Saved by the shell: Oyster reefs can shield juvenile blue crabs Callinectes sapidus

Juvenile blue crabs Callinectes sapidus use seagrass and other structured habitats as refuges from predation. Oyster reef habitats provide structural complexity that may offer refuge, but the value of these habitats for juvenile blue crabs has not been examined. We quantified survival of juvenile C. sapidus in structured oyster reef habitat versus unstructured soft-bottom habitat. In a field tethering experiment in the York River, lower Chesapeake Bay (USA), juvenile C. sapidus (10-50 mm carapace width [CW]) were tethered in sand (n = 40) or oyster reef (n = 39) habitats at subtidal sites 1-2 m deep. An underwater camera system was used to record predation activity during 24 h trials. Juvenile crab survival was significantly higher on the oyster reef habitat (53.8%) than on bare sand (15.0%), and tended to increase with crab CW in both habitats. The main successful predators on juvenile blue crabs were northern pufferfish Sphoeroides maculatus in the oyster reef habitat and adult blue crabs in the sand habitat. The high survival rate of juvenile C. sapidus in oyster reef habitats suggests that oyster reefs include physical habitat complexity that may offer refuge from predators. Restored and natural oyster reefs could provide an alternative nursery habitat for juvenile blue crabs, expanding the ecosystem services provided by restored oyster reefs.

Automated summary

This study found that juvenile blue crabs have a significantly higher survival rate on oyster reef habitats compared to bare sand habitats, and the survival rate tends to increase with crab carapace width in both habitats. In oyster reef habitats, the main successful predators on juvenile blue crabs were northern pufferfish, while in sand habitats, it was adult blue crabs. The high survival rate in oyster reef habitats suggests that they may provide refuge from predators for juvenile blue crabs, expanding the ecosystem services provided by oyster reefs.