Harbor Happenings: Artificial Oyster Reef

The National Aquarium is taking another step to revitalize Baltimore's Inner Harbor and attract native species with a new artificial oyster reef using shells from the Oyster Recovery Partnership!

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Oyster reefs are the Chesapeake Bay's equivalent of coral reefs; they're essential to the health of our marine ecosystem and provide critical habitat for hundreds of species. Similar to a coral reef, an oyster reef is a complex three-dimensional structure created by the eastern oyster, a keystone species of the Bay. Oyster reefs provide shelter, refuge, spawning, nursery and foraging habitats to a multitude of other species. The National Aquarium's Conservation team is bringing this vital habitat back to the Inner Harbor by utilizing existing infrastructure to create a cost-effective oyster reef.

On a footing of the suspension bridge connecting Piers 3 and 4, our team recently installed a Fibergrate frame—an oyster shell "fence"—on top of a submerged concrete column cap. This submerged concrete deck is at an ideal level in the water column for this project, since it's close enough to the water surface to be in a higher dissolved oxygen level zone. So far, 71 five-gallon buckets of recycled shell, collected from restaurants by the Oyster Recovery Partnership, have been added to form a 10-inch-deep shell base. Once the weather begins to warm, oyster shell with living baby oysters, called spat, attached will be added to form the top layer.

The stacked shells of the eastern oyster will create a structure that provides habitat, offers protection from predators and creates an opportunity to forage for prey for a variety of urban wildlife, from microscopic bacteria to larger predatory species:

Oyster shells provide a large surface area and will be quickly colonized by beneficial surface-growing bacteria—creating a coating known as biofilm—that will absorb excess nitrogen from the water. Small fishes and aquatic invertebrates will feed on these biofilms.

As the water temperatures warm up in late winter and early spring, species such as hydroids, ghost sea anemones, lacy bryozoan, bristle worms and nematodes will start to colonize the shell habitat. The free-swimming larvae of water-filtering invertebrates, such as dark false mussels and white barnacles, will settle on the oyster shells in large numbers and begin growing and reproducing.

Grass shrimp, mud crabs and blue crabs will utilize the oyster reef habitat for feeding and refuge from predators. American eels will weave in between the oyster shells, searching for food and seeking protection from predators. Oyster reef fish species such as naked gobies will lay their eggs on the smooth inner cups of oyster shells and guard them until they hatch. Mummichogs and banded killifish will deposit their sticky eggs over the oyster reef, and larger predatory fish—such as pumpkinseed sunfish, white perch and young striped bass—will forage for prey, including mud crabs, grass shrimp and small fishes, over the new oyster reef habitat.

Gizzard shad fish and mallard ducks will graze on the algae growing on the upper surface of the shells.

In addition to providing critical habitat for other native species, the oyster reef will help provide natural water filtering. Eastern oysters and other species that attach and grow on oysters' shells, such as mussels and barnacles, filter phytoplankton and other suspended materials out of the water; one oyster can filter over 50 gallons of water in a single day. The species that colonize the oyster reef will also help to remove excess nitrogen, which fuels algal and bacterial blooms, from the water.

The new oyster reef is just one of several projects in the slip between Piers 3 and 4 that attract native urban wildlife. In this location, there are also five Biohuts—which are smaller artificial oyster reefs—and our floating wetland prototype, an artificial island that mimics a salt marsh habitat and is part of our Waterfront Campus.

Along with the Chesapeake Bay Foundation and Waterfront Partnership of Baltimore, the National Aquarium is committed to spearheading urban oyster projects in the Inner Harbor that help restore the population of these critically important filter feeders.

Learn more about the National Aquarium's efforts to revitalize Baltimore's Inner Harbor, and how you can help!

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