The Structures and Dynamics of Fish Communities in an Okinawan Coral Reef: Effects of Coral-based Habitat Structures at Sites with Rocky and Sandy Sea Bottoms

Although there have been many studies on ecological factors responsible for the organization of reef fish communities, most of the studies have focused on isolated habitats. However, findings from isolated habitats cannot necessarily be applied to fish communities in other habitats (e.g., a continuous habitat). In this study, therefore, we examined the structures of fish communities (abundance, species richness and species composition), and the dynamics of fish communities (seasonal changes in abundance, species richness and species composition) over a 2-year period in two different habitats (continuous habitat and isolated habitat) in an Okinawan coral reef. We established eight permanent quadrats (8m × 8m) on a rocky reef flat (continuous habitat) and rock reef patches surrounded by a sandy sea bottom (isolated habitat). The abundance and species richness of fishes such as pomacentrids, labrids, chaetodontids and acanthurids were greater in quadrats located in the continuous habitat, whereas those of blenniids, gobiids and mullids were greater in quadrats located in the isolated habitat. This caused marked differences between the fish community structure at the two sites. Seasonal and annual changes in fish community structure were relatively small at the continuous habitat site (>0.7 similarity based on C index) but were large at the isolated habitat site (C < 0.4), indicating that the fish community structure was relatively stable at the continuous habitat site but unstable at the isolated habitat site throughout the study period. Spatial differences between the fish community structures in the four quadrats at the continuous habitat site were small (C > 0.65 in most sites), but these differences were large at the isolated habitat site (C < 0.4). Our findings suggest that habitat structure (spatial arrangement of habitats) affects both spatial and seasonal differences in the reef fish community structure. The results also suggest that the main mechanisms underlying organization of reef fish communities in continuous and isolated habitats are different.     

Contemporary Land Change Alters Fish Communities in a San Francisco Bay Watershed,California, U.S.A.

Urbanization is one of the leading threats to freshwater biodiversity, and urban regions continue to expand globally. Here we examined the relationship between recent urbanization and shifts in stream fish communities. We sampled fishes at 32 sites in the Alameda Creek Watershed, near San Francisco, California, in 1993–1994 and again in 2009, and we quantified univariate and multivariate changes in fish communities between the sampling periods. Sampling sites were classified into those downstream of a rapidly urbanizing area (“urbanized sites”), and those found in less impacted areas (“low-impacted sites”). We calculated the change from non-urban to urban land cover between 1993 and 2009 at two scales for each site (the total watershed and a 3km buffer zone immediately upstream of each site). Neither the mean relative abundance of native fish nor nonnative species richness changed significantly between the survey periods. However, we observed significant changes in fish community composition (as measured by Bray-Curtis dissimilarity) and a decrease in native species richness between the sampling periods at urbanized sites, but not at low-impacted sites. Moreover, the relative abundance of one native cyprinid (Lavinia symmetricus) decreased at the urbanized sites but not at low-impacted sites. Increased urbanization was associated with changes in the fish community, and this relationship was strongest at the smaller (3km buffer) scale. Our results suggest that ongoing land change alters fish communities and that contemporary resurveys are an important tool for examining how freshwater taxa are responding to recent environmental change.     

Use of fish parasite species richness indices in analyzing anthropogenically impacted coastal marine ecosystems

