Dinâmica populacional de Ostrea puelchana d Orbigny, 1841 e sua interação com gastrópode Cerithium atratum (Born, 1778) em um banco de gramas marinhas na Ilha do Japonês, Cabo Frio RJ

Abstract

The flat oyster Ostrea puelchana is distributed from southeastern Brazil to northern Patagonia, in Argentina, living on rocky bottoms and mussel bed. Seagrass beds usually grow in sandy or muddy sediments, although planktonic larvae of sessile invertebrates need a hard substratum to settle and grow on, thereby hard substrates available can be a limiting factor for such organisms in soft-bottom habitats. In spite of that, O. puelchana has high density and frequency in the seagrass beds in Ilha do Japonês, because it uses the gastropod Cerithium atratum s shells as a hard substrate for its attachment and growth, causing a positive, negative or no effect on this gastropod. In this context, the purpose of the current study was to investigate the population dynamics of O. puelchana and its effects on the development of the gastropod C. atratum. The study area chosen was Ilha do Japonês, city of Cabo Frio, State of Rio de Janeiro, on the tropical southeastern coast of Brazil (22° 52.925S, 42° 00.200W). Three transects of 50 m length each one were established, parallelly to the coast of Ilha do Japonês, with different degrees of exposure to the air: TA (ever exposed), TB (frequently exposed); TC (never exposed). Randomly, 10 samples per transect were collected with PVC corer (455 cm3), monthly, during a year. In each sample, O. puelchana individuals were counted and measured, and it was checked in which substrates they were found. O. puelchana individuals were fixed with epoxy on plates of 56,2 cm2 monthly, aiming to obtain the monthly growth rate of the species. Monthly, plates with the same area were installed in three points of each transect (points 00, 25 and 50m) to obtain data about juveniles recruitment. Several substrates, natural and artificial, were installed in three different points of the study area to determine preferences for certain substrates. With the objective to evaluate the influence of epibiotic oyster on the gastropod, we selected living O. puelchana individuals and empty shells of distinct sizes on C. atratum shells to the experiment of interaction between the species, using the method of tether and method of the "flag". In general, the results of the currently study indicated a population with a slow growth rate, with younger individuals tending to a faster growth. O. puelchana population presented high density with a predominance of young individuals structuring the population, which had been recruited during the year, but with a tendency to a temporal distribution. The larvae showed a preference for certain substrates, such as the live oysters of its own species and C. atratum. Regarding the interaction of O. puelchana and C. atratum, the work evidenced that the oyster epibiosis has directly influence in the development of gastropod in the study area.