The use of an endoscopic camera to estimate size of brachyuran crabs in burrows

Abstract

Studies on brachyuran burrowing crabs have shown a relationship between the dimensions of the burrow opening and the size of the constructor. Estimating specimen size using this relationship may nevertheless be biased since individuals of different species and sizes are commonly found using the same burrow. We describe the use of an endoscopic camera to estimate the carapace width (CW) of decapod crustaceans within their burrows, using Ocypode quadrata (Fabricius, 1787) (Brachyura, Ocypodidae) as a model. Videotapes of crabs were filmed inside an artificial burrow using an endoscopic camera fitted with a fixed rod. The length of the carpi and propodi of the third and fourth pereiopods and CW were measured in 35 individuals using a digital caliper. We used Paint.net to measure the lengths in pixels of the pereiopods and converted them to millimeters. The Pearson's correlation coefficient indicated a high correlation between caliper-measured CW and the CW estimated by the length of the perieopod articles as measured by a caliper (R2 minimum = 0.97, P < 0.01) and pereiopods images (R2 minimum = 0.97, P < 0.01). Our results show that images obtained with endoscopic cameras are feasible for effective and non-destructive estimation of the size of brachyuran crabs living inside their burrows.