Abstract Spatial distribution patterns (both horizontal and vertical) of meiofauna, with special focus on nematodes, on a tropical macrotidal beach across different climatic periods were analyzed in this study. Samplings were carried out at five stations in the intertidal zone in June (rainy season) and December (dry season), 2011. At each station, three samples were taken using a corer with 3cm diameter, which was thrust 10cm into the substrate and stratified in 0-2, 2-5, and 5-10cm. Meiofauna was comprised of 16 groups and Nematoda was the dominant. Meiofauna density during rainy season was higher at the central intertidal station and during dry season it was lower near the high tide mark, followed by an increasing trend towards the low tide mark. Meiofauna was more concentrated in the upper sediment layer during rainy season. However, during dry season, the highest density occurred in the lower sediment layer at both stations near the high tide mark. Nematoda association was comprised of 72 genera, with Daptonema and Theristus (both from the family Xyalidae) as the dominant ones in most stations and strata. The genera richness and diversity increased towards the low tide mark, with lower richness in the upper stratum at most stations. Non-selective deposit-feeders predominated during rainy season, while at dry season there was an alternation of dominance between non-selective deposit-feeders and epistrate feeders. Significant differences were found in the meiofauna community, as well as in the Nematoda association in regard to the months, stations, and sediment layers. The distribution patterns of interstitial organisms found in this study, in part, follow what is already known for microtidal beaches but other differential aspects were observed even if compared to environments of macrotidal beaches in temperate regions.

Resumo A carcinocultura reduz a demanda de estoques pesqueiros naturais e evita o dano ambiental resultante da pesca. Entretanto, tem o potencial de afetar a qualidade da água quando não manejada apropriadamente. Nesse trabalho, os impactos de uma fazenda de carcinocultura foram avaliados em um estuário amazônico focando nas mudanças de composição taxonômica, riqueza, densidade e diversidade de Nematoda. A amostragem ocorreu em agosto de 2004 (período seco) e janeiro de 2005 (período chuvoso) a montante e jusante em locais situados a diferentes distâncias do principal local de descarga de efluentes da fazenda. Trinta e oito gêneros foram encontrados, com dominância de Terschellingia na estação seca e Terschellingia, Daptonema, Ptycholaimellus e Gomphionema na estação chuvosa. As abundâncias foram similares às encontradas em outros estuários e, juntamente com a riqueza e diversidade, apresentaram um forte padrão sazonal com valores significativamente maiores na estação chuvosa. Nas estações de coleta não foram encontrados padrões claros de mudanças. O estuário de Curuçá mostrou alguns sinais de enriquecimento orgânico ainda não intensos, provavelmente devido à forte hidrodinâmica local e à idade da fazenda, que recentemente começou suas atividades. Recomenda-se que no futuro os trabalhos sobre impactos de cultivo, além dos parâmetros físico-químicos da água e sedimento ou refinamento taxonômico dos organismos estudados, considerem também outros fatores, tais como tempo de estabelecimento do cultivo, área ocupada pelos tanques e sua taxa de produção. Além disso, os dados apontam que a nematofauna pode ser uma ferramenta útil na avaliação de impactos da aquicultura devido sua fácil coleta e por serem organismos na base da cadeia alimentar marinha.

Abstract Shrimp farming reduces demand on wild fishery stocks and avoids environmental damage resulting from fishing practices, however, it has the potential to affect the water quality if not properly managed. In this study the impacts of a shrimp farm in an Amazonian estuary were evaluated, focusing on changes in nematodes regarding taxonomic composition, richness, density and diversity. Sampling was conducted in August 2004 (dry season) and January 2005 (rainy season) in the river at stations situated upstream and downstream at different distances from the main source of farm effluent discharge. Thirty-eight genera were recorded with Terschellingia dominating in the dry season and Terschellingia, Daptonema, Ptycholaimellus and Gomphionema in the rainy season. Abundances were within the range recorded in other estuaries and together with genera richness and diversity showed a strong temporal pattern with significantly higher values in the rainy season. No clear patterns of changes were observed at the stations. Some signs of organic enrichment were detected but they were not yet intense, probably a consequence of the strong local hydrodynamics and the age of the shrimp farm, which was just starting its operation. We recommend that in future studies on farming impacts a combination of factors, beyond the physical and chemical parameters of the water and sediments or taxonomic refinement, should be taken into account - such as the duration of the operation of the farm, the area occupied by ponds and the farm's production. Furthermore, we also believe that nematodes are a useful tool for evaluating aquaculture impacts due to the ease of sampling and because they are organisms at the base of marine food chain.

O presente estudo descreve a associação de nematódeos da Baía de Tamandaré (Brasil), praia arenosa tropical típica, durante as marés (baixa, enchente, alta e vazante) de dois ciclos de maré consecutivos, em quatro meses diferentes do ano (Maio, Julho, Setembro e Novembro). A associação de nematódeos foi dominada por Metachromadora e Perepsilonema e variou significativamente entre meses e marés. Densidades foram mais baixas em julho e as mudanças na associação ocorreram durante meses de transição entre chuvoso e seco mostrando a influência do ciclo de chuvas. No ciclo de maré a enchente e vazante pareceram exercer a maior influência, embora os padrões não fossem muito claros. Recomenda-se que os estudos devam ser feitos ao nível de gêneros/espécies para melhor compreensão dos padrões das associações de nematódeos durante ciclos de marés.

The present study describes the nematode assemblage of the bay of Tamandaré (Brazil), a tropical sandy beach, during the low, flood, high and ebb tides of two consecutive tidal cycles in four different months of the year (May, July, September and November). The nematode assemblage was dominated by Metachromadora and Perepsilonema and varied significantly between months and tides. Densities were lower in July, and changes in assemblage structure occurred during the transitional periods between rainy and dry months, which showed the influence of rainfall. Flood and ebb tides appeared to exercise the greatest influences over the tidal cycle, although the patterns were not very clear. Identification at genera/species level is recommended for future studies, to better understand the patterns of nematode assemblages during tidal cycles.

A estrutura populacional (machos, fêmeas e juvenis) e densidade de Mesacanthion hirsutum Gerlach foram estudadas durante as marés (baixa, enchente, alta e vazante) de dois ciclos de maré consecutivos, em quatro meses diferentes do ano (Maio, Julho, Setembro e Novembro). As variações de densidade de Mesacanthion hirsutum mostraram associação com o ciclo de chuvas, com densidades mais baixas durante Julho e Setembro e significativamente maiores em Maio e Novembro. A estrutura populacional constituiu-se em sua maior parte por juvenis indicando uma reprodução continua durante todo o período de estudo. Não foram encontradas diferenças significativas entre os períodos claros e escuros do dia, contudo maiores densidades foram detectadas durante as marés altas e vazantes demonstrando que a espécie pode estar se dispersando através da coluna d'água e/ou migrando dentro do sedimento.

The population structure (males, females and juveniles) and density of Mesacanthion hirsutum Gerlach were studied during the tides (low, flood, high and ebb) of two consecutive tidal cycles in four different months of the year (May, July, September and November). Mesacanthion hirsutum density variations showed association with the rainfall cycle, with lower densities during July and September and significantly higher values in May and November. The population structure was constituted mostly by juveniles indicating a continuous reproduction during all the studied period. There were no significant differences between light and dark periods of the day, however, the higher densities detected during the high and ebb tidal stages demonstrate that this species could be dispersing through the water column and/or migrating within the sediment.