The location and areal extent of eelgrass meadows

in northern and eastern Bellingham Bay, Washington

Introduction

Eelgrass meadows are important habitats for various life stages of fish and invertebrates. After moving from freshwater to the sea, juvenile salmon find food and cover in nearshore habitats, such as eelgrass meadows. Adult Dungeness crabs come into shallow water to molt and mate, often in eelgrass meadows. Oysters, clams, and juvenile starry flounder are examples of other animals that live in eelgrass meadows.

Eelgrass is found were growth requirements are available. Suitable substrate is sand or a mixture of sand and mud. Clear water that permits transmission of sunlight also is important for these vascular plants.

Various species of eelgrass occur throughout the world. Locally, Zostera marina is the native eelgrass that generally grows no higher than +1.0" MLLW. Maximum depth is subtidal between -6.0' and -25.0' MLLW depending on water clarity. An introduced species, Zostera japonica, is found in the bay and is intertidal in distribution.

Since settlement, Bellingham Bay has experienced many changes in its nearshore structure. Historically, gently sloping bottomlands were located at the base of bluffs throughout Bellingham Bay. Meeting the requirements of substrate and sunlight, nearshore bottomlands probably contained eelgrass meadows. Currently within urbanized parts of the bay, much of these bottomlands are filled and used for recreational, commercial, and industrial purposes. With a reduction in the probable extent of historic areas of eelgrass, it becomes important to assess the area and location of existing eelgrass meadows. Resultant findings can be used by resource managers at local and state levels, as well as recreational and wildlife interests.

 

Methods and materials

During summer 1994, a search of existing agency information found that with a few exceptions, locations of eelgrass meadows in Bellingham Bay were schematic or unknown. Similarly, review of infra-red aerial photographs showed isolated patches and no eelgrass information could be obtained for areas that were submerged at the time the photograph was taken.

Also during summer 1994, the shoreline of Bellingham Bay was surveyed from the Nooksack River delta to Post Point. Methods included reconnaissance and surveys. Eelgrass at each location was identified to species. Reconnaissance occurred while walking the shoreline on minus tides or skirting the shoreline in a boat. Surveys were conducted on the Nooksack River delta by recording a series of global positioning system (GPS) points while walking, on minus tides, around meadow perimeters. Surveys between Marine Park and Post Point were based on a series of transects started at the base of riprap and extended due west. Distance to the beginning and terminus of meadow was recorded. Often the western margin of the meadow was in the shallow subtidal and was found by swimming.

The size and shape of eelgrass meadows was calculated in several ways. Atlas-draw, a computer program, determined the configuration and area of eelgrass meadows on the Nooksack River delta. A series of polygons was used to approximate the area of the Marine Park eelgrass meadow. No attempt was made to determine the size of eelgrass patches found during reconnaissance surveys, although the size of small isolated meadows was estimated.

Results

The GPS points obtained while surveying the Nooksack River delta are contained in Tables 1 and 2 of Appendix IV. An introduced species, Zostera japonica, occupied the meadows located between 0.0 and +2.0 feet MLLW on both sides of the delta. The west side of the delta contained a sparsely colonized meadow of approximately 200 acres. The meadow located on the east of the delta occupied approximately 230 acres with dense shoot development on about fifty acres. These areas are mapped in Figure 8.

Located between -7.0' and+2.0 MLLW, the predominant species at Marine Park was Zostera marina, although interspersed patches of Zostera japonica were identified at higher intertidal elevations. Transect distances and a related map for the Marine Park meadow are contained in Table 3 and Figure 1 of Appendix IV. Total area was thirteen acres which forms the largest contiguous eelgrass meadow in urbanized Bellingham Bay. This area also is included in Figure 9.

Reconnaissance surveys found eelgrass, Zostera marina, in several locations. In the north bay, the area by the cement plant pier and near Hilton Harbor marina showed sparse colonization. Patches of colonizing Zostera marina were found from the Georgia Pacific warehouses at the base of Cornwall Avenue south to northern boundary of Boulevard Park. Zostera marina patches skirted the shoreline of Boulevard Park and a meadow of approximately one acre was located west of the pottery studio. Patches of Zostera marina were located between the southern end of Boulevard Park and the mouth of Padden Creek. Part of this area was included in an unpublished survey (Webber, 1993). Meadows, respectively one-half and one acre, were located at Taylor Street docks and in the embayment by Padden Creek Marine. Locations of patches and small meadows are illustrated in Figure 9.

