Effects of infection by the protistan parasite Marteilia relringens on the reproduction of cultured mussels Mytilus galloprovincialis in Galicia (NW Spain)

Abstract

Infection by the protistan Marteilia refringens affects the digestive glands of cultured mussels in Galicia, Spain. Effects of the infection on the reproduction of the mussel were studied at 3 sites. Gonad cycle of mussels involved gametogenesis utilizing stored reserves and leading to spring spawning (conservative strategy). This was followed by various sequences of gonad restoration and spawning utilizing the energy from concurrent feeding directly (opportunistic strategy). M. refringens significantly inhibited gonad development in the periods of opportunistic reproductive strategy, proportionally to infection intensity. However, the inhib~tory effect was not significant in the period of conservatlve strategy, probably because mussels had developed storage tissue before the infection progressed. Development of storage tissue was estimated by the abundance of adipogranular (ADG) cells in the mantle. Infection by M. refringens was clearly associated with inhibition of ADG cell development. The heavier the infection, the lower the abundance of ADG cells. Differences in abundance of ADG cells among categories of mussels with different infection intensity were significant at every site. No significant difference in susceptibility to progression of infection was detected between males and females and a similar mortality rate between sexes can be assumed. Evidence suggests that stress following spawning could enhance the progression of the infection.