Diversity, species composition and assemblage dynamics of Estuarine gelatinous and semi-gelatinous zooplankton from Brazil

Abstract

The literature on gelatinous (Cnidaria, Ctenophora, Tunicata) and semi-gelatinous (Chaetognatha) zooplankton from 32 Brazilian estuaries is reviewed. Altogether 104 species have been recorded, 70 cnidarians, 2 ctenophores, 14 chaetognaths, 13 appendicularians and 5 thaliaceans. All groups are understudied with only few detailed data available. Most of these gelatinous and semi-gelatinous taxa are typically oceanic, and thus the low diversity in estuarine systems was expected and is not probable to increase much with increasing sampling effort. Contrary, the meroplanktonic hydromedusae from the orders Anthoathecata and Leptothecata are diversified in estuarine ecosystems and the respectively 29 and 19 species currently reported from Brazilian estuaries are an underestimation and certainly will increase considerably with increased sampling effort. The best-studied taxa are the chaetognaths, followed by appendicularians, and very little is known about the other taxa, particularly concerning ctenophores and thaliaceans. We summarize the main tendencies of each taxon regarding diversity, abundance, temporal and spatial variations, species composition, and the most abundant species. In addition, we also provide general guidelines for future research on gelatinous and semigelatinous zooplankton taxa from Brazilian estuaries.