RECRUITMENT AND MORTALITY OF ALCYONIDIUM-HIRSUTUM (FLEMING) AND FLUSTRELLIDRA-HISPIDA (FABRICIUS) (BRYOZOA, CTENOSTOMATA) WITHIN A FUCUS-SERRATUS L COMMUNITY

The recruitment and mortality of two common ctenostome bryozoans withi n a Fucus serratus L. community in the Menai Strait, North Wales are d escribed. Larvae of Alcyonidium hirsutum (Fleming) settled between Aug ust and February, whereas those of Flustrellidra hispida (Fabricius) s ettled from April to November; maximum recruitment of these bryozoans occurred during early November and July respectively. Colonisation int ensity of both species varied between sites and between years. At each site variations in recruitment occurred between plants and within ind ividual plants, though concave surfaces of younger more distally locat ed frond segments were generally preferred, particularly by A. hirsutu m. Our data suggest that at settlement the larvae of Alcyonidium may b e capable of detecting the presence of conspecifics and potential comp etitors already present on the plant fronds. Both bryozoans experience d high levels of post-settlement mortality. Less than 1.5 % of the mon itored Alcyonidium colonies survived long enough to bleed successfully and release larvae. Mortality rates were higher on densely colonised fronds but it was generally from these plant regions that colonies sur vived to reproduce. Only a relatively small proportion of the total mo rtality of A. hirsutum (< 30 %) was attributable to frond loss. Habita t selection by A. hirsutum and F. hispida, and the relationship betwee n the life cycles of these two spatially dominant bryozoans and that o f their main host species, F. serratus, are briefly discussed.