Length-Weight Relationships for 15 Coral Reef Fish Species from the Northern Line Islands1

MARINE SPECIES DIVERSITY IN THO CHAU ARCHIPELAGO, KIEN GIANG PROVINCEThe research results in the field survey from March, 2011 to October, 2015 of Research Institute for Marine Fisheries (RIMF) presented an overall picture of the marine species diversity in coral reef ecosystems and other coastal areas surrounding Tho Chau archipelago, Kien Giang province. A total of 1,101 marine species were identified, including 161 species of phytoplankton; 75 species of zooplankton; 57 species of seaweed; 6 species of seagrass; 11 species of mangrove plant; 147 species of coral (131 species of hard coral, 16 species of soft coral); 261 species of coral reef fish; and 383 species of zoobenthos (223 species of mollusca, 77 species of echinodermata, 59 species of arthropoda, 24 species of annelida). These research results provided an important scientific foundation for management, conservation and development of marine resources in this area.

Coral reefs are known as “tropical rain forests” in the ocean. Fish diversity is extremely high, accounting for one-third of marine fishes. To better protect and manage coral reef fishes, this study systematically compiled documents and databases published in China. We counted 2855 species of coral reef fishes in China, which belong to 3 classes, 41 orders, 252 families, and 1017 genera. Among these, Perciformes was the dominant order, accounting for 57.31% of the total species. Gobiidae (7.43%), Labridae (5.36%), Pomacentridae (4.52%), and Serranidae (4.38%) were the main families, while other families accounted for less than 4%. Furthermore, 5.56% of coral reef fish species have entered the IUCN Red List. The present study found that coral reef fishes can be divided into nearshore and offshore. This was mainly because the nearshore coral reef fishes were more affected by human disturbance and runoff from the mainland, whereas offshore coral reef fishes were in areas with high salinity and temperature far from the mainland, where human disturbance was less. Coral reef fish species’ diversity had a significant positive correlation with coral species diversity (p < 0.05), mainly because corals provide habitat and shelter. This study is the first systematic compilation and analysis of coral reef fishes in China and provides a basic reference for global protection management and biological geographical analysis.

Simple SummaryThe coral reef ecosystem not only brings enormous economic value to humans but also provides livelihoods and a major source of protein for millions of people. Moreover, coral reefs provide refuge and food sources for many fish species and are also breeding grounds and spawning grounds for various fish species. However, due to climate and human factors, the coral reef ecosystem has been destroyed, and its ecological function has been damaged. Fishery resources have also been affected, with changes in fish species composition and community structure. This study analyzed the fish community structure of the largest atoll in the Xisha Islands in the South China Sea, summarized a list of coral reef fish in Yongle Atoll, and analyzed the reasons for the change in the fish community and the future variation trend. The completion of this study will contribute to the better protection and recovery of coral reef fish and provide an important reference for the enhancement and restoration of coral reef habitats in the Xisha Islands.Yongle Atoll was the largest atoll in the Xisha Islands of the South China Sea, and it was a coral reef ecosystem with important ecological and economic values. In order to better protect and manage the coral reef fish resources in Yongle Atoll, we analyzed field survey data from artisanal fishery, catches, and underwater video from 2020 to 2022 and combined historical research to explore the changes in fish species composition and community structure in Yongle Atoll over the past 50 years. The results showed that a total of 336 species of fish were found on Yongle Atoll, belonging to 17 orders and 60 families. Among them, Perciformes had the most fish species with 259 species accounting for 77.08% of the total number of species. The number of fish species in the coral reef of Yongle Atoll was exponentially correlated with its corresponding maximum length and significantly decreases with its increase. The fish community structure of Yongle Atoll changed, and the proportion of large carnivorous fish decreased significantly, while the proportion of small-sized and medium-sized fish increased. At the same time, Yongle Atoll has 18 species of fish listed on the IUCN Red List, 15 of which are large fish. The average taxonomic distinctness (Delta+, Δ+) and the variation taxonomic distinctness (Lambda+, Λ+) in 2020–2022 were lower than the historical data, and the number of fish orders, families, and genera in Yongle Atoll has decreased significantly, which indicates that the current coral reef fish species in Yongle Atoll have closer relatives and higher fish species uniformity. In addition, the similarity of fish species in Yongle Atoll was relatively low at various time periods, further proving that the fish community structure has undergone significant variation. In general, due to multiple impacts, such as overfishing, fishing methods, environmental changes, and habitat degradation, the fish species composition of Yongle Atoll may have basically evolved from carnivorous to herbivorous, from large fish to small fish, and from complexity to simplicity, leaving Yongle Atoll in an unstable state. Therefore, we need to strengthen the continuous monitoring of the coral reef ecosystem in Yongle Atoll to achieve the protection and restoration of its ecological environment and fishery resources, as well as sustainable utilization and management.

