THE ROLE OF LARVAL SETTLING BEHAVIOR IN DETERMINATION OF THE SPECIFICHABITAT OF THE HYDROZOAN DYNAMENA-PUMILA (L) - LARVAL SETTLEMENT IN DYNAMENA-PUMILA (L)

Dynamena pumila (L.) lives on the brown alga Laminaria saccharina and Fucus serratus, in areas exposed to waves and currents. An experimenta l study of settling behaviour and metamorphosis of the planulae was co nducted. Reconstruction of larval settlement showed that the colonies of D. pumila developed and fed in high flow environments, due not only to various adaptations of their morphology, but in great extent, due to the specific behaviour of larvae at, and prior to settlement and me tamorphosis. Positive phototaxis by newly liberated planulae of D. pum ila leads to colonization of illuminated zones on fucoid thalli and la minarian stipes and blades, where they metamorphosed in response to mi crobial films covering the algal surface. Crawling planulae of D. pumi la were far more resistant to rapid water flows than the planulae of o ther hydroids, what allows this hydroid to establish its colonies in p laces with strong water movements, where the other species could not d evelop. Temporary exposure to air facilitated attachment and metamorph osis of the planulae, which probably settle and undergo metamorphosis during the periods of low-tidal emersion.