Fishing degrades size structure of coral reef fish communities

Fishing pressure on coral reef ecosystems has been frequently linked to reductions of large fishes and reef fish biomass. Associated impacts on overall community structure are, however, less clear. In size‐structured aquatic ecosystems, fishing impacts are commonly quantified using size spectra, which describe the distribution of individual body sizes within a community. We examined the size spectra and biomass of coral reef fish communities at 38 US‐affiliated Pacific islands that ranged in human presence from near pristine to human population centers. Size spectra ‘steepened’ steadily with increasing human population and proximity to market due to a reduction in the relative biomass of large fishes and an increase in the dominance of small fishes. Reef fish biomass was substantially lower on inhabited islands than uninhabited ones, even at inhabited islands with the lowest levels of human presence. We found that on populated islands size spectra exponents decreased (analogous to size spectra steepening) linearly with declining biomass, whereas on uninhabited islands there was no relationship. Size spectra were steeper in regions of low sea surface temperature but were insensitive to variation in other environmental and geomorphic covariates. In contrast, reef fish biomass was highly sensitive to oceanographic conditions, being influenced by both oceanic productivity and sea surface temperature. Our results suggest that community size structure may be a more robust indicator than fish biomass to increasing human presence and that size spectra are reliable indicators of exploitation impacts across regions of different fish community compositions, environmental drivers, and fisheries types. Size‐based approaches that link directly to functional properties of fish communities, and are relatively insensitive to abiotic variation across biogeographic regions, offer great potential for developing our understanding of fishing impacts in coral reef ecosystems.     

Variation in reef fish and invertebrate communities with level of protection from fishing across the Eastern Tropical Pacific seascape

Aim To quantify general differences in reef community structure between well‐enforced and poorly enforced marine protected areas (MPAs) and fished sites across the Eastern Tropical Pacific (ETP) regional seascape Location The Pacific continental margin and oceanic islands of Costa Rica, Panama, Colombia and Ecuador, including World Heritage sites at Galapagos, Coiba, Cocos and Malpelo Methods Densities of reef fishes, mobile and sessile invertebrates, and macroalgae were quantified using underwater visual surveys at 136 ‘no‐take’ and 54 openly fished sites associated with seven large MPAs that encompassed a range of management strategies. Spatial variation in multivariate and univariate community metrics was related to three levels of fishing pressure (high‐protection MPAs, limited‐protection MPAs, fishing zones) for both continental and oceanic reefs. Results High‐protection MPAs possessed a much greater biomass of higher carnivorous fishes, lower densities of asteroids and Eucidaris spp. urchins, and higher coral cover than limited‐protection MPAs and fished zones. These results were generally consistent with the hypothesis that overfishing of predatory fishes within the ETP has led to increased densities of habitat‐modifying macroinvertebrates, which has contributed to regional declines in coral cover. Major differences in ecological patterns were also evident between continental and oceanic biogeographic provinces. Main conclusions Fishing down the food web, with associated trophic cascades, has occurred to a greater extent along the continental coast than off oceanic islands. Poorly enforced MPAs generate food webs more similar to those present in fished areas than in well‐protected MPAs.     

Hierarchical and scale‐dependent effects of fishing pressure and environment on the structure and size distribution of parrotfish communities

