Seasonality of competition in early development of subtidal encrusting communities

Settlement panels immersed at Lough Hyne, County Cork, Ireland, at six stat ions with widely different flow regimes were retrieved at monthly intervals . Between 40 and 62 taxa were identified at each station during the study p eriod. Percentage cover, number of interactions and number of recruits were recorded. Space occupied was found to vary more than 2.5 orders of magnitu de between stations and seasons (0.3 - 82 %), Competition for space was mos t intense during summer, when recruitment was highest. More than 3600 inter actions between pairs of species were recorded and competitive matrices are presented for the two stations with the most interactions. Both number of interactions and % cover were significantly higher at sites with greater wa ter Row. The nature and the degree of competition varied between sites, wit h the most intense competition occurring in the very high flow sites with a large proportion of intraspecific encounters. Colonial species were more e vident at the sites with high flow. Certain solitary species (notably Anemi a ephippium and Pomatoceres spp.) were successful competitors in encounters with cheilostomatid bryozoans. Solitary species may prevent space monopoli sation by the faster-growing bryozoans. 'Typical' early successional specie s, notably bryozoans such as Celleporella hyalina and Microporella ciliata, were more abundant at the more disturbed sites, implying either a larger a dult population and/or preferential settlement of these species at such sit es.