Measuring estuarine habitat quality: ribbed mussel (Geukensia demissa) growth and survival across tidal creek habitats

Measuring estuarine habitat quality: ribbed mussel (Geukensia demissa) growth and survival across tidal creek habitats

The functional similarity and overall quality of major intertidal marine habitats (e.g., mud flats, salt marshes, oyster reefs) were investigated experimentally within South Carolina marshes. Such data on the relative quality of coastal habitats are critical for enacting effective coastal conservation strategies. Relative habitat quality was assessed using an experimental, “bioassay” approach to determine differences in growth and survival of target species. Geukensia demissa, one of the selected target species, were transplanted into each of the dominant intertidal habitats in the Southeastern US. Appropriate experimental controls such as caging were used to account for ancillary factors (e.g., predation) that would confound assessment of habitat quality differences. Mussels from a single source site were sized prior to placement in the field and then deployed at multiple sites within 1 cm mesh cages placed at similar elevations in mud flat, salt marsh and oyster reef habitats. Growth, change in size (length, width, height) and mass (ash-free dry), and survival of the caged mussels were determined after 12 months. There were no significant differences in linear shell growth among the habitats with the mean increase in length ranging between 10.1 and 12.3 mm, but the yearly increase in tissue ash-free dry mass was significantly different among habitats. Caged mud flat mussels had a greater increase in tissue ash-free dry mass (789.1 mg/G) than either caged salt marsh (769.8 mg/G) or oyster reef mussels (736.6 mg/G). Mussel survival within cages (67 to 81%) was not significantly different among the three habitats. Results suggest that mud flats represent a better quality habitat for G. demissa producing greater tissue growth in the absence of predation.

Linda Walters,¹* Kevin Johnson,¹ Lisa M. Wall,¹ Neysa Martinez,¹ and Ray Grizzle.^{2 1}Department of Biology, University of Central Florida, 4000 Central Florida Blvd., Orlando, FL 32816, USA; ²Jackson Estuarine Laboratory, University of New Hampshire, Durham, NH 03824, USA.

C. M. Wapnick,¹* W. F. Precht,² and R. B. Aronson.^{1 1}Dauphin Island Sea Lab, 101 Bienville Boulevard, Dauphin Island, AL 36528, USA; ²Ecological Sciences Program, PBS&J, 2001 NW 107th Avenue, Miami, FL 33172, USA.

Caribbean coral reefs are encountering problems including reduced coral cover, increased macroalgal cover, declining fish abundance, the loss of herbivorous sea urchins, and decreasing accretion rates. Whether these recent shifts represent unusual conditions remains unanswered. These changes have been observed in the coral reefs at Discovery Bay, Jamaica, for decades. The goal of this study is to extract cores from Columbus Park in Discovery Bay and use fossil coral assemblages from the Holocene to reconstruct the community structure of these reefs in a broader historical context. We are testing the hypothesis that the modern transitions from acroporid corals to macroalgal dominance are unique on a centennial to millennial scale. Our guiding hypothesis is that A. cervicornis essentially dominated these reefs continuously prior to the 1980s. Like previously studied lagoonal reefs of Belize and Panama, it is likely that these reefs are currently exhibiting a community structure unique to the past several thousand years. Extreme levels of both human and natural disturbance have caused this species to decline precipitously. The search for large-scale, ecological upheavals in the past is critical to evaluating the role of human activities in degrading coral reefs. If no mass mortality of A. cervicornis occurred before the present episode, the contention that the current situation is novel would be supported. Understanding the recovery responses of the reef community to local mortality events through time is also critical to answering whether the recent shift is a unique event or repeated pattern.