Smithsonian Study Finds Juvenile Crabs Rely on Shrinking Shallow-Water Habitats To Escape Cannibalism by Adults
by Kristen Goodhue
An adult male blue crab attempts to cannibalize a smaller blue crab on a tether. (Credit: SERC Fisheries Conservation Lab)
The Chesapeake Bay’s most popular crustacean has a dark streak. Cannibalism is the No. 1 killer of juvenile blue crabs in mid-salinity waters where they are known to congregate, according to a new study from the Smithsonian Environmental Research Center (SERC), published March 16 in Proceedings of the National Academy of Sciences. But shallow waters can offer a vital refuge.
Blue crabs lead a life on the run. After spending roughly two months as larvae in the ocean, they are swept back into the lower bay to morph into juvenile crabs. There, the juveniles rely on seagrass to provide partial refuge from predatory fish like striped bass. But after growing to about 1 inch, many migrate up the bay to mid-salinities, where fish and seagrasses are scarcer. There they face another enemy: larger blue crabs.
“Blue crabs are notoriously cannibalistic,” said Tuck Hines, marine biologist and director emeritus of SERC. But although cannibalism is common throughout aquatic ecosystems, he added, long-term studies attempting to quantify it are rare. And the data could make a difference for managers trying to keep the blue crab fishery sustainable.
Sickle-leaved cymodocea seagrass (Thalassodendron ciliatum) in Zanzibar, Tanzania. (Credit: Ben Jones / Ocean Image Bank)
They’ve been called the “lungs of the sea.” And while certain marine microbes could also compete for that title, there’s no question that seagrasses are crucial for life on coastal lands and at sea. They provide oxygen, food, habitat and shoreline protection. But seagrasses are routinely overshadowed by flashier coral reefs or more charismatic marine animals.
“They’re just below the radar,” said Emmett Duffy, a marine scientist with the Smithsonian Environmental Research Center. “A lot of people don’t know what they are, don’t know that they’re important. They think it’s just something that gets tangled in your boat motor.”
Emmett Duffy on a research boat in Bocas Del Toro, Panama, in 2015. (Credit: Sean Mattson/Smithsonian Tropical Research Institute)
The Tennenbaum Marine Observatories Network (TMON) and Marine Global Earth Observatory (MarineGEO) program began as a wild dream. But it grew into something extraordinary under the leadership of its first director, Emmett Duffy. This year, Duffy announced his retirement from MarineGEO and the Smithsonian. His philosophy of team science and community building not only changed the lives of all those connected to MarineGEO, but also the field of marine ecology.
“Emmett’s leadership of MarineGEO reflected the very best of Smithsonian science—an unwavering drive to ask deeper questions and advance our understanding of marine ecosystems worldwide,” said Ellen Stofan, Undersecretary for Science and Research at the Smithsonian.
It’s been a wild six decades. The Smithsonian Environmental Research Center celebrated its 60th anniversary this past year. Since 1965, the site has gone from a remote field station on the western shore of Chesapeake Bay, without any full-time resident scientists of its own, to a cutting-edge research community with over 100 scientists and educators working around the world. As we bid farewell to our anniversary year, we dug into our archives to unearth some of our favorite stories and discoveries from the past 60 years.
Left: Storrs Olsen, ornithologist and resident manager of SERC when it was called the Chesapeake Bay Center for Environmental Studies, circa 1969. (Credit: Smithsonian Libraries & Archives) Right: SERC technician Cary Pelc samples water from a stream weir in 2021. (Credit: Stephen Voss, Smithsonian)
PNNL Earth scientist Peter Regier (left) takes a soil gas sample with then-postdoc Wei Huang of Oak Ridge National Laboratory in the TEMPEST forest. (Credit: Alice Stearns)
In a low-lying forest at the Smithsonian Environmental Research Center (SERC), a team of scientists are quietly predicting the future. For three summers, they’ve flooded the forest with brief deluges of freshwater and saltwater. They’re mimicking the heavy downpours and storm surges expected as more extreme weather batters the East Coast. Their mission: Find out why storms can make forests stress out, and how much stress a forest can take before it begins turning into a ghost forest.