The diversity of fish parasite life history strategies makes these species sensitive bioindicators of aquatic ecosystem health. While monoxenous (single-host) species may persist in highly perturbed, extreme environments, this is not necessarily true for heteroxenous (multiple-host) species. As many parasites possess complex life cycles and are transmitted through a chain of host species, their dependency on the latter to complete their life cycles renders them sensitive to perturbed environments. In the present study, parasite communities of grey mullet Liza aurata and Liza ramada (Mugilidae) were investigated at two Mediterranean coastal sites in northern Israel: the highly polluted Kishon Harbor (KH) and the relatively unspoiled reference site, Ma'agan Michael (MM). Both are estuarine sites in which grey mullet are one of the most common fish species. The results indicate that fish at the polluted site had significantly less trematode metacercariae than fish at the reference site. Heteroxenous gut helminths were completely absent at the polluted sampling site. Consequently, KH fish displayed lower mean parasite species richness. At the same time, KH fish mean monoxenous parasite richness was higher, although the prevalence of different monoxenous taxa was variable. Copepods had an increased prevalence while monogenean prevalence was significantly reduced at the polluted site. This variability may be attributed to the differential susceptibility of the parasites to the toxicity of different pollutants, their concentration, the exposure time and possible synergistic effects. In this study, we used the cumulative species curve model that extrapolates "true" species richness of a given habitat as a function of increasing sample size. We considered the heteroxenous and monoxenous species separately for each site, and comparison of curves yielded significant results. It is proposed to employ this approach, originally developed for estimating the "true" parasite species richness for a given habitat, in the characterization of communities of differentially impacted coastal marine ecosystems. Communicated by H. von Westernhagen, A. Diamant     

Small cryptopredators contribute to high predation rates on coral reefs

Small fishes suffer high mortality rates on coral reefs, primarily due to predation. Although studies have identified the predators of early post-settlement fishes, the predators of small cryptobenthic fishes remain largely unknown. We therefore used a series of mesocosm experiments with natural habitat and cryptobenthic fish communities to identify the impacts of a range of small potential predators, including several invertebrates, on prey fish populations. While there was high variability in predation rates, many members of the cryptobenthic fish community act as facultative cryptopredators, being prey when small and piscivores when larger. Surprisingly, we also found that smashing mantis shrimps may be important fish predators. Our results highlight the diversity of the predatory community on coral reefs and identify previously unknown trophic links in these complex ecosystems.

     

The relationship between habitat structure and fish faunas on New Zealand reefs

Reef fish abundances were sampled at 11 shallow reef localities extending over 1000 km of coastline in northern New Zealand. Sampling was restricted to the 4–10-m depth stratum and included six coastal and five island localities. These were either coralline reef flats dominated by echinoids, or algal reefs with high densities of laminarian and fucoid algae. Reefs dominated by macroscopic algae supported large numbers of small fishes, mainly labrids, and few large benthic-feeding fishes. Echinoid-dominated reefs supported a different fish fauna with more large benthic-feeding species. Additional sampling of echinoiddominated reefs and algal stands in deeper water provided confirmation of these findings. A second sampling programme was carried out at a series of eight sites within a single locality covering 5 km of coastline. These spanned a moderate exposure gradient and ranged from algal dominated reefs to typical coralline reef flats with high densities of grazing invertebrates. The relationship between habitat structure and reef fish species composition and size frequency was similar to that of the large-scale sampling programme. Thirdly, observations on reef fish foraging and feeding patterns within a single reef site suggested that larger benthic-feeding reef fishes were less likely to feed within macroscopic algal stands. Experimental reductions of grazing invertebrates designed to produce brown algal stands on echinoid-dominated reef flats supported these observations. Larger individuals capable of removing echinoids and grazing gastropods did not frequent or feed in laminarian and fucoid algal stands. This pattern is discernible at several spatial scales. Our conclusion is that the type of shallow reef habitat, echinoid- as opposed to algal-dominated, will have an important rôle in determining the associated reef fish fauna.     

Similar regional effects among local habitats on the structure of tropical reef fish and coral communities

