Decline of Blue Crabs in Chesapeake Bay: A Study on Carcinonemertes Carcinophila

A recent study conducted in collaboration between the Batten School of Coastal and Marine Sciences and the Virginia Institute of Marine Science has recorded historically low numbers of blue crabs in the Chesapeake Bay. This discovery has raised concerns among fisheries stakeholders and highlighted the need for new tools that can help balance economic and environmental priorities.

The Role of Carcinonemertes Carcinophila in Blue Crab Reproduction

The worm Carcinonemertes Carcinophila lives on the eggs of female blue crabs. Although it does not consume enough to significantly reduce crab production, it grows and changes color after feeding, making it a potential biological indicator for determining whether a female has spawned. Blue crabs in Chesapeake Bay face varying salinity levels, and it was previously unclear whether the worms could survive in the low salinity found in some parts of the bay.

Professor Jeffrey Shields from the Batten School and Virginia Institute explained, “Other species of Carcinonemertes cannot survive in salinity levels below 20 parts per thousand, which is common in the bay’s tributaries and during heavy rainfall events. We found that this worm is more resilient than other species.”

Assessing the Potential of Worms as Biological Indicators

The study continued the research initiated by former student Alex Schneider, focusing on the potential of Carcinonemertes Carcinophila to determine the spawning frequency of female crabs. In collaboration with student Alex Pomeroy, researchers collected worms from blue crabs and tested them across a wide range of salinity levels.

Researchers found that the worms thrive in medium to high salinity levels (20-30 parts per thousand), but they also discovered that the worms can adapt and survive in salinity as low as 10 parts per thousand and even endure and recover from short periods (up to 39 hours) in levels as low as 5 parts per thousand.

Implications for Fisheries Management

The blue crab is a commercially and recreationally important species in Chesapeake Bay. Egg production is a crucial component of many fisheries models, but determining the spawning frequency of female crabs has been challenging. Previous research showed that female crabs produce more offspring in their first egg batch, with reproductive capacity declining in subsequent batches.

In another study, Schneider and her colleagues used the worm to provide the first-ever estimate of the proportion of crabs that had spawned versus those that had not during the winter. This information helps managers understand the impacts of commercial and recreational harvesting on the reproductive demographic structure.

Conclusion

The worm Carcinonemertes Carcinophila is a valuable tool in determining the reproductive history of blue crabs, enabling improved management of this important species in Chesapeake Bay. By protecting crabs that produce more offspring, we can enhance population numbers and maintain the ecological and economic balance in the region.