O’DONNELL, M.J.: Quantification Of Hydrodynamic Microhabitats In The Intertidal Zone Of Wave-Swept Shores.

The intertidal zone of wave swept shores is an area of extreme hydrodynamic forces. Organisms have evolved many strategies for survival in the path of large, breaking waves. One such strategy, which many investigators have explored, is the use of microhabitats in which organisms experience reduced water velocity. Many studies have demonstrated correlations between organismal distributions and structures that have the potential to create microhabitats. However, the actual degree of protection that organisms receive from habitat structure is not well known. Some investigators have used turbulent boundary layer theory to hypothesize the degree of protection, but simple hydrodynamic theories often break down in the region under crashing waves. In this study, I explored the variation in the maximum hydrodynamic forces experienced by objects under breaking waves. I deployed maximum recording dynamometers at close (5-10 centimeter) spacing. Results indicate that there are, indeed, variations at this spacing in the hydrodynamic forces experienced by objects ~5mm in diameter. Interestingly, the actual forces experienced are higher than simple drag theory would predict. This suggests that intertidal organisms on the size scale of several millimeters may be experiencing larger hydrodynamic forces due to breaking waves than previously believed.