Predation rates on juvenile blue crabs in estuarine nursery habitats: evidence for the importance of macroalgae (Ulva lactuca)

Abstract

Rates of predation on juvenile blue crabs Cahnectes sapidus (12 to 64 mm carapace width) in eelgrass Zostera marina, sea lettuce Ulva lactuca, and paired adjacent unvegetated substrates, and a Spartina marsh creek were compared using 24 h tethering experiments from July to October 1987. Vegetation provided the best cover from predation, with mean predation rates in sea lettuce of 9 O/O and in eelgrass of 20 %, compared with mean rates of 40 % or greater in unvegetated controls and the marsh creek Seasonal changes in rates of predation on crabs occurred in eelgrass and sea lettuce habitats indicating that the refuge value of these macrophytes varied seasonally. Sea lettuce, previously considered a poor habitat for decapod crustaceans, provided effective refuge for blue crabs and should be considered a potential nursery habitat.