Warming oceans may lead even more tropical and subtropical fish to take up residence in shipwrecks off the North Carolina coast, research finds.
“The artificial reefs created by these structures may be acting as stepping stones for fish that are moving northward and living at the edge of their geographic range, or beyond it, in search of suitable habitat,” says lead author Avery B. Paxton, a visiting scholar at the Duke University Marine Laboratory.
“Globally, there is broad evidence that many tropical fish species are shifting their ranges poleward and to deeper waters in response to changing ocean conditions, and what we see on these reefs seems to fit that pattern,” she says.
One of the most surprising findings of the study is that the tropical and subtropical fish researchers observed off North Carolina exhibit a strong preference for hanging out on human-made structures versus natural rocky reefs found nearby, notes coauthor J. Christopher Taylor, a research ecologist at NOAA’s National Centers for Coastal Ocean Science.
“It could be that the zooplankton and smaller fish these species eat are more plentiful on artificial reefs. Or it could be that human-made reefs’ complex structures give the fish more nooks and crannies where they can evade predators. We’re still trying to figure it out,” Taylor says.
The fishes’ preference for artificial habitats suggests networks of the human-made structures—which are already common up and down the East Coast and in other waters worldwide—could act as underwater corridors the fish use to reach the habitats they need to survive, says Paxton, who also works with CSS Inc. under contract to NOAA’s National Centers for Coastal Ocean Science.
To conduct the study, teams of scuba-diving scientists conducted population and species counts at 30 artificial and natural reefs off the NC coast between 2013 and 2015. To track seasonal differences in fish populations, they visited most of the reefs four times a year.
Analysis of the data confirmed that the number and diversity of tropical and subtropical fish on deep artificial reefs was far greater than on nearby natural reefs.
Common tropical species researchers spotted on the artificial reefs included blue chromis, purple reef fish, and bluehead wrasse. Common subtropical species spotted there included vermilion snapper, greater amberjack, and bar jack.
Temperate fish species such as black sea bass and tautog, on the other hand, were far more prevalent on the area’s natural rocky reefs.
The depth of the artificial reef mattered hugely, Paxton notes.
“We didn’t see these patterns on artificial reefs at shallow or intermediate depths, we only saw them on deep reefs, located between 80 to 115 feet below the surface, where water temperatures often experience less seasonal change,” she says.
The paper appears in Nature Communications Biology.
Additional coauthors came from the University of North Carolina at Chapel Hill’s Institute of Marine Sciences and Duke University. Funding for the research came from the Bureau of Ocean Energy Management, the NC Coastal Recreational Fishing License Grant Program, a National Science Foundation Graduate Research Fellowship, a P.E.O. Scholar Award, and the Lenfest Oceans Program.
Source: Duke University