TRIDIMENSIONAL MATRICES OF MUSSELS PERUMYTILUS-PURPURATUS ON INTERTIDAL PLATFORMS WITH VARYING WAVE-FORCES IN CENTRAL CHILE

Perumytilus purpuratus is the dominant competitor for primary substrat e in the mid-intertidal zone of central Chile's rocky shores. This mus sel is capable of forming dense matrices (beds) that support rich infa unal and epiphytic communities. Three platforms, exposed, semi-exposed , and sheltered, were sampled to determine aspects of the mussel P. pu rpuratus size structure and temporal dynamics. Palumbi's dynamometers were used to measure intertidal wave forces. Mussel samples from the 3 platforms were collected approximately every second month between Apr il 1982 and June 1983. For sampling, mussels were removed sequentially in order to maintain the stratified structure (layers) of the mussel matrices. Populations of P. purpuratus show a bimodal size distributio n when considering their entire size range. Although this bimodality i s consistent through time and space, our results show important differ ences for the size distributions both spatially and temporally. Spatia lly, the differences could arise as a result of varying wave exposures . Adults showed a higher mean size with decreasing exposure. Temporall y, the differences arise due to changes in the number of recruits ente ring the population. Within platforms, the observed differences when c omparing upper and lower mussel layers could arise as a result of diff erential survival and growth rates between them. We also suggest that retention of recruits is higher in lower layers due to increased compl exity of the matrix and reduced water flow. The sampling method develo ped to collect separate mussel layers proved to be crucial for the rec ognition of population dynamics processes occurring within the stratif ied structure of mussel matrices.