A Comparison of the Effectiveness of Sandstone and Limestone As Cultch for Oysters, Crassostrea Virginica‪.‬

ABSTRACT Field studies were conducted to compare quartzitic sandstone to siliceous limestone in its ability to collect oyster spat, and to determine if sandstone is a suitable cultch for oysters. Thirty bags of sandstone and 30 bags of limestone were placed on each of 3 sites in Terrebonne Parish, Louisiana-South Sister Lake (SSL), North Sister Lake (NSL), and Bay Junop. The bags were deployed in late May and retrieved in early to mid July. (The Bay Junop bags were missing upon retrieval.) All recruits to the substrate (live spat, articulated dead shells and single shells) were counted as spat. South Sister Lake had higher salinities and higher spatfall than did NSL. The mean number of oyster spat per bag at SSL was 2156.5 for limestone and 338.5 for sandstone; at NSL mean number of spat per bag was 315.3 for limestone and 16.8 for sandstone. The difference between sandstone and limestone was highly significant (P 0.0001) at both sites. There was thus a clear preference of oyster larvae for limestone at high salinity and high-larval abundance, and at low salinity and low-larval abundance. Sandstone does not appear to be a suitable alternative to limestone as a cultch for oysters. KEY WORDS: Crassostrea virginica, oyster reef restoration, cultch, settlement, larvae