Are Blue Invaders in New England’s Future?

If you’ve dined on Southern seafood, you might recognize the blue crab as a star menu item in Maryland and New Orleans. Blue crabs are a warm-water species, but as sea temperatures rise, they might be able to thrive in more northern regions of New England. What could the blue newcomers mean for our local crabs and other species? Will they provide a new commercial fishery or will they devastate existing marine life?

Graduate student Tanya Rogers in Dr. David Kimbro’s lab at the Marine Science Center aims to find out how these invaders could impact local species. She’s studying the interactions between blue crabs and green crabs, which are an invasive European species that is already established in New England.

OGL is also interested in invasive species. Thanks to Tanya, the blue crab is the latest addition to our biorepository. Newcomer species can have huge impacts on ecosystems, so OGL seeks to track biodiversity over time and use genetic samples to help research on ecology and climate change

This blue crab, donated by MSC graduate student Tanya Rogers, is a new addition to OGL.
This blue crab, donated by Marine Science Center graduate student Tanya Rogers, is a new addition to OGL.
Savory Southern Swimmers

The blue crab (Callinectes sapidus) is an iconic commercial species and an important predator in warm-water marshes and bays. This long-spined and short-tempered crustacean often buries itself in the mud, but its paddle-shaped back legs also make it a fast fighter in the water. Did you know that its scientific name means “savory beautiful swimmer”?

The crabs that Tanya donated were mature males, called “jimmies” and recognizable by a narrow abdomen, which Chesapeake Bay locals might liken to the Washington Monument. A mature female crab, or “sook,” has a rounder abdomen shaped like the Capitol Building. The claws of a male crab are mostly blue, whereas a female’s claws are red at the tips.

The abdomen of a male crab is long and narrow, shaped like the Washington Monument.
The abdomen of a male crab is long and narrow, shaped like the Washington Monument.
Permanent Residents?

It’s rare to find blue crabs north of Cape Cod, but on several recent occasions they’ve been reported in Massachusetts, Maine, and Nova Scotia. During the unusually warm summer of 2012, a diver caught one in Marblehead, MA, just a few miles from the Northeastern University Marine Science Center. Researchers suspect that increasingly warm water temperatures might allow blue crabs to creep northward. So far, the reported crabs were thought to be just visitors, not breeding locally. But as sea temperatures rise, northern blue crab sightings may become more common.

Impact on New England

At the Marine Science Center, Tanya is studying what could happen if blue crabs expand their home range northward. One of many New England species that they’ll encounter is the green crab (Carcinus maenas), a European species that has also invaded sites on four continents due to human activity. If blue crabs move into northern New England, how would they interact with green crabs? Along the U.S. east coast, blue crabs are thought to prevent green crabs from invading farther southward, but the two species do coexist in certain regions. Tanya is examining how these two species interact and what happens when their home ranges overlap. She’s also studying the overall effects of climate change and newcomer species on salt marsh ecosystems.

Warming water temperatures could affect interactions between blue crabs (left) and green crabs (right). Illustration by Tanya Rogers.
Warming water temperatures could affect interactions between blue crabs (left) and green crabs (right). Illustration by Tanya Rogers.
Biodiversity in a Changing Ocean

Warming waters are likely to bring major changes to many species and human communities. For example, blue crabs arriving in the Gulf of Maine might prey on softshell clams, get eaten by striped bass, and shake up the local seafood industry. To understand and help predict these changes, it’s important to monitor species patterns over time.

By preserving genetic samples and data, OGL aims to help understand the changing marine environment. Genetic samples can help determine whether species are interbreeding, how closely related they are, and where an individual may have come from. Scientists can also use DNA to identify an animal, even if the only remaining piece is a claw or a scrap of fin. OGL is eager to follow Tanya’s project and other research on how a changing environment will affect resident species, including us.

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