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The U.S. South Atlantic Marine Ecosystem: An Ecosystem In Transition

December 10, 2021

According to a new report from NOAA Fisheries, the U.S. South Atlantic marine ecosystem is showing signs of chronic stress and changing ocean conditions, in addition to pressure from a growing coastal population.

The sun setting over the ocean. Sunset at a North Carolina beach. Credit: NOAA Fisheries/Todd Kellison.

Today, NOAA released the first U.S. South Atlantic Ecosystem Status Report. This report gives an overview of the current status and long-term trends of key marine ecosystem indicators. Some of the trends it examines are:

  • Sea surface temperature
  • Ocean acidification
  • Gulf Stream dynamics
  • Status of fish communities and harvested stocks
  • Trends in protected species
  • Recreational fishing pressure 

This report provides a look at the ecosystem as a whole, rather than its individual parts. This helps resource managers, such as the South Atlantic Fishery Management Council, scientists, and other partners understand how the ecosystem is connected and is changing. The report provides a holistic assessment of the ecosystem that can be used to inform management and policy decisions.

“Having one place for scientific information on the entire marine ecosystem is crucial to enhancing our understanding of how the ecosystem functions and may be changing over time,” said Kevin Craig, Research Fishery Biologist at NOAA’s Southeast Fisheries Science Center. “This is needed to effectively manage the many resources the ecosystem provides, including support for economically valuable fisheries. We all need to see the whole picture, not just one piece.” 

Overview of the Ecosystem

The U.S. South Atlantic is a transitional ecosystem between the more tropical Gulf of Mexico and Caribbean to the south, and the more temperate ecosystems to the north. It shares characteristics with both. For example, South Florida is home to some of the most extensive warm-water coral reefs in the United States. North Carolina has the second-largest estuary on the Atlantic seaboard. In between, a broad, gradual sloping shelf and extensive marsh habitats characterize Georgia and South Carolina.

Graphic showing the ocean ecosystem of the coastal waters off of the U.S. South Atlantic.
The U.S. South Atlantic marine ecosystem. Credit: NOAA/Seann Regan.

Chronic Stress

Similar to many other marine ecosystems, the U.S. South Atlantic is showing signs of chronic stress. Rising sea levels, ocean acidification, increased nutrient inputs, and recent ocean temperature warming are all affecting the ecosystem. For example, coral reef ecosystems off Florida are now experiencing stressful thermal conditions that lead to bleaching and coral mortality for much longer portions of the year compared to the 1980s.  

Changing Ocean Conditions

One intriguing result from the report is that ocean conditions in the U.S. South Atlantic appear to be changing. The report documents indications of rising sea surface temperatures and decreases in upwelling—a process that brings nutrient-rich bottom waters up to the surface. There are also changes in the variability of the Gulf Stream location, the major physical driver in the system. Many of these changes have occurred recently, over the last 5–7 years. Changing ocean dynamics have important implications for marine food webs, beginning with plankton (microscopic floating organisms). Changes at the base of the food web can impact other species that depend on plankton for food, including economically important species that support fisheries in the region.

Sea Level Rise

Image
Car driving through standing water at an intersection.
Sea level rise is turning nuisance flooding into a “sunny day” event — high-tide flooding that occurs even without a storm. Credit: NOAA.

Sea level rise in the southeastern United States has accelerated in recent years due to changing ocean-atmospheric conditions. Along the U.S. South Atlantic coast, the highest rates of sea level rise are projected for South Florida and the Cape Hatteras region in North Carolina. Rising sea level has the potential to impact infrastructure and coastal communities. It could also impact many coastal species, particularly those dependent on marsh and coastal beach habitat, such as beach-nesting sea turtles and several marine birds. 

Acidification

The South Atlantic continental shelf waters are also becoming more acidic because of absorption of carbon dioxide from the atmosphere and coastal run-off from the land. While not as severe as in some other regions, increasing acidity can have negative consequences for species that use calcium carbonate to form their skeletons or shells, like corals, shrimp, and oysters. Many of these species support some of the most valuable fisheries in the South Atlantic region (shrimp, oysters, and crabs). Others, such as coral reefs, provide protection from storms and habitat for fish, as well as support for economically important industries like diving and recreational fishing.    

Increased Nutrient Inputs

Agriculture and urban activities are leading to increases in nutrient inputs to coastal ecosystems. Between 2002 and 2012, nitrogen and phosphorus runoff into coastal waters of the South Atlantic increased, on average, 22 and 20 percent, respectively. Increased nutrient loads are an important driver of harmful algal blooms and hypoxia (oxygen depletion) that have negative effects on marine ecosystems and marine life.  

Warming Ocean Temperatures

Multiple indicators show that sea surface temperatures are increasing in the South Atlantic. Temperature has important effects on numerous physical and biological processes. For example, there is concern that ocean warming may be causing the geographic distribution of some species to shift north, though scientific studies are in the early stages. Temperature is also linked to other processes like stratification and nutrient upwelling that influence the amount of phytoplankton and zooplankton that are produced in the ocean. 

There are indications that upwelling has also declined in the South Atlantic in concert with increasing temperatures. Changes in productivity at the base of marine food webs due to changing ocean conditions can impact the survival of fish larvae, a process known as recruitment. This can lead to declines in the abundance of adults that support economically important fisheries.  Declines in recruitment have been reported for several snappers and groupers in the South Atlantic. Studies are underway to investigate the underlying causes of these declines.

Increasing Coastal Population

Image
Miami skyline from the water.
Coastal populations in areas such as Miami have increased since 2010. Credit: NOAA.

The coastal population of the South Atlantic states is also growing rapidly. Migration and urbanization are increasing in cities along the South Atlantic coast. This has changed the balance of fisheries in the region over time, with recreational fishing effort considerably exceeding commercial effort in recent years.

The four states that border the U.S. South Atlantic (North Carolina, South Carolina, Georgia, and Florida) were within the top 15 in the United States in terms of human population growth. Their state populations increased from 11 to 16 percent from 2010 to 2020. The net migration southward is part of a larger trend occurring in the United States. It has led to increases in employment in the ocean economy and ocean-related gross domestic product in the South Atlantic region, but also increasing coastal development and urban land cover that stress coastal ecosystems.

An increase in recreational fishing and a decrease in commercial fishing activities has occurred in association with these demographic changes. While the South Atlantic has always had a strong recreational fishing sector, recreational landings have more than doubled since the 1980s. Landings in the commercial sector are now less than half of their peaks in the 1950s to 1980s. For federally managed species, for example, more than 80 percent of the landings in recent years have come from recreational fishing.

Ecosystem-Based Management

This report is part of a larger effort to support ecosystem-based fishery management. Ecosystem-based fishery management is defined as an integrated approach that incorporates the entire ecosystem, including humans, into resource management decisions. 

Scientists used NOAA’s Integrated Ecosystem Assessment approach to provide the science to support ecosystem management and develop this report. This approach helps researchers provide the data and science that serves as the basis for management decisions. Scientists integrate information about the physical, chemical, biological, and social environment to get a full picture of what is happening. This full picture allows managers to eventually balance trade-offs and make more informed decisions. 

NOAA scientists will continue to work with the South Atlantic Fishery Management Council and other regional stakeholders to refine and regularly update the information in the report.

 

Last updated by on December 10, 2021