Blue crabs connect North Carolina’s fisheries, estuaries, submerged aquatic vegetation, water quality,
and coastal communities. Coastal Carolina Riverwatch is working with researchers at NC State University’s
Center for Marine Sciences and Technology (CMAST), the North Carolina Division of Marine Fisheries,
and North Carolina Sea Grant to better understand how disease, nursery habitat, and environmental conditions
interact across coastal North Carolina.
Why This Project Matters
Blue crab (Callinectes sapidus) is one of North Carolina’s most economically important coastal fisheries.
The state’s 2018 benchmark stock assessment found the stock was overfished and that overfishing was occurring.
In September 2026, the North Carolina Division of Marine Fisheries reported that commercial landings,
fishing trips, and fishery-independent indices of juvenile abundance continue to show declining trends.
A new benchmark stock assessment is underway, with results expected in late 2026.
Habitat is part of the story. A 2026 analysis from the Albemarle-Pamlico National Estuary Partnership found
that high-salinity seagrass habitat declined by at least 16,129 acres, or 16.2%, between 2006 and 2020.
North Carolina still supports an estimated 88,531 acres of seagrass, the largest acreage along the East Coast,
making protection of these underwater meadows especially important.
Declining indicators
Blue crab management
Current monitoring continues to show concern for juvenile recruitment and other blue crab indicators
while the state completes a new benchmark stock assessment.
16.2% decline
High-salinity seagrass
APNEP’s 2026 comparable-area analysis documented at least a 16.2% decline in high-salinity seagrass
between 2006 and 2020.
The connection we are investigating
Juvenile blue crabs use submerged aquatic vegetation, or SAV, as nursery and refuge habitat.
The parasite Hematodinium can cause serious disease in blue crabs, particularly juveniles.
Prior research has linked disease risk and mortality with warm, higher-salinity conditions.
This project asks how disease patterns may also relate to habitat availability, water quality,
surrounding land use, and changing environmental conditions.
Project Overview
This research was developed to address important blue crab management and habitat questions identified
in the North Carolina Blue Crab Fishery Management Plan. The study is designed to quantify
Hematodinium infection in blue crabs and examine whether disease patterns are associated with
nursery habitat, surrounding land use, and water-quality conditions.
1. Collect
Blue crabs are sampled through research field surveys and in coordination with North Carolina
Division of Marine Fisheries monitoring. The research design includes multiple blue crab life stages
and coastal waterbodies.
2. Test
Samples are processed at NC State CMAST. Researchers extract DNA and use quantitative PCR, or qPCR,
to detect and quantify Hematodinium.
3. Connect the Data
Disease results can be compared with seagrass extent, salinity, temperature, dissolved oxygen,
and other habitat, water-quality, and landscape variables to look for patterns.
Research in the field and laboratory
seagrass, and Hematodinium perezi. Photo: NC State CMAST.
PRELIMINARY RESEARCH SNAPSHOT — 2025
What student research found so far
Materials from Alden Mazo’s 2025 Semester at CMAST project report an interim dataset of
104 blue crab samples, with 31 testing positive for Hematodinium
(29.8%). In that interim dataset, monthly infection prevalence ranged from
16% to 57% across samples collected from May through August.
These figures are preliminary project results and should not be interpreted as a final statewide prevalence estimate.
CCRW will update this page as the broader analysis is completed and results are approved for public release by the research team.
What Is Hematodinium?
Hematodinium perezi is a parasitic dinoflagellate associated with “bitter crab disease.”
It was first documented in blue crabs collected in Beaufort, North Carolina, in 1968.
The parasite can infect multiple tissues and can cause high mortality in infected crabs,
especially juveniles. Research from other Atlantic coast systems has found that warm,
higher-salinity conditions can increase disease risk and mortality.
Important public-health note
Hematodinium is a crab disease and is not considered a threat to human health.
The concern is its potential effect on blue crab survival, juvenile recruitment, and the sustainability of the fishery.
Why Seagrass Matters to Blue Crabs
Blue crabs have a complex life cycle connecting the open ocean and estuaries.
Females spawn in high-salinity waters, larvae develop offshore, and later stages return to estuaries.
Young blue crabs settle into structurally complex habitats such as seagrass beds, marsh edges,
and oyster habitat, where they find refuge and food as they grow.
North Carolina’s high-salinity seagrass community includes eelgrass (Zostera marina),
shoalgrass (Halodule wrightii), and widgeongrass (Ruppia maritima).
These underwater meadows provide habitat for fish and invertebrates, recycle nutrients,
trap sediment, support water quality, store carbon, and help protect shorelines.
Because seagrass needs sunlight, it is especially sensitive to conditions that reduce water clarity.
The next phase of analysis is especially important because it connects two management questions:
where disease is occurring and what the surrounding habitat and water-quality conditions look like.
Who Is Involved
Dr. Y. Stacy Zhang
Dr. Zhang is a marine community ecologist at NC State studying biodiversity,
species interactions, environmental change, essential fish habitat, and coastal ecosystem restoration.
Dr. Tal Ben-Horin
Dr. Ben-Horin is an aquatic pathologist at NC State whose research focuses on infectious disease ecology,
aquatic animal health, and disease processes affecting fisheries and aquaculture.
“Interconnected Estuaries: Blue Crabs, Seagrass, and Hematodinium perezi.”
Photo: NC State CMAST.
Students and project partners
NC State students have contributed through Semester at CMAST and related research experiences,
including field sampling, laboratory processing, data analysis, and public outreach.
Coastal Carolina Riverwatch works with NC State CMAST, the North Carolina Division of Marine Fisheries,
and North Carolina Sea Grant to connect scientific research with fisheries management,
public education, and coastal community engagement.
From Research to Community Action
Coastal Carolina Riverwatch’s role is to help translate the science into information that fishing communities,
coastal residents, decision-makers, and the broader public can use. This project builds on CCRW’s
Water Quality for Fisheries
program, which brings fishermen, researchers, managers, and community partners together around
water-quality threats affecting fisheries.
Public outreach is part of the research plan. CCRW and the research team are developing educational materials
that explain blue crab life history, nursery habitat, water quality, land use, and Hematodinium.
CCRW’s 10-part Seagrass Saturday series has already introduced these connections in an accessible format,
and new findings will continue to be added as the research advances.
Coming next: an interactive Blue Crab StoryMap
The project’s planned ArcGIS StoryMap will connect place and science by helping people explore blue crab life history,
sampling locations, seagrass habitat, disease patterns, and environmental conditions such as salinity and temperature.
As analyses are finalized, the StoryMap will become an interactive companion to this webpage.
Explore the Science and Management Context
These resources provide authoritative background on North Carolina blue crab management,
submerged aquatic vegetation, current seagrass trends, and the student research connected to this project.
Follow the Project
This page will continue to be updated as project analyses are completed and new maps,
photographs, and outreach materials become available. Follow Coastal Carolina Riverwatch
on Instagram and Facebook at @coastalcarolinariverwatch, and join our mailing list
for research updates, volunteer opportunities, and Water Quality for Fisheries news.
Preliminary research figures on this page are clearly identified and will be updated
when the broader project analysis is completed and approved for public release.