Antifouling effects of epithallial shedding in three crustose coralline algae (Rhodophyta, Coralinales) on a coral reef

Crustose coralline algae cover a substantial fraction of surfaces on the shallow parts of coral reefs. The shedding of surface layers of cells by three common species was studied using light and electron microscopy. All three species examined shed epithallial cells in one of two ways: synchronous epithallial shedding involving the simultaneous shedding of a sheet of cells across a large area of the thallus surface (Sporolithon ptychoides and Neogoniolithon fosliei), or nonsynchronous epithallial shedding which occurs when epithallial cells degenerate individually (Hydrolithon onkodes). Experiments were done to determine whether these types of epithallial shedding could produce an anti-fouling effect. Recruitment onto the surfaces of live and bleach-killed coralline fragments was compared for two synchronous and one non-synchronous shedding species. In all cases, the killed corallines became overgrown within a few weeks. Live corallines remained largely free of other organisms for the duration of the experiment. The results thus demonstrate that both types of epithallial shedding can influence recruitment in the reef ecosystem.