A method for recording predator–prey encounters between crabs and limpets using wax replicas

Abstract

This study examined the use of replica limpets made from modelling wax to provide an index of encounter frequency between crabs and their limpet prey. Video observations at Port Erin Marine Laboratory, showed that the intertidal crabs, Carcinus maenas (L.), Necora puber (L.) and to a lesser extent Cancer pagarus L., regularly examined and tried to remove both real and replica limpets with their chelae. Replica limpets became scratched or gouged as a result of these encounters. The frequency of attack was similar for both real and replica limpets. Hence marks on the limpet models provided a reliable index of attacks on real limpets. The frequency, timing and spatial distribution of encounters between limpets and crabs were recorded by scoring the marks made on model limpets deployed amongst real limpets on the shore. During a 28-day period at Port St Mary on the Isle of Man, limpet models were marked more frequently and with longer scratches on the lower shore than on the upper shore, suggesting that larger crabs were present on the lower shore. Models, deployed at Prawle Point, Devon, showed that encounters between crabs and limpets occurred during both day and night-time high tides. The models were durable and provided an inexpensive method for recording encounters between crabs and limpets. Some replicas were also marked by the teeth of small fish and rodents. Model prey such as these could also be used to study other predator–prey encounters, particularly in conditions which preclude direct observation or video recording, or for use with animals that might be disturbed by observers or cameras.