Morphological analysis of growth forms of branching marine sessile organisms along environmental gradients

In this paper a series of growth forms of the sponge Haliclona oculata, the hydrozoan Millepora alcicornis and the scleractinian coral Pocillopora dam icornis are morphologically analysed. The growth forms of these species wer e collected along a gradient of the amount of water movement. In this analy sis it is demonstrated that, although these species are from very different taxonomical groups, the degree of compactness of the growth forms shows a similar trend as a response to the exposure to water movement. In all three species the growth forms gradually change from thin-branching to more comp act shapes, as evaluated by measurements of various morphological character istics. Other morphological measurements, in particular the average distanc e between branch tips and neighbouring branches ("branch spacing") show a m ore species-specific pattern. Species in which fusion of branches is almost never observed, as for example P. damicornis, are characterized by a relat ively low standard deviation of branch spacing. Species in which anastomosi s frequently occurs (H. oculata and M. alcicornis) are characterized by a r elatively high standard deviation in branch spacing. The final aim of this research approach is to use the morphological data acquired here in combina tion with morphological simulation models to gain a better understanding of the growth and form of these organisms and the impact of the physical envi ronment (hydrodynamics and availability of light required for photosynthesi s).