Suspension feeding adaptations to extreme flow environments in a marine bryozoan

We describe the effects of extreme flow on the growth and morphology of a b ryozoan, Membranipora membranacea, encrusting laminarian fronds in the Rapi ds of Laugh Hyne (= Ine), County Cork, Ireland. An ultrasonic current meter was used to characterize ambient flow regimes at the level of the algal ca nopy over a complete tidal cycle at three sites within the Rapids. Colonies collected from sites exposed to different flows showed a trend towards min iaturization with increased flow: the zooids were less elongate, the lophop hores were smaller in diameter and had fewer tentacles, and the distances b etween excurrent jets were shorter. These morphological changes probably pl ace feeding surfaces into slower flow regimes of the boundary layer. Simila r growth rates of colonies at sites differing in flow provide evidence that this miniaturization is adaptive and that bryozoans are capable of adoptin g appropriate morphological responses to varying environmental regimes. Suc h plasticity should be considered when assessing feeding from different flo w regimes because particular colonies may be adapted to a limited and speci fic range of flow conditions.