Gulf of Maine: Council on the Marine Environment

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Identification of Important Habitats in Coastal New Hampshire

Chapter 3. Algae

Irish moss (Chondrus crispus), tufted red weed (Mastocarpus stellata) and rockweed, (Ascophyllum nodosum) are three species of macroalgae common to Gulf of Maine marine and estuarine intertidal areas. These plants often occur in adjacent stands. Their distribution is influenced by tidal elevation, salinity, wave energy, exposure to ice, and substrate. While all three typically grow adhering to rocky substrate, a form of rockweed (Ascophyllum nodosum ecad scorpioides) grows in saltmarshes, over organic and sandy soils. These species are of major ecological importance as cover or structure for fishes, birds, and invertebrates, and as primary producers of organic matter for coastal food chains; they also are of commercial importance as food and sources for pharmacologic products.

Algae habitat was identified from observations by Mathieson and Fralick (1972) and Mathieson and Hehre (1986); these data were supplied to us by A. Mathieson in a tabulated format, by species, with coordinates and descriptions of stations. We used the coordinates to produce a GIS point coverage, then verified or manually relocated the points (on 1:24,000 coastline base maps) to best correspond to the narrative descriptions. We were advised that the points represented the general locations of patches of algae.

The Great Bay Aerial Salt Marsh Mapping Project (Ward et al. 1991) delineated intertidal algae vegetation in Great Bay and the Piscataqua River, by aerial photo-interpretation. We used scanned copies of the original photos to screen-digitize additional algae polygons within our study area. Unlike the point occurrences, these polygons were not identified by species. On the other hand, the polygons showed the actual boundaries of the vegetated areas. We used GIS procedures to select polygons within 200' of the above point locations, then identified those polygons on the basis of the nearest point occurrence. The combined final coverage was converted to a grid-cell format. Each point occupies one cell, or about 0.2 acres, while polygons converted to clusters of cells. All were assigned a habitat quality score of 10 (0 to 10 scale) since the actual presence of the species demonstrated the suitability of conditions (Figures of; Irish Moss, Tufted Red Weed, Rockweed).