Title: The growth and morphology of a marine sponge, Raspailia inaequalis.

Edward Abraham

National Institute of Water and Atmospheric Research
P.O. Box 14-901, Kilbirnie, Wellington, New Zealand
Tel: +64 (4) 386 0329
Fax: +64 (4) 386 2153

Abstract: The Kaandorp model of the radiative-accretive growth of marine inverterbrates neatly demonstrated how organisms such as sponges can use the flow to organise their growth. There have, however, been few studies comparing the growth of sponges with the growth-rules assumed in the model. This talk presents the preliminary results of a detailed study of the growth of a branching finger sponge, Raspailia inaequalis. This species grows as a planar fan, oriented perpindicular to the prevailing current. A number of specimens were photographed several times over a year, giving good data on the growth of the finger-tips, and some specimens were harvested from a neighbouring site for a morphometric analysis. The measurements suggest that the growth-rate of the tips is not strongly dependent on their position relative to the substrate or relative to the rest of the sponge. This conclusion is supported by comparing the results of a Horton analysis of the sponges morphology with forms generated by a simple model of a self-avoiding branching process. Other factors, not included in the original Kaandorp model, such as the loss of branches through mechanical damage and disease are also found to be important in structuring the growth pattern.