Spatial distribution of bivalves in relation to environmental conditions (middle Danube catchment, Hungary)

The spatial distribution of bivalves in relation to environmental conditions was studied along a second- and third order stream – medium-sized river (River Ipoly) – large river (River Danube) continuum in the Hungarian Danube River system. Quantitative samples were collected four times in 2007 and a total of 1662 specimens, belonging to 22 bivalve species were identified. Among these species, two are endangered (Pseudanodonta complanata, Unio crassus) and five are invasive (Dreissena polymorpha, D. rostriformis bugensis, Corbicula fluminea, C. fluminalis, Anodonta woodiana) in Hungary. The higher density presented by Pisidium subtruncatum, P. supinum, P. henslowanum and C. fluminea suggests that these species may have a key role in this ecosystem. Three different faunal groups were distinguished but no significant temporal change was detected. The lowest density and diversity with two species (P. casertanum and P. personatum) occurred in streams. The highest density and diversity was found in the River Ipoly, in the side arms of the Danube and in the main arm of the Danube with sand and silt substrate, being dominated by P. subtruncatum and P. henslowanum. Moderate density and species richness were observed in the main arm of the Danube with pebble and stone substrate, being dominated by C. fluminea and S. rivicola. Ten environmental variables were found to have significant influence on the distribution of bivalves, the strongest explanatory factors being substrate types, current velocity and sedimentological characteristics.The project was financially supported by the Hungarian Scientific Research Fund under the contract No. OTKA T/046180. Special thanks to the DanubeIpoly National Park for the help in field work.info:eu-repo/semantics/publishedVersio

Ecological analogies between estuarine bottom trawl fish assemblages from Patos Lagoon, Rio Grande do Sul, Brazil and York River, Virginia, USA

The structure of estuarine fish assemblages at temperate latitudes in Patos Lagoon (32°05’S, 52°04’W), Rio Grande do Sul, Brazil and York River (37°17’N, 76°33’W), Virginia, USA was compared using mid and late 1970’s data from bottom trawl collection to investigate whether geographically isolated fish assemblages have similar ecological structure given similar latitudinal positions on the warm-temperate southwestern and northwestern Atlantic regions, respectively. Since estuarine species often exhibit an ontogenetic shift in habitat requirements or preferences we examined Capture per Unity of Effort by size class (CPUE-SC) and split species into “size ecological taxa” (SET) for analysis. The use of CPUE-SC also allowed the abundance of a SET to be computed by summing the mean CPUE of each size class within that SET and use this information to follows SET’s temporal and or spatial abundance. A total of 65 and 63 species was collected during a year of bottom trawling in the Patos Lagoon and York River estuaries, respectively. In both localities the strongest modal size class was < 80 mm TL, and several abundant species were smaller than 100 mm TL. The size between 80 and 100 TL effectively separated several species into discrete SET’s in both systems. Those SET’s could have different ecological preferences, temporal and spatial distributions and so identified as different "ecological taxa". In warm months, when predation by large fish is most likely, the abundance of fish between 80 and 100 mm TL in "bottom trawl" demersal fish assemblages was low in both systems. Only the sea catfishes, in Patos Lagoon, protected by strong dorsal and pectoral spines, and the Hogchoker, in the York River, protected by burrowing in the bottom substrate, peak in abundance at this size class. The seasonal pattern of estuarine use was similar between localities and did not differ from other warm-temperate estuarine fish assemblages.A estrutura das assembléias de peixes de dois estuários temperados – Lagoa dos Patos, Brasil e York River, Estados Unidos – foi comparada usando dados de rede de arrasto de fundo, da década de 70, em ambas as regiões. O objetivo do trabalho foi o de investigar se a fauna de peixes de dois estuários, localizados em duas regiões temperadas-quente do Atlântico, embora isolados geograficamente (Hemisfério Sul e Norte), apresentavam a mesma estrutura ecológica. Considerando a ontogenia das espécies utilizou-se o método da Captura por Unidade de Esforço por Classe de Tamanho (CPUE-CT) para separar as espécies dominantes em Unidades Ecológicas de Tamanho (UET). O uso da técnica do CPUE-CT permite que a abundância das UET seja computada através da soma da abundância de cada uma das classes de tamanho que incorporam estas UET e desta forma usar o CPUE das UET para estudar sua variação temporal ou espacial de abundância. Após um ano de coleta mensal foram observadas 65 espécies nas coletas de arrasto de fundo na Laguna dos Patos e 63 espécies no York River. Em ambas as localidades as maiores modas de tamanho foram menores que 80 mm de comprimento total (CT), e diversas espécies ocorrem em tamanho menor do que 100 mm CT. Entre 80 e 100 mm CT foi possível separar efetivamente diversas espécies em UET. Diferentes UET de uma mesma espécie ocorrem em diferentes habitats e em épocas distintas, podendo assim ser classificadas como “Taxas Ecológicos” distintos de uma mesma espécie. Nos meses quentes, quando ocorre a maior pressão de predação dos grandes peixes piscívoros, a abundância dos peixes com tamanhos entre 80 e 100 mm CT nas coletas de arrasto de fundo é baixa em ambos os sistemas. Somente dois grupos de peixes são abundantes neste tamanho, os bagres marinhos da Laguna dos Patos que estão protegidos da predação pelos espinhos dorsais e peitorais, e o linguado-Zebra no York River, que se enterra no substrato evitando a predação