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EELGRASS
2.4 DISCUSSION
2.4.1 Distribution in Project Vicinity
The distribution of eelgrass in the vicinity of Sears Island is probably limited by light penetration rather than other factors. The lower depth limit in 1992 was approximately -7 ft (-2.1 m) MLW; in 1994, eelgrass was observed at greater depths (-9.7 ft; -2.9m MLW). Eelgrass occurred in most substrate types identified in the nearshore area, ranging from silt and fine sands to cobble. Substrate conditions (Figure 2-1), in conjunction with current regime, may partially account for the varied distribution in the project area. Fonseca et al. (1983) distinguished three current regimes (low <50 cm/sec, medium >50 to <90 cm/sec, and high >90 cm/sec maximum monthly surface velocity) that control sedimentary conditions in eelgrass beds. Fonseca et al. (1983) found that the low current regime allowed even distribution of silt-clay particles; fine particle distribution under a high current regime was related to the canopy height and vertical gradient in velocity and therefore not uniform. Near-surface tidal currents up to 52 cm/sec have been measured in the immediate vicinity of the proposed terminal (NAI 1975; 1991), placing this area in the medium current regime (Fonseca et al. 1983). Other researchers (reported in Thayer et al. 1984) found that a current regime of 20-40 cm/sec promoted the most luxuriant growth. The current regime around Sears Island (documented in NAI 1975) generally falls in the range suitable for eelgrass growth, except in the southeastern portion. Short (1994) observed this distribution pattern to exist in 1994 while ground truthing 1992 aerial photographs.
Historical presence of eelgrass in the vicinity of Sears Island was noted in the EIS (USDOT and MDOT 1987). Beds of eelgrass had been studied in Long Cove and Stockton Harbor during 1974 and 1975. At that time coverage was about one acre (0.4 hectare) in Long Cove (near Kidder Point) and three acres (1.2 ha) in Stockton Harbor. Timson (1976) identified eelgrass beds only at the head of Long Cove. Short found this area to be a macroalgae-covered mussel bed in 1994 (pers. comm., 8/2/94). During a 1986 transect survey to document substrate and biological (especially species of fisheries value) conditions in Long Cove and the northwestern shoreline of Sears Island, divers observed a small patch off the eastern shore of Mack Point (USDOT and MDOT 1987). No eelgrass was observed along Sears Island at that time.
In Stockton Harbor, eelgrass has been documented as undergoing relatively long-term (decadal) fluctuations in standing crop. Eelgrass was reportedly virtually absent from the northwestern shoreline of Cape Jellison during the 1980s but was present in dense stands in 1991 and 1992 (NAT 1992a). The same pattern occurred in Long Cove (W. Hamilton, Searsport Harbonnaster, 11/15/93, personal communication). Wasting disease was documented as contributing to extensive dieback of eelgrass in southern Maine and New Hampshire during the 1980s (Short et al. 1986) and may have been a factor in the population shifts in the Penobscot Bay region. In 1992, biologists from NAI observed dead shoots within the bed, an indication that wasting disease could have been present at that time. Typically dead leaves float out of the bed, usually carried to the wrack line. Wasting disease tends to cause release of internal gases so dead leaves sink rather than float (Dr. F. Short, UNH, pers. comm., 11/30/93). Because the beds were not examined in greater detail for evidence of wasting disease, there is no information available to evaluate the extent of disease locally. However, as the beds observed around Sears Island in July 1994 (Short 1994) appeared to be healthy, it is unlikely that the disease is prevalent
Maine Department of Marine Resources is in the process of mapping eelgrass resources in Cobscook Bay, Penobscot Bay, Casco Bay and the Piscataqua River and plans to map other areas in the future (S. Barker, MDMR, 2/2/94, pers. comm.). The only regional information presently available is Short’s (1994) review and ground truthing of aerial photographs of portions of upper Penobscot Bay.
Aerial photographs taken in early October 1992 covering the areas from Sandy Point (Stockton Springs, north of Cape Jellison) to Brown’s Head (East Northport, south of Belfast) were examined for evidence of eelgrass and ground truthed in July, 1994 (Short 1994). Relatively large beds of eelgrass were observed at Sandy Point, the head of Stockton Harbor, southwestern Cape Jellison, the entire perimeter of Sears Island (except the southeastern and southern portion) the mouth of the Passawassakeag River (Belfast) and the cove near Browns Head (East Northport). Smaller patches occurred in several other locations, including near Delta Chemical in Stockton Harbor and east and south of Mack Point (Short 1994).
Ground truthing revealed variability in depth distribution in the areas examined. Off Sandy Point, eelgrass was limited to areas shallower than -2.3 ft (-0.7 m) MLW and to -8.3 ft (-2.5 m) MLW off Browns Head. Along the western shore of Sears Island, eelgrass occurred to -9.7 ft (-2.9 m) MLW in 1994. Preliminary review of aerial photographs from the rest of Penobscot Bay suggests that large eelgrass beds are present in the Bagaduce River and along Islesboro Island (F. Short, U7NH, 8/2/94, pers. comm.). In particular, the 1994 observations around Sears Island indicate how eelgrass coverage can change among years. Short (1994) found a virtually continuous band of eelgrass south of the proposed terminal site, including the cobbly area in the southern portion of the area investigated that was unvegetated in 1992 (see Figures 2-1 and 2-2).