richness for herbivores and corallivores but not the other five foraging guilds. The differences between mesophotic and shallow fish assemblages indicate that both have unique communities of high conservation importance.

Scale‐dependency of the environmental influence on fish β‐diversity: Implications for ecoregionalization and conservation

AbstractAimTo determine the ecoregions (spatial marine areas with similar environmental and physical conditions associated with relatively homogeneous fish assemblages) for shallow reef fish assemblages based on predictive models of beta diversity (β‐diversity) that account for both large‐scale environmental factors and local habitat characteristics. We assessed the influence of a spatial scale to rank the importance of these factors.LocationNew Caledonian (south‐west Pacific Ocean, 17–24° S, 158–172° W) Exclusive Economic Zone, Coral Sea Marine Park.TaxonFish.MethodsFish and habitat data that were collected at 13 sites around New Caledonia using unbaited rotating underwater video (285 sampling stations) were analysed. Gradient forest modelling was used to predict the fish β‐diversity along the gradients of environmental factors. Ecoregions were obtained by applying clustering methods to gradient forest predictions.ResultsThe gradient forest models of β‐diversity retained 59 species (total: 206 fish species) with R² > 0, including 19 fish species with R² from 0.03% to 69%. For these 19 species, the models explained up to 26% of the variance. At a large scale, β‐diversity was significantly explained by nutrient concentrations, sea surface salinity and temperature. Among the eight ecoregions that were delineated based on the β‐diversity predictions, three regions corresponded to remote sites under oceanic influence where human pressures are low and the surface nutrient concentrations are high. On the local scale, the benthic habitat explained β‐diversity better than the physical and chemical parameters, particularly in the areas subject to anthropogenic pressures.Main conclusionsOn the local scale, the respective importance of environmental factors (physical and chemical parameters versus benthic habitat) differed according to ecosystem health. Our findings suggest that nutrient enrichment due to avifauna may have a positive effect on fish β‐diversity when an ecosystem is healthy. The ecoregions reflect fish species composition in relation to a large set of environmental parameters.

Thermal stress, thermal safety margins and acclimation capacity in tropical shallow waters—An experimental approach testing multiple end-points in two common fish

Tropical organisms are predicted to be among the most impacted by increasing sea surface temperatures, particularly those from intertidal habitats. In this study, a complete thermal biology assessment was conducted for two widespread tropical Atlantic shallow reef fish: Abudefduf saxatilis (damselfish) and Scartella cristata (blenny), which make extensive use of tide pools. The main objectives were to measure the time-course changes during one month in i) thermal and oxidative stress biomarkers (in gills, muscle and skin), ii) upper thermal limits, acclimation capacity and thermal safety margins and iii) body size, condition and energy reserves (total protein and lipid contents), under two temperature treatments (control – mean summer temperature, and elevated temperature −+3°C, as projected by climate warming scenarios for the end of this century).Results from biomarker analyses suggest that under increased temperature, both species displayed a typical response of physiological stress characterized by the activation of molecular chaperones and antioxidant protection. Both species presented a significant acclimation potential in the long term, as shown by increased critical thermal maxima values at higher temperature. However, these species may already be at risk during summer heat waves, as thermal safety margins for both species were low. Additionally, despite acclimation, some energetic tradeoffs may exist, since specimens from both species showed smaller body sizes at higher temperature (even though maintaining body condition). Finally, temperature treatments had a significant influence not only in the total amount of energy reserves (lipid contents) but also in their rate of deposition or depletion (total proteins and lipid contents). This is the first multi-end-point holistic approach to assess the impact of warming in shallow tropical water fish and it highlights the high risk that intertidal organisms are facing in both present and future sea surface temperature conditions.

Shallow reef fish communities of South Bahia coast, Brazil

This study aims to describe for the first time the fish community structure of five shallow reefs located off the cities of Santa Cruz de Cabrália and Porto Seguro (Araripe-AR, Itacipanema-IT, Alagados-AL, Naufrágio-NA and Recife de Fora Marine Park-RF Reefs), South Bahia, Northeastern Brazil. Fish density and richness were assessed through stationary point counts of 2 m radius for small cryptic species and 3 m for more conspicuous species. A total of 1 802 fishes belonging to 23 families and 54 species were observed. The most abundant species were the pomacentrids Stegastes fuscus and Abudefduf saxatilis. No significant differences were found for species richness or density of conspicuous species, but density of small cryptic species was low on reefs with high bottom rugosity, where there were more holes and crevices available. Herbivores were dominant on AR, AL and RF, invertivores on AL and both groups were dominant on IT. Some habitat variables such as rugosity and benthic cover were strongly correlated to species and sites. High bottom heterogeneity was found among reefs but they still presented similar species composition, richness and density. Within small-scale studies, such similarities in composition and richness are to be expected for reef fish communities, as most of the species concerned have a wide distribution range.

Regional biogeography of shallow reef fish and macro‐invertebrate communities in the Galapagos archipelago

AbstractAim To delineate biogeographical patterns in Galapagos shallow‐water reef fauna at regional scales.Location Galapagos Islands.Methods Fishes and macro‐invertebrates were quantitatively censused using underwater visual techniques along more than 500 transects at defined depth strata across the Galapagos archipelago. Data were analysed using multivariate techniques to define regional patterns and identify species typical of different regions.Results Subtidal communities of fishes and macro‐invertebrates on shallow reefs differed consistently in species composition across the Galapagos archipelago, with three major biogeographical groupings: (1) the ‘far‐northern area’ containing the islands of Darwin and Wolf, (2) the ‘central/south‐eastern area’, including the east coast of Isabela, and (3) the ‘western area’, encompassing Fernandina and western Isabela. In addition, the northern islands of Pinta, Marchena and Genovesa form a separate region in the central/south‐eastern area, and Bahia Elizabeth and Canal Bolivar separate from other parts of the western area. The far‐northern bioregion is characterized by high fish species richness overall, including a high proportion of species of Indo‐Pacific origin. However, very few endemic fishes or species with distributions extending south from Ecuador (‘Peruvian’ species) are present, and the bioregion also possesses relatively low species richness of mobile macro‐invertebrate taxa. By contrast, the ‘western’ bioregion possesses disproportionately high numbers of endemic fish taxa, high numbers of cool‐temperate Peruvian fish species, and high invertebrate species richness, but very few species of Indo‐Pacific origin. The Bahia Elizabeth/Canal Bolivar bioregion possesses more endemic species and fewer species with Peruvian affinities than coasts within the western bioregion. The northern bioregion of Pinta, Marchena and Genovesa represents an overlap zone with affinities to both the far‐northern and south‐eastern islands. The south‐eastern bioregion includes species from a variety of different sources, particularly ‘Panamic’ species with distributions extending north to Central America.Main conclusions On the basis of congruent divisions for reef fish and macro‐invertebrate communities, the Galapagos archipelago can be separated into three major biogeographical areas, two of which can be further subdivided into two regions. Each of these five bioregions possesses communities characterized by a distinctive mix of species derived from Indo‐Pacific, Panamic, Peruvian and endemic source areas. The conservation significance of different regions is not reflected in counts of total species richness. The regions with the lowest overall fish species richness possess a temperate rather than tropical climate and highest levels of endemism.