Aim We examined data on corals and reef fishes to determine how particular local habitat types contribute to variation in community structure across regions covering gradients in species richness and how consistent this was over time. Location Great Barrier Reef (GBR), Australia. Methods We compared large‐scale (1300 km), long‐term (11 years) data on fishes and corals that were collected annually at fixed sites in three habitats (inshore, mid‐shelf and outer‐shelf reefs) and six regions (latitudinal sectors) along a gradient of regional species richness in both communities. We used canonical approaches to partition variation in community structure (sites × species abundance data matrices) into components associated with habitat, region and time and Procrustes analyses to assess the degree of concordance between coral and fish community structure. Results Remarkably similar patterns emerged for both fish and coral communities occupying the same sites. Reefs that had similar coral communities also had similar fish communities. The fraction of the community data that could be explained by regional effects, independent of pure habitat effects, was similar in both fish (33%) and coral (36.9%) communities. Pure habitat effects were slightly greater in the fish (31.3%) than in the coral (20.1%) community. Time explained relatively little variation (fish = 7.9%, corals = 9.6%) compared with these two spatial factors. Conclusions Our results indicate either that fish and coral communities were structured in similar ways by processes associated with region, habitat and time, or that the variation in fish community structure tracked variation associated with the coral communities at these sites and thereby reflects an indirect link between the environment and the structure of fish communities mediated by corals. Irrespective of the causes of such commonality, we demonstrate that community structure, not just species richness, can be related to both habitat differences and regional setting simultaneously.     

Nearshore subtidal community structure compared between inner coast and outer coast sites in Southeast Alaska

Processes that structure subarctic marine communities, particularly in glaciated regions, are not well understood. This understanding is needed as a baseline and to manage these communities in the face of future climate-driven changes. This study investigates two coastal regions of Southeast Alaska with the goals to (a) identify and compare patterns of subtidal community structure for macroalgal, fish, macroinvertebrate (>5?cm), and small epibenthic invertebrate (<5?cm) communities between inner coast and outer coast sites and (b) link patterns of community structure to habitat and environmental parameters. Species assemblage and benthic habitat data were used to compare species diversity and community composition at 6?m and 12?m depths at nine inner coast and nine outer coast sites. Multivariate analysis was applied to reduce environmental variables to major gradients, to resolve community structure, and to relate community structure to habitat and environmental variables. Increased salinity and decreased temperature at outer coast sites compared with inner coast sites were associated with community structure, with greater species diversity at outer coast sites at 6?m depth. Invertebrate community composition was associated with benthic habitat, including crust and coralline algae for macroinvertebrates, and algal cover and substrate for small epibenthic invertebrates. This research suggests that marine communities in glaciated regions are strongly influenced by freshwater input and that future climate-driven changes in freshwater input will likely result in marine community composition changes.     

Resilience of fishes and invertebrates to prolonged drought in two California streams

Long-term data are needed to assess spatial and temporal variability of communities and their resilience to natural and anthropogenic disturbances, particularly in climatic regions marked by high interannual variability (e.g. mediterranean-climate). A long-term study at four sites on two streams in mediterranean-climate California (annual sampling over 20  yr) allowed us to quantify the influence of a 5-yr prolonged drought on stream invertebrate and fish communities. Invertebrate community composition did not show recovery following drought. The primary environmental factors influencing community composition, identified through principle components and multiple correspondence analyses were precipitation and flow permanence. Invertebrate taxon richness and abundance exhibited few responses (some site specific) and recovered quickly. Native fish abundance was lowest during the drought period and highest during the wet years that occurred at the end of the study period. Importantly, the prolonged drought facilitated the establishment and success of the invasive green sunfish (Centrarchidae: Lepomis cyanellus ) that was then resilient to subsequent large flow events. There was high spatial synchrony in the temporal changes among all four sites, and three distinct periods were identified: early drought, late drought, and post-drought years. However, we still found differences among sites along the flow permanence gradient from temporary to perennial in the response to drought of both invertebrate and fish assemblages likely as a result of changes in substrate, vegetation, and other habitat characteristics. The observed lack of resilience and negative impacts to biodiversity due to prolonged drought associated with long-term habitat changes is important because hydroclimatic extremes are predicted to increase in frequency and magnitude with global climate change.     

