(Smithsonian Institution photo)

Down at the bottom of the Chesapeake Bay lives a family of small creatures that play a large role in the estuary’s ecosystem. Most people have never set eyes on them; many don’t even know they exist. These are bristle worms, mud-dwelling members of the Polychaete class (marine segmented worms). 

They’re better known in Maine, where they account for a multimillion-dollar industry. Down East clam diggers harvest two species of bristle worms, bloodworms and sandworms, prized bait items for the sportfishing and home aquarium markets. Six-inch-long bloodworms may sell for $99/dozen, making them among the most valuable animals in the world, pound for pound. 

Chesapeake Bay is home to over one hundred species of bristle worms, including bloodworms, but doesn’t support a commercial harvest. The primary value of these animals is ecological, not monetary. But if you want to see bloodworms in the wild, or harvest a few for your rod and reel, you could try digging around in the soft, intertidal mud. Do be careful — they can deliver a nasty bite. They won’t win any beauty contests but show them some love; they’re a vital component of the Bay’s complex ecosystem.

Bristle worms are found all over the world, from the frozen seas to the boiling springs of deep-sea thermal vents. They number some ten thousand species and range in length from less than an inch to several feet. They’re all soft-bodied and segmented, with each segment bearing a pair of appendages (parapodia, for locomotion) from which stiff, hairlike bristles project. Most creep along the sea floor, but some burrow into the sediment, live in tubes, are parasitic, or even swim in the water column. They mainly graze on algae and tiny animals or scavenge dead organic matter, sucking in the material through a tubelike proboscis.

Most bristle worms reproduce by shedding eggs and sperm into the water where the fertilized eggs go through a plankton stage before maturing into adult worms. Some species demonstrate engrossing mating rituals. Chesapeake Bay clamworms (Neanthis succinea) make Spring Break seem tame. Around the time of the June new moon, females emit a pheromone signal, enticing males to emerge from their bottom burrows and wriggle toward the surface, discharging sperm on the way up. Females soon join them, releasing their eggs. A frenzied, dance-like swarm ensues. The festivities go on for a few days; then the spent worms die while the new larvae carry on as the next generation.

Bristle worms are vital for the Bay’s ecosystem because they’re a significant part of the estuary’s food web. Not only are they a key prey item for birds, crabs, and fish, but also, as detritivores, they browse on dead organic matter, feeding their growing bodies and recycling nutrients into the surrounding environment. 

Bristle worm populations are stable in the Bay, but they face threats. The primary risk is hypoxia (low oxygen) in the sediments where the worms live. Hypoxia occurs when excessive nutrient runoff from farming and other human activities triggers large blooms of algae. When the algae die, their decomposition consumes oxygen, especially near the bottom where the waters are not well mixed. This can even lead to dead zones, where little but bacteria can survive. University of Maryland scientists have found that the Bay’s bristle worm communities are changing, with species shifts to worms that are more tolerant of hypoxia stresses.

Hardening shorelines, to protect homeowners’ waterfront properties from erosion, can also threaten bristle worm populations by disrupting their near-shore habitats. In turn, this can reduce food for larger, foraging species.

Bristle worms don’t show up on Chesapeake Bay’s iconic species lists. But they’re at least as important as ospreys, striped bass, blue crabs, and oysters. Without bristle worms the Bay would suffer. They deserve our attention and support — and even a little love.

Henry (“Hank”) S. Parker is a scientist and writer who previously lived in Annapolis but now resides in Vermont.

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Henry S. Parker is an adjunct associate professor at Georgetown University. He can be contacted at [email protected]