Seagrass Indicators Development

Patrick Biber, Ph.D. - GCRL Botany

Healthy seagrass bed (Thalassia testudinum) in Biscayne Bay, Fla. Note the clear water.

Submersed Aquatic Vegetation (SAV or seagrasses) are important indicators of estuarine health.

Dennison et al. (1993) made the analogy between canaries used in mining and SAV as “early-warning” indicators.

SAV are potentially sensitive indicators of declining water quality (i.e., increased light attenuation) because of their high light requirements (15-25% of light at the water surface), compared to that of other aquatic primary producers (typically <5%).

Increased light attenuation is a function of increased:

  1. turbidity, expressed as total suspended particulate matter (mg/L SPM),
  2. phytoplankton, expressed as chlorophyll concentration (ug/L Chl a),
  3. colored dissolved organic matter (CDOM), a result of natural leaching from decaying vegetation.
  4. macroalgae and epiphytic microalgae that grow on the seagrass. These are usually most problematic when eutrophication is taking place.

We are using a bio-optical modeling approach (Gallegos 1994, 2001) to enable us to determine the relative contributions of SPM, CHL a, and CDOM to light attenuation.  This is a very important step in understanding and managing water quality for SAV protection as it makes explicit the relative contribution of these three parameters to light attenuation.

To develop PREDICTIVE indicators of SAV health for management purposes we are concentrating on developing software applications using the bio-optical models and existing monitoring data.

Learn more about our bio-optical modeling approach. (490KB PDF)