Composição da meiofauna e nematofauna associada à macrófita aninga (Montrichardia linifera) em um estuário amazônico

Abstract

Amazonian estuaries are extremely productive and complex environments with great diversity of organisms and vegetation consisting on herbaceous macrophytes such as Aninga (Montrichardia linifera), a pioneer species with great importance in margin protection and sediment input. The benthic meiofauna are one of the most abundant groups in the world and possesses Nematodes as a very versatile representative, due to it’s place all over the trophic guild and representes over than 90% total abundance in estuarine ecossitems. This study represents the first evaluation of meiofauna composition associated to floodplain vegetation and aimed to describe space-temporal patterns of meiofauna and nematofauna comunity associated to Aningas in the Guajará estuary. In field, monthly samples were collected in environments with and without vegetation within 12 months, which were divided into 4 climatic periods (Trasition 1: rainy-dry, Dry, Transition 2: dry-rainy, Rainy) at Guajará estuary. A cylindrical sampler with a diameter of 3 cm and a length of 10 cm was used to take the biological samples, which were then fixed in 4% formaldehyde. Also were collected sediment samples for granulometric analyses and organic matter and sampled the number of aningas and height of 15 random individuals. For each sample, density and richness of meiofauna groups’s and Nematoda genera were calculated. Univariate analyses (ANOVA 2-WAY) and multivariate analyses (PERMANOVA, PCoA, Simper and BIO-ENV). In general, the environments showed a similar granulometric composition between the periods, consisting mainly of fine sediments (silt + clay). The M. linifera macrophyte showed greater heights during T1 period and greater densities during the rainfall season. Meiofauna was represented by 12 taxonomic groups, which Nematoda was the most abundant in both environments along all periods and presenting frequency of occurrence (FO) equal to 100%. As for the other groups, 1 group was classified as accessory group (FO<50%), 4 groups were classified as sporadic group (FO<25%) and 5 groups were classified as rare (FO<12,5%). Density showed the highest values during T1 with high pluviosity while richness showed the highest values during dry and T2 periods. 89 genera of Nematoda belonging to 39 families were identified. The most abundant and richest Family was Xyalidae, with the genus Zygonemella accounting for more than 23% of total density. Anonchus and Zygonemella were the most spatially widespread genera, occurring in both environments during all climatic periods. The Nematode assemblage was mostly composed of detritivores (40 genera). Both meiofauna and nematofauna were influenced by seasonality of rainfall and the amount of nutrients available in the sediment. Besides, the vegetation presence was a determinant factor in sediment stabilization and structural habitats, providing refuge and nutrients for various groups of meiofauna as well as many genera of Nematoda.