Diversity Of Fish Assemblages Research Articles

Fish Assemblage Structure Comparison between Freshwater and Estuarine Habitats in the Lower Nakdong River, South Korea

Variabilities of biological communities in lower reaches of urban river systems are highly influenced by artificial constructions, alterations of flow regimes and episodic weather events. Impacts of estuary weirs on fish assemblages are particularly distinct because the weirs are disturbed in linking between freshwater and estuarine fish communities, and migration successes for regional fish fauna. This study conducted fish sampling at the lower reaches of the Nakdong River to assess spatio-temporal variations in fish assemblages, and effects of estuary weir on structuring fish assemblage between freshwater and estuary habitats. In total, 20,386 specimens comprising 78 species and 41 families were collected. The numerical dominant fish species were Tachysurus nitidus (48.8% in total abundance), Hemibarbus labeo (10.7%) and Chanodichthys erythropterus (3.6%) in the freshwater region, and Engraulis japonicus (10.0%), Nuchequula nuchalis (7.7%) and Clupea pallasii (5.2%) in the estuarine site. The fish sampled were primarily small species or the juveniles of larger species at the estuary region, while all life stages of fishes were observed at the freshwater habitats. The diversity patterns of fish assemblages varied greatly according to study site and season, with higher trends at estuarine sites during the warm-rainy season. No significant difference in diversity between freshwater and estuarine sites during the cold-dry season were found. Multivariate analyses of fish assemblage showed spatial and seasonal differences of assemblage structures. Higher effects of between-site variability but not within seasonal variability at each site were observed. Variations in assemblage structures were due to different contributions of dominant species in each habitat. Common freshwater species characterized the fish assemblage in the freshwater region, while marine juveniles were significantly associated with the estuarine habitat. The results from the ecological guild analyses showed distinct ecological roles for freshwater and marine species, and overlapping roles for fish sampled at the fishways. The lower reaches of the Nakdong River are an important ecosystem for both freshwater and marine juveniles. Nakdong River estuarine residents and migrant fishes, however, have been negatively affected by the construction of the weir (gravity dam), due to the obstruction to migration from and to freshwater habitats. Conservation and management policies aimed at minimizing anthropogenic influences on estuary ecosystems should focus on evaluating ecological functions of estuary weirs.

Effect of water quality variation on fish assemblages in an anthropogenically impacted tropical estuary, Colombian Pacific

In tropical estuaries, fish diversity varies spatially and temporally due to behavioral processes such as reproductive migrations, predator avoidance, and foraging, which are affected by water quality. Eutrophication is one of the main factors affecting water quality in estuaries. The objective of this study was to determine variation in fish assemblage explained by fluctuating water quality in the Buenaventura Bay. Fish were captured using artisanal trawl nets during the wet, dry, and transitional seasons at four sampling sites. Additionally, alkalinity; phosphate, nitrite, and nitrate concentrations; dissolved oxygen; pH; temperature; and suspended solids were measured. Multivariate analysis was used to assess the effect of water quality on fish assemblage. In Buenaventura Bay, the assemblage composition of Pseudupeneus grandisquamis, Daector dowi, and Citharichthys gilberti was affected by nitrate concentration. Moreover, large fish biomasses were associated with high nitrite concentration, intermediate salinity, and low dissolved oxygen, suggesting that these estuaries are dominated by species tolerant to poor water quality. Species richness was associated with low nitrate and phosphate concentrations, more suitable water quality indicators, and intermediate temperatures. These results suggest that the deteriorating water quality of estuaries as a result of the anthropogenic impact could increase dominance and decrease richness, resulting in structural changes of fish assemblages.

Functional response of fish assemblage to multiple stressors in a highly regulated Mediterranean river system

