Impact of a marina construction on a seagrass bed at Lanzarote (Canary Islands)

Abstract

Interannual changes in the shoot density, biomass and leaf length of the seagrass Cymodocea nodosa and two descriptors of the associated fish communities (total fish abundance and species richness) were evaluated at Playa Blanca (Lanzarote, Canary Islands) from March 2001 to April 2002 to provide evidence for responses to the impact of a marina construction. The seagrass bed under influence, as well as a control location, were sampled using an experimental design which consisted of three sites nested within each of these two locations. We tested the null hypothesis that these parameters would not change over time as a result of this construction.

A three-way mixed and symmetrical ANOVA detected significant ‘Time of sampling × Control vs Impact’ interactions for the shoot density, biomass and leaf length. The same interactions were observed for the descriptors of the fish communities using a two way orthogonal ANOVA. We detected an initial fast increase in the mean leaf length as a possible morphological response to a reduction in the amount of light at the bottom. Furthermore, a significant decrease was obtained for the penetration of light into the water column in the perturbed bed. Therefore, we obtained significant evidence to reject the null hypothesis offered by our study.