Alternative substrate types promote eastern oyster recruitment and benthic community productivity

Restoration of eastern oyster Crassostrea virginica reefs in Chesapeake Bay (USA) can provide habitat for estuarine communities. Oyster shell, a preferred settlement substrate, has become a limited resource. Thus, alternatives like concrete structures need to be evaluated in their performance relative to oyster shell substrate. Our goals were to (1) compare oyster recruitment among natural (shell and granite) and concrete-mix (castle, diamond, c-dome, and x-reef) reef types, and (2) determine how reef type influences macrofaunal community productivity. To address these goals, 2 replicates of each of the 6 reef types were deployed in a randomized-block experimental design at 3 sites. One year after deployment, oysters and the macrofaunal community associated with the reefs were sampled to determine density, biomass, and productivity. Oyster density (9853 ind. m -2 ) and biomass (744 g ash-free dry weight [AFDW] m -2 ) were highest on the natural shell reef type followed by the x-reef (3817 ind. m -2 ; 532 g AFDW m -2 ), and all reef types had density and biomass that far exceeded the target for successful restoration in Chesapeake Bay (50 ind. m -2 and 50 g dry weight). All reef structures also had high oyster productivity. Notably, macrofaunal secondary productivity was highest on granite reefs (800 g C m -2 yr -1 ), and productivity of all concrete-mix structures ranged from 97 to 800 g C m -2 yr -1 , with some substrates rivaling that of the natural shell substrate (644 g C m -2 yr -1 ). Hence, concrete-mix substrates are a viable alternative to using natural oyster shell for restoration.