There has been ongoing flattening of Caribbean coral reefs with the loss of habitat having severe implications for these systems. Complexity and its structural components are important to fish species richness and community composition, but little is known about its role for other taxa or species-specific responses. This study reveals the importance of reef habitat complexity and structural components to different taxa of macrofauna, total species richness, and individual coral and fish species in the Caribbean. Species presence and richness of different taxa were visually quantified in one hundred 25-m(2) plots in three marine reserves in the Caribbean. Sampling was evenly distributed across five levels of visually estimated reef complexity, with five structural components also recorded: the number of corals, number of large corals, slope angle, maximum sponge and maximum octocoral height. Taking advantage of natural heterogeneity in structural complexity within a particular coral reef habitat (Orbicella reefs) and discrete environmental envelope, thus minimizing other sources of variability, the relative importance of reef complexity and structural components was quantified for different taxa and individual fish and coral species on Caribbean coral reefs using boosted regression trees (BRTs). Boosted regression tree models performed very well when explaining variability in total (82·3%), coral (80·6%) and fish species richness (77·3%), for which the greatest declines in richness occurred below intermediate reef complexity levels. Complexity accounted for very little of the variability in octocorals, sponges, arthropods, annelids or anemones. BRTs revealed species-specific variability and importance for reef complexity and structural components. Coral and fish species occupancy generally declined at low complexity levels, with the exception of two coral species (Pseudodiploria strigosa and Porites divaricata) and four fish species (Halichoeres bivittatus, H. maculipinna, Malacoctenus triangulatus and Stegastes partitus) more common at lower reef complexity levels. A significant interaction between country and reef complexity revealed a non-additive decline in species richness in areas of low complexity and the reserve in Puerto Rico. Flattening of Caribbean coral reefs will result in substantial species losses, with few winners. Individual structural components have considerable value to different species, and their loss may have profound impacts on population responses of coral and fish due to identity effects of key species, which underpin population richness and resilience and may affect essential ecosystem processes and services.

Many coral reef fish species use mangrove and seagrass beds as nursery areas. However, in certain regions, the absence or scarcity of such habitats suggests that juvenile coral reef fish may be seeking refuge elsewhere. The underlying biogenic substratum of most coral reefs is structurally complex and provides many types of refuge. However, on young or subtropical coral reefs, species may be more reliant on the living coral layer as nursery areas. Such is the case on the high-latitude coral reefs of South Africa where the coral communities consist of a thin veneer of coral overlaying late Pleistocene bedrock. Thus, the morphology of coral species may be a major determinant in the availability of refuge space. Acropora austera is a branching species that forms large patches with high structural complexity. Associated with these patches is a diverse community of fish species, particularly juveniles. Over the past decade, several large (>100 m2) A. austera patches at Sodwana Bay have been diminishing for unknown reasons and there is little evidence of their replacement or regrowth. Seven patches of A. austera (AP) and non-A. austera (NAP) were selected and monitored for 12 months using visual surveys to investigate the importance of AP as refugia and nursery areas. There were significant differences in fish communities between AP and NAP habitats. In total, 110 species were recorded within the patches compared to 101 species outside the patches. Labrids and pomacentrids were the dominant species in the AP habitats, while juvenile scarids, acanthurids, chaetodons and serranids were also abundant. The diversity and abundance of fish species increased significantly with AP size. As the most structurally complex coral species on the reefs, the loss of APs may have significant implications for the recruitment and survival of certain fish species.

Increased habitat diversity is often predicted to promote the diversity of animal communities because a greater variety of habitats increases the opportunities for species to specialize on different resources and coexist. Although positive correlations between the diversities of habitat and associated animals are often observed, the underlying mechanisms are only now starting to emerge, and none have been tested specifically in the marine environment. Scleractinian corals constitute the primary habitat-forming organisms on coral reefs and, as such, play an important role in structuring associated reef fish communities. Using the same field experimental design in two geographic localities differing in regional fish species composition, we tested the effects of coral species richness and composition on the diversity, abundance, and structure of the local fish community. Richness of coral species overall had a positive effect on fish species richness but had no effect on total fish abundance or evenness. At both localities, certain individual coral species supported similar levels of fish diversity and abundance as the high coral richness treatments, suggesting that particular coral species are disproportionately important in promoting high local fish diversity. Furthermore, in both localities, different microhabitats (coral species) supported very different fish communities, indicating that most reef fish species distinguish habitat at the level of coral species. Fish communities colonizing treatments of higher coral species richness represented a combination of those inhabiting the constituent coral species. These findings suggest that mechanisms underlying habitat-animal interaction in the terrestrial environment also apply to marine systems and highlight the importance of coral diversity to local fish diversity. The loss of particular key coral species is likely to have a disproportionate impact on the biodiversity of associated fish communities.

