OYSTER REEF RESTORATION USING ARTIFICIAL SUBSTRATES

The high national priority of developing artificial oyster reef substrates is a consequence of scarcity and consequential expense of natural oyster shells available for restoration. Restoration is imperative because the historical abundance of native oyster populations has declined 99% over the past 100 years. A common artificial reef substrate is concrete made with silica sand, however, conventional concrete results in reduced long-term oyster survival and increased competition with other organisms like barnacles. The aim of this research is to test alternative concrete formulations in oyster restoration efforts. Specifically, we field-tested the statistical hypothesis that wild juvenile oysters would strike to and grow on concrete casts of oyster shells made with limestone sand as often as striking to casts made of concrete with silica sand. Natural oyster shells were used as a control and reference substrate. An initial Kruskal-Wallis post hoc test suggests that after one spawning and recruitment period (14 weeks, 2016), shell casts made with limestone sand attracted similar abundances (168, n=80, median=1, Q1=0, Q3=2) of oyster spat as normal concrete casts (191, n=80, median=1, Q1=0, Q3=2; p = 0.11). However, both shell cast varieties attracted less spat than natural oyster shells (399, n=80, median=3, Q1=0, Q3=4; p < 0.001). The long term effects of the limestone-rich concrete formulation are currently being examined, however, this study suggests that formulations of concrete that benefit oyster spat can be advantageous as an alternative substrate for oyster restoration due to the similar abundances found on both formulations. We suggest that future restoration efforts should consider using alternative substrates that cater to the preferences of oyster spat to reduce overall cost while maintaining optimal recruitment success.