Effects of coral restoration on fish communities: snapshots of long‐term,multiregional responses and implications for practice

Coral restoration is widely used around the world to address dramatic declines in coral cover; however, very few studies have looked specifically at the temporal response of fish assemblages (i.e. abundance and diversity) to coral restoration. Several critical reef functions and processes are driven by fishes, thereby making their recovery and responses around restoration structures key indicators of success. This study evaluates fish abundance and community composition on restoration plots following 8–12 years of restoration activity, in four locations (two Caribbean and two Indo‐Pacific). Responses were very complex with region‐, site‐, and body size‐specific patterns. Overall, fish abundance only increased in Indo‐Pacific sites where damselfish responded positively to increased coral cover and topographic complexity. Restoration effects on other fish families and particularly on larger bodied reef fish were negative or neutral at all locations. If restoration initiatives are going to substantively improve the condition and recovery of degraded reef fish communities, restoration efforts need to be planned, designed, and monitored based on fish‐specific habitat requirements and locally specific community dynamics.     

Non-Random Variability in Functional Composition of Coral Reef Fish Communities along an Environmental Gradient

Changes in the coral reef complex can affect predator-prey relationships, resource availability and niche utilisation in the associated fish community, which may be reflected in decreased stability of the functional traits present in a community. This is because particular traits may be favoured by a changing environment, or by habitat degradation. Furthermore, other traits can be selected against because degradation can relax the association between fishes and benthic habitat. We characterised six important ecological traits for fish species occurring at seven sites across a disturbed coral reef archipelago in Indonesia, where reefs have been exposed to eutrophication and destructive fishing practices for decades. Functional diversity was assessed using two complementary indices (FRic and RaoQ) and correlated to important environmental factors (live coral cover and rugosity, representing local reef health, and distance from shore, representing a cross-shelf environmental gradient). Indices were examined for both a change in their mean, as well as temporal (short-term; hours) and spatial (cross-shelf) variability, to assess whether fish-habitat association became relaxed along with habitat degradation. Furthermore, variability in individual traits was examined to identify the traits that are most affected by habitat change. Increases in the general reef health indicators, live coral cover and rugosity (correlated with distance from the mainland), were associated with decreases in the variability of functional diversity and with community-level changes in the abundance of several traits (notably home range size, maximum length, microalgae, detritus and small invertebrate feeding and reproductive turnover). A decrease in coral cover increased variability of RaoQ while rugosity and distance both inversely affected variability of FRic; however, averages for these indices did not reveal patterns associated with the environment. These results suggest that increased degradation of coral reefs is associated with increased variability in fish community functional composition resulting from selective impacts on specific traits, thereby affecting the functional response of these communities to increasing perturbations.     

Effects of habitat heterogeneity at multiple spatial scales on fish community assembly

Habitat variability at multiple spatial scales may affect community structure within a given habitat patch, even within seemingly homogenous landscapes. In this context, we tested the importance of habitat variables at two spatial scales (patch and landscape) in driving fish community assembly using experimental artificial reefs constructed across a gradient of seagrass cover in a coastal bay of The Bahamas. We found that species richness and benthic fish abundance increased over time, but eventually reached an asymptote. The correlation between habitat variables and community structure strengthened over time, suggesting deterministic processes were detectable in community assembly. Abundance of benthic fishes, as well as overall community structure, were predicted by both patch- and landscape-scale variables, with the cover of seagrass at the landscape-scale emerging as the most important explanatory variable. Results of this study indicate that landscape features can drive differences in community assembly even within a general habitat type (i.e., within seagrass beds). A primary implication of this finding is that human activities driving changes in seagrass cover may cause significant shifts in faunal community structure well before complete losses of seagrass habitat.     

The effectiveness of different meso-scale rugosity metrics for predicting intra-habitat variation in coral-reef fish assemblages

