Spiny Spider Crab

Photo: B.A · CC BY-NC

Spider crabs aggregate in their thousands under the limestone arches from April through June during their annual moulting migration, forming mounds of interlocked animals that create a surreal spectacle in the arch ceilings. The aggregation behaviour provides mutual protection during the vulnerable soft-shell phase immediately after moulting, when predation risk is highest. They are an ecologically important benthic omnivore that reprocesses organic material across the rocky substrate.