Parrotfishes are considered to have a major influence on coral reef ecosystems through grazing the benthic biota and are also primary fishery targets in the Indo‐Pacific. Consequently, the impact of human exploitation on parrotfish communities is of prime interest. As anthropogenic and environmental factors interact across spatial scales, sampling programs designed to disentangle these are required by both ecologists and resource managers. We present a multi‐scale examination of patterns in parrotfish assemblage structure, size distribution and diversity across eight oceanic islands of Micronesia. Results indicate that correlates of assemblage structure are scale‐dependent; biogeographic distributions of species and island geomorphology hierarchically influenced community patterns across islands whereas biophysical features and anthropogenic pressure influenced community assemblage structure at the within‐island scale. Species richness and phylogenetic diversity increased with greater broad‐scale habitat diversity associated with different island geomorphologies. However, within‐island patterns of abundance and biomass varied in response to biophysical factors and levels of human influence unique to particular islands. While the effect of fishing activities on community composition and phylogenetic diversity was obscured across island types, fishing pressure was the primary correlate of mean parrotfish length at all spatial scales. Despite widespread fishery‐induced pressure on Pacific coral reefs, the structuring of parrotfish communities at broad spatial scales remains a story largely dependent on habitat. Thus, we propose better incorporation of scale‐dependent habitat effects in future assessments of overexploitation on reef fish assemblages. However, strong community‐level responses within islands necessitate an improved understanding of the phylogenetic and functional consequences of altering community structure.     

Reef Fishes at All Trophic Levels Respond Positively to Effective Marine Protected Areas

Marine Protected Areas (MPAs) offer a unique opportunity to test the assumption that fishing pressure affects some trophic groups more than others. Removal of larger predators through fishing is often suggested to have positive flow-on effects for some lower trophic groups, in which case protection from fishing should result in suppression of lower trophic groups as predator populations recover. We tested this by assessing differences in the trophic structure of reef fish communities associated with 79 MPAs and open-access sites worldwide, using a standardised quantitative dataset on reef fish community structure. The biomass of all major trophic groups (higher carnivores, benthic carnivores, planktivores and herbivores) was significantly greater (by 40% - 200%) in effective no-take MPAs relative to fished open-access areas. This effect was most pronounced for individuals in large size classes, but with no size class of any trophic group showing signs of depressed biomass in MPAs, as predicted from higher predator abundance. Thus, greater biomass in effective MPAs implies that exploitation on shallow rocky and coral reefs negatively affects biomass of all fish trophic groups and size classes. These direct effects of fishing on trophic structure appear stronger than any top down effects on lower trophic levels that would be imposed by intact predator populations. We propose that exploitation affects fish assemblages at all trophic levels, and that local ecosystem function is generally modified by fishing.     

Size-structural shifts reveal intensity of exploitation in coral reef fisheries

Fisheries exploitation represents a considerable threat to coral reef fish resources because even modest levels of extraction can alter ecological dynamics via shifts of stock size, species composition, and size-structure of the fish assemblage. Although species occupying higher trophic groups are known to suffer the majority of exploitative effects, changes in composition among lower trophic groups may be major, though are not frequently explored. Using size-based biomass spectrum analysis, we investigate the effects of fishing on the size-structure of coral reef fish assemblages spanning four geopolitical regions and determine if patterns of exploitation vary across trophic groups. Our analyses reveal striking evidence for the variety of effects fisheries exploitation can have on coral reef fish assemblages. When examining biomass spectra across the entire fish assemblage we found consistent evidence of size-specific exploitation, in which large-bodied individuals experience disproportionate reductions. The pattern was paralleled by and likely driven by, strongly size-specific reductions among top predators. In contrast, evidence of exploitation patterns was variable among lower trophic groups, in many cases including evidence of reductions across all size classes. The breadth of size classes and trophic groups that showed evidence of exploitation related positively to local human population density and diversity of fishing methods employed. Our findings highlight the complexity of coral reef fisheries and that the effects of exploitation on coral reefs can be realized throughout the entire fish assemblage, across multiple trophic groups and not solely restricted to large-bodied top-predators. Size-specific changes among fishes of lower trophic groups likely lead to altered ecological functioning of heavily exploited coral reefs. Together these findings reinforce the value of taking a multi-trophic group approach to monitoring and managing coral reef fisheries.     

