CONNELLY,, P.W.*; TURNER,, R.L.; Florida Institute of Technology, Melbourne: Analysis of High Intertidal Algal Communities: Comparisons between Living and Non-Living Substrata

Living and non-living substrata differ in their chemical cues and the microhabitats that they present to settling organisms. These differences allow for variations in physical and biological conditions experienced at the surfaces of both substrata. Microhabitats are especially known to alter conditions such as wave exposure, heat, and desiccation pressure. The diversity of algal communities might, therefore, differ between living and non-living substrata. The eastern surf chiton, Ceratozona squalida, has a diverse algal community growing on its dorsal surface. It lives in the supralittoral, often near patches of the rhodophyte Polysiphonia howei. We tested the hypothesis that algal and invertebrate communities on C. squalida are different from communities living on adjacent rocks. For each chiton collected (n = 15), an adjacent patch of algae was scraped off coquina rock at Stuart on the eastern coast of Florida. Chitons and algae were collected from vertical or near-vertical, fully exposed surfaces (no pits or crevices). Samples were separated, identified to the lowest possible taxon, and quantified as dry mass. Invertebrate taxa were included in the analysis as absolute abundance. The data indicate that the epilithic algae are less diverse and are dominated by P. howei. Conversely, the chiton (epibiotic) community has a greater diversity and contains P. howei with relatively equal amounts of the red alga Gelidiella setacea or the brown alga Acinetospora crinita. There appears to be no difference in invertebrate taxa. Differences in the algal community might be due to differences in microhabitat or chemical cue provided by the chiton. This study was supported in part by a grant to P.W.C. from the Astronaut Trail Shell Club.