Mediterranean rivers are characterised by strong environmental constrains and species-poor, highly endemic fish fauna. In Europe, these systems are exposed to multiple stressors due to extensive human activities. Studies on the effects of some stressors on riverine fish are available but complex responses of fish assemblages to interplay of flow alteration with physical habitat changes and invasive species have not been evaluated up to date. This study analysed the response of functional diversity of fish assemblages to multiple stressors in the Segura River system in the southern Spain. Fish assemblages were sampled in 16 sites in two consecutive periods (2009–2010 and 2013–2015). Subsequently, we assessed the responses of functional specialisation, originality and entropy (based on nine functional traits and abundances) as well as species richness and abundance to interplay of flow regime alteration and ecological status, fragmentation as well as non-native species abundance across spatial and temporal scales. The governing role of flow regime in structuring fish assemblage was superimposed on physical habitat changes, water quality deterioration and fragmentation as well as the presence of non-native fish species. We found an increase of species richness and abundance but decrease of functional specialisation and originality in river reaches with high level of base flow and more stable hydrological conditions. Opposite pattern was observed in reaches with severe reduction of base flow and marked inversion in the seasonal pattern of high and low flows. We postulate that the use of tools that consider the functional identity of the species as method to assess the effects of environmental alterations on fish biodiversity could improve conservation measures for Mediterranean fish fauna. Furthermore, design flows that mimic natural flow regime patterns characteristic for Mediterranean rivers are a promising tool to provide environmental conditions that would favour native fish within the assemblage and benefit their conservation.

Examining the relationship between morphological variation and modeled broadband scattering responses of reef-associated fishes from the Southeast United States

Non-lethal methods are sought to provide indices or measure of absolute abundance to fit fishery stock assessment models, including those computed for reef fishes. Calibrated scientific echosounders provide the foundation for stock assessments in low-diversity ecosystems but are hampered by complicated target strength responses in high diversity systems like coral and rocky reefs. Newly available broadband echosounders present advantages over narrowband predecessors including increased spatial resolution, increased signal to noise and spectral resolution; however, a better understanding of the sound scattering properties is necessary for operational use in surveys of diverse reef fish assemblages. To gain insight into the feasibility of implementing broadband techniques, we first model the frequency dependent backscatter of ecologically and commercially important species; results will aid our understanding of the backscattering as well as provide a supporting dataset to develop algorithms for classification of species/functional groups. Computed-tomography (CT) scans were performed on 149 individuals across reef fish species from the northeastern Gulf of Mexico to generate three-dimensional swim bladder models for estimation of morphometrics to input into numerical scattering models. Principal component analysis of the swim bladder morphology indicated significant variation among species; however, closely related species (confamilials) were not different. We employed boundary element method modeling to examine the frequency-dependent backscatter responses across a range of fish orientations (+/- 45°). Comparisons of frequency-dependent backscatter revealed strongest similarities between closely related species and greatest differences between more distantly related species or species groups. Patterns in the spectra have the potential to be used to classify targets toward species (or species group) for estimates of density from marine ecosystem acoustic surveys. Given that broadband echosounders are not yet commonplace, and many surveys in the region utilize narrowband echosounders, we also developed narrowband target strength – length relationships for six of the reef fish species with model fits ranging widely (r2 = 0.05 to 0.93). The potential utility of broadband echosounders to enhance ecosystem studies, or to develop fisheries-independent indices of abundance for use in stock assessment is discussed.

Weak population structure and recent demographic expansion of the monogenean parasite Kapentagyrus spp. infecting clupeid fishes of Lake Tanganyika, East Africa

Lake Tanganyika, East Africa, is the oldest and deepest African Great Lake and harbours one of the most diverse fish assemblages on earth. Two clupeid fishes, Limnothrissa miodon and Stolothrissa tanganicae, constitute a major part of the total fish catch, making them indispensable for local food security. Parasites have been proposed as indicators of stock structure in highly mobile pelagic hosts. We examined the monogeneans Kapentagyrus limnotrissae and Kapentagyrus tanganicanus (Dactylogyridae) infecting these clupeids to explore the parasites’ lake-wide population structure and patterns of demographic history. Samples were collected at seven sites distributed across three sub-basins of the lake. Intraspecific morphological variation of the monogeneans (n = 380) was analysed using morphometrics and geomorphometrics of sclerotised structures. Genetic population structure of both parasite species (n = 246) was assessed based on a 415 bp fragment of the mitochondrial cytochrome c oxidase subunit I (COI) gene. Overall, we observed a lack of clear geographical morphological differentiation in both parasites along a north–south axis. This lack of geographical population structure was also reflected by a large proportion of shared haplotypes, and a pattern of seemingly unrestricted gene flow between populations. Significant morphological and genetic differentiation between some populations might reflect temporal differentiation rather than geographical isolation. Overall, the shallow population structure of both species of Kapentagyrus reflects the near-panmictic population structure of both host species as previously reported. Morphological differences related to host species identity of K. tanganicanus were consistent with incipient speciation at the genetic level. Both parasite species experienced a recent demographic expansion, which might be linked to paleohydrological events. Finally, interspecific hybridisation was found in Kapentagyrus, representing the first case in dactylogyrid monogeneans.

