Grantee Research Project Results

Based on these criteria, indictors that are being investigated include:

The indicators investigated ranged in their ability to predict the demise of the plants because of light stress. Contrary to expectation, PEA was not promising because of continuing acclimation by the plants to low light conditions. PEA is unlikely to be a suitable tool to measure sublethal chronic stress responses in seagrass. Leaf chlorophyll a was found to be a very sensitive measure of physiological changes in response to light deprivation, as has been indicated by previous researchers. We are investigating the utility of leaf reflectance spectra as a nondestructive technique to measure chlorophyll content in seagrass leaves.

A pilot experiment indicated that Zostera marina (eelgrass) potentially could tolerate up to 30-45 days of zero light conditions before 100 percent mortality occurred. The tropical species, Halodule wrightii (shoalgrass) however, experienced total mortality in less than 28 days. These interspecific differences in tolerance to light deprivation are complicated by the ability of different individuals to withstand light deprivation over a range of durations.

A second light-stress experiment was started in January 2003, to address the ability of leaf reflectance spectra to indicate physiological stress in seagrass plants at various stages of maturity grown under a range of limiting light conditions.

Field experiments also were commenced in early 2003, to establish links between water quality and seagrass survival under various conditions along the gradient of water quality that exists in North River. To date, results indicate that hydrodynamic regime may be more important than light availability in determining the success of seagrass in this estuary.

Future Activities:

Future activities include ongoing sampling throughout 2003 of water quality in both North River and Pamlico Sound to parameterize the optical indicator model being evaluated by Chuck Gallegos. Development of the indicator requires estimates of the mass-specific absorption and scattering coefficients of the suspended particulate matter from each of these locations. Cooperative efforts between the Atlantic Slope Consortium and the Atlantic Coast Environmental Indicators Consortium Estuarine and Great Lakes projects are being undertaken to develop a regionally extensive atlas of optical properties for broad geographic application of this indicator.

Testing and refinement of an in situ seagrass bioassay is underway to evaluate the effects of water quality on seagrass survival and growth. Plans for 2004 are to evaluate the performance of this method in the Chesapeake Bay to develop regional level confidence in the bioassay.

For the remainder of 2003, we will undertake light stress experiments on Zostera marina (eelgrass), the winter dominant species, and compare with Halodule wrightii (shoalgrass), the summer dominant species in North Carolina. These experiments are designed to determine minimum light requirements for these two species and evaluate potential indicator measurements. The results will be broadly applicable to seagrass habitats along the entire eastern seaboard of the United States.

Further refinement of leaf reflectance data as a noninvasive, nondestructive measure of chlorophyll content is being conducted. Destructive analyses of tissue samples to develop regressions for reflectance versus chlorophyll concentration is ongoing, and will provide the first data on this approach for both Zostera and Halodule spp.

Journal Articles:

Supplemental Keywords:

Progress and Final Reports: