Elazzaoui, A.; Kalla, Y.; Lefrere, L.; Bouhaimi, A., and Moukrim, A., 2022. Using Mediterranean mussel bio-indicators to assess the initial health state of ecosystems receiving desalination plant effluents in Agadir Bay (Morocco). Journal of Coastal Research, 38(1), 154–167. Coconut Creek (Florida), ISSN 0749-0208.

Mussels are often used as a biological bio-indicator for the quality assessment of marine ecosystems. Adopting this approach, the present work aims to study the initial health status of two ecosystems in Agadir Bay, Morocco expected to receive seawater desalination plant effluents. This study was conducted between February 2015 and March 2017 in two stations, Tifnit-Douira and Cap Ghir. In addition to the gametic development, variations of sex ratio and gonadal index were also determined. The reproductive cycle of Mytilus galloprovincialis is spread throughout the year. Under natural conditions, three collective spawning periods were observed. The main one was during the spring and the two other periods were optional and were in winter and summer. Variations of seawater temperature can make some changes in mussel spawning, with one principal period lasting during spring and summer and the optional one during winter. In both studied stations, sexual rest was manifested by a small percentage of the population particularly during summer, and could not reach the whole population at the same time. This finding is consistent with the gonadal index that never reached the value of 1. A unique hermaphroditism case was revealed in Tifnit-Douira mussels, and it remained statistically insignificant. The sex ratio was perfectly balanced in both stations and was in favour of males. The gonad histology did not show any cellular abnormalities in the germinal tissue. These results are of great importance since they characterize the current state of the studied stations area before the installation of the desalination plant. This state must be maintained after installation in order to preserve the typical halieutic resources of these ecosystems. The present findings confirm the good environmental health status and the aquaculture potential of Agadir Bay, especially in the north ecosystems (Cap Ghir) due to upwelling-nutritional intake and optimum seawater temperature.