A diverse assemblage of pycnodont fishes (Actinopterygii, Pycnodontiformes) from the mid-Cretaceous, continental Kem Kem Group of south-east Morocco

Pycnodont fishes (Actinopterygii, Pycnodontiformes) contributed a major role to many ichthyological assemblages in the Mesozoic, however their occurrence in the continental mid-Cretaceous Kem Kem Group of Morocco was only briefly noted by Sereno et al., 1996, but were not described. Here we describe the first diverse pycnodont assemblage in the Kem Kem beds of the Tafilalt region, based mainly on recent collecting. Pycnodont remains are represented by rare, mostly incomplete fragments of vomerine and prearticular dentitions, but despite their rarity, they are surprisingly diverse with four morphotypes represented, including two new taxa: Neoproscinetesafricanus sp. nov. and Agassizilia gen. nov. From a sample of eight specimens, four species are recorded, three of which are new. The palaeoecology, taphonomy and biostratinomy of the specimens is discussed in the context of their occurrence in a predominantly freshwater sequence. Comparisons are made with the pycnodont assemblage of the approximately coeval Santana Group (Brazil) which contains taxa with similarities to the new Moroccan pycnodonts. These new pycnodont taxa increase the already diverse assemblage of the Kem Kem Group ichthyofauna.

The rise of a marine generalist predator and the fall of beta diversity.

Determining the importance of physical and biological drivers in shaping biodiversity in diverse ecosystems remains a global challenge. Advancements have been made towards this end in large marine ecosystems with several studies suggesting environmental forcing as the primary driver. However, both empirical and theoretical studies point to additional drivers of changes in diversity involving trophic interactions and, in particular, predation. Moreover, a more integrated but less common approach to the assessment of biodiversity changes involves analyses of spatial β diversity, whereas most studies to date assess only changes in species richness (α diversity). Recent research has established that when cod, a dominant generalist predator, was overfished and collapsed in a northwest Atlantic food web, spatial β diversity increased; that is, the spatial structure of the fish assemblage became increasingly heterogeneous. If cod were to recover, would this situation be reversible, given the inherent complexity and non-linear dynamics that typify such systems? A dramatic increase of cod in an ecologically similar large marine ecosystem may provide an answer. Here we show that spatial β diversity of fish assemblages in the Barents Sea decreased with increasing cod abundance, while decadal scale changes in temperature did not play a significant role. These findings indicate a reversibility of the fish assemblage structure in response to changing levels of an apex predator and highlight the frequently overlooked importance of trophic interactions in determining large-scale biodiversity patterns. As increased cod abundance was largely driven by changes in fisheries management, our study also shows that management policies and practices, particularly those involving apex predators, can have a strong effect in shaping spatial diversity patterns, and one should not restrict the focus to effects of climate change alone.

Correction: Coupling environment and physiology to predict effects of climate change on the taxonomic and functional diversity of fish assemblages in the Murray-Darling Basin, Australia

[This corrects the article DOI: 10.1371/journal.pone.0225128.].

Habitat Use by Fish across Tidal Cycles in a Tropical Estuarine Mangrove Ecosystem (Dongzhaigang Bay, Hainan, China)

Zhang, Y.; Yan, S.; Wang, W., and Wang, M., 2021. Habitat use by fish across tidal cycles in a tropical estuarine mangrove ecosystem (Dongzhaigang Bay, Hainan, China). Journal of Coastal Research, 37(1), 156–167. Coconut Creek (Florida), ISSN 0749-0208.Mangroves wetlands are recognized as nursery areas for large numbers of marine organisms. Yet, many properties of this nursery function remain poorly understood. In this study, the seasonal use of a tropical mangrove bay by fish assemblages over tidal cycles was investigated in 2009. Fish were sampled using centipede nets from three sites (located in the mouth, middle, and top of the bay) at Dongzhaigang Bay, Hainan, China. At each site, three replicates were sampled from each of the three different habitat types (i.e. vegetated area, creek, and mudflat). A generalized linear mixture model was used to explore the spatial and temporal variations in fish assemblages. The results showed that fish species richness, abundance, and biomass per sampling unit were significantly lower in the vegetated areas and mudflats than in the creeks. In the vegetated areas, fish species richness, abundance, and biomass per sampling day were significantly higher during spring tides than during neap tides. However, a similar pattern was not found both along the creeks and on the mudflats. In addition, tidal height showed a positive effect on biomass per sampling unit, especially in the vegetated areas; meanwhile, effects on species richness and abundance were not significant. The results indicate that larger tidal amplitude could support more fish (both richness and abundance) in the vegetated areas, which might occur because larger tidal amplitude provides fish with access to more habitats. These results provide basic knowledge related to mangrove management at an important fish nursery ground.