Coral reef mesopredators switch prey,shortening food chains,in response to habitat degradation

Diet specificity is likely to be the key predictor of a predator's vulnerability to changing habitat and prey conditions. Understanding the degree to which predatory coral reef fishes adjust or maintain prey choice, in response to declines in coral cover and changes in prey availability, is critical for predicting how they may respond to reef habitat degradation. Here, we use stable isotope analyses to characterize the trophic structure of predator–prey interactions on coral reefs of the Keppel Island Group on the southern Great Barrier Reef, Australia. These reefs, previously typified by exceptionally high coral cover, have recently lost much of their coral cover due to coral bleaching and frequent inundation by sediment‐laden, freshwater flood plumes associated with increased rainfall patterns. Long‐term monitoring of these reefs demonstrates that, as coral cover declined, there has been a decrease in prey biomass, and a shift in dominant prey species from pelagic plankton‐feeding damselfishes to territorial benthic algal‐feeding damselfishes, resulting in differences in the principal carbon pathways in the food web. Using isotopes, we tested whether this changing prey availability could be detected in the diet of a mesopredator (coral grouper, Plectropomus maculatus). The δ¹³C signature in grouper tissue in the Keppel Islands shifted from a more pelagic to a more benthic signal, demonstrating a change in carbon sources aligning with the change in prey availability due to habitat degradation. Grouper with a more benthic carbon signature were also feeding at a lower trophic level, indicating a shortening in food chains. Further, we found a decline in the coral grouper population accompanying a decrease in total available prey biomass. Thus, while the ability to adapt diets could ameliorate the short‐term impacts of habitat degradation on mesopredators, long‐term effects may negatively impact mesopredator populations and alter the trophic structure of coral reef food webs.     

捕捞对北部湾海洋生态系统的影响

利用Ecopath with Ecosim (EwE) 5.1软件构建了北部湾海洋生态系统1959—1960年的Ecosim模型,包含渔业、海洋哺乳动物、海鸟、中上层鱼类、底层鱼类、底栖无脊椎动物等20个功能组,通过与1997—1999年调查数据对比,分析了捕捞活动对北部湾生态系统的结构和功能的影响.结果表明：近40年来在捕捞强度不断增加的压力下,生态系统的结构和功能发生显著变化,长寿命、高营养级的肉食性鱼类生物量下降明显,系统以短寿命、小型鱼类和无脊椎动物占优势.1999年的大中型鱼类的生物量仅为1960年的6%,而小型鱼类和无脊椎动物则明显上升,尤其是头足类生物量上升了2.7倍,渔获物的营养级则从1960年的3.2降低到1999年的298,体现了“捕捞降低海洋食物网”的特点,目前的开发模式是不可持续的.利用20世纪90年代数据预测了降低捕捞压力后生态系统的变化.本研究证实了可以使用Ecosim模型预测捕捞压力对生态系统的影响.     

Reassessing the trophic role of reef sharks as apex predators on coral reefs

Apex predators often have strong top-down effects on ecosystem components and are therefore a priority for conservation and management. Due to their large size and conspicuous predatory behaviour, reef sharks are typically assumed to be apex predators, but their functional role is yet to be confirmed. In this study, we used stomach contents and stable isotopes to estimate diet, trophic position and carbon sources for three common species of reef shark (Triaenodon obesus, Carcharhinus melanopterus and C. amblyrhynchos) from the Great Barrier Reef (Australia) and evaluated their assumed functional role as apex predators by qualitative and quantitative comparisons with other sharks and large predatory fishes. We found that reef sharks do not occupy the apex of coral reef food chains, but instead have functional roles similar to those of large predatory fishes such as snappers, emperors and groupers, which are typically regarded as high-level mesopredators. We hypothesise that a degree of functional redundancy exists within this guild of predators, potentially explaining why shark-induced trophic cascades are rare or subtle in coral reef ecosystems. We also found that reef sharks participate in multiple food webs (pelagic and benthic) and are sustained by multiple sources of primary production. We conclude that large conspicuous predators, be they elasmobranchs or any other taxon, should not axiomatically be regarded as apex predators without thorough analysis of their diet. In the case of reef sharks, our dietary analyses suggest they should be reassigned to an alternative trophic group such as high-level mesopredators. This change will facilitate improved understanding of how reef communities function and how removal of predators (e.g., via fishing) might affect ecosystem properties.     

