Effect of exposure on rocky shore zonation patterns in the Maltese Islands

Abstract

Previous work on Maltese rocky shore ecology has shown that, in the virtual absence of tides, the major physical factor affecting the zonation of organisms on rocky shores is wave exposure. A transect survey of gently sloping rocky shores having different exposure levels was conducted in order to quantify the effect of varying wave action on the distribution of rocky shore organisms on Maltese shores. The general zonation patterns were found to be similar to those of other shores in the central Mediterranean, often exhibiting features typical of both the western and eastern shores of the same sea. Statistical analyses of the data indicated the presence of three main zones, together with a separate sub-zone by vermetid molluscs, corresponding to mediolittoral fringe. characterized a 15 - 20cm. Increased exposure to wave action brought about several effects such as widening of the major zones on shore, increase in the total width of the littoral, increased numbers of infralittoral species in the lower mediolittoral zone, and changes in the distribution of the species. The effect of microtopography on the distribution of some species is discussed as is the effect of exposure on the growth form of some algal species.