In 2018, Delaware dug about 1 million tons of rock from a shipping channel and put it underwater instead of discarding it; The new reefs became rich blue-mussel habitat

A pile of rock removed from a shipping channel might seem like material with no further purpose. In Delaware, however, the same rock became part of an underwater experiment, helping create hard surfaces in a region where marine organisms often struggle to find them. Rather than being disposed of in landfills or being viewed as some form of waste, they were utilized for creating an underwater habitat. The result of dredging operations turned out to be much more productive than expected because a system of artificial reefs was created where rocks provided a firm substrate for sea creatures.

During the Delaware River navigation channel deepening project in 2018, about about 1 million tons of rock were extracted from the channel and later reused for artificial reef construction. However, the rock material has been utilized for the artificial reef projects of the state instead of being disposed of. According to a report published in DNREC, the rock material has been incorporated into the reef project areas, and it turned out to be one of the best materials utilized in the program for several reasons. First of all, the seabed of the mid-Atlantic region is made up of soft sand or mud, but not of a hard surface required by the organisms in the ocean. As a result, the rock has created a habitat rich in blue mussels.

Turning dredged rock into habitat


Delaware's artificial reef strategy is fairly simple. When there are no areas along a coast where fish and shellfish live that provide a hard bottom surface for them to use, then it can be created in specific locations. This is exactly what Delaware has done since 1995, when its artificial reef program began.

By the time the channel project produced the rock, Delaware already had an established process for deploying reef materials underwater, and the state does not use unsuitable waste materials but instead relies on approved structures and materials that meet environmental requirements. Through the years, Delaware has managed to include recycled concrete, decommissioned boats, subway trains, military equipment, and ships in the artificial reef complex. The 2018 inclusion of rock was another step in the right direction as it provided a natural hard-bottom material, ideal for the soft-bottom marine habitat of the region. But the reason why reef construction is important is not only that it creates something for fish to swim in. It creates cracks, ledges, and hard surfaces that allow invertebrates to settle first, followed by fish.

Why blue mussels matter

As DNREC notes, the natural rock put on the reefs fosters a large and diverse community of invertebrates that are dominated by blue mussels. This is significant in more ways than one. Mussels are known for cleaning the water, colonizing hard surfaces fast, and building the type of foundation that will attract more marine life. By colonizing the reef, mussels bring additional food and structure to the habitat; small fish live among the mussels, while big fish come to eat the small ones. Over time, these interactions help transform the artificial reef into a functioning ecosystem. Delaware’s artificial reef program now includes 14 permitted reef sites in Delaware Bay and along the Atlantic Coast. This means that any structural additions, including rock, would have a great impact on ecology here.

A reef program built for more than fishing

Presently, there are 14 artificial reef permit sites in Delaware Bay and along the Atlantic Coast. Although this program caters to recreational fishing and diving, the artificial reefs serve an environmental purpose too. By placing sturdy structures where marine organisms can benefit, the state expands habitat in an area with little naturally hard seafloor.

There have been changes in the types of materials used over time. Early reefs comprised concrete rubble and tire units. Over time, Delaware has added different approved materials to its reef sites, including vessels and other large structures. While each structure contributed differently to the environment beneath the water, the channel rock had special characteristics which made it an excellent choice for a certain area. It provided habitat that was rare in the area.rovided habitat that was rare in the locality.

The value of reusing what a project creates

This particular example is a demonstration of how even the most straightforward infrastructure project may lead to multiple results. First, the main goal of dredging Delaware’s channel was to provide safe passage for ships, but the extracted rock did not have to serve only that purpose. It was used as an additional building material to form reefs.

The result of such a solution had two advantages simultaneously. The project created habitat for blue mussels while expanding Delaware’s existing artificial reef network, which is helpful for fishing, diving, and conservation purposes. In a zone that lacks hard habitat, such recycling can be just as important as construction itself.