High Complexity Food Webs in Low-diversity Eastern Pacific Reef–Coral Communities

Community-wide feeding interrelationships in a low-diversity coral reef off the Pacific coast of Panamá (Uva Island reef) demonstrate complex pathways involving herbivore, strong corallivore, and carnivore interactions. Four trophic levels with 31 interguild links are identified in a generalized food web, and documented feeding interrelationships with 287+ species links are portrayed in a coral–corallivore subweb. The importance of trophic groups changes greatly with time, from unknown causes over annual to decadal-scale periods, and during very strong El Niño–Southern Oscillation events such that intermittent intense herbivory by echinoids (Diadema) and corallivory by gastropod mollusks, the crown-of-thorns sea star Acanthaster, hermit crabs, and fishes result in high levels of coral mortality and bioerosion of reef substratum. Intraregional differences in species composition and abundances affecting food-web interactions are briefly described for nonupwelling (Uva Island) and upwelling areas (Pearl Islands) in Panamá. Seasonal upwelling in the Pearl Islands results in high plankton productivity, which likely augments production in invertebrates, fishes, marine mammals, and seabirds, but these pathways still remain largely unquantified. The corallivore Acanthaster is absent from upwelling centers in Panamá and from upwelling and nonupwelling areas in the southern and central Galápagos Islands, and the highly destructive, facultative corallivore Eucidaris galapagensis occurs only in the latter offshore islands and at Cocos Island. Relatively recent declines in the abundances of manta rays, sharks, and spiny lobsters are correlated with, but not necessarily causally linked to, increasing fishing activities in the late 1970s to early 1980s. The extent to which the complex yet highly unstable Uva Island food web is representative of other eastern Pacific coral reef ecosystems remains to be investigated.     

The biogeography of tropical reef fishes: endemism and provinciality through time

The largest marine biodiversity hotspot straddles the Indian and Pacific Oceans, driven by taxa associated with tropical coral reefs. Centred on the Indo‐Australian Archipelago (IAA), this biodiversity hotspot forms the ‘bullseye’ of a steep gradient in species richness from this centre to the periphery of the vast Indo‐Pacific region. Complex patterns of endemism, wide‐ranging species and assemblage differences have obscured our understanding of the genesis of this biodiversity pattern and its maintenance across two‐thirds of the world's oceans. But time‐calibrated molecular phylogenies coupled with ancestral biogeographic estimates have provided a valuable framework in which to examine the origins of coral reef fish biodiversity across the tropics. Herein, we examine phylogenetic and biogeographic data for coral reef fishes to highlight temporal patterns of marine endemism and tropical provinciality. The ages and distribution of endemic lineages have often been used to identify areas of species creation and demise in the marine tropics and discriminate among multiple hypotheses regarding the origins of biodiversity in the IAA. Despite a general under‐sampling of endemic fishes in phylogenetic studies, the majority of locations today contain a mixture of potential paleo‐ and neo‐endemic fishes, pointing to multiple historical processes involved in the origin and maintenance of the IAA biodiversity hotspot. Increased precision and sampling of geographic ranges for reef fishes has permitted the division of discrete realms, regions and provinces across the tropics. Yet, such metrics are only beginning to integrate phylogenetic relatedness and ancestral biogeography. Here, we integrate phylogenetic diversity with ancestral biogeographic estimation of lineages to show how assemblage structure and tropical provinciality has changed through time.     

