Can crustacean cuticle preserve a record of chronological age? Investigating the utility of decapod crustacean eyestalks for age determination of two European spider crab species

Abstract

Until recently it was not thought possible to directly and accurately age crustacean species as any calcified structure that could preserve a record of chronological age is lost at moulting. Recent research has suggested that it may be possible to directly infer age from the number of endocuticular bands present within the eyestalks of snow crab (Chionoecetes opilio) and Antarctic krill (Euphausia superba). Using captive-reared Mediterranean spider crabs (Maja squinado), and wild-caught north-east Atlantic spider crabs (Maja brachydactyla), the present study aimed to determine if endocuticular bands of potentially annual periodicity are present within the eyestalks of these brachyurans. Although clear and readable bands were present within the endocuticle of their eyestalks, no bands of potentially annual periodicity were identified. The number of endocuticular bands did not correlate with the known-age of the M. squinado individuals; but did correlate positively with carapace length for both M. squinado and M. brachydactyla, suggesting they form as a result of growth and the size of individuals. It is hypothesised that these endocuticular bands, and potentially those identified by other studies purporting them to be annual growth bands, are in fact lamellae that appear due to the layers of calcite crystal aggregates interspersed with chitin and protein fibres that form the mineral of the cuticle in decapod crustaceans. Further research is needed to determine the processes that control and result in the deposition of crustacean cuticle, particularly during the post-moult period.