Spatiotemporal Variation in Broodstock Reserve Fecundity at Multiple Scales

Abstract

A major expectation of marine no-take reserves is that organisms within a reserve, over time, will export eggs and larvae to help sustain populations within and outside of reserves. Because fecundity and reproductive output can vary in space and time, the success of broodstock reserves depends on selecting the habitat or location that maximizes reproductive output to the target population. The goals of this study were to quantify spatial and temporal variation in (1) per capita fecundity (# eggs/individual) of female eastern oysters (Crassostrea virginica) within a network of marine broodstock reserves in Pamlico Sound, North Carolina; (2) fecundity per square meter (eggs/m2); (3) reserve fecundity (# eggs/reserve); and (4) the effects of endogenous and exogenous factors on spatiotemporal variation in per capita fecundity. A total of 1768 oysters were collected by scuba divers from six broodstock reserves over five sampling periods during 2006-2008 and processed in the laboratory for fecundity. Per capita fecundity ranged from 0 to 340,500 eggs, and mean per capita fecundity increased exponentially with oyster size (LVL mm) peaking in May of all years. In general, there were distinct spatial differences in fecundity depending upon the response variable, with per capita fecundity highest at more inshore reserves of moderate salinity, and fecundity m2 and reserve fecundity highest at more seaward reserves with relatively high salinity. Ranking of broodstock reserves for management purposes will likely depend upon the specific management goal. For example, if the goal is to expand broodstock reserves at locations that maximize reproductive potential per square meter of habitat created or improved, then reserves such as Ocracoke and Hatteras, that combine the joint effects of relatively high oyster density, size and per capita fecundity, would be ranked highest for expansion. If the management goal is to rank conservation of current broodstock sanctuaries, then relatively high salinity reserves such as Hatteras, that combine the joint effects of relatively high m2 fecundity and large substrate surface area, provide the greatest reproductive potential in terms of reserve fecundity. Lastly, if the management goal is to augment oyster densities via stocking with oyster spat at sites with high reproductive potential at the individual level, then more inland reserves such as Bluff Point and West Bay would be ranked highest. These results highlight the need to consider time and space when measuring reproductive potential of marine reserves, as well as the need to consider a comprehensive suite of response variables that best inform managers.