Geography and island geomorphology shape fish assemblage structure on isolated coral reef systems

We quantify the relative importance of multi‐scale drivers of reef fish assemblage structure on isolated coral reefs at the intersection of the Indian and Indo‐Pacific biogeographical provinces. Large (>30 cm), functionally‐important and commonly targeted species of fish, were surveyed on the outer reef crest/front at 38 coral reef sites spread across three oceanic coral reef systems (i.e. Christmas Island, Cocos (Keeling) Islands and the Rowley Shoals), in the tropical Indian Ocean (c. 1.126 x 106 km²). The effects of coral cover, exposure, fishing pressure, lagoon size and geographical context, on observed patterns of fish assemblage structure were modelled using Multivariate Regression Trees. Reef fish assemblages were clearly separated in space with geographical location explaining ~53 % of the observed variation. Lagoon size, within each isolated reef system was an equally effective proxy for explaining fish assemblage structure. Among local‐scale variables, ‘distance from port’, a proxy for the influence of fishing, explained 5.2% of total variation and separated the four most isolated reefs from Cocos (Keeling) Island, from reefs with closer boating access. Other factors were not significant. Major divisions in assemblage structure were driven by sister taxa that displayed little geographical overlap between reef systems and low abundances of several species on Christmas Island corresponding to small lagoon habitats. Exclusion of geographical context from the analysis resulted in local processes explaining 47.3% of the variation, highlighting the importance of controlling for spatial correlation to understand the drivers of fish assemblage structure. Our results suggest reef fish assemblage structure on remote coral reef systems in the tropical eastern Indian Ocean reflects a biogeographical legacy of isolation between Indian and Pacific fish faunas and geomorphological variation within the region, more than local fishing pressure or reef condition. Our findings re‐emphasise the importance that historical processes play in structuring contemporary biotic communities.     

Coral reef monitoring in the Iles Eparses,Mozambique Channel (2011–2013)

Monitoring of coral reefs has become a major tool for understanding how they are changing, and for managing them in a context of increasing degradation of coastal ecosystems. The Global Coral Reef Monitoring Network (GCRMN) has near-global coverage, but there are few remote sites free of direct human impact that can serve as reference sites. This study provides baseline data for the French Iles Eparses in the Mozambique Channel, Western Indian Ocean (WIO), whose coral reefs are little known owing to their limited accessibility, and have been free from fishing pressure for over 20 years. Surveys of coral reef health and fish community structure were undertaken at four of the islands (Europa, Bassas da India, Juan de Nova and Glorieuses) in 2011–2013. Monitoring was conducted using standardized GCRMN methods for benthos and fish communities, at the highest taxonomic level. Benthic cover showed a latitudinal gradient, with higher coral cover and conversely lower algae cover (60% and 14% respectively) in the south of the Mozambique Channel. This could be due to the geomorphology of the islands, the latitudinal temperature gradient, and/or the history of chronic stress and bleaching events during the last decades. Fish also showed a latitudinal gradient with higher diversity in the north, in a center of diversity for the western Indian Ocean already recognized for corals. An exceptional biomass fish was recorded (approximately 3500 kg/ha excluding sharks, compared to a maximum of 1400 kg/ha elsewhere in the WIO). The presence of large predators and sharks in all the islands as well as the absence of fleshy benthic algae were indicators of the good health of the reef systems. Nevertheless, these islands are beginning to experience illegal fishing, particularly in the north of the Mozambique Channel, demonstrating their vulnerability to exploitation and the need to protect them as reference sites for coral reef studies, including of climate change impacts, for the region and globally.     

New insights on the trophic ecology of blue (Prionace glauca) and shortfin mako sharks (Isurus oxyrinchus) from the oceanic eastern South Pacific

The blue shark (Prionace glauca) and the shortfin mako shark (Isurus oxyrinchus) are two large and highly migratory sharks distributed in most oceans. Although they are often caught in the south Pacific Ocean long-line fisheries, their trophic ecology is poorly understood. Stable isotopes with Bayesian mixing and dependence concentration models were performed to determine the diet and trophic differences between the two species in the South-eastern Pacific Ocean. According to the mixing models, fishes are the most important prey of these sharks. Dolphin calves and remains were found in the stomachs of both species, which represents a novel finding in trophic ecology of South Pacific sharks. Intra-specific differences were found in P. glauca, but not in specimens of I. oxyrinchus. The two sharks showed a high degree of diet overlap (73%), primarily over mackerel and dolphin carcasses. Our results indicate that blue and shortfin mako sharks have a generalist feeding strategy in the eastern Pacific Ocean, with a strong preference for teleost fishes and also for dolphin carcasses. Therefore, trophic studies are useful to understand energy flow through the food web, and the trophic position of key species.     

