JOURNAL OF THE WORLD AQUACULTURE SOCIETY Vol. 31, No. 4 December, 2000 Oyster Crassostrea virginica Spat Settlement as it Relates to the Restoration of Fish River Reef in Mobile Bay, Alabama IMAD G. SAOUD, DAVID B. ROUSE,' RICHARD K. WALLACE, JEFFREY HOWE, AND BLAN PAGE Department of Fisheries and Allied Aquacultures, Swingle Hall 203, Auburn University, Alabama 36849 USA Ahsrrucr.4yster spat settlement at four oyster reefs in Mobile Bay, Alabama, USA, was studied from Au- gust through October 1998 and May through mid No- vember 1999. Spat collectors at the reefs were replaced every 2 wk and spat-set estimated as number of oysters per meter square per day. Water quality data at Fish River Reef was monitored using remote sensors. Spat- set data revealed significant variation between the four sites and between the 2 yr. Spat settlement was 5 to 10 times greater at the other three reefs than at Fish River Reef. Dates and intensity of oyster settlement at Fish River Reef were different from dates and intensity of oyster settlement at Shell Bank Reef, both on the eastern side of the bay. However, settlement was sim- ilar between Cedar Point Reef and White House Reef, both on the western side of the bay. Spat set appears to occur 3 wk after a rapid decline in water tempera- ture, provided adequate oxygen concentrations are pre- sent at the time of settlement. Data collected suggest that intensity of settlement at Fish River Reef is con- siderably less than at other reefs in this study but could be adequate to reestablish the reef, if cultch and en- vironmental conditions are suitable. The data also sug- gest that the source of larval oysters at Fish River Reef is different from the source of larval oysters at the other sites tested in the present study. Several hard-bottom, mud-free areas ex- ist in Bon Secour Bay on the eastern side of Mobile Bay, Alabama, yet few oysters grow in these areas (Smith 1999). Historical data suggest that these areas were once vi- able oyster reefs (Ritter 1895; Eckmayer 1979). A variety of factors have been sug- gested as explanations for the lack of har- vestable oysters on the relic reefs of Bon Secour Bay (Ritter 1895; Mackin 1951; May 1972, 1973; Eckmayer 1979; Cake and Eckmayer 1982; Eckmayer 1983). Most studies have reported die-offs during particular events but research-based data that explains why viable oyster populations I Corresponding author. are not present today is lacking. Reasons for lack of viable oyster populations dis- cussed include a lack of cultch on the reefs, and possibly a lack of adequate oyster-spat recruitment. An integral part in the management of oyster reefs is the need for adequate sub- strate for larval settlement. A survey of the reefs of Bon Secour Bay in 1998 indicated a near-total absence of cultch material on Fish River Reef (Smith 1999). The Marine Resources Division (MRD) of the Alabama Department of Conservation and Natural Resources has indicated an interest in de- ploying oyster shell as cultch at Fish River Reef to help restore the reef. If cultch is deployed too early, siltation and fouling may decrease or eliminate potential settle- ment and recruitment of spat (Ingle 1951; Shaw 1967; Hoese et al. 1972; MacKenzie 1977; Osman et al. 1989). Timely cultch dispersal requires a proper understanding of oyster population dynamics, reproductive cycles and larval dispersal patterns. Ken- nedy (1996) provides a review of factors related to the timeliness of cultch dispersal, oyster reproduction, larval dispersal and spat settlement. Oyster spatfall in Mobile Bay normally has two peaks, the higher of which is the fall set (Hoese et al. 1972; Lee 1979; Hayes and Menzel 1981). The present study was performed to evaluate the incidence of oys- ter settlement at Fish River Reef in order to determine if settlement is adequate to re- store the reef should new cultch be de- ployed. Settlement at Fish River Reef was compared to settlement at three other reefs in Mobile Bay during one spring and two fall spawning periods. 0 Copyright by the World Aqunculture Society 2000 L A n