Oyster reef restoration: substrate suitability may depend on specific restoration goals

Oyster reef restoration is an increasingly used tool to combat habitat loss and restore ecosystem services that reefs provide. A limited supply of oyster shell for restoration practices has prompted research focused on understanding the value of alternative substrates for reef construction. We restored 6 acres of subtidal oyster reef complex in the Mission-Aransas Estuary, TX, in July 2013 using replicated sections of concrete, limestone, river rock, and oyster shell substrates. Oyster and reef-associated faunal development were assessed for 18 months post-construction. Oyster populations varied seasonally and by substrate; the highest oyster abundance across all substrates was observed during July 2014 (X= 1288 m-2). Concrete (X =1022 m-2) and limestone (X = 939 m-2) supported the greatest number of oysters over all dates. Motile macrofauna also varied with season and substrate type; abundance and was highest during July 2014 (X = 2766 m-2) and October 2014 (X = 1748 m-2). Oyster shell (X =1533 m-2) and concrete (X = 1047 m-2) substrates supported the highest abundances of motile fauna. Faunal diversity (Hill's NI) peaked in April 2014 (X = 4.1) and did not vary by substrate material. All substrates were successful at providing habitat for oyster and faunal communities-but were effective to varying degrees for different metrics-suggesting that substrate choice should be dependent on restoration goals. We developed a simple benefit-cost ratio to determine which substrates had the best return on investment for our restoration goals. The metric is flexible so practitioners can adapt it to suit their own project goals and substrate costs. As oyster reef restoration activities continue at small and large scales, substrate selection criteria are critical for assisting stakeholders in ensuring restoration investments are maximizing enviromnental benefits per dollar spent.