We examined the relationship between water temperature, depth, and invasive lionfish and native fish communities, off the coast of North Carolina. By understanding how present conditions influence lionfish and native fish communities we can inform management decisions by using lionfish presence as an indicator of changing climatic conditions. This baseline information is essential to understanding how fish communities may shift with temperature changes in the ocean.
Why We Care
North Carolina hardbottom reefs support ecologically and economically valuable fisheries and recreational diving industries. There are many potential threats to reef habitats and fisheries, including climate change, overfishing, invasive species and energy development activities. These threats make it imperative to understand the present status of fishery resources off North Carolina.
The unique location of North Carolina at the convergence of two water masses, the warm Gulf Stream and the cold Labrador Current, makes it an important location to study impacts of climate change. This area is the northern boundary of many southern species as well as the southern limit of many northern species all of which are sensitive to changes in temperature. By understanding present conditions within these communities, we can better detect, manage and predict future impacts, both positive and negative, to valuable fisheries and habitats.
What We Did
We conducted geographically and temporally comprehensive lionfish and native fish community surveys, and water temperature collections, along a temperature-depth gradient off North Carolina. This baseline assessment represents a snapshot of present conditions, and will be compared with future assessments to detect community changes and to address the potential cause of those shifts.
We collaborated with researchers from National Marine Fisheries Service and University of North Carolina, Wilmington to survey the fish, invertebrate, and algal communities found on hard bottom offshore North Carolina.
What We Found
- Bottom water temperature is an important factor for fish community structure off North Carolina: We found three distinct fish communities in water depths from 5 to 46m that are, to a large extent, defined by winter water temperature differences among three depth zones. These zones represent a gradient of temperature from shallower, colder nearshore depths to warmer, deeper waters.
- Depth was also a significant factor, as it correlated closely with water temperature: deeper offshore areas, with close proximity to the warm Gulf Stream, had fish communities that were dominated by tropical species.
- Average winter water temperature was an important factor in limiting lionfish distribution along the North Carolina coast: This suggests that the presence of the invasive lionfish, a tropical species, may be used as an additional indicator of changing climatic conditions.
- There is a thermal threshold for invasive lionfish off North Carolina: Lionfish were present in locations where mean winter water temperature was above 59°F (15°C). This threshold can be used for predicting lionfish presence off North Carolina.
The specific role of depth and other factors (i.e. reef structure, sea floor habitat, etc.) in structuring fish community differences across the region remains to be explored. However, as winter water temperatures continue to warm, the fish species off North Carolina will likely become increasingly tropical, and the invasive lionfish distribution will also expand to nearshore, shallower areas. Shifting community interactions may result in unforeseen impacts to fisheries and habitats within the region.