Critical Habitat
Eelgrass Supports
Fish, shellfish, birds, and epiphytes all come together to live in eelgrass. Eelgrass supports fisheries and recreational viewing of the diverse habitat it sustains.
Eelgrass creates complex habitat structures.
Consistent evidence tells us that eelgrass provides a vital habitat for fish and shellfish. As a juvenile habitat, individuals that use eelgrass habitat grow faster and have a higher chance of survival [1]. The complex structure of the eelgrass habitat allows creatures that live on the sea floor - benthic creatures - to hint, hide and climb. Fish can hide from larger predators in the canopy of seagrass blades. And many animals benefit from the grazing opportunities that the leaves provide.
Tautog, silversides, and cunner all receive protection from predators like bluefish [2], which hunt around eelgrass beds. Blue crab juveniles also take refuge from predators in eelgrass. In moderate densities, eelgrass provides canopy cover for the crabs and space between the roots and rhizomes to burrow into the sand for safety [3].
Bay scallops even find safety within the eelgrass meadows while they are young. As these scallops grow, they attach and even climb eelgrass blades to rise above the crab predators that cannot follow them [4]. The higher the scallop can climb, the safer it is from its benthic predators. The bay scallop must attach lower on the blade as it grows; as a result, it is exposed to more predation. Once it reaches a critical size, crabs cannot eat it. Bay scallops must grow fast in this life stage to survive. Many take up a position on the outer edge of eelgrass meadows where they compromise safety to maximize food availability that will help them grow [5].
Meadows create lively habitats for tiny animals and plants.
Seagrasses face a challenge that coral reefs and tropical forests do not. Most of the life sustained in seagrass beds is small, cryptic, and uncharismatic [6]. The occasional dugong or manatee can bring public attention to these vital habitats. However, for the most part, seagrass habitats do not provide flashy services. The humble eelgrass around Fishers Island hosts a microscopic world of marine epiphytes.
Epiphytes are immobile or planktonic organisms that settle on eelgrass. They attach themselves to the surface of the blades or stems, sustaining themselves using nutrients from the water and light. Epiphytes include sponges, aquatic mosses, sea squirts, bacteria, fungi, and algae. There is a bustling community of epiphytes and grazers below the surface of the waters off Fishers Island.
Algal epiphytes gather most on the older blades of eelgrass, usually near the blade's tip [7, 8]. This class of epiphytes accounts for as much as 99% of the epiphyte biomass found on eelgrass [9]. Epiphyte grazers control the population of epiphytes living on eelgrass. Grazers prevent overgrowth that blocks the sunlight from reaching eelgrass. Grazers such as snails, sea slugs, and arthropods consume up to 40% of the algae living on eelgrass [10].
Birds also take advantage of eelgrass meadows.
Brant geese eat eelgrass to keep themselves strong through their migrations. Vegetarian (or primarily vegetarian) birds consume seagrass beds where the eelgrass is shallow and exposed at low tide. Some grazing events are so intense that eelgrass beds cannot recover the following year [11]. Depth matters for Brant geese as they are not adept divers, so they only feast on shallow eelgrass. They are so dependent on eelgrass for their diet that they suffered a population decline directly linked to the 1930s wasting disease epidemic that killed most of the eelgrass in the Atlantic [12, 13, 14].
Not all birds associated with eelgrass are destructive. Ospreys use eelgrass as nest lining and hunt for their prey in the meadows during the summer [15, 16]. Eelgrass naturally sheds its leaves approximately once a month as part of its natural growth cycle [17], which explains why the leaves are readily available for the osprey.
Without Eelgrass…
If our eelgrass around Fishers Island disappears, we lose one of the last remaining eelgrass habitats in Long Island Sound. This habitat means safety for juveniles; it is where bay scallops, blue crabs, and tautog can find refuge from predators like bluefish.
Eelgrass is an essential structure for less charismatic marine creatures like snails, algae, and bacteria. Grazers come through eelgrass to feast on the grasses and epiphytes as their primary food source. Without eelgrass, this habitat is gone. Ospreys will need to find new nest-lining materials when eelgrass becomes less abundant.
The eelgrass in deeper waters will disappear as loose sediment from lost eelgrass clouds the waters. Fishing around Fishers Island will be less successful as the eelgrass dies off; fishers will likely notice smaller takes and individuals. The abundance of food fish will diminish, and their distribution will change.