Feeding of the spider crab Maja squinado in rocky subtidal areas of the Ria de Arousa (north-west Spain)

The diet of the spider crab, Maja squinado, was studied in the rocky subtid al areas of the Ria de Arousa (Galicia, north-west Spain), by analysing the gut contents of crabs caught in the summer and winter of 1992. The highly diverse diet was made up primarily of macroalgae and benthic invertebrates that were either sessile or had little mobility. The most important prey we re the seaweeds Laminariaceae (43% of the frequency of occurrence and 15% o f the food dry weight), Corallina spp. (38% and 3%), molluscs [the chiton A canthochitona crinitus (15% and 1%), the gastropods Bittium sp. (30% and 2% ), Trochiidae and others and the bivalve Mytilus sp. (32% and 12%)], echino derms [the holothurian Aslia lefevrei (32% and 18%) and the echinoid Parace ntrotus lividus (16% and 7%)] and solitary ascidians (18% and 6%). The vari ability in diet composition was determined by the season (Laminariaceae, Co rallina spp., P. lividus, Mytilus sp., gastropods and chitons appeared in g reater frequency in winter, while the solitary ascidians and A. lefevrei we re consumed to a greater er;tent in summer:) in addition to sexual maturity (prey such as Bittium sp, or Trochiidae were more common in juveniles). Mo reover, the changes in the food consumption rate were linked primarily to t he moult stage. Feeding activity plummeted during the phases immediately pr eceding and following ecdysis (stages D-0-D3-4 and A), and the diet was les s diverse during these phases. No feeding differences were found that could be linked to sex. The composition of the diet of Maja squinado appears to be determined by the seasonal abundance of the different prey in subtidal r ocky areas and by their availability (depending on their behavioural and an atomical characteristics, mainly mobility and the presence of hard external structures). Moreover, life history factors have little importance in the variability of the diet composition and only the moult cycle has a consider able effect on feeding rate.