Malacofauna associada ao prado de Halodule wrightii Ascherson em Barra Grande, Piauí

Abstract

The environment composed by Halodule wrightiiat coastal zone is very important for fish and invertebrate communities. Among invertebrates, mollusks are one of themost important groupin sea grass environments. The present study focused on quantitative and qualitative analysis of the mollusk community associated with seagrass patches of Halodule wrightii at Barra Grande (PI) beach, evaluating seasonal and spatial variation on characteristics of the seagrass bank and sediment in an attempt to explain variation on this community. Campaigns every two months were performed from Dec/2013 to Oct/2014 to collect samples of sediment, seagrass and mollusks at three seagrass patches located at intertidal zone. In the laboratory, samples were washed with a 0.05 mm mesh and mollusks specimens were screened and identified. We analyzed vegetal biomass, stems density and sediment properties (i.e. grain size, organic matter, percentage of mud). Despite of some biomass differences being observed, the bank properties showed no significant variation between dry and wet periods. We verified that there was significant variation in seagrass biomass but not in stem density among the patches. Sediment also showed variation between periods, in the grain size, and among patches in all evaluatedproperties. We have found 1476 individuals of gastropods, belonging to 25 species and representing 88.4% of all mollusks found at the seagrass bank. One polyplacophora species was registered too. TheBivalviataxon wasrepresented by189individuals, distributed in 24species, representing 11.3%of the mollusks associated to H. wrightii. The mollusks community studied showed significant variation on abundance, richness and composition between both, periods of the study and patches sampled. The results indicates that bivalve assemblage seems to respond more closely than gastropods to variation in seagrass bank parameters,such as vegetation biomass and stem density, mostly because of modifications caused by the bank on sediment properties. On the other hand, gastropods are more sensible to seasonal variations, like precipitation rate or intertidal dryness. Lastly, the seagrass bank composed by Halodule wrightii at Barra Grande showed to be one of most dense banks of Brazil and to have great importance to the associated mollusk fauna justifying the implementation offuther studies and inclusion of these ecosystems on the management plan of APA Delta do Parnaíba for better conservation of Piauí’s shore biodiversity.