Coral species inventory at War in the Pacific National Historical Park: Final report

While there is increasing evidence for habitat specialization in coral reef fishes, the extent to which different corals support different fish communities is not well understood. Here we quantitatively assess the relative importance of different coral species in structuring fish communities and evaluate whether sampling scale and coral colony size affect the perceived strength of fish-habitat relationships. Fish communities present on colonies of eight coral species (Porites cylindrica, Echinopora horrida, Hydnophora rigida, Stylophora pistillata, Seriatopora hystrix, Acropora formosa, A. tenuis and A. millepora) were examined in the Lizard Island lagoon, Great Barrier Reef, Australia. Additionally, the differences in fish communities supported by three coral species (P. cylindrica, E. horrida, H. rigida) were investigated at three spatial scales of sampling (2x2 m, 1x1 m, 0.5x0.5 m). Substantial differences in fish communities were observed across the different coral species, with E. horrida and H. rigida supporting the most fish species and individuals. Coral species explained more of the variability in fish species richness (20.9–53.6%), than in fish abundance (0–15%). Most coral species supported distinctive fish communities, with dissimilarities ranging from 50 to 90%. For three focal coral species, a greater amount of total variation in fish species richness and fish abundance was evident at a larger scale of sampling. Together, these results indicate that the structure of reef fish communities is finely tuned to coral species. Loss of preferred coral species could have profound effects on reef fish biodiversity, potentially more so than would be predicted on the basis of declining coral cover alone.

Coral reef fish density and species richness are often higher at sites with more structural complexity. This association may be due to greater availability of shelters, but surprisingly little is known about the size and density of shelters and their use by coral reef fishes. We quantified shelter availability and use by fishes for the first time on a Caribbean coral reef by counting all holes and overhangs with a minimum entrance diameter ≥3 cm in 30 quadrats (25 m2) on two fringing reefs in Barbados. Shelter size was highly variable, ranging from 42 cm3 to over 4,000,000 cm3, with many more small than large shelters. On average, there were 3.8 shelters m−2, with a median volume of 1,200 cm3 and a total volume of 52,000 cm3m−2. The number of fish per occupied shelter ranged from 1 to 35 individual fishes belonging to 66 species, with a median of 1. The proportion of shelters occupied and the number of occupants increased strongly with shelter size. Shelter density and total volume increased with substrate complexity, and this relationship varied among reef zones. The density of shelter-using fish was much more strongly predicted by shelter density and median size than by substrate complexity and increased linearly with shelter density, indicating that shelter availability is a limiting resource for some coral reef fishes. The results demonstrate the importance of large shelters for fish density and support the hypothesis that structural complexity is associated with fish abundance, at least in part, due to its association with shelter availability. This information can help identify critical habitat for coral reef fishes, predict the effects of reductions in structural complexity of natural reefs and improve the design of artificial reefs.

Intraspecific genetic variation among samples of six species of reef fishes,Chromis cyanea, Stegastes partitus, S. planifrons, S. leucostictus, S. dorsopunicans, andThalassoma bifasciatum collected over a 2 wk period in 1990 at La Parguera, Puerto Rico, USA and Discovery Bay, Jamaica, was evaluated using starch-gel electrophoresis. On average, products of 33 protein-coding loci were resolved in each species. Levels of polymorphism (0.95 criterion) ranged from 3.1% inS. dorsopunicans to 42.4% inC. cyanea. Estimates of genetic divergence among samples and indices of genetic subdivision were small in all six study species: mean genetic distances ranged from 0.000 to 0.002 and mean fixation indices ranged from 0.004 to 0.035. Estimates of numbers of migrants per generation (mN e) ranged from 5.1 to 11.6, indicating that substantial genetic exchange probably occurs over the relatively large geographic distance (ca. 1000 km) separating coral reef communities of La Parguera and Discovery Bay. The estimates ofmN e may be biased by a sampling strategy involving only two localities, and should therefore be interpreted with caution. With inferences based solely on allozyme frequency data under a primary assumption of neutrality, genetic substructuring of populations of the six study species on a macrogeographic scale appears virtually nonexistent.

