2003 Progress Report: Environmental Indicators in the Estuarine Environment: Seagrass Photosynthetic Efficiency as an Indicator of Coastal Ecosystem Health

EPA Grant Number: R828677C004
Subproject: this is subproject number 004 , established and managed by the Center Director under grant R828677
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: EAGLES - Atlantic Coast Environmental Indicators Consortium
Center Director: Paerl, Hans
Title: Environmental Indicators in the Estuarine Environment: Seagrass Photosynthetic Efficiency as an Indicator of Coastal Ecosystem Health
Investigators: Fonseca, Mark , Biber, Patrick , Kenworthy, Judson
Current Investigators: Fonseca, Mark , Biber, Patrick , Field, Donald , Gallegos, Charles L. , Kenworthy, Judson , Thursby, G.
Institution: National Oceanic and Atmospheric Administration (NOAA) , University of North Carolina at Chapel Hill
EPA Project Officer: Hiscock, Michael
Project Period: March 1, 2001 through February 28, 2003
Project Period Covered by this Report: March 1, 2002 through February 28, 2003
RFA: Environmental Indicators in the Estuarine Environment Research Program (2000) RFA Text |  Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Water , Ecosystems

Objective:

The objectives of this research project are to: (1)evaluate indicators of seagrass health and their role in estuarine processes; (2) examine physiological state of seagrass in response to environmental conditions (light, temperature, salinity) and correlate the plant’s physiological state with ambient conditions based on both in situ and remote sensed data sources; and (3) evaluate the feasibility of scaling field assessments to remote sensed data sources

Progress Summary:

Light availability to benthic seagrasses has been determined to be the major criterion limiting the distribution of seagrass in otherwise appropriate conditions. As light availability is based on water-column clarity, which is itself influenced by a multitude of anthropogenic and natural factors, issues related to monitoring light availability are paramount to managing seagrass habitats (see Figure 1). We have initiated a monthly water-sampling program in North River, NC, an estuary that contains considerable seagrass beds, along with a strong gradient in water clarity. Water samples are analyzed for absorption and scattering properties, and these are related to components of attenuation: chlorophyll, turbidity, and color. Data are being analyzed in collaboration with Dr. C. Gallegos at the Smithsonian Environmental Research Center (SERC).

Research has been initiated to link potential indicators of plant responses to water quality and light availability in an estuarine setting. Criteria for selection of successful indicators include:

  • Non-destructive, repeatable measures on the same plant.
  • Rapid response.
  • Sensitive to physiological processes within the plant.

Conceptual Diagram of Light Attenuation Down the Water Column (PLW), and the Relative Contributions of Turbidity, Chlorophyll, and Color to Attenuation, Resulting in Significantly Reduced Light at Depth

Figure 1. (A) Conceptual Diagram of Light Attenuation Down the Water Column (PLW), and the Relative Contributions of Turbidity, Chlorophyll, and Color to Attenuation, Resulting in Significantly Reduced Light at Depth. Additional attenuation can occur at the leaf surface due to epiphyte fouling (PLL), which occurs primarily under heavily eutrophic conditions. (B) Graphical representation of the bio-optical model. Components of light attenuation in the water column are presented on the axes as concentrations in which they are typically measured. Median concentrations for one sample are plotted on this graph and compared to a minimum-light water quality requirement for a given depth (red line of constant attenuation), which is calculated using a radiative-transfer model and knowledge of seagrass species light requirements. Target minimum water-clarity requirements for seagrass survival are found at the intersection of vectors perpendicular to the axes or the origin from the median sample concentration. The target concentrations in this figure suggest that both TSS and Chl-a need to be reduced to meet the minimum light requirements of this seagrass species.

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

  • Photosystem fluorescence using a Plant Efficiency Analyzer (PEA).
  • Leaf morphology (length and width).
  • Leaf reflectance spectra as a proxy for chlorophyll content.

The indicators investigated ranged in their ability to predict 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 sub-lethal 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 also are investigating the utility of leaf reflectance spectra as a non-destructive technique to measure chlorophyll content in seagrass leaves.

Ongoing sampling of water quality in both the North River and Pamlico Sound occurred throughout 2003 to parameterize the bio-optical model created by Dr. C. Gallegos. A total of 152 water samples were collected from 9 sites in the North River (see Figure 2), around beds of the seagrass Zostera marina, for the purpose of generalizing the bio-optical indicator model. Another 54 samples were collected from 9 stations in Pamlico Sound. Development of the indicator required estimates of the mass-specific absorption and scattering coefficients of the suspended particulate matter from each of these locations. Analyses indicate that absorption and scattering per unit mass of suspended solids at the more energetic sites in North River are lower than at the more protected sites being studied in the Chesapeake Bay by the Atlantic Slope Consortium (ASC). Cooperative efforts between the ASC and the Atlantic Coast Environmental Indicators Consortium (ACE INC) EaGLes projects are being undertaken to develop a regionally extensive atlas of optical properties for broad geographic application of this indicator.

Selected Results From a Monthly Water-Quality Monitoring Program in the North River

Figure 2. Selected Results From a Monthly Water-Quality Monitoring Program in the North River. Time-Space contour plots of temperature, salinity, Chl-a concentration, and turbidity measured monthly from September 2002 to December 2003. Sites are numbered from downstream (1) to upstream (9).

We tested two in situ seagrass bioassays: (1) RopeAssay was successful; (2) TubAssay was unsuccessful, to evaluate the effects of water quality on seagrass survival and growth (see Figure 3).

