Epibiosis and ornamental cover patterns of the spider crab Maja squinado on the galician coast, northwestern Spain: Influence of behavioral and ecological characteristics of the host

Abstract

This paper examines the variation in the body-covering patterns of the spider crab Maja squinado in the Ria de Arousa (Galicia, northwestern Spain), as related to habitat, season, size, terminal molt, and migrations of the host. Individuals inhabiting shallow zones, generally characterized by their smaller size and more frequent molts (juveniles), showed a marked self-decorating behavior and a higher level of body coveting than in adults inhabiting deeper areas. In adults, epibiosis was more common than self-decoration. The availability of material for decoration, primarily seaweeds, was greater in the spring and summer seasons, when the highest coveting levels were reached. There was a negative correlation between the degree of covering and spider-crab size, with a decline in decorative behavior after the terminal molt. After the terminal molt, the animals migrate to deeper areas, where epibiosis is dominant, with a heightened presence of bryozoans, barnacles, and encrusting seaweeds, which require a stable substrate (absence of molts) in order to develop. In shallow zones, the erect seaweeds were dominant, occupying in many cases 100% of the body surface. In the deeper zones, the dorsal cephalothorax was the area with the greatest amount of cover. The legs were more sparsely covered and the ventral cephalothorax, affected only by epibiosis, was characterized by low levels of coverage.