Discussion

Documented colonization by Zostera japonica on the Nooksack River delta is of interest for several reasons. It identifies the extent to which this species is spreading since its documented introduction at Semiahmoo and Boundary bays. Eelgrass at the Nooksack River delta did not appear on 1992 infra-red aerial photographs for several possible reasons Infra-red aerial photographs sometimes are unable to detect areas of sparse vegetation. It is also possible that colonization occurred since 1992. Mild winters with little flooding would facilitate continued growth of eelgrass. By contrast, sustained freezes could kill rhizomes and flood sediments could cover rhizomes, particularly vulnerable because of intertidal location.

As evidenced by the location of fish trap pilings on the delta, historically, water was deeper in the areas presently occupied by Zostera japonica. The delta has been growing rapidly, since the 1930's, when Nooksack River discharge was directed to Bellingham Bay. Deposition has resulted in a tremendous increase in intertidal area at the delta, a portion of which now is being colonized by Zostera japonica. A sequence has occurred, accelerated over the past 65 years, starting with deeper water, then deposition, then colonization by an introduced species. Zostera japonica provides food for migratory birds and its nutritional value, compared with Zostera marina, presently is being investigated (Thomas Mumford, 1992). Although this eelgrass provides food, its location in the mid intertidal minimizes the time it can be used as cover habitat for marine fish and invertebrates. As the delta front advances, it is possible that deeper Zostera marina meadows will be covered by sediment and, in time, colonized by Zostera japonica.

Patches of eelgrass located in the northern and eastern bay are important indications that with suitable substrate and sunlight, eelgrass will recolonize disturbed areas. Locations were this is in evidence include patches near the cement plant pier, Hilton Harbor marina, the area between the Georgia Pacific warehouses and Boulevard Park, and the area between Boulevard Park and Padden Creek. Although present day shorelines differ from historical shorelines, eelgrass recolonization supports the concept that, historically, eelgrass meadows fringed much of the northern and eastern bay. Eelgrass recolonization also suggests that suitable growth requirements presently exist in the bay that could support additional colonization. The fate of these colonizing areas should be considered when reviewing nearby land use proposals with the intent of fostering continued growth.

The area between the Georgia Pacific warehouses and Boulevard Park is one of the few remaining in urbanized Bellingham Bay in which the historical shoreline is modified only by the railroad bed. Most other existing shorelines in the urban bay are modified with fill and shore armoring. This area could be considered for restoration of a large eelgrass meadow, a marine wetland, should funding become available. Should restoration be considered, design and execution must be consistent with growth parameters such as sediment type, the gradient of submerged bottomlands, and the depth to which light will penetrate.

Eelgrass patches and meadows between Boulevard Park and Padden Creek are being considered in plans of the Bellingham Parks Department. To date, other wildlife enhancements, such as bird houses, have been placed by Taylor Street docks. Continuing support of park plans for this area will promote public shoreline contact and could augment growth of existing eelgrass habitat.

The eelgrass meadow located between Marine Park and Post Point is the largest contiguous meadow in urbanized Bellingham Bay. As such, an effort should be made to conserve it. Review of nearby land use proposals should consider potential affects to the meadow. Because areas near the meadow are extensively used for recreational purposes such as clamming and beach exploration, efforts should be made with public education about the important role this habitat provides for several fish and invertebrates. Education efforts should also address ways in which individuals, through beach etiquette, can minimize damage to beaches and eelgrass meadows.

In summary, eelgrass meadows are one of the most important nearshore habitats in estuarine areas, such as Bellingham Bay. Changes to the areal extent of colonizing Zostera japonica on the Nooksack River delta should be monitored. Patches of colonizing Zostera marina in the northern and eastern bay suggest eelgrass meadows can coexist with adjoining urban land uses. The area between the Georgia Pacific warehouses and Boulevard Park should be considered for future restoration of an eelgrass meadow. Efforts should be made to support plans that will conserve eelgrass patches and meadows located from Boulevard Park to Post Point. It appears that given suitable conditions in Bellingham Bay, eelgrass meadows can coexist with urban land uses and increase in areal extent.

 

References

Mumford, T. 1992. Department of Natural Resources. Personal communication.