Growth at Moult, Intermoult Period, and Moulting Seasonality of the Spider Crab Maja Brachydactyla: Combining Information from Mark-Recapture and Experimental Studies

Growth at moult (for both the prepubertal and terminal moults), and moulting seasonality in the spider crab Maja brachydactyla in the Ría de A Coruña (NW Spain) was quantified within a mark-recapture experiment. Crabs |$70-130\;{\rm{mm}}$| carapace length (CL) underwent a mean increase at moult of |$32.4\% $| from their pre-moult size, with no significant differences between sexes or moult types. Generalised Linear Models (GLMs) were used to construct growth models, employing a combination of information from the mark-recapture study and previous studies performed in laboratory and extensive culture to characterize driving factors. The first model revealed that study method growth did not differ between males and females. However, the effects of the study method (mark-recapture, laboratory, and extensive culture), the pre-moult CL and the interaction between them were significant. The smallest-sized crabs underwent a greater increase in size in the laboratory and culture studies, while the largest individuals underwent greater growth in the field. In the second model, the significant effects were pre-moult CL, moult type, and the interaction between the two variables, indicating that larger crabs showed higher growth rates in prepubertal moults. Mean intermoult period estimated for prepubertal moults in the field ranged 50-86 days, which was slightly lower than the 84.7 days observed in the laboratory. Prepubertal moults occurred primarily in spring and autumn in the field, while under culture conditions, the crabs moulted mainly in the spring. The intermoult period for terminal moults was estimated to be 90 days, slightly lower than the 104 days from the laboratory. The terminal moult took place generally in summer (June-September) both at sea as well as in culture. The intermoult period of juveniles at sea was highly variable, and some of the specimens did not moult for more than 5 months.