Influence of the geography of speciation on current patterns of coral reef fish biodiversity across the Indo‐Pacific

The role of speciation processes in shaping current biodiversity patterns represents a major scientific question for ecologists and biogeographers. Hence, numerous methods have been developed to determine the geography of speciation based on co‐occurrence between sister‐species. Most of these methods rely on the correlation between divergence time and several metrics based on the geographic ranges of sister‐taxa (i.e. overlap, asymmetry). The relationship between divergence time and these metrics has scarcely been examined in a spatial context beyond regression curves. Mapping this relationship across spatial grids, however, may unravel how speciation processes have shaped current biodiversity patterns through space and time. This can be particularly relevant for coral reef fishes of the Indo‐Pacific since the origin of the exceptional concentration of biodiversity in the Indo‐Australian Archipelago (IAA) has been actively debated, with several alternative hypotheses involving species diversification and dispersal. We reconstructed the phylogenetic relationships between three species‐rich families of coral reef fish (Chaetodontidae, Labridae, Pomacentridae) and calculated co‐occurrence metrics between closely related lineages of those families. We demonstrated that repeated biogeographic processes can be identified in present‐day species distribution by projecting co‐occurrence metrics between related lineages in a geographical context. Our study also evidence that sister‐species do not co‐occur randomly across the Indo‐Pacific, but tend to overlap their range within the IAA. We identified the imprint of two important biogeographic processes that caused this pattern in 48% of the sister‐taxa considered: speciation events within the IAA and repeated divergence between the Indian and Pacific Ocean, with subsequent secondary contact in the IAA.     

Impacts of predator depletion by fishing on the biomass and diversity of non-target reef fish communities

 An understanding of the indirect effects of fishing on predator-prey relationships is required for the development of valid multispecies yield models for reef fisheries and for determining the factors governing fish community structure at larger scales. We used an underwater visual census technique to examine the indirect effects of fishing on the biomass and diversity (species richness) of reef fishes in a series of ten traditional Fijian fishing grounds (qoliqoli) subject to a range of fishing intensities. All members of the families Chaetodontidae (butterflyfishes), Labridae (wrasses), Lutjanidae (snappers), Mullidae (goatfishes), Scaridae (parrotfishes) and the sub-family Epinephelinae (groupers and coral trout) which could be reliably identified were censused. Each species censused was assigned to one of three trophic groups: herbivore, invertebrate feeder or piscivore. The biomass of all piscivorous fishes and of large (>30 cm) piscivorous fishes differed significantly between qoliqoli and was significantly correlated with fishing intensity. However, the biomass of piscivorous fishes was not correlated with the biomass or diversity of their potential prey (which were not targeted by the fishery). This suggested that the indirect effects of fishing did not have an important bearing on fish diversity or biomass and that predation by the target species did not play an important role in structuring these Fijian reef fish communities. The results contrast with those from a number of studies at smaller scales and provided further indications that the structure of reef fish communities is not governed by a single dominant process, but by a range of processes which operate on different scales in different circumstances. Accepted: 29 July 1996     

Fish predation regimes modify benthic diatom community structures: Experimental evidence from an in situ mesocosm study

Diatoms are important primary producers in shallow water environments. Few studies have assessed the importance of biological interactions in structuring these communities. In the present study, benthic diatom community structure in relation to manipulated food webs was assessed using in situ mesocosms, whereby predator‐free environments and environments comprising two different fish species were assessed. Zooplankton abundance, settled algal biomass and the diatom community were monitored over a 12‐day period across each of the three trophic scenarios. Differences among treatments over time were observed in zooplankton abundances, particularly copepods. Similarly, the benthic diatom community structure changed significantly over time across the three trophic treatments. However, no differences in total algal biomass were found among treatments. This was likely the result of non‐diatom phytoplankton contributions. We propose that the benthic diatom community structure within the mesocosms was influenced by trophic cascades and potentially through direct consumption by the fish. The study highlights that not only are organisms at the base of the food web affected by predators at the top of the food web, but that predator identity is potentially an important consideration for predator–prey interaction outcomes with consequences for multiple trophic levels.     

