TEMPORAL VARIATION IN FISH BIOMASS ON ARTIFICIAL HABITATS INSTALLED IN GABES GULF, SOUTHERN TUNISIA

摘要

The total area of the seagrass meadows in Gabes Gulf in the southern part of Tunisia, which consists mainly of the endemic seagrass Posidonia oceanica, has decreased in recent years. Small artificial reefs made of concrete blocks were deployed at three sites without seagrass in the Gulf viz. Mahares, Zarat and Ajim. Fish abundance was monitored at these sites as well as adjacent control sites by underwater belt transect method from July 2006 to October 2008. Variation in fish biomass (in unit water volume observed) was then estimated by using length-to-weight conversion formulae for calculating body weight of each species. Fish biomass increased significantly within each site after deployment of the artificial reefs, viz. 6.3 +/- 1.9g to 4586.6 +/- 864.8g in Mahares, 45.4 +/- 3.8g to 6360.0 +/- 1238.5g in Zarat and 34.8 +/- 8.0g to 3244.0 +/- 298.3g in Ajim. This study showed that deploying artificial habitat with careful planning and regular monitoring may be one of the effective mitigating measures to be implemented in depleted seagrass meadows in the Mediterranean.