Abstract:
The pattern of newly-settled Alcyonidium spp. and Flustrellidrahispida larvae onto Fucus serratus fronds was examined from the field and in the laboratory.  Prevailing field conditions had a marked effect on the settlement of both Alcyonidium spp. and F. hispida larvae at Porth Cwyfan but not at the wave-protected sites of Rhoscolyn and Church Island (only F. hispida was sampled at Church Island).  In the laboratory, settlement of Alcyonidiumhirsutum and F. hispida larvae onto F. serratus was affected by water turbulence.  In turbulent water, maximum settlement of larvae of both species was shifted basally relative to the settlement in still water.  Further water agitation, post-settlement, accentuated the differences in settlement density between basal, middle and distal frond dichotomies.

Growth and survival were determined for A. hirsutum and F. hispida transplanted to Porth Cwyfan b and Rhoscolyn for 11 weeks from larvae settled in the laboratory.  A. hirsutum growth and survival did not differ significantly between basal, middle or distal dichotomies at either site.  In contrast, F. hispida survival decreased significantly from basal to distal dichotomies at Porth Cwyfan b whereas at Rhoscolyn the converse was true.  Growth of F. hispida was not significantly different between the frond regions at either site.  However, F. hispida colonies at Rhoscolyn were significantly larger in area after the 11 weeks and possessed more zooids per unit area than colonies at Porth Cwyfan b.

Possible detrimental effects of delaying settlement for 2 and 6 hours in turbulent water (2H & 6H) and 6 hours in still water (6L) were examined in the laboratory for F. hispida larvae.  After 5 weeks, 2H colonies were significantly larger in area than 6H colonies but not 6L colonies.  The relationship between zooid number (feeding or total) and colony area was not significantly different between the three treatments.