Prepared by the University of Connecticut and the Connecticut DEP, with the support of researchers and organizations throughout the Long Island Sound watershed.
Establishing restoration objectives for eelgrass in Long Island Sound

Habitat Criteria

The Habitat Requirements Approach

Primary Requirement - Light

Much of the research defining habitat requirements for Zostera marina was conducted in the Chesapeake Bay area. The original guidelines for habitat suitability identified adequate light availability as one of the most important requirements for seagrass (Batiuk et al. 1992; Dennison et al. 1993).

Note the fouling organisms on the eelgrass leaves. Epiphytes reduce the light reaching the leaf surface by an average of 30%. Seen in the picture are epiphytic macroalgae, white Spirorbis borealis "coiled worm" tubes, and the orange Pacific colonial tunicate, Botrylloides violaceaus. The spider crab is a common forager in eelgrass beds. (photo courtesy of P. Auster, University of Connecticut)
The light reaching the leaf surface is influenced by the water column light attenuation coefficient, which results from absorption and scattering of light by particles in the water, and by absorption of light by the water itself. The particles in the water responsible for absorption and scattering are primarily phytoplankton, measured as chlorophyll a, and total organic and inorganic particles, measured as total suspended solids. The epiphytes on the leaf surface also contribute to the light absorption. In a revision of the original habitat guidelines for Chesapeake Bay, a relationship was developed to estimate the contribution of the epiphyte biomass to light attenuation (Batiuk et al. 2000; Kemp et al. 2004).

The Chesapeake Bay guidelines identified minimum habitat requirements by statistically analyzing those components of the environment that interact to control eelgrass distribution. Nutrients were included as they stimulate the production of both phytoplankton and epiphytes.

Yarish et al. (2006) applied the Chesapeake Bay minimum habitat requirements to seagrass in Long Island Sound, both through historical data and new research, and developed modifications to the Chesapeake Bay numbers for Long Island Sound (see summary table).

The newest revision of the habitat requirements for the Chesapeake Bay standards focus on the percent of light received by the leaf as the primary standard, versus the light extinction coefficient of the water. This allows the standard to be flexible based on the restoration goals for the area (figure 1). For instance, if eelgrass in a particular cove traditionally occupied depths to only 1.5 m due to bathymetry limitations or some other factors, the maximum allowable Kd would be 1.0 m-1. If the restoration goal was to restore eelgrass to a depth of 3.0 m in a particular area, the maximum allowable Kd would be 0.5 m-1.

Figure 1. Maximum allowable Kd (m-1) for eelgrass growth at the listed depth and a minimum requirement of 22% of surface light. Calculated using the Lambert-Beer equation.

Secondary Requirements - Nitrogen, Chlorophyll, Total Suspended Solids (TSS), Sediment Percent Organics

Water column dissolved inorganic nitrogen concentration (DIN), chlorophyll a concentration (chl a), and total suspended solids (TSS) have been identified as secondary habitat requirements. The secondary requirements can be used to explain the absence of eelgrass if light availability is sufficient but one of these factors greatly exceeds the tolerance limits of eelgrass (see summary table). Dissolved inorganic phosphorous (DIP) is included in the Chesapeake Bay Guidelines, which also include the management of a number of freshwater vascular plant species. In Long Island Sound, the submerged aquatic vegetation of interest are all marine, and are primarily limited by nitrogen. Sediment percent organics is considered a "habitat constraint," meaning that the value typically is found within a certain range where eelgrass is able to grow.

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Multiple Requirements

More than just light must be suitable for eelgrass to colonize an area. The following diagram illustrates the major requirements and the interactions between these factors which constitue a healthy eelgrass ecosystem.

Figure created by J. Vaudrey, based on the interactions diagram presented in Batiuk et al. 2000. Symbols courtesy of the Integration and Application Network (ian.umces.edu/symbols/), University of Maryland Center for Environmental Science.

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References

Batiuk, R. A., R. J. Orth, K. A. Moore, W. C. Dennison, and J. C. Stevenson. 1992. Chesapeake Bay submerged aquatic vegetation habitat requirements and restoration targets: A technical synthesis. report number CBP/TRS-83/92. Virginia Inst. of Marine Science, Gloucester Point (USA)

Batiuk, R. A., P. Bergstrom, M. Kemp, E. W. Koch, L. Murray, J. C. Stevenson, R. Bartleson, V. Carter, N. B. Rybicki, J. M. Landwehr, C. L. Gallegos, L. Karrh, M. Naylor, D. Wilcox, K. A. Moore, S. Ailstock, and M. Teichberg. 2000. Chesapeake Bay submerged aquatic vegetation water quality and habitat-based requirements and restoration targets: A second technical synthesis. Annapolis, Maryland: United States Environmental Protection Agency. Report for the Chesapeake Bay Program. report number CBP/TRS 245/00 EPA 903-R-00-014.

Dennison, W. C., R. J. Orth, K. A. Moore, J. C. Stevenson, V. Carter, S. Kollar, P. Bergstrom, and R. A. Batiuk. 1993. Assessing water quality with submersed aquatic vegetation. Bioscience 43:86-94.

Kemp, M., R. Batiuk, R. Bartleson, P. Bergstrom, V. Carter, C. L. Gallegos, W. Hunley, L. Karrh, E. W. Koch, and et al. 2004. Habitat Requirements for Submerged Aquatic Vegetation in Chesapeake Bay: Water Quality, Light Regime, and Physical-Chemical Factors. Estuaries 27:363-377.

Yarish, C., R. E. Linden, G. Capriulo, E. W. Koch, S. Beer, J. Rehnberg, R. Troy, E. A. Morales, F. R. Trainor, M. DiGiacomo-Cohen, and R. Lewis. 2006. Environmental monitoring, seagrass mapping and biotechnology as means of fisheries habitat enhancement along the Connecticut coast. Stamford, Connecticut: University of Connecticut. Final Report submitted to the Connecticut Department of Environmental Protection, Hartford, CT. report number CWF 314-R.

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