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2.0 EELGRASS
2.1 INTRODUCTION
Evidence that the attached vascular plant, eelgrass (Zostera marina), has occurred in the Long Cove area historically was presented in the EIS (USDOT and MDOT 1987). During 1974 and 1975, Central Maine Power authorized an extensive survey of marine resources in the waters around Sears Island. Included in this survey were investigations on the distribution and production of eelgrass (NAI 1975). Beds of eelgrass were mapped in Long Cove north of the causeway (in mid-September 1974 and mid-June 1975) and at the head of Stockton Harbor (in mid-June 1975; NAI 1975). Beds in both areas extended from mean low water to about -2 feet (-0.6 in). Although a transect was examined for flora in the vicinity of the proposed cargo terminal on Sears Island, no eelgrass was reported.
On October 1 and 2, 1986, divers swam 1500 foot (457 meter) long transects emanating from the shorelines of Mack Point, Long Cove and Sears Island (USDOT and MDOT 1987). On these transects, divers recorded information on habitat conditions, including substrate characteristics and vegetation. Eelgrass was observed on only one transect in Long Cove. No eelgrass was recorded on either of the transects located off of Sears Island. However, the primary focus of these investigations was to collect information on commercially important fisheries resources.
2.2 METHODS
Members of the Sears Island Marine Resources Technical Team, including MDOT, MDMR, NMFS, USEPA and NAI, convened to develop appropriate protocol for evaluating existing eelgrass conditions in the proposed project area. Low-tide aerial photographs of the western shoreline of Sears Island, flown in August 1990, were reviewed for evidence of eelgrass but were inconclusive. A preliminary field survey, designed to identify substrate conditions and presence of eelgrass, was developed by the team. It was determined that representatives from NMFS and USEPA would participate with NAI in the preliminary field survey so that the results could be evaluated immediately and areas requiring additional investigations could be identified.
The area encompassing alternative project locations on the northwest portion of Sears Island was examined for eelgrass on August 31, 1992. Survey boundaries correspond to the High Intensity Study Area established for the wildlife survey (NAI 1993a). The maximum depth that eelgrass was expected to occur in the area was -18 feet (-5.5 m) MLW, based on anticipated water clarity. This was assumed to be the seaward limit of the survey, subject to modification in the field based on initial findings.
Starting at the southern end of the survey area, field personnel, including representatives from NMFS, USEPA and NAI were split into three groups. Two biologists waded along the shoreline; mid-depth areas (-6 to -8 feet, or -1.8 to -2.4 m, deep at MLW) were observed through a viewbox and by a snorkler. SCUBA divers swam along the -11 foot (-3.3 m) MLW contour. North of the existing jetty, the tide was too high to observe eelgrass successfully from the shoreline. In this area, divers swam longshore transects at depths less than -7 feet (-2.1 m)(MLW), although they were instructed to determine the offshore location of eelgrass if it were beyond this depth zone. Observers recorded substrate conditions and semiquantitative observations on eelgrass. For the day of the eelgrass survey, NOAA Tide Tables predicted low tide (-1.0 ft, or -0.3 m, MLW) to occur at 0743 (daylight savings time) and high tide (+11.2 ft. or +3.4 m, MLW) at 1403 (DST) in the Searsport area. The survey was conducted between 0700 and 1400 hr (DST). Calm wind and wave conditions prevailed throughout the survey, so no adjustments to depth due to these factors were considered necessary. Actual depth, based variously on divers depth gauges and a Hummingbird Model LCR400 depth meter, and time were recorded at seaward edge of eelgrass beds so that depths could be corrected to mean low water.
An assessment of the distribution of eelgrass in Penobscott Bay is currently being conducted by Dr. F. Short (UNH). Initial evaluation of aerial photographs (taken October 1992) has been completed and Dr. Short is supplementing these results with low-altitude reconnaissance (in 1993-1994) and, in some cases, ground-truthing (in 1994) to improve the accuracy of these delineations. Dr. Short has provided NAI with preliminary informationconcerning areas he ground-truthed in July 1994 (Sandy Point in Stockton Springs to Browns Head in East Northport). These results are briefly described where they are relevant to the 1992 survey.
2.3 RESULTS
Sketch maps of subtidal substrate conditions and approximate eelgrass cover were prepared from observers’ field notes (Figures 2-1 and 2-2). The substrate offshore of Sears Island consisted predominantly of a silt or sand matrix with varying proportions of gravel, cobble, boulders, and mussels (Figure 2-2). Eelgrass shoots were observed in most substrate conditions, with the exceptions of ledge, on boulders and a mussel bed associated with cobble. Eelgrass was observed even in very gravelly areas where wave-induced abrasion could be high. In some areas north of the jetty, dead shoots were observed within the beds.
Eelgrass was not observed in water depths greater than -7 feet (-2.1 m) MLW in 1992. Eelgrass was observed growing close to the edge of the dredged area approximately 200 feet (61 m) south of the jetty. The post-dredging bathymetric survey (Owen Haskell Inc. 1985) indicated that the depth of the top of the 1:1 dredged slope in this area was shallower than -7 ft (-2.1 m) MLW in 1985. In July 1994, eelgrass was observed to occur in depths up to -9.7 ft (-2.9m) MLW in the vicinity of the proposed project (F. Short, UNH, pers. comm. 8/2/94).
Although eelgrass was not quantitatively sampled, estimates of cover were made. Relative cover provides an indication of whether the eelgrass was scattered or concentrated in a cohesive bed. Areas where eelgrass occurred as scattered shoots with distances between shoots generally greater than 1.5 ft (0.5 m) were categorized as sparse. The small patch category encompassed areas where inter-shoot distances were generally smaller but densely vegetated patches were less than approximately 1.5 ft (0.5 m) in diameter and unvegetated areas were distinct. The large patch category included areas where the vegetation was relatively uniformly distributed but substrate was clearly visible. In comparison, the very dense category was used for areas where eelgrass dominated the field of vision. These categories describe conditions existing on August 31, 1992.
The eelgrass beds along the Sears Island shoreline provided habitat for other organisms. Juvenile starfish, mussels and snails were observed on eelgrass blades. Winter flounder, cancer crabs, green crabs and starfish were observed within vegetated areas. Epiphytes occurred on some plants.