Variação temporal da macrofauna bentônica sublitoral da praia da Urca (RJ) após a ocorrência de ressacas, com ênfase na fauna de anelídeos poliquetas

Abstract

Evaluate the role of storms on macrobenthic faunal structure of Urca beach, with special emphasis on polychaete fauna. Urca beach is located at the western point of Guanabara bay, situated at Rio de Janeiro state. Density of the macrofauna was monitored along a year, after the beginning of a great storm at that region in 2th July, 1997, being considered the most strong event at the last thirty years. During the period studied, three more storms were registered, although with a minor intensity. Twenty-eight samples were surveyed with intervals of fifteen days each (except the first three samples, which were with weekly intervals), at an area of 200 m² and 5 m depth. The most representative taxonomic groups found were polychaetes and crustaceans. Evaluating the response of the role community after the storms, it did not show a strong variation, probably due to the different responses of each group separately. Lower densities of polychaetes were registered after the storms. Besides, crustaceans densities were higher after that event. The different response of these groups could be related to the morphologic and behavioral adaptations and life history of each one. The polychaete community structure of Urca beach showed a variation in biological parameters values, such as diversity, richness and evenness after storms. Lower diversity, richness and evenness values after the first storm could be related to a greater instability of the environment, due to wave impact, as could be stated by a dominance of few species. The temporal variation of polychaete species was related to the behavior and biology of each species. The behaviour of the polychaete species P. steenstrupi could be related to the sediment dynamics of the finer sediment fraction, as the sediment and the polychaete were revolved due to the wave action caused by the storms. On the other hand, the tubicolous species Mooreonuphis lineata presented higher wave resistance when compared with other polychaete species due to its higher substrate adherence. This study reveals that hydrodynamical events of great intensity and less predictability tend to change the community structure of macrobenthic fauna of sand beaches.