Environmental and spatial effects on coastal stream fishes in the Atlantic rain forest

AbstractContemporary and historical factors influence assemblage structure. The environmental and spatial influences acting on fish organization of rain forest coastal streams in the Atlantic rain forest of Brazil were examined. Fish (and functional traits such as morphology, diet, velocity preference, body size), environmental variables (pH, water conductivity, dissolved oxygen, temperature, stream width, flow, depth, substrate), and altitude were measured from 59 stream reaches. Asymmetric eigenvector maps were used to model the spatial structure considering direction of fish movements. Elevation played an important role—fish abundance, biomass, and richness all decrease with increasing elevation. Fish communities are influenced by both environmental and spatial factors, but downstream movements were shown to be more important in explaining the observed spatial variation than were bidirectional and upstream movements. Spatial factors, as well as environmental variables influenced by the spatial structure, explained most of the variation in fish assemblages. The strong spatial structuring is probably attributable to asymmetric dispersal limitation along the altitudinal profile: Dispersal is likely to be more limiting moving upstream than downstream. These fish assemblages reflect scale‐dependent processes: At the stream‐reach scale, fish respond to local environmental filters (habitat structure, water chemistry, and food supply), which are in turn influenced by a larger scale, namely the altitudinal gradient expected in steep coastal mountains. Thus, environmental drivers are not independent of spatial factors, and the effects of local factors can be confounded across the altitudinal gradient. These results may have implications for conservation, because downstream reaches are often neglected in management and conservation plans.Abstract in Portuguese is available with online material.

Spatio-temporal variation of fish assemblages in Babai River of Dang district, Province No. 5, Nepal

Spatial and temporal variation of fish assemblages were investigated seasonally from October 2018 to May 2019. Fish assemblages were agglomerated with environmental variables both to spatial and temporal scales. Water temperature, dissolved Oygen, free carbon-dioxide, pH and water velocity of water of each site were measured. Based on analysis of similarities (ANOSIM), fish assemblages were significantly different in spatial variation but not in temporal variation. A total of 1,024 individuals belonging to 5 orders, 9 families and 15 genera and 24 species were collected. The dominated species were Puntius sophore, followed by P. terio, P. ticto and Barilius bendelisis. The Redundancy Analysis (RDA) vindicated that environmental variables of water temperature, pH, water velocity and free carbon-dioxide were found to be contributed variables to shape the fish assemblage structure of Babai River. The cluster analysis delineated that similarity between fish species decreases as the distance of sites increased.

Discrimination of hydrologic variations for spatial distribution of fish assemblage in a large subtropical temperate river

AbstractThis study examines the effects of the flow and flood pulses on spatial dispersion of fish assemblages in the floodplain of the Paraná River in Argentina. We tested the hypothesis that high water levels and greater lateral connectivity promote fish dispersal and spatial homogenization of assemblage structure. We sampled four sites during different phases of the annual hydrologic cycle from 2010 to 2016. Water surface in the area was estimated during each phase. We computed multivariate statistics and estimates of ß‐diversity to analyse assemblage variations in relation to hydrological phases. Three hydrological phases were defined: low flow pulses (water levels between 2.3 and 3.2, approximately 10% of the floodplain covered by water), high flow pulses (between 3.2 and 4.5, from 11 to 84%), and floods (> 4.5 m, more than 84%). Although difference between high flow pulses and flood was not significant, ß‐diversity values for these stages were higher than for low flow pulses. This suggests that floods and high flow pulses increase the spatial variability of fish assemblages, whereas homogenization processes occur later during low flow periods. This work provides further knowledge about the flood homogenization effect in a large unregulated floodplain where lateral connectivity still plays a significant role on ecological structuring processes.

