Shrinking Habitats: How Have Oyster Reefs Changed Over the Last Six Decades?
In a crucial North Carolina estuary, scientists combed through historical data to better understand both biodiversity and seafood supply.
Like other coastal and estuarine environments, the Newport River Estuary in North Carolina is vulnerable to the impacts of human activities. Rising sea levels, storm water drainage infrastructure, and dredging channels for ships, for instance, can change the estuary’s tides and the saltiness of the water, which in turn affect plants and animals, including oysters.
The oysters and other species in the estuary play an important role ecologically and economically, in part because they create habitats for other organisms and supply seafood.
Scientists have been studying the Newport River Estuary, which sits next to multiple marine labs and a state port, for over one hundred years. By looking at historical data, can we get a sense of what the future might hold?
DECADES OF DATA
In 1955 and 1956, scientists collected samples from different sites in the Newport River Estuary and brought them to a laboratory to identify the species living in them. Over half a century later, from 2013 to 2015, Joel Fodrie from the University of North Carolina at Chapel Hill’s Institute of Marine Sciences led a research team that revisited these sites and collected new samples to compare with the historical data. The team also looked at records of the estuary’s salinity and reef distribution, some of which dated back to the 1920s — and even the 1880s.
After data collection, scientists identified patterns in the communities of species that live in oyster reefs in the estuary.
They found that the diversity and the number of species in the oyster communities have decreased between the 1950s and the 2010s. These differences are linked with the estuary’s salinity levels, which have risen over time. The salinity of the reefs closest to the Beaufort Inlet did not increase as much as the reefs further upstream.
North Carolina’s two types of oyster reef — subtidal (below the water’s surface) and intertidal (above or below the surface, depending on the tide) — were affected differently over time. Scientists found that oyster communities in the 2010s tended to cluster around intertidal reefs, closer to land, more than they had in the past. This shift occurred because certain species, including oyster predators, had expanded farther up into the estuary. Subtidal reefs up the estuary had degraded due to environmental conditions, which made them more favorable for aggressive, reef-destroying species.
A 75% LOSS OF HARVESTABLE HABITAT
Changes to oyster communities in the reefs, along with water quality issues, have shrunk the areas suitable for oyster habitats. As a result, the area where people can harvest oysters has decreased by over 75% since scientists first described the natural history of reefs in this system a century ago.
The shrinking of harvestable oyster areas raises concerns for biodiversity and seafood supply. This research highlights the importance of protecting and restoring critical habitats like the Newport River Estuary.
North Carolina Division of Marine Fisheries Coastal Recreational Fishing License Program and the National Science Foundation funded this study.
the full study in Ecological Applications:
“Coastal Squeeze on Temperate Reefs: Long-Term Shifts in Salinity, Water Quality, and Oyster-Associated Communities”
go.ncsu.edu/oyster-reefs
lead photo credit: NCDMF.
Maya Afilalo is the 2023-2024 Communication Fellow with North Carolina Sea Grant’s award-winning Hook, Line & Science series, which originally published this story. HookLineScience.com
