Gulf of Maine Council

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Identification of Important Habitats in Coastal New Hampshire

Chapter 7. Eelgrass

Eelgrass (Zostera marina)is a submergent vascular plant typically growing in subtidal inshore waters along the middle and northern Atlantic seaboard. It requires a muddy to sandy sediment, which is usually associated with moderate water currents and limited wave action. Eelgrass beds serve as structure and cover for marine and estuarine vertebrates and invertebrates, and as a primary producer of organic matter. Short (1992) documented the value of eelgrass to the Great Bay ecosystem.

DATA SOURCES: Dr. Fred Short (Jackson Estuarine Research Laboratory) provided us with a coverage of eelgrass beds in Great Bay based on 1990 photography, and a hard copy map of additional areas in the upper Piscataqua River mapped from a 1995 field survey. We obtained a coverage of eelgrass in the Maine side of the Piscataqua River produced by Seth Barker (Maine DMR), based on true color 1992 to 1995 1:12,000 aerial photos. We also digitized a map depicting eelgrass beds in Great Bay, Little Bay, and the Piscataqua River from 1980-1981 surveys by New Hampshire Fish and Game. The F. Short 1995 map and the Fish and Game maps were scanned, registered, and clipped to avoid overlap with uplands/intertidal wetlands and areas over 30' deep.

MAPPING OF HABITATS: Our eelgrass coverage was created by combining data from the above sources, updating or replacing older polygons representing specific eelgrass beds with the most accurate sources. Most of the polygons from the oldest surveys were matched with and replaced by polygons from the other coverages. The 1980-1981 survey mapped extensive eelgrass beds in Little Bay; these beds have been absent or greatly reduced in recent years (F. Short, pers. comm.), and so we did not regard them as currently suitable habitat. They were retained for reference in an intermediate coverage. The final habitat coverage included all polygons from the F. Short 1990 coverage and the S. Barker coverage, and polygons from the F. Short 1995 map which were not represented in either of those two coverages. It should be noted that other parts of coastal New Hampshire were not surveyed and may have eelgrass; these include Little Harbor, Portsmouth Harbor, and Back Bay.

The polygon coverage was converted to grid-cell format. All cells were assigned a habitat quality score of 10, or optimal habitat, since the actual presence of the species demonstrated the suitability of conditions (Figure of Eelgrass).