Human activity selectively impacts the ecosystem roles of parrotfishes on coral reefs

Around the globe, coral reefs and other marine ecosystems are increasingly overfished. Conventionally, studies of fishing impacts have focused on the population size and dynamics of targeted stocks rather than the broader ecosystem-wide effects of harvesting. Using parrotfishes as an example, we show how coral reef fish populations respond to escalating fishing pressure across the Indian and Pacific Oceans. Based on these fish abundance data, we infer the potential impact on four key functional roles performed by parrotfishes. Rates of bioerosion and coral predation are highly sensitive to human activity, whereas grazing and sediment removal are resilient to fishing. Our results offer new insights into the vulnerability and resilience of coral reefs to the ever-growing human footprint. The depletion of fishes causes differential decline of key ecosystem functions, radically changing the dynamics of coral reefs and setting the stage for future ecological surprises.     

Global assessment of the status of coral reef herbivorous fishes: evidence for fishing effects

On coral reefs, herbivorous fishes consume benthic primary producers and regulate competition between fleshy algae and reef-building corals. Many of these species are also important fishery targets, yet little is known about their global status. Using a large-scale synthesis of peer-reviewed and unpublished data, we examine variability in abundance and biomass of herbivorous reef fishes and explore evidence for fishing impacts globally and within regions. We show that biomass is more than twice as high in locations not accessible to fisheries relative to fisheries-accessible locations. Although there are large biogeographic differences in total biomass, the effects of fishing are consistent in nearly all regions. We also show that exposure to fishing alters the structure of the herbivore community by disproportionately reducing biomass of large-bodied functional groups (scraper/excavators, browsers, grazer/detritivores), while increasing biomass and abundance of territorial algal-farming damselfishes (Pomacentridae). The browser functional group that consumes macroalgae and can help to prevent coral–macroalgal phase shifts appears to be most susceptible to fishing. This fishing down the herbivore guild probably alters the effectiveness of these fishes in regulating algal abundance on reefs. Finally, data from remote and unfished locations provide important baselines for setting management and conservation targets for this important group of fishes.     

永兴岛附近海域珊瑚礁鱼类群落结构特征

为更好地保护和管理西沙永兴岛附近海域珊瑚礁鱼类,于2020—2021年对永兴岛上岸渔获物进行了调查研究,分析了鱼类群落结构组成及其变化和演替特征。结果表明:调查共发现永兴岛附近海域珊瑚礁鱼类101种,隶属于5目21科,以鲈形目鱼类最多,占总种类的84.16%,生物量超总渔获物的90%;科级水平鹦嘴鱼科鱼类最多,达21种,生物量超总渔获物的45%。28种珊瑚礁鱼类是永兴岛附近海域主要捕捞对象,占总渔获物的80%以上。永兴岛附近海域珊瑚礁鱼类呈现过度捕捞,一是主要渔获物中的中大型鱼类均重偏小;二是本海域个体体型最大的鱼类出现较多消亡;三是肉食性鱼类大量消亡;四是植食性鱼类生物量占比超过了肉食性鱼类。永兴岛附近海域珊瑚礁鱼类已经演替到以植食性鱼类为主导的生态系统;大量海胆的出现,表明了这一珊瑚礁生态系统在进一步衰退,向以海胆为主导的生态系统演变。保护西沙永兴岛附近海域珊瑚礁鱼类已经刻不容缓,需要严格地控制本海域的捕捞强度。