Elucidating the impact of anthropogenic supplementation, isolation and ecological heterogeneity on Brook Trout (Salvelinus fontinalis) genetic structure

Preservation of genetic diversity is a commonly cited, yet under-evaluated aspect of species conservation plans. Understanding the influence of human-mediated translocations and habitat constraints on landscape patterns of genetic structure in threatened fish species is essential to maintaining biodiversity and adaptive potential. We evaluated the degree of influence from supplemental stocking, assessed the spatial population genetic structure, and examined the potential relationship between hybridization and ecology for Brook Trout (Salvelinus fontinalis) in the Black River watershed in New York State, USA. We used 13 microsatellite loci from over 450 fish at 18 sampling locations to map genetic structure and diversity, estimate the level of influence from stocked conspecifics, and model the relationship between hybridization and ecological characteristics. We found widespread genetic introgression attributable to state-based stocking activities and a pattern of hierarchical genetic diversity across the landscape, which has additionally been influenced by geography. Site-specific fish assemblage variables appear to be unrelated to introgressive hybridization from stocked conspecifics, and only one hydrochemical variable, SO42−, exhibited strong explanatory power in predicting hybridization between wild and supplemented fish. A single locality exhibited genetic structure consistent with no history of introgression potentially associated with differences in elevation, and thus contributed disproportionately to the level of genetic diversity observed across the landscape. When examining genetic structure in fluvial riverine networks, it is important to consider the combined and interacting effects of both hybridization and habitat, which may result in augmented genetic structure not predictable from any single factor.

Mesopelagic fish composition and diets of three myctophid species with potential incidence of microplastics, across the southern tropical gyre

The species occurrence of mesopelagic fish collected in the scattering layers was studied across the Indian Ocean subtropical gyre during the dry season (2015). Ocean eddies can retain zooplankton and plastic debris, and determine biological composition through advection. The conditions inside the gyre were stabilised by low chlorophyll-a concentrations and a deep nutricline. A diverse assemblage of mesopelagic fish, dominated by myctophids, exhibited diel migrations to the upper water layers for feeding since the early night. Myctophids were concentrated ca. 100 m depth, where the deep chlorophyll maximum was located, and coinciding with the nutricline. Another group of mesopelagic fish remained in deeper waters during the daytime, with a higher occurrence of Stomiiformes (Phoshycthyidae and Sternoptychidae) at the 500–600 m Deep Scattering Layer. Moreover, the diets of 220 myctophid specimens belonging to the species Ceratoscopelus warmingii, Diaphus effulgens, and Symbolophorus evermanni, were investigated based on stomach content analysis. Calanoid copepods, mainly Pleuromamma abdominalis, made up 30% of the diet in the three myctophid species, with interspecific differences in the preferred second item: C. warmingii preferred ostracods, D. effulgens, non-calanoid copepods, and S. evermanni, euphausiids. Thus, partial dietary segregation was observed among the three species. We hypothesized that these myctophid diets differed between stations located at the gyre core and its outer edge. Any dietary pattern indicating aggregation of food resources, or an enhancement of the foraging opportunities for myctophids, was discerned as an effect of the gyre advection. However, prey composition diverged between the core and the outer edge stations regardless of the fish species, with a higher dietary representation of P. abdominalis and euphausiids (migratory zooplankton) in the individuals collected in the core-influenced area. A total of six plastic pieces were present in the stomachs of D. effulgens and S. evermanni, in contrast with the high presence of plastic particles found at the surface in most sampling stations (average number of plastic pieces was 41 per hour). The selected myctophid species did not appear to be important transport vectors for microplastics in comparison with species from other oceans.

The abundance and habitat use of demersal fishes on a rocky offshore bank using the ROPOS remotely operated vehicle

Offshore rocky banks are ecologically important refuge habitats for a number of U.S. commercial groundfish species. However, they are challenging to survey, and data on the abundance and ecology of fish populations at deep banks are limited. We used the remotely operated vehicle ROPOS to carry out visual surveys at two sites on Cherry Bank in the Southern California Bight, eastern Pacific Ocean. We observed differences in fish assemblages related to depth and habitat type and found that rockfishes (Sebastes spp) made up 65% of fishes recorded. Rockfishes and combfish (Zaniolepis spp) were associated with relatively shallow areas with hard substrate whereas flatfishes (Pleuronectiformes) and poachers (Agonidae) were found on unconsolidated sediments. Thornyheads (Sebastolobus spp) and hagfishes (Myxinidae) mainly occurred in areas of patchy habitat. Habitat and depth explained 52% of the variation in fish assemblages between transects with habitat explaining a greater proportion of the variation than depth. We observed large differences in the number of juvenile rockfishes and Sebastomus rockfishes between study sites with hard substrates and also had higher abundances of juvenile rockfishes versus sites characterized by mixed substrates. With the exception of unidentified Sebastomus, the current design had relatively low power to reliably detect observed differences for most taxa, so we report the number of additional transects that would be required to detect a 50% increase in densities. These data provide a baseline on groundfish densities and habitat associations at Cherry Bank and key information for the design of future work including Bayesian approaches to estimating coast-wide abundance.

