Oyster reef habitat depends on environmental conditions and management across large spatial scales

Oyster reefs provide important services to ecosystems and people, with many of these benefits depending on structurally complex reef habitat. Despite the key role of oyster reef habitat, we have yet to understand natural and anthropogenic drivers of subtidal reef habitat over large spatial scales (>200 km). Chesapeake Bay (USA) offers a valuable system to explore how salinity, restoration, and harvest compare in their influence on subtidal oyster reef habitat because of its broad environmental gradient and mosaic of management types. We applied a remote rapid assessment method using underwater photographs to survey oyster reef habitat in 12 tributaries and scored images based on estimates of oyster percent cover and vertical relief. The broad spatial scale (similar to 215 km) of the survey includes reefs that vary in management status and salinity. Bay-wide habitat scores were higher with greater estimated oyster percent cover and vertical relief on unharvested and restored reefs. Salinity also contributed to Chesapeake Bay-wide patterns, but the relationship depended on harvest status. In assessing the separate management jurisdictions, scores were higher on restored reefs in Maryland and on anthropogenic (i.e. artificially supplemented) reefs in Virginia. A time series over 4 yr in 2 Maryland tributaries showed high and persistent habitat scores in restored sanctuaries, but habitat scores increased for all reefs over time. The results highlight the combined roles of the natural environment and management decisions on oyster reef habitat. The effect of harvest and restoration on habitat underscores the importance of local management decisions in determining the future status of oyster reefs.