Oyster reefs are not as well-known as coral reefs, but serve a very similar ecological role. Oyster reefs are “ecosystem engineers,” meaning that they not only exist as habitat, but also create habitat, for other species. These reefs are formed when oyster larvae settle and grow on the shells of adult oysters, creating structures for other species to live, find food, spawn and mature, similar to coral reefs.
More than 300 species of fish and marine invertebrates depend on oyster reef habitats. Eastern oysters are a keystone species for the Chesapeake Bay; when a keystone species disappears, all the species that depend on its existence also disappear.
Not only do oyster reefs provide habitat for marine species, but they also purify the water that those species live in! Oysters are filter feeders that feed on microscopic algae, removing excess nutrients and sediments that can cause harmful algal blooms, as well as excess nitrogen. One adult oyster is capable of filtering 50 gallons of water per day!
Due to overharvesting and disease, the Chesapeake Bay’s wild oyster population is currently less than 1% of its historic levels. Restoration of these critical Bay habitats is more important than ever. The best way to bring oyster populations back to the Bay is through the creation of self-sustaining oyster reefs. Now, two artificial oyster reefs, installed by National Aquarium staff, sit in the Inner Harbor between Pier 3 and Pier 4.
In the past, oyster reefs were naturally present in local waters, but changes to the environment, degraded water quality and an influx of fresh water from record rainfall have all diminished the oyster’s ability to reproduce in these low-salinity waters.
The need for an oyster shell habitat in the Inner Harbor is greater than ever, with native species—including striped blennies and naked gobies—requiring oyster shell habitat for refuge, foraging and as a place to breed. Oyster shell also provides a hard surface for hooked mussels, barnacles and dark false mussels to settle and grow on.
Right now, the Aquarium’s oyster shell habitat is being utilized by an increasing number of fish species, mud crabs and other invertebrates. Providing these valuable habitats for Baltimore’s native species is an important step forward in revitalizing the Inner Harbor and larger Chesapeake Bay ecosystem.
Recently, Aquarium staff, in partnership with Coastal Conservation Association through its Living Action Reef Campaign, also installed new reef balls on top of the existing oyster reefs to add to restoration efforts. Reef balls are hollow concrete structures that are fabricated to aid in oyster reef restoration. The concrete provides a hard surface for encrusting organisms like barnacles, mussels and oysters to settle on and grow. An open top and round hole through the reef ball's sides allows for easy access to its hollow core, which provides refuge for fishes, crabs and many other species.
This is one of the first times that reef balls have been deployed in urban waters. Aquarium staff are looking forward to seeing how Inner Harbor wildlife will benefit from the presence of these structures!
In honor of Chesapeake Bay Awareness Week, learn more about actions you can take to restore valuable Chesapeake Bay habitats!