Patty Levasseur holds diamondback terrapin hatchlings on Poplar Island, near Jefferson Island. (Credit: Patty Levasseur)
Diamondback terrapins are an icon of the Chesapeake. They are the only turtle species known to live exclusively in brackish waters—where the saltiness hovers between pure freshwater and open seawater, common around bays and estuaries. They’re also the official state reptile of Maryland and symbolic mascot for coastal ecosystems spanning from Texas to Cape Cod.
While their popularity has increased, wild terrapin populations have dwindled. Over the past 50 years, they’ve suffered an estimated 75% decline across the bulk of their range due to habitat loss, nest predation and crab trapping.
One scientist at the Smithsonian Environmental Research Center (SERC) is hoping to find out if island restoration efforts can give terrapin populations a much-needed boost.
Since April, Patty Levasseur has served as SERC’s resident terrapin expert. As a postdoctoral researcher working for SERC’s Spatial Ecology and Conservation Lab, Levasseur is leading SERC’s terrapin monitoring efforts on Jefferson Island.
Bluestriped grunts and gray snapper, two important subsistence fish in the Mesoamerican region, school in a marine sanctuary in Belize. (Credit: Claudio Contreras-Koob)
Around the world, an estimated 52.8 million people engage in subsistence fishing—the practice of fishing to feed one’s family and community, where most of the food stays local. As ocean temperatures rise, so do concerns about how this will impact the fish populations these communities depend on.
Subsistence fisheries are difficult to track, due to lower reporting of catch numbers compared to industrial fishing. Subsistence fish are also usually smaller species that aren’t as economically valuable. But they are vital to the food security of these communities.
“We want to know if the communities that depend on these fish as food sources will still have that resource under different, end-of-century climate scenarios,” said Cortese.
For many forest creatures, trees offer the ultimate all-you-can-eat buffet. Insects, mammals and even fungal pathogens see trees as a free meal. They’ll feast on tree leaves with no hesitation.
These trees, however, are not defenseless. To defend against predatory enemies, trees produce special chemicals called “secondary metabolites” within their leaves. If a tree produces enough distasteful metabolites, it may be able to deter hungry herbivores.
A recent study, spearheaded by researchers at the Smithsonian Environmental Research Center (SERC), found that trees growing in more diverse communities produce a wider array of chemical compounds on their leaves. This then changes how animals interact with those trees—often in ways the team didn’t expect.
Volunteer Sarah Ryan Hudson holds a sample she collected for Chesapeake Water Watch in the lower Chesapeake Bay. (Credit Sarah Ryan Hudson)
What if satellites could better track the health of Chesapeake Bay rivers and nearshore waters from space? That’s the goal of Chesapeake Water Watch, a participatory science project run for the past four years by the Smithsonian Environmental Research Center (SERC), the City College of New York and NASA. For the first time this summer, the project used its data—roughly 2,500 water samples collected almost entirely by volunteers—to improve satellite observations of the Bay, in a new study.
Satellites have monitored aquatic ecosystems across the globe for over 20 years. They use the water’s changing colors to better understand algal blooms, water clarity and other key environmental health factors. But training those satellites on smaller tributaries and coastal waters like those along the Chesapeake Bay has proven more difficult. Most “ocean color” satellites aren’t high-resolution enough to capture the detailed shifts that happen on the coasts. For satellites that can capture higher-res images, there isn’t always enough data on the ground to cross-check their findings.
Tuck Hines holds a female blue crab during a trip to China (Credit: SERC)
In its 60-year history on Chesapeake Bay, few people have shaped the Smithsonian Environmental Research Center (SERC) more than Anson “Tuck” Hines. During his 46 years as a research ecologist at SERC, Hines led the center as associate director for research for 18 years and as director for the past 20 years—longer than any previous SERC director.
This June Hines passed the torch to William “Monty” Graham, an oceanographer from the Florida Institute of Oceanography. He left behind a campus transformed under his leadership, into a world-renowned coastal research center that reaches around the globe.
