Eric T. Koepfler

Ecosystem response to bivalve density reduction: management implications

Coastal ecosystems are easily overexploited and changed by physical and biological factors. In this paper, we discuss current ideas and arguments for coastal ecosystem management with an emphasis on systems that have large bivalve filter feeder components. For centuries the species or population approach has been utilized in fisheries management. With the growing knowledge base on specific environmental effects and relationships, it has become increasingly evident that a broad or holistic approach to fisheries management in these systems is usually more appropriate. An ongoing ecosystem scale experiment in which oysters are completely removed from tidal creeks is described and used as a case study. The experimental design takes estimates of the systems carrying capacity into account. Using the population or species approach to monitor the oysters, the only observable change after the experimental manipulation was a slight increase in summer somatic growth and elevated recruitment of oysters in creeks with oyster reefs removed. These data are interpreted as an indication that the creeks with oysters present are below or near carrying capacity. However, when nekton, plankton and water chemistry data are also examined a much more complicated picture emerges. During the summer growing season, nekton biomass in all creeks is often greater than oyster biomass. Also, our calculations show that oysters do not produce enough ammonium to satisfy phytoplankton productivity, but nekton, water column remineralization and sediments can account for most of the deficit. Finally, microflagellates, which are a preferred food for the oysters, dominate the phytoplankton during the summer growing season and diatoms dominate the colder months. The timing of the change in phase of phytoplankton dominance seems to mirror the seasonal arrival and departure times of nekton in the creeks. We argue that dense bivalve reefs and beds are indicative of intense positive feedback loops that make their ecosystems susceptible to dramatic changes in structure. Such changes have not been reported for natural systems, but are found in systems influenced by over-fishing, nutrient loading and pollution. Thus, the management of sustainable fisheries in coastal ecosystems requires an understanding of the ecosystem science and the realization that systems dominated by bivalves exhibit complex responses that are not easily explained by linear dynamics.

Relationships among Water-Quality Parameters from the North Inlet–Winyah Bay National Estuarine Research Reserve, South Carolina

Abstract Estuaries integrate atmospheric, watershed, oceanic, and human influences over space and time. Therefore, spatial and temporal patterns in estuarine water-column properties are useful as metrics to evaluate external factors related to internal processes. The National Estuarine Research Reserve monitoring program, including the North Inlet–Winyah Bay complex in South Carolina, provides an ideal setting to track water quality relationships. Our goal was to assess hydrography, chlorophyll a, and particulate and dissolved materials from monitoring data collected at sites from both the salt and estuarine marsh components since 1993–94. Salinity, turbidity, dissolved organic carbon, suspended solids, and chlorophyll a were much greater at the estuarine site, whereas organic nitrogen dominated the total nitrogen pool at both locations. Nitrate was a significant fraction of the total nitrogen pool at the estuarine site but not within the salt marsh. Whereas dissolved organic nitrogen was positively correlated to water temperature, nitrate concentrations were the lowest in the summer. Principal components analysis identified seasonal patterns within the salt marsh for temperature, chlorophyll a, ammonium, suspended solids, and particulate nitrogen. These parameters, grouped together as a primary component, were positively correlated to Spartina alterniflora biomass. In contrast, the estuarine site was more characterized by salinity, pH, and dissolved organic carbon. Although the water-column properties of the salt marsh site reflected a high degree of internal production and remineralization in the summer, patterns at the estuarine site were more likely influenced by seasonal changes in circulation and biogeochemical processing common to coastal plain estuaries.

Spatiotemporal Variability in Dissolved Organic Matter Composition is More Strongly Related to Bacterioplankton Community Composition than to Metabolic Capability in a Blackwater Estuarine System

The composition and metabolic capability of bacterioplankton communities were examined over seasonal and spatial gradients and related to the source, composition, and quantity of dissolved organic matter (DOM) in the blackwater estuary Winyah Bay, Georgetown County, SC, USA and its tributary rivers. Bacterial community composition (BCC) was measured by terminal restriction fragment length polymorphism, and bacterial metabolic capability (BMC) was measured by defined substrate utilization patterns (Biolog GN2 plates). Spatial patterns were not important, despite the anticipated watershed effects and the well-documented influence of salinity gradients on estuarine bacterioplankton, but DOM, BCC, and BMC all showed varying degrees of temporal patterns; DOM-based groupings differentiated BCC samples better than spatiotemporal categories, but not BMC. BCC was closely related to properties describing DOM composition, particularly those related to DOM source (i.e., cypress swamps vs. in situ phytoplankton production, indicated by chlorophyll a, colored DOM spectral slope, α355/dissolved organic carbon (DOC), and DOC concentration), and to associated physicochemical variables, such as temperature, pH, and salinity. BMC was more strongly related to abiotic factors, such as temperature and dissolved nutrients, as well as to chlorophyll a and percent bioavailable DOC. In contrast with previous studies, BCC and BMC were significantly correlated in this highly heterotrophic estuary, suggesting that DOM source variability may select for specialist phylotypes above a background of generalists. This study, therefore, supports a causative pathway from DOM to BMC to BCC while suggesting that BCC and BMC may be simultaneously influenced by different suites of DOM characteristics and physicochemical parameters.