Although numerous coral reef fish species utilize substrates with high structural complexities as habitats and refuge spaces, quantitative analysis of nocturnal fish substrate associations has not been sufficiently examined yet. The aims of the present study were to clarify the nocturnal substrate associations of 17 coral reef fish species (nine parrotfish, two surgeonfish, two grouper and four butterflyfish) in relation to substrate architectural characteristics. Substrate architectural characteristics were categorized into seven types: (1) eave-like space, (2) large inter-branch space, (3) overhang by protrusion of fine branching structure, (4) overhang by coarse structure, (5) uneven structure without large space or overhang, (6) flat and (7) macroalgae. Overall, fishes were primarily associated with three architectural characteristics (eave-like space, large inter-branch space and overhang by coarse structure). The main providers of these three architectural characteristics were tabular and corymbose Acropora, staghorn Acropora, and rock. Species-specific significant positive associations with particular architectural characteristics were found as follows. For the nine parrotfish species, Chlorurus microrhinos with large inter-branch space and overhang by coarse structure; Ch. spilurus with eave-like space and large inter-branch space; Hipposcarus longiceps with large inter-branch space; Scarus ghobban with overhang by coarse structure; five species (Scarus forsteni, S. niger, S. oviceps, S. rivulatus and S.schlegeli) with eave-like space. For the two surgeonfish species, Naso unicornis with overhang by coarse structure; N. lituratus with eave-like space. For the two grouper species, Plectropomus leopardus with eave-like space; Epinephelus ongus with overhang by coarse structure. For the four butterflyfish species, Chaetodon trifascialis with eave-like space and large inter-branch space; C. lunulatus and C. ephippium with large inter-branch space; C. auriga showed no significant associations with any architectural characteristics. Four species (Ch. microrhinos, H. longiceps, S. niger and N. unicornis) also showed clear variations in substrate associations among the different fish size classes. Since parrotfishes, surgeonfishes and groupers are main fisheries targets in coral reefs, conservation and restoration of coral species that provide eave-like space (tabular and corymbose Acropora) and large inter-branch space (staghorn Acropora) as well as hard substrates with coarse structure that provide overhang (rock) should be considered for effective fisheries management in coral reefs. For butterflyfishes, coral species that provide eave-like space (tabular Acropora) and large inter-branch space (staghorn Acropora) should also be conserved and restored for provision of sleeping sites.

This article proposes a mechanism that triggers first maturation and spawning in coral reef (bony) fish, which allows for predicting their length at first maturity. Thus, mean lengths at first maturity (Lm) and the corresponding maximum lengths (Lmax) in 207 populations of 131 species of coral reef fish were assembled and used to test the hypotheses that (a) there is, in coral reef fish, a single value of a size-related parameter acting as a trigger for their maturation and eventual spawning, and (b) that this single value is statistically the same as that published previously for other bony fish. The results, based on the assembled Lm and Lmax data and on estimates of the parameter D, which link the length of fish with the relative surface of their gills, covered 44 families and Lmax values ranging from 1.8 to 181.6 cm and confirmed that the threshold in (a) exists. Also, we assessed (in b) that this threshold value, i.e., LmaxD/LmD = 1.35 (±0.02), is not statistically different from similar estimates for other groups of teleosts, notably semelparous salmonids, cichlids, sturgeons and Chinese and Turkish freshwater and marine fish. One implication is that given ocean warming and deoxygenation, coral reef fish will not only be smaller than they currently are, but also mature and spawn at smaller sizes, and thus produce fewer, smaller eggs.

The adults of many coral reef fish species are site-attached, and their habitat is selected at the time of settlement by their larvae. The length of the planktonic larval period varies both intra- and interspecifically, and it is unknown how the age and size of larvae may affect their selection of habitat. To investigate the influence of age and size on habitat selection, I collected newly settled Hawaiian domino damselfish, Dascyllus albisella, daily from grids containing three coral species at four locations in Kaneohe Bay, Oahu, Hawaii. I recorded the coral species each fish was collected on, and measured and aged (by otoliths) the collected fish. The results indicate that the coral Pocillopora meandrina was selected by settling fish significantly more than the other two coral species. Younger and smaller larvae selected this coral species more frequently than older/larger larvae. In addition, younger/smaller individuals were found more commonly inside the bay than older/larger settling larvae. Differences in the choice of coral species and location of settlement may be partly due to ontogenetic differences in the sensory capacities of larvae to detect corals, conspecifics, and predators, or to a larval competency period.