Habitat structure is frequently an important variable affecting species’ abundances and diversity, and identifying the key aspects and spatial scales of habitat complexity is critical for understanding the ecology and conservation of a range of communities. Many coral-reef fishes are intimately linked with benthic habitat structure, and previous research has demonstrated rugosity as an important predictive variable of assemblage parameters. However, these studies typically consider rugosity at small scales, amalgamate multiple habitat features, or are semi-quantitative. This study considers meso-scale rugosity (within 51 plots of 25 m² on a Belizean forereef) generated by varying coral densities, heights, and complexities. Seven rugosity metrics were calculated for each plot, and were regressed against each of 11 fish assemblage parameters. Intra-habitat variability of each fish parameter was significantly positively or curvilinearly correlated to at least one metric of meso-scale rugosity, but the metric generating the strongest correlation varied. The abundance of small fishes, and consequently most of the assemblage statistics (e.g., total fish abundance and diversity) were best predicted by the number of tall (>50 cm) corals. The abundance of damselfishes, parrotfish biomass, the abundances of medium-sized and large fishes, and total fish biomass were curvilinearly related to mean coral height. The abundances of wrasses and surgeonfishes were most strongly correlated with the number of corals within a plot. Because coral-generated meso-scale rugosity is an important factor influencing intra-habitat variation in fishes, it should be explicitly considered when investigating fish-habitat relationships and predicting the impacts of coral mortality on ecosystem processes and services.     

Spatio-temporal dynamics of species richness in coastal fish communities

Determining patterns of change in species richness and the processes underlying the dynamics of biodiversity are of key interest within the field of ecology, but few studies have investigated the dynamics of vertebrate communities at a decadal temporal scale. Here, we report findings on the spatio-temporal variability in the richness and composition of fish communities along the Norwegian Skagerrak coast having been surveyed for more than half a century. Using statistical models incorporating non-detection and associated sampling variance, we estimate local species richness and changes in species composition allowing us to compute temporal variability in species richness. We tested whether temporal variation could be related to distance to the open sea and to local levels of pollution. Clear differences in mean species richness and temporal variability are observed between fjords that were and were not exposed to the effects of pollution. Altogether this indicates that the fjord is an appropriate scale for studying changes in coastal fish communities in space and time. The year-to-year rates of local extinction and turnover were found to be smaller than spatial differences in community composition. At the regional level, exposure to the open sea plays a homogenizing role, possibly due to coastal currents and advection.     

鄱阳湖湖区及支流修水夏季鱼类系统发育群落结构分析

群落的物种共存及构建机制是生态学研究的核心问题之一, 系统发育群落结构分析为探究群落的构建机制提供了新的方法。研究在鄱阳湖湖区及其支流修水设立24个采样点, 采用系统发育群落结构的方法分析了不同空间尺度下鱼类群落的构建机制。结果表明: (1)鄱阳湖鱼类主要以鲤形目、鲤科鱼类为主, 表现出东亚江湖鱼类的组成特点; (2)依据物种组成和空间位置, 鄱阳湖湖区及修水鱼类群落属于不同的组群, 鄱阳湖湖区鱼类群落可以进一步分为北方群、南方群和东部群; (3)在采样点尺度, 24个采样点中, 有12个采样点靠近鄱阳湖支流的入湖口区域, 环境特别, 群落构成表现为环境过滤作用, 有12个采样点相对容纳了较多的远缘物种, 群落构成表现为竞争作用; 在区间分析的尺度, 北方群、东部群及修水群表现为竞争作用, 南方群表现为环境过滤作用; 在湖区及支流流域的尺度, 鄱阳湖湖区群为竞争作用, 修水群转变为环境过滤作用。因此, 鄱阳湖的湖区和支流修水等鱼类群落具有不同的物种组成和群落构建机制。研究结果加深了对群落构建机制的理解, 可以为鄱阳湖鱼类资源的保护提供参考。     

Larval fish assemblage recovery: a reflection of environmental change in a large degraded river