Plankton Composition in Relation to Water Quality in the Coastal Waters of Nigeria

Coastal waters of Ondo State, Nigeria have diverse assemblage of fish, yet there is dearth of information on its plankton composition. This study investigates plankton components in relation to physicochemical characteristics of the coastal waters bordering Olotu, Ayetoro and Bijimi in providing baseline information that can be used for planning and implementation of policies for monitoring, impacts assessment and conservation. Surface water samples were collected on monthly basis from March to June 2015 to analyze physicochemical parameters while plankton net of 55μm mesh size was used for collection of plankton using standard methods prescribed by APHA. The light and dark bottle method was used to determine primary productivity. Shannon-wiener, Margalef and Equitability Indices were used for diversity. Values of the physicochemical parameters observed ranged as follows: temperature, 27.47±2.06-29.27±0.31ºC; turbidity, 43.43±0.91-65.33±2.52NTU; pH, 5.54±0.31-6.12±0.30; BOD, 2.20±0.29-5.43±0.54 mg/l; COD, 6.08±2.71-6.66±1.52 mg/l; dissolved oxygen, 6.39±0.39-7.78±0.19 mg/l and salinity, 2.03±0.06-3.77±0.04 mg/l. Fifteen species of phytoplankton and three developmental stages of zooplankton were recorded. Phytoplankton accounted for 83.3% as against 16.7% zooplankton. Diatoms (93.3%) and dinoflagellates (6.7%) represented phytoplankton whereas 66.7% of zooplankton belonged to the phylum Arthropoda. Primary productivity ranged between 132.194±13.48m-3hr-1 and 134.48±15.27m-3hr-1. Some dominant species recorded were Coscinodiscus, Biddulphia, Copepod, Skeletonema and Ditylum. pH and Temperature were major determinant of the composition, diversity and abundance of plankton. The observed plankton group indicates the suitability of the creeks as habitat and breeding ground for diverse aquatic species. The water quality falls within acceptable range hence the environment can be classified as healthy ecosystem.

Coupling environment and physiology to predict effects of climate change on the taxonomic and functional diversity of fish assemblages in the Murray-Darling Basin, Australia.

This study uses species distribution modeling and physiological and functional traits to predict the impacts of climate change on native freshwater fish in the Murray-Darling Basin, Australia. We modelled future changes in taxonomic and functional diversity in 2050 and 2080 for two scenarios of carbon emissions, identifying areas of great interest for conservation. Climatic-environmental variables were used to model the range of 23 species of native fish under each scenario. The consensus model, followed by the physiological filter of lethal temperature was retained for interpretation. Our study predicts a severe negative impact of climate change on both taxonomic and functional components of ichthyofauna of the Murray-Darling Basin. There was a predicted marked contraction of species ranges under both scenarios. The predictions showed loss of climatically suitable areas, species and functional characters. There was a decrease in areas with high values of functional richness, dispersion and uniqueness. Some traits are predicted to be extirpated, especially in the most pessimistic scenario. The climatic refuges for fish fauna are predicted to be in the southern portion of the basin, in the upper Murray catchment. Incorporating future predictions about the distribution of ichthyofauna in conservation management planning will enhance resilience to climate change.

