Abstract:
The ability of common epialgal bryozoans to feed at different flow velocities was examined in the laboratory.  At a free-stream velocity of 6-7cm.s-1, colonies of Electra pilosa, Celleporella hyalina, Alcyonidium hirsutum, A. gelatinosum and Flustrellidra hispida were capable of extending their lophophores and feeding.  The low-profile colonies of E. pilosa, C. hyalina and M. membranacea continued to feed unhindered in fast flow up to 23cm.s-1.  In contrast, lophophores of Alcyonidium spp. and F. hispida were pushed over in the direction of the flow; the proportion of lophophores which were pushed over in fast flow was inversely related to colony size.  Sudden changes in flow resulted in the retraction of lophophores by the 6 species examined.  Re-eversion of lophophores following sudden increases in flow was most rapid in F. hispida.

F. hispida colonies exhibited a degree of acclimation to increasing free-stream velocity which had to be accounted for in subsequent experiments.  The effect of spine development in F. hispida on lophophore bending was investigated.  Spinose Rhoscolyn colonies were less susceptible to lophophore bending than Church Island or laboratory-reared colonies which had fewer spines.

The extension of lophophores by F. hispida and A. hirsutum ancestrulae held in three different free-stream velocities was examined.  For ancestrulae of both species, the ability to extend their lophophores was affected by settlement position and free-stream velocity.  Ancestrulae on glass slides were affected less by position than ancestrulae on different Fucus serratus frond micro-habitats.  The extension of lophophores was reduced for ancestrulae on the upstream quartile of glass slides and on the frond and midrib micro-habitats of F. serratus fronds.
 

Flowtank