Community Succession In Phototrophic Shell-Degrading Endoliths Attacking Intertidal Mussels

Intertidal mussels are important ecosystem engineers that increase habitat complexity and provide shelter, substratum and food to associated communities. They thus play a key role in the maintenance of local biodiversity. Intertidal mussels are frequently parasitized by endolithic cyanobacteria that erode and significantly weaken their shells. We examined succession of cyanobacterial infestation in the shells of the mussels Perna Perna and Mytilus galloprovincialis on the south coast of South Africa. We examined variations in species composition of the endolithic cyanobacterial community across regions of mussel shells of different ages (variation in space) and by exposing non-infested shells in field experiments for known periods (variation in time). The results on the spatial distribution of endolith species within a shell supported those from the field experiment evaluating temporal succession. Endolithic species that were early colonists of clean shells were similar to those that were found at the distal edge, the new and growing region of the shell. These species were also found near the umbo, the oldest region of the shell, but cyanobacterial communities near the umbo also included species that appeared late in time. Thus, succession when viewed in either time or space involved the accumulation, lathe' than the replacement of species. Species that arrived late in the succession were similar to endolithic species found near the umbo, the oldest region of the shell. Overall, the study shows clear patterns of endolithic cyanobacterial succession within mussel shells.