Spatial pattern of a fish assemblage in a seasonal tropical wetland: effects of habitat, herbaceous plant biomass, water depth, and distance from species sources

Abstract

The influence of habitat, biomass of herbaceous vegetation, depth and distance from permanent water bodies on the structure of fish assemblages of a seasonal floodplain was evaluated using data collected along 22 transects in an area of 25 km 2 in the floodplain of Cuiabá River, Pantanal, Brazil. Each transect was sampled for fish using throw traps and gillnets during the flood period of 2006. Multivariate multiple regression analysis and multivariate analysis of covariance indicated that depth was the only variable that affected the structure of the fish assemblage, both for quantitative data (abundance) and qualitative data (presence-absence). Species such as Neofundulus parvipinnis and Laetacara dorsigera were more abundant in shallower sites (below 25 cm), while Serrasalmus maculatus and Metynnis mola were found mostly in the deepest areas (over 55 cm). However, species such as Hoplias malabaricus and Hoplerythrinus unitaeniatus occurred at all sampled depths. Although the distribution of most species was restricted to a few sites, there was a positive relationship between species richness and depth of the water body. Surprisingly, the replacement of native vegetation by exotic pasture did not affect the fish assemblage in the area, at the probability level considered.A influência do habitat, biomassa de vegetação herbácea, da profundidade e da distância de corpos d'água permanentes sobre a estrutura da assembleia de peixes da planície sazonalmente inundada foi avaliada com dados coletados em 22 transectos em uma área de 25 km² na planície de inundação do rio Cuiabá, Pantanal. Cada transecto foi amostrado para peixes usando "throw trap" e rede de espera no período de cheia de 2006. Análises de regressão múltipla multivariada e análises de covariância multivariada indicaram que a profundidade foi a única das variáveis consideradas no estudo que afetou a estrutura da assembleia de peixes, tanto para os dados quantitativos (abundância) quanto para os dados qualitativos (presença-ausência). Espécies como Neofundulus parvipinnis e Laetacara dorsigera foram mais abundantes em locais mais rasos (abaixo de 25 cm), enquanto as espécies Serrasalmus maculatus e Metynnis mola foram encontradas principalmente nos locais mais profundos (acima de 55 cm). Entretanto espécies como Hoplias malabaricus e Hoplerythrinus unitaeniatus ocorreram em todas as profundidades amostradas. Apesar de grande parte das espécies apresentarem distribuição restrita a poucos locais, houve uma relação positiva entre a riqueza de espécies e a profundidade do corpo d'água. Surpreendentemente, no nível de probabilidade considerado, a substituição da vegetação nativa por pastagens exóticas não afetou a assembleia de peixes na área estudada.

Spatial distribution of fish assemblages along environmental gradients in the temporary ponds of Northern Pantanal, Brazil

“…Hence, the common occurrence of Hypessobrycon, Serrapinnus, Astyanax and Hoplosternum littorale in this study -also verified by Okada et al (2003) in temporary ponds in the dry season of the upper Paraná river (Brazil) -indicates a widespread adaptation and survival of these groups of species in ephemeral habitats subject to environmental stress. Also, the great abundance and widespread occurrence of Hyphessobrycon elachys and Serrapinnus calliurus shows that the stress caused by the drying process does not limit the successful occupation of these species in temporary ponds, as noted by Fernandes et al (2010a) in the same region and by Cunico et al (2002) in the upper Paraná river (Brazil). Moreover, the richness found in a single sampling represented almost 60% (49 species and 1117 individuals) of the richness registered by Fernandes et al (2010a) for the same region during a one-month collection using two methods (throw trap and gill net), thus emphasising the effectiveness of the sampling method for the study of fish fauna in rapid assessment of floodplain biodiversity.…”

“…Studies on temporary floodplain environments have verified that depth and hydroperiod are the main influential factors on the structure of the assemblages in these environments (Baber et al, 2002;Pazin et al, 2006;Fernandes et al, 2010a). This indicated that the influence of depth on composition is due not only to morphological and behavioural adaptations of the species, but also to the survival probability related to hydroperiod variation.…”

“…From April onwards, water depth decreases, resulting in the loss of spatial connectivity of floodwaters and the formation of permanent/temporary ponds in depressions in the terrain. The temporary ponds of the sampled area are already monitored through projects related to the Long Term Program-PELD (Fantin-Cruz et al, 2008Fernandes et al, 2010aFernandes et al, , 2010b. Ponds are considered temporary when they have a predictable annual dry phase, usually of the order of 3-8 months (Collinson et al, 1995).…”

“…Regarding the organisation and structure of fish assemblages in temporary water bodies in floodplains, the influence of hydroperiod (i.e., the duration time of ponds), depth, connection, and distance between water bodies have been recognised (Baber et al, 2002;Pazin et al, 2006;Fernandes et al, 2010a). These factors describe the increasing isolation of water bodies, which in turn increases fish density and reduces migration (Scarabotti et al, 2011).…”

“…Still, the temporary water bodies or seasonally flooded plains in this region, especially those near the floodplain of Cuiabá river, have been receiving attention only recently. Some notable examples of research on this subject are the pioneering studies on microcrustaceans (Fantin-Cruz et al, 2008), aquatic invertebrates (Santos and Callil, 2010), fish fauna (Fernandes et al, 2010a(Fernandes et al, , 2010b, and seed banks (Pagotto et al, 2011). Several fish species of temporary environments in this region have great importance since they are major food items for wading birds and so they contribute to maintain aquatic and terrestrial food webs.…”