Assessing the erect bryozoan Myriapora truncata (Pallas, 1766) as indicator of recreational diving impact on coralligenous reef communities

Recreational diving effects on Mediterranean benthic communities have been scarcely studied to date. In this study, we evaluate the recreational diving impact on the Mediterranean bryozoan Myriapora truncata. Eight localities with different diving rates and protection levels were sampled before and after summer, the season of maximum presence of divers in the region. A photographic sampling technique was used, which made possible to increase the number of replicates. In each sample: number; mean, maximum and total area; total and mean perimeter and exposure; and aggregation levels of M. truncata colonies were measured by image treatment software. ANOVA, MDS and PERMANOVA were the statistical techniques used to detect and evaluate the effects of the five factors considered (time, protection, impact, locality and site) on M. truncata colonies. The number, area and perimeter of colonies significantly decreased after summer at localities with high presence of divers; whereas hidden colonies went through a positive increase comparing with exposed colonies. Our results evidence M. truncata as a good indicator species for recreational diving impact on coralligenous reef communities. The monitoring of a combination of representative parameters of this species could play an important role on the management of diving areas.