Oceanic hydrodynamic mechanisms have a fundamental role in shaping coral reef ecosystems. Consequently, regional processes such as deep-water upwelling affect nutrient fluxes and the function of coral reefs at a local scale. Despite the importance of upwelling to marine ecosystems worldwide, there is limited knowledge about how this dynamic oceanographic process affects reef-building coral communities. Although depth is used to group different reef zones, the extent of nutrient fluxes across reef slopes is dependent on complex biophysical drivers. As mixotrophic organisms, reef-building corals rely on resources provided by their endosymbiotic dinoflagellates (herein ‘symbionts’; autotrophy) as well as energy from feeding on particulate organic matter in the water column (heterotrophy). Although reduced light availability in deeper reefs may lead to a reduced dependence on autotrophy and a potential increase in heterotrophy, potential shifts in trophic strategies can be decoupled with depth due to the complex nature of the coral holobiont (Chapter 1). Chapter 2 investigated the influence of upwelling on the trophic ecology of a community of reef-building corals common to shallow and deep reefs in the remote atoll system of the Maldives, Indian Ocean. Due to the structure of the central Maldives atolls, we considered different fore reef exposures including oceanic reefs and reefs facing the shallower Inner Sea. Trophic strategies of three species of coral (Galaxea fascicularis, Pachyseris speciosa, and Pocillopora verrucosa) were analyzed using carbon and nitrogen stable isotope ratios (δ13C and δ15N) of coral hosts, their symbionts, and potential food sources of corals including particulate organic matter and plankton. Further, in situseawater temperature was recorded to characterize water column mixing and potential differences in resource availability associated with depth. The results indicated that the water column was well mixed between 10 and 30 m reef depth and coral host isotopic ratios indicated an atoll-wide reliance on deep-water nitrogen across depth. However, coral host isotopic ratios indicated species-specific trophic strategies that revealed distinct patterns among the three species of coral. Only one coral species (G. fascicularis) had different δ13C values between shallow and deep reefs, indicating an autotrophy strategy in shallow reefs but reduced autotrophy and a potential increase in heterotrophy in deep reefs. In contrast, P. verrucosaand P. speciosashowed consistent isotopic ratios regardless of reef depth. Among the three species, P. verrucosawas relatively more heterotrophic while P. speciosadepended more on autotrophy across the reef slope. The ability to shift trophic strategies to increase heterotrophic feeding is important to the survival and recovery of corals subject to thermal stress conditions. In 2016 a global thermal stress event impacted coral reefs worldwide, including the Maldives, and caused mass coral bleaching and mortality. Eight months after the thermal stress event in the Maldives, the same coral reefs were surveyed to investigate potential shifts in isotopic niches due to changes in trophic strategy (Chapter 3). Changes in the coral isotopic niches were observed following the thermal stress event. Shallow G. fascicularishad a decreased isotopic niche that was consistent with reduced autotrophy while the isotopic niche size of deep populations of G. fascicularisincreased. The latter supports the ability of G. fascicularisto increase heterotrophic feeding in response to thermal stress. Increased isotopic niche size of both shallow and deep P. speciosasupports an increase in heterotrophy that in turn helped maintain autotrophy, its main trophic strategy. Minimal changes in the isotopic niche sizes of P. verrucosawere consistent with its dependence on heterotrophy. Chapter 4 used a different set of biochemical tracers – fatty acids – to investigate the role of heterotrophy in the same three species of reef-building coral. The composition and various indices of fatty acids were compared among the three coral host species and their symbionts, including established indices applied in a novel context of coral trophic ecology. Further, a linear discriminant analysis was used to estimate the contribution of polyunsaturated fatty acids derived from various potential sources (symbionts and a diverse taxonomic range of plankton) to the three coral host species. This chapter provides insight into the importance of heterotrophy in coral nutrition, especially in productive reef systems, and provides extensive evidence of the utility of fatty acids in understanding coral trophic ecology.In summary, this thesis examined a range of biochemical evidence associated with the trophic strategies of reef-building corals. Comparing these coral species with diverse trophic strategies, the relative contribution of autotrophy and heterotrophy was estimated for each species (Chapter 5). Despite the general dependence on symbiont autotrophy, the three species of coral hosts showed different abilities to utilize heterotrophy for nutrition. Although local oceanography plays a key role in nutrient cycling in reef systems, the inherent physiology of the coral holobiont strongly influences the ecological niche. Despite differences between shallow and deep reefs, diverse nutritional strategies enable corals to occupy the same habits while maintaining different trophic niches.

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