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

Variation in rates and patterns of hydroid larval settlement and spatial as sociations were analyzed through continuous observations of short term (1 a nd 2 mo) experimental panels immersed in the sea over a period of 1 yr. Bas ed on species composition and abundance of hydroid settlers, two distinct a ssemblages were recognized one on panels immersed during colder months of t he year and the other on those immersed during wanner months. Regarding sea sonality, we differentiated three categories of settling patterns; first, s pecies which settled in restricted times of the year; secondly, species whi ch had year-round settlement and little seasonality; and thirdly, species w hich displayed irregular or erratic peaks of settlement. The 10 most common species, with high rates of panel occupation, also had high rates of stolo nal growth and short life cycles, as expected in opportunistic shallow-wate r hydroids. A majority of species investigated showed a pattern of conspeci fic aggregated dispersion that could be explained either by the shared larv al response to a particular habitat or by passively deposition of larvae by a specific flow regime.