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Divers and scientists who visit shipwrecks know these sunken sites are often teeming with life, as historical wrecks provide habitat for a wide variety of marine animals. Now, new research shows that old harbor infrastructure and sea walls offer a similar boost to biodiversity.

Researchers in the United Kingdom found that many kinds of wildlife make their homes in and around the nooks and crannies of stone walls—sometimes with even more diversity than on natural shorelines. The findings support the continued preservation of marine heritage sites, the researchers say. Beyond that, they say this realization could inform the design of new underwater infrastructure.

Study author Tim Baxter, a doctoral candidate at Oxford University in England, says the life inhabiting historical intertidal structures like sea walls and built harbors has been far less studied than that on shipwrecks.

“Maybe shipwrecks are just more romantic than stone walls,” he says with a laugh. “I think historic harbors and sea walls tend to be seen more as functional assets rather than objects with heritage value or, indeed, ecological value.”

But by conducting field surveys at seven sites across the United Kingdom—counting the seaweeds and animals hidden among the cracks and crevices—Baxter and his colleagues found an abundance of life. Another surprise: the artificial structures were no more attractive to invasive species than the natural shoreline.

Old masonry, they found, offers a wide variety of microhabitats suitable for many different kinds of sponges, sea stars, crustaceans, and fish. And the compositions of those communities changed as the scientists peered deeper into the fragmented surfaces.

Baxter says that until his study, the habitats within the structures had not been examined closely. “Something I found quite exhilarating was finding these nooks and crannies and looking into them with a torch because that’s often where you’d find the most exciting types of marine wildlife.”

Baxter particularly loved spotting blenny—small charismatic fish that perch on rocks and can survive briefly outside the water. “Those were always exciting to find because the first thing you’d see were those big eyes looking back at you,” he says.

The common blenny is an inshore fish that can spend brief periods out of the water, where it waits to surprise unsuspecting scientists. Photo by Tim Baxter

For a follow-up study, Baxter hopes to continue looking at intertidal structures, this time focusing on marine ruins.

“I want to look at historic harbors which have been abandoned or destroyed,” he says, “to see whether those habitats provide similar ecological benefits or even improved benefits.”

Katie Marshall, a zoologist who studies biodiversity in the intertidal zone and other habitats at the University of British Columbia and who was not involved in the study, notes that while researchers have investigated the biodiversity effects of other structures, like artificial reefs, less is known about how human constructions affect intertidal ecosystems.

“This paper shows ways of mitigating some potential impacts of concrete structures,” she says. It shows “that maybe there are ways to build intertidal structures that might not make things worse or at least have less impact on the environment.”

Marshall notes that Indigenous peoples, like those in western North America, have been using artificial structures like clam gardens to support marine habitat for thousands of years and suggests that future research incorporate such knowledge.