The prevalence of the pea crab Afropinnotheres monodi in mussels depending on the degree of habitat exposure: Implications for mussel culture

Abstract

The African parasitic pea crab Afropinnotheres monodi lives in association with a high number of different bivalve species, although in its reproductive phase (soft females) a high prevalence has been observed infesting mainly intertidal Mytilus galloprovincialis. In recent years this pea crab has been recorded in the south of Iberian Peninsula, with well-established populations in the Gulf of Cadiz, and it has been observed that infested mussels showed a decrease of their condition index of 14.7%, on average. Until now, a high prevalence of A. monodi has been observed only in intertidal mussels inhabiting sheltered and relatively shallow habitats, but it has not yet been found in aquaculture farms located offshore in the surrounding zone. Considering the commercially-important mussel farms located in the Galician Rias and Ebro Delta (sheltered systems), the aim of this study was to test whether the prevalence of this pea crab in subtidal mussels depends on the degree of exposure/shallowness of their habitats and consequently on the coexistence of the primary hosts of all crab demographic categories in a reduced area. For this, we have assessed the prevalence of A. monodi in mussels attached to the submerged chains of the navigational buoys of the navigable channel of the Bay of Cadiz. The results show that A. monodi prevalence is correlated with the distance of mussels from the nearest inshore areas, where bivalves host the initial phases of this species (r = −0.92, p < .01). On average, the highest prevalence corresponded to B10 (the nearest inshore buoy sampled), with 74.5% of mussels hosting crabs and the lowest to B2 (the furthest buoy sampled) where only 17.0% of mussels hosted crabs. These results confirm that A. monodi infects subtidal mussels, in a condition similar to the cultured mussels in rafts and long-lines. Therefore, if the pea crab reaches sheltered areas where mussels are cultivated (i.e. the Galician Rias and Ebro Delta bays), it could become successfully established, with negative commercial consequences for these aquaculture farms.