Seasonal recruitment of hydroids (Cnidaria) on experimental panels in the São Sebastião Channel, southeastern Brazil

Variation in rates and patterns of hydroid larval settlement and spatial associations were analyzed through continuous observations of short term (1 and 2 mo) experimental panels immersed in the sea over a period of 1 yr. Based on species composition and abundance of hydroid settlers, two distinct assemblages were recognized, one on panels immersed during colder months of the year and the other on those immersed during warmer months. Regarding seasonality, we differentiated three categories of settling patterns; first, species which settled in restricted times of the year; secondly, species which had year-round settlement and little seasonality; and thirdly, species which displayed irregular or erratic peaks of settlement. The 10 most common species, with high rates of panel occupation, also had high rates of stolonal growth and short life cycles, as expected in opportunistic shallow-water hydroids. A majority of species investigated showed a pattern of conspecific aggregated dispersion that could be explained either by the shared larval response to a particular habitat or by passively deposition of larvae by a specific flow regime.