Abstract
Freshwater sponges, being sessile animals, heavily depend upon a substrate on which their larvae or their gemmules will settle. It is expected different sponge species to exhibit preferences or adaptations to specific substrates and habitats. Studies targeted to evaluate the role substrates play in the distribution of freshwater sponge communities are rare. Here we evaluate the effect of different substrates and habitats in the distribution of freshwater sponge communities in the igapos of Anavilhanas, the world largest freshwater archipelago. Two surveys aiming to uncover the sponge fauna and corresponding substrates were performed in the Anavilhanas National Park at the low water period, when seasonally flooded surfaces are exposed. Two transects were carried out by boat along the margins of the River Negro and its canals among the islands or inside parts of the yet inundated forest. Also several higher parts of the islands at the time free of the flooding waters were crossed by foot. The sponge crusts were first visually searched for and next sampled, having its GPS taken and its environments and substrates shortly described. The association between the presence of nine sponge species, seven different environments and seven types of substrates detected were used in a Redundancy Analysis (RDA). The first two axes of RDA accounted for 45.9% of variation in the species data. The overall RDA was significant (P = 0.005; Number of permutations = 199). Substrates, especially trunks, branches, leaves and sand, were more important than environments to explain the variability in the distribution of sponge species. Key words: Continental sponges, substrates, shaded habitats, flooding pulses, Brazilian Amazonia.
Highlights
Floodplains stand for about 8% of the Amazonian Biome, there included the Brazilian, Peruvian, Bolivian and Colombian Amazônia (Ferreira et al, 2005)
We explored the association between the presence of sponge species in the different environments and substrates with Redundancy Analysis (RDA), a method of choice for direct gradient analysis in community ecology for short gradients (Legendre and Legendre, 1998)
The Archipelago sponge fauna showed no sign of endemism, the surveyed species being common in the Amazon Basin
Summary
Floodplains stand for about 8% of the Amazonian Biome, there included the Brazilian, Peruvian, Bolivian and Colombian Amazônia (Ferreira et al, 2005). The hard selection pressure exercised by the flooding pulses came out to favor freshwater sponges all along Central Amazonia because of their production of gemmules by which means they overcome the dry periods in várzea as well as in the igapó flooded areas (Volkmer-Ribeiro, 1981, 1999; Batista et al, 2003; Volkmer-Ribeiro and Almeida, 2005). Because of their abundant occurrence in such environments the sponges cannot be disregarded in studies devoted to aquatic biocenosis surveys and community structures
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