Effects of diver frequentation on Mediterranean sublittoral populations of the bryozoan Pentapora fascialis

The erect, foliaceous bryozoan Pentapora fascialis was selected as an indicator of the abrasive effects of heavy diving activity in Mediterranean coralligenous communities. A comparative survey of bryozoan populations at diver-frequented and unfrequented sites was undertaken in the Medes Islands Protected Area (NW Mediterranean) in 1992. Density, colony diameter, and colony height of P. fascialis populations were significantly lower and colony position was more cryptic at frequented sites than at unfrequented sites. Human frequentation may affect not only the structure of P. fascialis populations, but also that of the coralligenous community as a whole.