Metabolic Responses of Estuarine Microbial Communities to Discharge of Surface Runoff and Groundwater from Contrasting Landscapes

Groundwater discharge is increasingly recognized as a significant source of nutrient input to coastal waters, relative to surface water inputs. There remains limited information, however, on the extent to which nutrients and organic matter from each of these two flowpaths influence the functional responses of coastal microbial communities. As such, this study determined dissolved organic carbon (DOC) and nutrient concentrations of surface water runoff and groundwater from both an urbanized and a relatively pristine forested drainage basin near Myrtle Beach, South Carolina, and quantified the changes in production rates and biomass of phytoplankton and bacterioplankton in response to these inputs during two microcosm incubation experiments (August and October, 2011). Rainwater in the urbanized basin that would otherwise enter the groundwater appeared to be largely rerouted into the surface flowpath by impervious surfaces, bypassing ecosystem buffers and filtration mechanisms. Surface runoff from the developed basin was most enriched in nutrients and DOC and yielded the highest production rates of the various source waters upon addition to coastal waters. The metabolic responses of phytoplankton and bacterioplankton were generally well predicted as a function of initial chemical composition of the various source waters, though more so with bacterial production. Primary and bacterial productivities often correlated at reciprocal time points (24-h measurement of one with the 72-h measurement of the other). These results suggest human modification of coastal watersheds enhances the magnitude of dissolved constituents delivered to coastal waters as well as alters their distributions between surface and groundwater flowpaths, with significant implications for microbial community structure and function in coastal receiving waters.

A Case History of the Science and Management Collaboration in Understanding Hypoxia Events in Long Bay, South Carolina, USA

Communication of knowledge between the scientific and management communities is a difficult process complicated by the distinctive nature of professional career goals of scientists and decision-makers. This article provides a case history highlighting a collaboration between the science and management communities that resulted from a response to a 2004 hypoxia, or low dissolved oxygen, event in Long Bay, off Myrtle Beach, South Carolina. A working group of scientists and decision-makers was established at the time of the event and has continued to interact to develop a firm understanding of the drivers responsible for hypoxia formation in Long Bay. Several factors were found to be important to ensure that these collaborative efforts were productive: (1) genuine interest in collaboratively working across disciplines to examine a problem; (2) commitment by agency leadership, decision-makers, and researchers to create successful communication mechanisms; (3) respect for each others’ perspectives and an understanding how science and management are performed and that they are not mutually exclusive; (4) networking among researchers and decision-makers to ensure appropriate team members are involved in the process; (5) use of decision-maker input in the formulation of research and monitoring projects; and (6) commitment of resources for facilitation to ensure that researchers and decision-makers are communicating effectively.

Local-scale characteristics of high-marsh communities next to developed and undeveloped shorelines in an ocean-dominated estuary, Murrells Inlet, SC

Anthropogenic alteration of terrestrial shorelines can have pronounced effects on marine environments at the upland-marsh boundary. Possible terrestrial development effects on several physical and biological variables of high-marsh habitats were examined along developed and undeveloped shorelines in an ocean-dominated, southeastern US estuary. Analyses of sediment characteristics suggested development of the upland boundary affected physical conditions within the high-marsh. For example, pore water salinities were greater along undeveloped shorelines during a non-drought period even after rain events. Significant floral and faunal differences also existed between shoreline treatments. Black needle rush stems were significantly taller and marsh periwinkle densities significantly greater, but eastern coffee bean snail densities were significantly reduced along developed shorelines. Benthic infaunal community abundance and composition also were significantly different between shoreline treatments with sand fly larvae, human pest precursors, either only present or present in greater densities along developed shorelines. Sediment respirometry experiments indicated significant differences in heterotrophic and autotrophic processes occurring between shoreline treatments. Greater sediment surface temperatures along developed shorelines provided one possible mechanism driving high-marsh responses to boundary alteration. The history and extent of shoreline development along with a tendency in ocean-dominated southeastern marshes to resist change likely influenced current ecological conditions within our high-marsh study areas. A greater understanding of the driving mechanisms producing localized effects on salt marshes and recognizing regional differences in marsh resistance to change will facilitate predictions of shoreline development consequences and help in proposing effective management strategies for coastal boundaries.

Benthic-Pelagic Coupling in Marsh-Estuarine Ecosystems

Active and passive mechanisms utilized by many organisms in marsh-estuarine ecosystems couple the water column to the bottom. These linkages are often engineered by dense populations of plants (marshes) or animals (beds and reefs) that use their organismic structure, i.e., bodies or shells, and functional processes, i.e., water pumping, suspension feeding, etc., to enhance the movement of materials between the two habitats. These adaptations to the benthic boundary layer result in organismically mediated fluxes of materials between the water and the bottom that may dramatically alter either or both habitats. Dense stiff blades of grass dominate the salt marsh component of marsh-estuarine ecosystems. This structure ensures low water flow, low shear velocities, high drag and high roughness at the benthic boundary. These physical factors allow molecular diffusion and sedimentation to dominate exchange mechanisms. Marsh mussels magnify benthic-pelagic coupling by their active pumping and filtration of water. The shells of bivalve beds form a rough benthic surface that enhances turbulent mixing and increases the width of the benthic boundary layer. These beds can remove, via sedimentation (passive) and filtration (active) mechanisms, enormous quantities of suspended materials (phytoplankton, etc.) from the water and release, as a result of metabolism, large amounts of dissolved inorganic substances into tidal currents. In some systems, bivalve beds are equivalent to saltmarshes in processing materials. There have been few studies on benthic-pelagic coupling by marsh-estuarine mudflats. In marsh related mudflats, there is low water flow, shear velocities, drag and smooth surfaces. Both passive and active coupling mechanisms are common to mudflats, but there is little direct information available. The high ratio of bottom surface area to tidal water volume over these flats suggests a great potential for material exchanges. At the system level, coupling processes directly involve marshes and animals in the cycling of major nutrients not only within the shallow tidal marsh-estuarine ecosystem, but also with the adjacent coastal ocean. The magnitude of these system level couplings has only been identified in a few locations, but they are almost always related to high productivity sub-systems, i.e., mussel beds and oyster reefs.