• Reproductive biology and parasite (Perkinsus marinus) prevalence in the eastern oyster, Crassostrea virginica, within a Georgia tidal river

      O'Beirn, F.X.; Walker, R.L.; Jansen, M.L. (Elisha Mitchell Scientific Society, 1997)
      Recruitment, in 1992, of the eastern oyster, Crassostrea virginica, at one site (Flume Dock) within the Sapelo Island National Estuarine Research Reserve (SINERR) was lower than other sampling sites. Recruitment allied with gametogenesis and parasite (Perkinsus marinus) prevalence within the oysters was examined in 1993, in an attempt to explain the differences observed the previous year. Sampling occurred at three sites (Marsh Landing, Jack Hammock, and Flume Dock) along the Duplin River within the SINERR. Oyster recruitment in 1993 was reduced in all sites within the SINERR. No oyster recruitment was recorded at the Flume Dock site during any monthly collections or on collectors deployed for the duration of the sampling study. Oysters developed gametogenically and spawned at the Marsh Landing site two weeks prior to their occurrence at the Jack Hammock site. Gametogenic development in oysters at the Flume Dock site was retarded a further two weeks where the males appeared to spawn six weeks after the females, which could account for reduced recruitment levels at this site. Approximately, twice as many females as males occurred in all sites. Monthly sampling of prevalence and intensity of Perkinsus marinus (Dermo) revealed high levels of both parameters. Smaller oysters did display lower prevalences of Dermo than larger forms.
    • Toward design criteria in constructed oyster reefs: oyster recruitment as a function of substrate type and tidal height

      O'Beirn, F.X.; Luchenbach, M.W.; Nestlerode, J.A.; Coates, G.M. (National Shellfisheries Association, 2000)
      Restoration of degraded oyster reef habitat generally begins with the addition of substrate that serves as a reef base and site for oyster spat attachment. Remarkably, little is known about how substrate type and reef morphology affect the development of oyster populations on restored reefs. Three-dimensional, intertidal reefs were constructed near Fisherman's Island, Virginia: two reefs in 1995 using surfclam (Spisula solidissima) shell and six reefs in 1996 using surfclam shell, oyster shell, and stabilized coal ash. We have monitored oyster recruitment and growth quarterly at three tidal heights (intertidal, mean low water, and subtidal) on each reef type since their construction. Oyster recruitment in 1995 exceeded that observed in the two subsequent years. High initial densities on the 1995 reefs decreased and stabilized at a mean of 418 oyster/m2. Oyster settlement occurred on all reef types and tidal heights in 1996; however, postsettlement mortality on the surfclam shell and coal ash reefs exceeded that on the oyster shell reefs, which remained relatively constant throughout the year (mean = 935 oysters/m2). Field observations suggest that predation accounts for most of the observed mortality and that the clam shell and coal ash reefs, which have little interstitial space, suffer greater predation. Oyster abundance was consistently greatest higher in the intertidal zone on all reefs in each year studied. The patterns observed here lead to the preliminary conclusion that the provision of spatial refugia (both intertidal and interstitial) from predation is an essential feature of successful oyster reef restoration in this region. In addition, high levels of recruitment can provide a numerical refuge, whereby the oysters themselves will provide structure and increase the probability of an oyster population establishing successfully on the reef.