The Effect of Differential Flow Speeds and Kelp Morphology on Membranipora membranacea Settlement

Abstract

Kelp provides important habitats for a large variety of organisms such as epiphytic bryozoans. The relationship between the bryozoan and their kelp substrate is influenced by biological, chemical, and physical factors. In this study, I explored how flow regimes and kelp morphology influence settlement patterns of the bryozoan Membranipora membranacea. Settlement on two species of kelp, Costaria costata and Alaria marginata, was studied due to their different morphologies: C. costata is heavily corrugated, while A. marginata has a relatively smooth blade. Multiple individuals were placed into a location of high flow and a location of low flow to observe differences in the number of newly settled colonies. To accompany this, both kelp species were placed in a flume tank with dye to visualize flow patterns across the blade. I found that flow speed had no effect on the number of newly settled bryozoans over the experiment duration. There was a higher abundance of newly settled bryozoans on the heavily corrugated kelp blade versus the smooth kelp blade. Flow visualizations revealed increased turbulence along C. costata blades as well as fluid lingering in blade troughs for a period of time and quickly dissipating along ridges. These data suggests that M. membranacea prefer to settle on kelp that increase turbulence along the blade by having corrugations. Troughs provide regions of low turbulence and give planktonic M. membranacea sufficient time to select a location for settlement while ridges could provide regions of elevated food availability.