How geographic distance and depth drive ecological variability and isolation of demersal fish communities in an archipelago system (Cape Verde, Eastern Atlantic Ocean) (original) (raw)
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Demersal fish communities may indicate priority areas for marine resources conservation
This study analyses the composition and temporal variation of the fish community from two close coastal marine sites off the central coast of Brazil: Itaoca and Manguinhos, both sites located between 500 and 1000 meters from the coastline. The material analysed comprised a total of 6,072 specimens of 66 fish species collected on board a bottom trawl vessel. Greater variability in catch rates and species composition was observed in Manguinhos. Itaoca presented lower level of temporal variability, higher species richness and an important abundance of juveniles in winter. This study shows that these two close marine environments present very different fish communities and play different roles regarding the aspects of diversity, species reproduction and nursery for the young specimens.
Fisheries Oceanography, 2015
Biodiversity is changing at an unprecedented rate on a global scale as a complex response to several anthropogenic changes, in addition to the background natural environmental variability and cycles. In the Benguela Current Large Marine Ecosystem region (BCLME), aspects of demersal fish species diversity were studied between 1985 and 2010 in three countries (Angola, Namibia, and South Africa) using scientific survey data (depending on country). The study was aimed to address multi‐tiered objectives: to document patterns of diversity (as measured by the different indices of diversity) in the three countries; to relate these patterns to various explanatory variables (depth, latitude, longitude, bottom temperature, and total catch) using a generalized additive model; and to compare the patterns of diversity and importance of potential drivers of biodiversity across the BCLME region. Results showed contrasting diversity patterns between the three countries in terms of both the form and ...
Habitat specialization in tropical continental shelf demersal fish assemblages
2012
The implications of shallow water impacts such as fishing and climate change on fish assemblages are generally considered in isolation from the distribution and abundance of these fish assemblages in adjacent deeper waters. We investigate the abundance and length of demersal fish assemblages across a section of tropical continental shelf at Ningaloo Reef, Western Australia, to identify fish and fish habitat relationships across steep gradients in depth and in different benthic habitat types. The assemblage composition of demersal fish were assessed from baited remote underwater stereo-video samples (n = 304) collected from 16 depth and habitat combinations. Samples were collected across a depth range poorly represented in the literature from the fringing reef lagoon (1-10 m depth), down the fore reef slope to the reef base (10-30 m depth) then across the adjacent continental shelf (30-110 m depth). Multivariate analyses showed that there were distinctive fish assemblages and different sized fish were associated with each habitat/depth category. Species richness, MaxN and diversity declined with depth, while average length and trophic level increased. The assemblage structure, diversity, size and trophic structure of demersal fishes changes from shallow inshore habitats to deeper water habitats. More habitat specialists (unique species per habitat/depth category) were associated with the reef slope and reef base than other habitats, but offshore sponge-dominated habitats and inshore coral-dominated reef also supported unique species. This suggests that marine protected areas in shallow coral-dominated reef habitats may not adequately protect those species whose depth distribution extends beyond shallow habitats, or other significant elements of demersal fish biodiversity. The ontogenetic habitat partitioning which is characteristic of many species, suggests that to maintain entire species life histories it is necessary to protect corridors of connected habitats through which fish can migrate.
Reviews in Fish Biology and Fisheries, 2014
Distributional change, expressed as range expansion or contraction, has been observed in many marine populations and related to changes in the environment. The extent of such distributional changes is also expected to increase in response to future climate change. The Benguela Current Large Marine Ecosystem (BCLME) which adjoins the south-western coast of Africa is a global marine hotspot with longterm warming occurring over a large area. The area is also an important centre of marine food production for three countries-South Africa, Namibia and Angola and is considered to be vulnerable to future climate change or increased climate variability. In this study we analysed change in distribution and range size of several demersal fish species in the BCLME over the period 1985-2010, including both commercial and non-commercial fish populations. Some of the observed changes in distribution and range size correspond to what is expected with increased warming whereas others appear to the contrary. Overall the results of the study highlight the complex nature of the response of fish population to climate change.
Marine Ecology Progress Series, 2007
The number of fish species in subtropical and tropical estuaries is much greater than in temperate regions and is greater in large estuaries than in small ones. Thus, large estuaries of the tropics are of primary interest for biodiversity conservation, and the processes underpinning the distribution of fish diversity in these ecosystems deserve attention. Factors controlling biodiversity patterns have been the focus of numerous recent investigations and include species interactions, speciation, environmental gradients and heterogeneity, with all of these operating differently at each observation scale. Today, the question is no longer whether particular biodiversity patterns occur, but why they occur and whether they are consistent across scales and organisms under study. In this study we combined the results of 2 classical ecological patterns, namely diversity-biomass relationships and species co-occurrences, into a common framework. Fish sampling was carried out in the coastal Terminos Lagoon (southern Gulf of Mexico) during 2 periods (1980-1981 and 1998-1999) using 408 tows. A total of 22 834 individuals representing 106 fish species were collected. Our study revealed that both diversity-biomass relationships and species co-occurrences show inconsistent patterns across years, seasons and zones. However, taken together, our results show that C-score values, which measure spatiotemporal segregation among species, were closely related to the shape of observed richness-biomass relationships. When fish assemblages showed positive C-score values (species segregation), the relationship between species richness and fish biomass was either humpshaped or non-significant. Conversely, negative C-score values (species aggregation) were associated with an increase in fish species richness along the total biomass gradient. Our results support the idea that species segregation due to competition or spatiotemporal partitioning can be an important determinant of biodiversity patterns in species-rich tropical fish assemblages, but only during some periods and for some spatial strata.
