The effect of hydrozoan fouling on the burrowing of Donax marincovichi (Bivalvia, Donacidae) at Chinchorro beach, Northern Chile

Abstract

Surf clams Donax marincovichi inhabit the intertidal zone of high-energy sandy beaches from southern Peru to northern Chile. These bivalves are well adapted to their dynamic environment by being able to quickly borrow into the sediment, once the clams are washed out or undergo their tidal migration. This behaviour is necessary to escape predators. At reflected beaches north of Arica, the posterior end of the bivalves is commonly monospecifically fouled by hydrozoans (Clytia sp.), an epibiosis that has not been described before. This study investigated the effect of these epibionts on the burrowing performance of D. marincovichi. Burial time and burrowing intensity were obtained from 64 individuals, of which 32 were colonized by Clytia sp. and 32 were macroscopically clean. The burial times of the tested individuals did not correlate with shell length (25 to 33 mm). Burial times were not significantly different between fouled and clean D. marincovichi. However, significantly more fouled individuals completed burrowing, while more clean clams stopped just before the valves were covered with sediment. Burrowing time averaged at 25.7 seconds and is therefore within the range of swash periods on Chinchorro beach (10 to 32 seconds) enabling the clams to hide from fish, crab and birds