Seagrass habitat loss and fragmentation influence management strategies for a blue crab Callinectes sapidus fishery

Abstract

Marine biodiversity is increasingly threatened by multiple processes, and management strategies therefore must explicitly address the synergistic effects of multiple threats to marine spe- cies. The effects of harvesting and habitat degradation may be magnified for many coastal marine fishery species that rely on structurally complex nursery habitats to enhance survival and growth of postlarval and juvenile life history stages. Fishery management strategies that do not account for pro- cesses reducing juvenile survival and growth may overestimate the amount of biomass that can be taken; similarly, conservation and restoration strategies for nursery habitats that do not account for variable recruitment may fail. We used the blue crab Callinectes sapidus as a case study to investi- gate the population-level effects of harvest and seagrass habitat loss and fragmentation. We used available data to parameterize a stochastic stage-based model to test combinations of management strategies, namely reduced harvest rates and introductions of juvenile crabs to nursery habitat. Under a no-harvest scenario, large continuous areas of seagrass supported the largest blue crab popula- tions. However, when harvest rates exceeded 20%, median population abundance was maximized in seascapes composed of smaller, fragmented seagrass patches. Populations in isolated patches of sea- grass benefitted more from the introduction of crabs rather than harvest reduction, but the opposite was true for crab populations inhabiting highly connected seagrass seascapes. Management of spe- cies that use seagrass beds as nursery habitat must consider the spatial context of multiple threats and their potential synergies to maintain population persistence.