Environmental Biology of Fishes, 2015
Understanding the distribution patterns of reef fish and the relationships between those patterns and habitat and anthropogenic factors is important for the development of conservation policies by environmental managers. Fish assemblage structure was studied over 22 rocky shores with different physical complexity and benthic cover in Ilha Grande Bay, Southeastern Brazil. We aimed to test the relative influences on rocky reef fish assemblage descriptors (richness, density and biomass) of three categories of predictors: 1) biological features as dominant benthic cover (in percentage), i.e., fleshy algae, turf algae and soft coral; 2) physical factors, i.e., depth and a physical structure index; and 3) anthropogenic factors, i.e., distance from the coast, population of the nearest city, and influence of a marine protection area. The main explanatory variables determining fish assemblage structure according to the distance based linear model (DistTLM) were depth (explaining 16.7 % of the variation) and distance from the coast (14.0 %), followed by population of the nearest city (3.7 %) and turf algae (2.9 %). Similarly, fish species richness was positively associated with deeper areas and greater distance from the coast, thus being less accessible to human influence. Fish density and biomass increased with distance from the coast, and this relationship is likely linked to the presence of large top predators and herbivores. Moreover, fish richness and density increased with the physical complexity indicated by the physical structure index, suggesting that the presence of a variety of refuges enhances the availability of shelter. We recommend that areas farthest from the urban centres and with higher physical complexity should be prioritised in conservation policies.
ICES Journal of Marine Science, 2013
This study made use of distribution and abundance data of demersal fish and cephalopod species targeted during trawl surveys off Angola, Namibia and the west coast of South Africa, to determine species richness patterns including the location of diversity hotspots in the Benguela Current Large Marine Ecosystem. The reliability of alternative techniques for determining species richness patterns over the study domain, including geostatistical and non-geostatistical interpolation methods and regression type modelling, was tested using a cross-validation method. Generalized additive models were found to be the most effective method and were used to generate horizontal maps of species richness for different periods in each country. Despite changes in community structure that have been documented during the study period and which may be associated with climatic changes, this study showed the presence of consistently predictable hotspot areas over a 20-30-year study period (depending on country). The relationship between species richness and physical/environmental variables was inconsistent between countries, but generally hotspots of species richness were associated with greater depths and cooler bottom temperatures. Range shifts of species associated, for example, with warming of temperatures could conceivably affect the spatio-temporal persistence of hotspots in the long term.
Estuarine Coastal and Shelf Science, 2007
This study analyzed the factors structuring demersal fish community in a tropical bay in southeastern Brazil. The results were used to quantify the partitioning of ecological variation among the environmental, spatial and temporal components molding the fish community. Three bay zones (inner, middle and outer) were defined according to depth and salinity gradient. Monthly samplings were conducted by bottom trawl tows during daylight hours, between October 1998 and September 1999. In each zone, three replicate samples were taken. Ninety-three fish species from 73 genera and 37 families were recorded in the 108 samples. Two demersal fish assemblages were evidenced, one in the inner and the other in the outer zone. These assemblages were characterized by changes in species composition and relative abundance. Depth, followed by transparency and salinity, influenced spatial pattern of fish assemblages. The largest part of the explained variation occurred as a result of the spatial structure of environmental variables, which means that both species and environmental variables presented similar spatial structure. The spatial effect, not the seasonal, explained the highest part of species variations. The amount of unexplained variation was relatively high (76%), even assuming that part of it is due to nondeterministic fluctuation, which could be due to local effects of unmeasured (biotic and abiotic) controlling variables. Knowing the relative importance of these factors can be of decisive importance when applying casual hypotheses in the framework of some precise ecological theory and should facilitate management, planning, and usage of bay resources.
Journal of Fish Biology, 2016
This study assessed the influence of the seasonal fluctuation of abiotic conditions (wet v. dry season) on the functional diversity (FD) of tropical coastal fish assemblages. Sampling was carried out in three regions of northeast Brazil with contrasting coastlines (influenced by reef, lagoon and estuary). In each region, fishes were sampled from three depth strata (10, 20 and 30 m) and FD was estimated using an index based on key phenotypic and behavioural characteristics. All three regions had higher FD in the wet season at shallower depths, indicating the coexistence of species with low functional redundancy in sites subject to seasonal flushing of fresh water. Deeper sites had lower FD than shallower sites, although this difference was less pronounced for region 3, which is strongly affected by its proximity to the São Francisco estuary. The results broadly support the hypothesis that alterations in abiotic conditions in the wet season allow estuarine-adapted fishes with a different suite of functional traits to invade shallow coastal regions.
Neotropical Ichthyology, 2011
In recent years, many studies investigated how density-dependent factors, such as shortages in microhabitat and food availability influence the structure of reef fish assemblages. Most of what is currently known, however, comes from comparisons of isolated patch reefs and from correlations between fish abundance and one or few microhabitat variables. In addition, most studies were done in the Caribbean and Indo-Pacific regions, whereas the South Atlantic region has been, to date, understudied. The present study evaluated spatial and temporal variations in reef fish abundance and species richness in a continuous rocky reef and adjacent unconsolidated habitats in a Southwestern Atlantic reef, using underwater techniques to assess both fish numbers and microhabitat variables (depth, rugosity, number of crevices and percent cover of live benthic organisms, bare rock, sand, and limestone). Higher species richness was observed at consolidated substratum stations on both sampling periods (May and October), but fish abundance did not show a significant spatial variation. Topographical complexity and percent cover of algae (except coralline algae) were amongst the most important determinants of species richness, and correlations between fish size and refuge crevice size were observed. The non-random patterns of spatial variation in species richness, and to a lesser extent, fish abundance, were related to differences in substratum characteristics and the inherent characteristics of fishes (i.e. habitat preferences) and not to geographical barriers restraining fish movement. This study highlights the importance of concomitantly assessing several microhabitat variables to determine their relative influence in reef fish assemblages.