Stream Size and Network Position Affect Fish Assemblage Diversity Differently in Headwater Streams of the Interior Highlands, USA

Stream fish assemblages in small streams are often less diverse than those in larger streams. Two models to explain this have emerged, one which focuses on local habitat conditions derived from processes related to discharge, and the other which links patterns of network connectivity to dispersal ability and network position in the watershed. Both models now have some support in stream fishes, but how they might interact is not well studied. We draw on observations from stream invertebrates to propose that stream size will affect niche specialization and network position will affect functional trait-based diversity. We test this hypothesis using data from the Interior Highlands, USA. Diversity of upland-adapted groups and trait-based assemblage metrics tied to strategies dependent on depth, flow, and stream width showed strong relationships to stream size. Diversity of lowland-adapted groups and metrics of assemblage morphological diversity showed strong relationships to network position. Examination of patterns of spatial b-diversity supports the idea that dispersal of lowland-adapted groups is linked to network connectivity. Responses to both network position and stream size included longer, later reproductive seasons with more species exhibiting parental care. We support that both stream size and network position interact to lower fish diversity in small streams, but that they do so in different manners. We further discuss the ecological uniqueness and need for research and conservation efforts of small streams low in watershed networks.

Structural Complexity and Benthic Cover Explain Reef-Scale Variability of Fish Assemblages in Los Roques National Park, Venezuela

Global and local stressors are causing the worldwide loss of coral cover and structural complexity at an unprecedented pace on reefs. In consequence the habitat of coral reef fish has suffered a profound degradation affecting the abundance, biodiversity and species composition of this taxonomic group. Thus, understanding the link between coral reef fish assemblages and their habitats is paramount to predict their responses to increasing human threats. Herein, we implemented Structure from Motion (SfM) techniques and digital mosaics to characterize the habitat of reef fish in terms of structural complexity and cover of benthic organisms, and we examined the relationships between these metrics and the variation in fish assemblages among sites using a multivariate approach. We found that fish assemblage attributes varied across reef sites in Los Roques, depending on the highly specific features of the benthic habitat. Results indicate that 69% of the variation in species-specific abundance of fish (i.e., reef fish assemblage structure) was explained by cover of massive coral and turf algae, the number and sizes of holes, and the site. Furthermore, when fish biomass per species was utilized as a response variable, 64% of the variation in assemblage structures was explained by a model that included: cover of crustose coralline algae (CCA), variation and the maximum height of reef structures along the transect, the number of holes and the site. All these variables together also explained > 60% of variation of total abundance, biomass and species richness. When data were sorted by trophic groups, CCA cover explained 70% of the variation in forager biomass, whereas the number of holes explained up to 60% of variation in carnivore biomass. These results suggest that each trophic group relates differently to the benthic habitat. We conclude that variation in fish assemblages among sites can be explained by features of the benthic habitat, but more importantly the absence of specific attributes may impact fish trophic groups differently.

Oyster Reefs in Northern Gulf of Mexico Estuaries Harbor Diverse Fish and Decapod Crustacean Assemblages: A Meta-Synthesis

Oyster reefs provide habitat for numerous fish and decapod crustacean species that mediate ecosystem functioning and support vibrant fisheries. Recent focus on the restoration of eastern oyster (Crassostrea virginica) reefs stems from this role as a critical ecosystem engineer. Within the shallow estuaries of the northern Gulf of Mexico (nGoM), the eastern oyster is the dominant reef building organism. This study synthesizes data on fish and decapod crustacean occupancy of oyster reefs across nGoM with the goal of providing management and restoration benchmarks, something that is currently lacking for the region. Relevant data from 23 studies were identified, representing data from all five U.S. nGoM states over the last 28 years. Cumulatively, these studies documented over 120,000 individuals from 115 fish and 41 decapod crustacean species. Densities as high as 2800 ind m-2 were reported, with individual reef assemblages composed of as many as 52 species. Small, cryptic organisms that occupy interstitial spaces within the reefs, and sampled using trays, were found at an average density of 647 and 20 ind m-2 for decapod crustaceans (range: 18 - 2843) and fishes (range: 2 - 56), respectively. Both groups of organisms were comprised, on average, of 8 species (range: 3 - 15). Larger-bodied fishes captured adjacent to the reef using gill nets were found at an average density of 6 ind m-2 (range: 1- 68) which came from 23 species (range: 9 - 46). Decapod crustaceans sampled with gill nets had a much lower average density, < 1 ind m-2, and only contained 2 species. On average, seines captured the greatest number of fish species (n = 33), which were made up of both facultative residents and transients. These data provide general gear-specific benchmarks, based on values currently found in the region, to assist managers in assessing nekton occupancy of oyster reefs, and assessing trends or changes in status of oyster reef associated nekton support. More explicit reef descriptions (e.g., rugosity, height, area, adjacent habitat) would allow for more precise benchmarks as these factors are important in determining nekton assemblages, and sampling efficiency.