Efeitos da Variação Sazonal de um banco de Halodule wrightii Ascherson sobre comunidades bentônicas associadas, na Praia das Goiabeiras, Fortaleza-CE

Abstract

Brazil, specific morphological variation of Halodule wrightii has been rarely reported in the literature, difficulting the comparison among populations of different areas. Studies on associated faunal assemblages are also considered rare regarding plant-animal interactions. Environmental factors can strongly influence the morphology of these plants but there are few studies concerning H. wrightii. The main goal of this study was to observe the behavior of a H. wrightii meadow over a period of time in Goiabeiras Beach, Fortaleza-CE, and its interaction with the associated macrofauna. Monthly samples were collected between April of 2006 and July of 2007. For the seagrass and associated fauna studies, five samples were removed and separated as above and below sediment fractions with a corer of 10 cm diameter buried at a 10 cm depth. One hundred leaves were collected randomly for the biometric study as well as sediment samples for granulometric analysis and organic matter percentage. In addition, water and air temperatures, pH, salinity and dissolved oxygen were measured at the sampling site. Data on monthly averages of rainfall, wind speed, waves and wave period was obtained from other studies. It was observed that the winds – which increased the hydrodynamism during the dry season – caused the invasion of medium sand originated from areas adjacent to the seagrass meadow, removed fine sediments and organic matter in addition to removing the larger and more mature seagrass leaves. As a result, it was during the dry season that the plants had smaller leaves and the biomass decreased, unlike what is often seen in H. wrightii meadows from other areas. The leaves were the seagrass stratum more affected by the abiotic factors, responsible for the seasonality of the area. The wind was the main influence on the variation of spacial and temporal distribution of some representatives of the fauna, increasing the density/dry weight of seagrass and other factors, in both strata. The more frequent, dense and dominant animal species found in association with the seagrass, in both strata, were: capitellid polychaetes, Cumacea, Nemertea and Hyale media amphipod. The presence of epiphytic macroalgae Hypnea musciformis had a secondary role on the increase of macroepifauna. There was a qualitative similarity among the fauna collected in both strata due to the low depth reached in sampling. The main observed result in this study was related to temporal variation, specially because the fauna of both strata changed simultaneously in response to the regional climate change. In conclusion, the factors responsible for the variations in the macrofauna during this study were the modifications of the seagrass, regulated by the wind and its effect on the ecosystem.