Estuaries are globally important to fisheries but face many anthropogenic stressors that reduce water quality and degrade benthic habitat. The Maumee River estuary has been degraded by industrial contaminants, high sediment and nutrient loads, channelization and elimination of surrounding wetlands, lessening its value as spawning habitat for fishes of Lake Erie. Regulation and better management practices (BMPs) in the watershed have improved the water quality in this estuary, which should result in a response of the biotic community. We compared recent (2010/2011) larval fish assemblage data to similar data from the 1970s (1976/1977) in order to identify changes due to improved water and habitat quality. Family‐level diversity was greater in recent study years compared to the 1970s and family richness increased from 6 to 10. In addition, the abundance of lithophilic spawning fishes was significantly greater in the recent study years. Increased diversity and family richness were consistent with increased water quality in the Maumee River whereas the observed increase in abundance of lithophilic spawners was consistent with an increase in the amount or quality of benthic habitat used by species in these families for spawning. Better wastewater management and agricultural practices in coastal watersheds can benefit the early life stages of fishes, thus benefitting coastal fisheries. Furthermore, larval fish assemblages may be useful indicators of biological integrity because of their sensitivities to environmental change. Routine sampling of estuarine larval fish assemblages could provide practitioners with insight into ecosystem changes and measure the response of the biotic community to restoration.     

Fish community composition and diversity at restored estuarine habitats in Tampa Bay,Florida, United States

Estuary restoration in Tampa Bay, Florida, United States, is an ongoing focus of natural resource managers because of pressure from an increasing coastal population, historic habitat loss, and restoration's importance to economic development, recreational activities, and fish habitat. A growing population can also limit future large‐scale restorations due to associations with cost and land availability. This limitation might be overcome by applying the habitat mosaic approach to restoration, which creates distinct habitat types at small spatial scales. This approach was applied to create three types of estuarine habitat, reconnected tidal creek, salt marsh, and tidal pond. The objectives of this study were to (1) initiate monitoring of a restored wetland mosaic and (2) determine how fish diversity and community structure vary among restored habitat types. Replicated sampling using a 3‐mm mesh seine was used to characterize the fish communities. Our results indicate that the habitat mosaic approach creates suitable habitat for a variety of fish species where 37% of fish species were captured in just one habitat type. In particular, the recreationally important Centropomus undecimalis (common snook) was more common in the mangrove‐lined creek and the non‐native Sarotherodon melanotheron (blackchin tilapia) was common in the tidal pond. Greater emphasis should be placed on applied restoration research to identify how habitat types within a larger restoration mosaic contribute to local species diversity and recreationally and commercially important fishes, while limiting non‐natives. This emphasis could reveal how restoration approaches can be modified to include habitat mosaics, maximizing their contribution to productive fish habitat.     

Altitudinal gradients in stream fish diversity and the prevalence of diadromy in the Sixaola River basin,Costa Rica

Landscape-scale patterns of freshwater fish diversity and assemblage structure remain poorly documented in many areas of Central America, while aquatic ecosystems throughout the region have been impacted by habitat degradation and hydrologic alterations. Diadromous fishes may be especially vulnerable to these changes, but there is currently very little information available regarding their distribution and abundance in Central American river systems. We sampled small streams at 20 sites in the Sixaola River basin in southeastern Costa Rica to examine altitudinal variation in the diversity and species composition of stream fish assemblages, with a particular focus on diadromous species. A set of environmental variables was also measured in the study sites to evaluate how changes in fish assemblage structure were related to gradients in stream habitat. Overall, fish diversity and abundance declined steeply with increasing elevation, with very limited species turnover. The contribution of diadromous fishes to local species richness and abundance increased significantly with elevation, and diadromous species dominated assemblages at the highest elevation sites. Ordination of the sampling sites based on fish species composition generally arranged sites by elevation, but also showed some clustering based on geographic proximity. The dominant gradient in fish community structure was strongly correlated with an altitudinal habitat gradient identified through ordination of the environmental variables. The variation we observed in stream fish assemblages over relatively small spatial scales has significant conservation implications and highlights the ecological importance of longitudinal connectivity in Central American river systems.     

