THE PARASITE SACCULINA CARCINI THOMPSON, 1836 (CIRRIPEDIA, RHIZOCEPHALA) IN THE CRAB CARCINUS MAENAS (LINNAEUS, 1758) (DECAPODA, PORTUNIDAE): INFLUENCE OF ENVIRONMENTAL CONDITIONS, COLOUR MORPHOTYPE AND SEX

Parasitism is increasingly recognized as an important factor that can influence the structure and function of natural communities. The presence of externae of the parasite Sacculina carcini Thompson, 1836 was investigated in a population of the crab Carcinus maenas (Linnaeus, 1758) from the Mondego estuary, Portugal. A seasonal pattern of the S. carcini externae presence was observed with the highest values recorded in winter and the lowest in summer, ranging from 0.6 to 10%. The parasite seems to affect more females than males and the red morphotype presented higher prevalence than the green one. The size class [25, 35 mm] was the one with the highest prevalence. The mouth of the estuary was the area where the most externally sacculinized crabs were caught. Apparently, the presence of the parasite tends to promote crabs migration to the mouth. This area coincides with the preferential spawning local of non-parasitized females. The infection by S. carcini influences the crab's demography and its life history.