Direct setting of Crassostrea virginica larvae in a tidal tributary: applications for shellfish restoration and aquaculture

Recent efforts to restore eastern oyster Crassostrea virginica populations in Chesapeake Bay have targeted regions where low larval supply limits recruitment. A common practice in areas of minimal spat set incorporates remote setting, a method of setting hatchery-reared larvae in tanks, and then transporting them to the field. Although remote setting is effective, inefficiencies exist. Repeated shell handling, spat mortality during transport, and decreased cultch supply suggest that other restoration methods merit consideration. We present the results of the first known field test of directly seeding a submerged oyster reef with larvae and setting an additional cohort on the reef the following year. We surrounded a 65 m(2) reef located in 2.5 m of water with a flexible enclosure and added 2.3 x 10(6) larvae. Larvae were allowed 3 d to set on either clean or fouled shell valves, after which we removed the enclosure. Setting efficiencies in the enclosure (spat produced per larvae introduced), were 26 and 7% for clean and fouled shell, respectively, in 2012, and 10 and 16% in 2013. These are comparable to published remote setting efficiencies, and were significantly higher than in our representative shoreside tank. Spat densities on site 1 mo post-set (median = 189 spat m(-2)) and the following spring (115 juveniles m(-2)) met best practice restoration metrics. Larvae were re-set on the reef in 2013, but in lower densities than 2012, supplementing the reef with 23 spat m(-2). In areas of minimal natural recruitment, or low cultch availability, direct setting of larvae in the field may be a viable alternative to remote setting.