VARIAÇÃO ESPAÇO-TEMPORAL DA MACROFAUNA BENTÔNICA NA PRAIA DO CASSINO, EXTREMO SUL DO BRASIL
The zonation (vertical distribution), longshore distribution as well as the temporal variability of the macroinfauna on Cassino beach, Rio Grande do Sul, Brazil, were studied during one year (from June 2004 to May 2005) on a monthly basis sampling. For that, 3 sites were chosen 50 m apart from each other. On each site 3 transects, 2 m apart from each other were anchored. Each transect extended from the base of the primary dunes to approximately 1 m depth into the infralittoral. The distances to the sampling levels in each transect were 20 m to the upper limit of the swash zone, from which the distances were of 10 m. The zonation pattern was variable over the year, and this variability was mainly due to the large instability of the lower levels of the beach, which includes the lower intertidal and the inner surf zone. This was highlighted seasonally, with the formation of different faunal groups in according to the peculiarity of each season. These clustering were strongly influenced by fluctuations in the macrobenthos densities, caused mainly by recruitments and superimposing organism distribution due to the water level elevation during storms. Longshore variation of the macroinfauna community was not highlighted in a 50 m to 100 m range, probably because the absence of streams in the studied area. In a hundred or kilometer scale, macroinfauna longshore variation would be expected, as a consequence of the wave regime, characteristics of the sediment and beach morphology. The temporal variation of the macroinfauna abundance can be attributed to positive effects such as recruitment peaks and migration of certain species to the swash zone and to negative effects like the migration of some species into the deeper waters, mortality for natural causes (stranding and predator action) and human disturbance (harvesting and vehicles traffic). Among these, we consider recruitment as the main factor causing expressive temporal increasing of the macroinfauna abundance, while stranding (the imprisonment of the organisms on the upper parts of the beach) is probably the main factor responsible for the abrupt drops in the abundance of the benthic macroinfauna.
Advisor:César Vieira Cordazzo; Paulo Ricardo Pezzuto; José Guilherme Bersano Filho; Carlos Emílio Bemvenuti
School:Fundação Universidade Federal do Rio Grande
Source Type:Master's Thesis
Date of Publication:04/10/2006