Activity patterns and zonation of the swimming crabs Arenaeus cribrarius and Callinectes ornatus

Abstract

Home range, movements and zonation of Arenaeus cribrarius and Callinectes ornatus were analyzed in Ensenada de La Vela, in the Venezuelan Caribbean, using acoustic telemetry. Transmitters were attached to the carapace of 11 A. cribrarius and 11 C. ornatus, which were tracked during five campaigns between October 2002 and December 2003. The positions of each crab were registered every 12 hours, for periods of up to 10 days, and data were obtained on geographical localizations, distances traveled, speed, depth, perpendicular distance to the beachline, as well as type of bottom and physicochemical variables of the water. We found significant differences between the two species regarding home range size (sensu lato), movements, distance to the coastline, depth and the type of sediment where they appeared. Callinectes ornatus had a larger home range (x- = 72,475 m2) than A. cribrarius (x- = 16,625 m2) and presented one to three centers of activity, while individuals of A. cribrarius had only one center, with a few exceptions. Both species used intensively about half of their home range. Arenaeus cribrarius preferred the foreshore, while C. ornatus inhabited more distant waters; however, a certain degree of habitat interpenetration was observed. Callinectes ornatus was more active (x- = 74.6 m/12 hours, SE = 6.6) than A. cribrarius (x- = 56.6 m/12 hours, SE = 6.5), but a high variability in the movement rates existed even within an individual. Arenaeus cribrarius was associated with bottoms conformed by very fine mixed sands and low contents of organic matter, whereas C. ornatus appeared in silty bottoms with higher organic contents. New elements on the zonation of these swimming crabs are included in this study, complementing the patterns found in previous works.