Species composition and dynamics of larval and juvenile fishes in the surf zone of Mauritius

The importance of the surf zone as a nursery ground for larval and juvenile fishes has been widely recognized, however the zone has yet to be studied in Mauritius. Recently, the coastal area of the island has been increasingly affected by human activities, especially by tourism. We collected fish samples with a hand pulled seine net during the period of August 2001 to March 2003 to clarify the fish fauna and the dynamics of fishes in the surf zone. Two sampling sites adjacent to river mouth areas and one sampling site adjacent to a mangrove area were selected for comparison of fish fauna in relation to environmental conditions. A total of 9,429 fish larvae and juveniles, representing at least 112 species from 48 families were collected. The abundant species were hardyhead silverside, Atherinomorus lacunosus, bluespot mullet, Valamugil seheli, and Ambassis spp., each contributing 16.2, 12.4, and 11.8% of the total number of individuals, respectively. Estuarine species dominated in the surf zone adjacent to the river mouth areas. Species composition and diversity changed seasonally. The number of fish increased during the rainy season. Species diversity increased at the turn of the seasons from the dry season to the rainy season. We conclude that species composition in each site was affected by environmental factors, such as the scale of the flux from the rivers, which is related to the precipitation. The results indicated that freshwater from the river is a trigger to aggregate larvae and juveniles in the surf zone.     

Predictability of littoral-zone fish communities through ontogeny in Lake Texoma,Oklahoma-Texas,USA

Synopsis We sampled larval, juvenile and adult fishes from littoral-zone areas of a large reservoir (Lake Texoma, Oklahoma-Texas) (1) to characterize environmental factors that influenced fish community structure, (2) to examine how consistent fish–environment relationships were through ontogeny (i.e., larval vs. juvenile and adult), and (3) to measure the concordance of larval communities sampled during spring to juvenile and adult communities sampled at the same sites later in the year. Larval, juvenile and adult fish communities were dominated by Atherinidae (mainly inland silverside, Menidia beryllina) and Moronidae (mainly juvenile striped bass, Morone saxatilis) and were consistently structured along a gradient of site exposure to prevailing winds and waves. Larval, juvenile and adult communities along this gradient varied from atherinids and moronids at highly exposed sites to mostly centrarchids (primarily Lepomis and Micropterus spp.) at protected sites. Secondarily, zooplankton densities, water clarity, and land-use characteristics were related to fish community structure. Rank correlation analyses and Mantel tests indicated that the spatial consistency and predictability of fish communities was high as larval fishes sampled during spring were concordant with juvenile and adult fishes sampled at the same sites during summer and fall in terms of abundance, richness, and community structure. We propose that the high predictability and spatial consistency of littoral-zone fishes in Lake Texoma was a function of relatively simple communities (dominated by 1–2 species) that were structured by factors, such as site exposure to winds and waves, that varied little through time.     

An Analysis of Artificial Reef Fish Community Structure along the Northwestern Gulf of Mexico Shelf: Potential Impacts of “Rigs-to-Reefs” Programs

Artificial structures are the dominant complex marine habitat type along the northwestern Gulf of Mexico (GOM) shelf. These habitats can consist of a variety of materials, but in this region are primarily comprised of active and reefed oil and gas platforms. Despite being established for several decades, the fish communities inhabiting these structures remain poorly investigated. Between 2012 and 2013 we assessed fish communities at 15 sites using remotely operated vehicles (ROVs). Fish assemblages were quantified from standing platforms and an array of artificial reef types (Liberty Ships and partially removed or toppled platforms) distributed over the Texas continental shelf. The depth gradient covered by the surveys (30–84 m) and variability in structure density and relief also permitted analyses of the effects of these characteristics on fish richness, diversity, and assemblage composition. ROVs captured a variety of species inhabiting these reefs from large transient piscivores to small herbivorous reef fishes. While structure type and relief were shown to influence species richness and community structure, major trends in species composition were largely explained by the bottom depth where these structures occurred. We observed a shift in fish communities and relatively high diversity at approximately 60 m bottom depth, confirming trends observed in previous studies of standing platforms. This depth was also correlated with some of the largest Red Snapper captured on supplementary vertical longline surveys. Our work indicates that managers of artificial reefing programs (e.g., Rigs-to-Reefs) in the GOM should carefully consider the ambient environmental conditions when designing reef sites. For the Texas continental shelf, reefing materials at a 50–60 m bottom depth can serve a dual purpose of enhancing diving experiences and providing the best potential habitat for relatively large Red Snapper.