Schematic of Seagrass RopeAssay (A) and TubAssay (B) To Detect Responses of Plants to Water Quality and Light-Attenuation With Increasing Depth

Figure 3. Schematic of Seagrass RopeAssay (A) and TubAssay (B) To Detect Responses of Plants to Water Quality and Light-Attenuation With Increasing Depth. Plants are placed in each container and changes between initial and final parameters are recorded. The effect of water quality on plant survival and growth is evaluated between sites by comparing the magnitude of the changes observed.

A pilot experiment in 2002 indicated that Z. marina (eelgrass) could potentially 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.

In 2003 we undertook two additional full-scale light-stress experiments on Z. marina, the winter dominant, and compared it with H. wrightii, the summer dominant species in North Carolina (see Figure 4). These experiments were designed to determine minimum light requirements for these two species and evaluate potential indicator measurements. The results are broadly applicable to seagrass habitats along the entire eastern seaboard of the United States.

Products

The Bio-optical Modeling Pamphlet was distributed at numerous state agency and national meetings.

Plant Growth and Photosynthesis Responses for Z. marina and H

Figure 4. Plant Growth and Photosynthesis Responses for Z. marina and H. wrightii in the Seven Irradiance Treatments (units of μmol m-2 s-1) in the Light Gradient Experiment. Selected variables shown are: mean number of shoots per plant (n = 18), length of longest leaf measured as a proxy for canopy height, leaf area (single surface), and photosynthesis yield ratio (Fv/Fm).

Future Activities:

We will continue ongoing sampling of water quality in both the North River and Pamlico Sound through the end of 2004, to monitor conditions suitable for SAV survival, and further the bio-optical model parameterization. In support of the bio-optical indicator development, we also will determine the depth limits of three decadally-stable Zostera beds in North River, to test and refine predictions of the model.

We will continue ongoing assessment of the suitability of the RopeAssay for use in water-quality assessments for SAV suitability. Two deployments are planned for 2004, one in March/April using Zostera, and a second in August/September using Halodule. Concurrent with both seagrass deployments, we are collaborating with R. Snyder of UWF (CEER-GOM EaGLe) to deploy his biofilm collectors, and train two of his graduate students on HPLC and other techniques routinely undertaken at the Paerl laboratory.

We will perform two experiments in the NOAA greenhouse facility to determine the importance of timing and duration of light attenuation events (e.g., turbidity plumes/extreme phyto blooms) on seagrass survival. This experiment will compare the responses of Zostera seedlings (2-3 months old) against adults of the same species (> 1year) and against Halodule, a second ubiquitous seagrass species.

We will develop and implement real-time operational indicators of water quality aspects of relevance to SAV. This is primarily a software-based implementation of an expert-system that relies on the knowledge developed in this project and will be a tool that is available to resource managers to assist in the setting of relevant TMDL’s to protect SAV resources.

We will run a pilot project to assess PAR (Photosynthetically Available Radiation) versus PUR (Photosynthetically Usable Radiation) along a latitudinal gradient in water quality from Chesapeake Bay to Belize. This is a collaboration with Dr. C. Gallegos at SERC.

We will further refine leaf reflectance data as a non-invasive, non-destructive measure of chlorophyll content. Destructive analyses of tissue samples to develop regressions for reflectance versus Chl-a concentration are ongoing, and will provide the first data on this approach for both Zostera and Halodule species.


Journal Articles on this Report : 1 Displayed | Download in RIS Format

Other subproject views: All 37 publications 7 publications in selected types All 6 journal articles
Other center views: All 383 publications 99 publications in selected types All 88 journal articles
Type Citation Sub Project Document Sources
Journal Article Biber PD, Harwell MA, Cropper, Jr. WP. Modeling the dynamics of three functional groups of macroalgae in tropical seagrass habitats. Ecological Modeling (accepted, 2003). R828677C004 (2003)
R827453 (2002)
R827453 (Final)
not available

Supplemental Keywords:

seagrass, bio-optics, nutrients, bioindicators, conservation, environmental assets, scaling, aquatic, habitat, estuary, coastal, regionalization, integrated assessment, restoration, water quality and habitat management, remote sensing,, RFA, Scientific Discipline, Water, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, RESEARCH, estuarine research, Ecosystem/Assessment/Indicators, Ecosystem Protection, Ecological Effects - Environmental Exposure & Risk, Monitoring, Environmental Monitoring, Ecological Monitoring, Ecological Risk Assessment, Ecology and Ecosystems, Ecological Indicators, remote sensing, bioindicator, bioassessment, ecoindicator, aquatic biota , indicator plants, diagnostic indicators, estuarine ecosystems, ecosystem indicators, estuarine ecoindicator, aquatic ecosystems, environmental indicators, water quality, estuarine waters, seagrass photosynthesis, biogeochemistry, environmental stress indicators, bio-optics

Relevant Websites:

http://www.aceinc.org Exit

http://www.marine.unc.edu/paerllab/research/seagrass/index.html Exit

Progress and Final Reports:

Original Abstract
  • 2001
  • Final Report

  • Main Center Abstract and Reports:

    R828677    EAGLES - Atlantic Coast Environmental Indicators Consortium

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R828677C001 Phytoplankton Community Structure as an Indicator of Coastal Ecosystem Health
    R828677C002 Trophic Indicators of Ecosystem Health in Chesapeake Bay
    R828677C003 Coastal Wetland Indicators
    R828677C004 Environmental Indicators in the Estuarine Environment: Seagrass Photosynthetic Efficiency as an Indicator of Coastal Ecosystem Health