Biodiversidade do meiobentos com ênfase na diversidade taxonômica e funcional da nematofauna estuarina tropical (~7ºS, Brasil)

Abstract

Meiofauna are microscopic organisms (44-500 µm in diameter) that are interstitial and/or burrowing, with a short life cycle and are closely associated with sediment composition. These are some of the characteristics that define these organisms as a good tool for assessing the environmental quality status (EcoQ) of aquatic ecosystems. Nematodes are the most abundant taxon and have the greatest taxonomic and functional diversity among the animals of the meiofauna of unconsolidated bottoms. From an ecological and environmental monitoring point of view, these organisms are considered a particularly interesting group for detecting ecological trends or natural and/or anthropogenic disturbances. Our study investigated the spatial distribution of meiofauna, with emphasis on the structuring of the metacommunity and the taxonomic and functional diversity of nematodes in unconsolidated sediments of two tropical estuaries in Northeastern Brazil: Mamanguape River (less impacted) and Paraíba River (impacted). Eight stations were defined in each estuary, with three replicate samples collected per station, ~1 meter apart (total of 48 samples). The objectives of this work were: 1) to describe the spatial distribution of meiofauna and test the hypothesis that the Ecological Quality Status (EcoQ) is dependent on human pressure (chapter 1); 2) to describe the generic diversity of free-living nematodes in two tropical estuaries, to test whether i) the metacommunity is structured by taxon selection or ii) by the mass effect in estuarine gradients (chapter 2); and 3) to understand the distribution of nematofauna functional diversity in two tropical estuaries and evaluate whether this approach has greater power in detecting axes of environmental variation (chapter 3). The biological characteristics of 1487 animals (67 genera) were analyzed separately and also combined to identify environmental patterns in community composition along estuarine gradients. We used 26 categories of 6 biological traits that represent important ecosystem functions. These traits are related to animal morphotype, tail shape, cuticle type, amphid shape, life history, and trophic structure. Our results in Chapter 1 indicated that there are similar and even lower EcoQ values in the more pristine estuary (Mamanguape River); inconsistencies were greater in the sandy mud regions, suggesting that EcoQ, as currently used, is more dependent on the particle size profile than on anthropogenic impact. Thus, we reject the hypothesis that the meiofauna-based EcoQ is a good indicator of anthropogenic impact in tropical estuaries. In Chapter 2, we discuss the high genera diversity (67) recorded in this study, with diversity estimators suggesting that this diversity would be even greater with increasing sampling effort. Beta diversity was particularly high and the results indicate a taxonomic composition structured by 11

the selection of taxa along the granulometric gradient. In Chapter 3, we present data from the comparison between taxonomic and functional approaches of the nematofauna. There was a tendency to form taxonomic and functional groups according to the granulometric profile, particularly in the Paraíba River estuary. In the comparison between the taxonomic and functional approaches, the functional approach revealed a greater degree of explanation, increasing the capacity to detect environmental patterns. We reinforce the importance of meiofauna and tropical estuarine spatial gradients for the detection of axes of environmental variation (in situ) and show how the functional approach to nematofauna can increase the perception of these ecological trends, deepening our understanding of the biodiversityfunction relationship in the ecosystem.