The Status of Eelgrass, Zostera marina, as Bay Scallop Habitat: Consequences for the Fishery in the Western Atlantic

Zostera marina is a member of a widely distributed genus of seagrasses, all commonly called eelgrass. The reported distribution of eelgrass along the east coast of the United States is from Maine to North Carolina. Eelgrass inhabits a variety of coastal habitats, due in part to its ability to tolerate a wide range of environmental parameters. Eelgrass meadows provide habitat, nurseries, and feeding grounds for a number of commercially and ecologically important species, including the bay scallop, Argopecten irradians. In the early 1930’s, a marine event, termed the “wasting disease,” was responsible for catastrophic declines in eelgrass beds of the coastal waters of North America and Europe, with the virtual elimination of Z. marina meadows in the Atlantic basin. Following eelgrass declines, disastrous losses were documented for bay scallop populations, evidence of the importance of eelgrass in supporting healthy scallop stocks. Today, increased turbidity arising from point and non-point source nutrient loading and sediment runoff are the primary threats to eelgrass along the Atlantic coast and, along with recruitment limitation, are likely reasons for the lack of recovery by eelgrass to pre-1930’s levels. Eelgrass is at a historical low for most of the western Atlantic with uncertain prospects for systematic improvement. However, of all the North American seagrasses, eelgrass has a growth rate and strategy that makes it especially conducive to restoration and several states maintain ongoing mapping, monitoring, and restoration programs to enhance and improve this critical resource. The lack of eelgrass recovery in some areas, coupled with increasing anthropogenic impacts to seagrasses over the last century and heavy fishing pressure on scallops which naturally have erratic annual quantities, all point to a fishery with profound challenges for survival. The plant is almost always submerged or partially floating at low tide. In the western Atlantic it is only occasionally intertidal (Fig. 2). However, eelgrass is actually not a grass—it is in the same Class grouping as other monocotyledonous plants, but it then branches into strictly aquatic plant groups at lower taxonomic levels: Phylum: Anthophyta (flowering plants), Class: Liliopsida (monocots), Order: Potamogetonales, Family: Zosteraceae (Greek ‘zoster,’ meaning ‘belt’), Genus/species: Zostera marina. Authority: Linnaeus, 1758. A summary of the key identification features are as follows: Relatively thin, flattened, blade-like leaves up to ~ 1 cm in width, dark green in color; Leaves usually 20–50 cm but up to 2 m in length, 4–10 mm wide, with 5–11 veins and rounded leaf tips, sometimes with a very small, sharp point; Leaf sheath forms an envelope around the aboveground stem; Reproductive shoot, terminal, branched, and substantially longer than vegetative shoots; Seeds ovoid or ellipsoid, ~2–3 mm long with 16–25 distinct ribs; Rhizome color (when living) is dark brown and has a polished appearance; At each rhizome node, there are typically two root bundles; Branching is alternate along the rhizome and frequently irregular; each branch becomes an independent shoot. To the casual observer there is little morphological difference between the two seagrass species that co-occur with eelgrass in the western Atlantic, shoal grass, Halodule wrightii Aschers, and widgeon grass, Ruppia maritima L. However, the three species can be distinguished particularly by their blade tips and rhizomes (Fig. 3). The leaf tip of eelgrass is round, sometimes with a very small apical point, whereas H. wrightii has a bicuspidate (crowned) appearance