Summer students dig into crab stomachs | Science News for Students

Summer students dig into crab stomachs

Two teens spent their summer catching crabs to help solve a mystery
Sep 18, 2014 — 12:08 pm EST
Anna Ramgren and Hannah Newhall

Focus is everything as Anna Ramgren (front) and Hannah Newhall carefully dig out the stomach contents of green crabs for their summer research project.

Jane Disney

Most people crack open a crab to pull out its tasty meat. When Anna Ramgren, 17, and Hannah Newhall, 18, open a green crab, they aren’t looking for dinner. At least, they aren’t looking for their dinner. The two students spent this past summer cutting up crabs for science at Mount Desert Island Biological Laboratory (MDIBL) in Bar Harbor, Maine.

The two were tasked with studying the crabs’ stomach contents. Green crabs are an invasive species, thriving far from their original home in the waters of Europe. When species like green crabs move into new waters, they can bully the native species, gobbling up organisms that can’t defend themselves.  The findings by these Maine teens could help scientists figure out if this invasive species has been eating its way through the habitat in nearby Frenchman Bay.

Anna was a rising senior at Waterville Senior High School in Waterville. Hannah had just graduated from Cape Elizabeth High School in Cape Elizabeth. Both received MDIBL research fellowships and ended up in the laboratory of Karen James.

James has been interested in learning why the eelgrass in Frenchman Bay is dying. This plant grows in brackish bays and estuaries. Salt water from the ocean and fresh water from rivers mix in these areas. Underwater beds of eelgrass provide important habitat for many fish and shellfish species that people like to eat. Eelgrass also helps to stabilize mud on bay bottoms. But the eelgrass in Frenchman Bay is in trouble.

Anna Ramgren and Hannah Newhall learned how to dissect out a crab stomach during their summer research. Their video of how to do it could help others who want to follow in their footsteps.

H. Newhall and A. Ramgren

“Eelgrass beds have been dying back alarmingly and rapidly over the last few years,” James explains. “This last autumn there was a very sudden and dramatic die back, but we don’t know what the culprit is. It could be climate change; the water in the area was very warm. It could be changes in elements like silica. Plants use silica in their structure, to make them tough and able to stand up in the water. It could be the invasive green crabs, damaging the grass. It could be a combination of two or more of these things. It’s a detective story.”

James decided to probe the possible role of green crabs (Carcinus maenas). “They could be foraging for organisms around the base of the eelgrass and damaging it. Or they could be eating eelgrass itself as part of their diet,” she says. To find out, she needed to see what was in their stomachs.

She sent Anna and Hannah to collect green crabs from around Frenchman Bay. The teens then dissected the crabs, removing their stomachs. Inside each crab’s stomach was partially digested food. To identify what it was, James’ lab studied the materials’ DNA. DNA is a long spiral molecule containing a specific genetic “code,” a sequence of small molecules. The molecules provide the “instructions” to make all the parts of an organism. Each organism’s DNA code is unique to every living thing (which is why it’s sometimes referred to as its genetic fingerprint). Hannah and Anna collected samples of partially digested food from crab stomachs. They then performed experiments to determine what DNA molecules were in the crab’s last meal. That code can be used to help identify the species it came from. 

Digging out a crab’s stomach requires a bit of creativity and a lot of time. Hannah and Anna developed a method for extracting a crab’s stomach which they posted to YouTube. They are still waiting on the results of their experiments. But James notes that no matter what they learn, these data will help scientists understand how the invasive crabs are interacting with the local species.

Both teens had tried research programs before, and were eager to get more experience. Anna has always loved science. Yet the experiments she did in school never excited her. “You’re just repeating something that has already been done, and the goal is to get the same results as everyone else,” she says. In the lab this summer, “I found it exciting knowing that what we were doing would create original data.”

Anna also says summer research gave her a new perspective on science. “Unlike the studies in a classroom, experiments in a lab don’t end with an answer,” she explains. “They also raise more questions.” Anna hopes to continue to do research in the future.

Hannah is starting her freshman year at Colby College in Waterville, where she plans to study science. “I learned that it’s never too early or too late to start doing science,” she says. This past summer, she says she “met people that know they wanted to be a scientist before they could talk — and people who didn’t know they wanted to be a scientist until after their kids were in college.

“Science is a field driven by a passion for discovery,” she says. “And anyone can do it.”

*Karen James is a personal friend of mine. You can follow her on Twitter at @kejames.

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Power Words

DNA  (short for deoxyribonucleic acid) A long, spiral-shaped molecule inside most living cells that carries genetic instructions. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make.

DNA sequencing  The process of determining the exact order of the paired building blocks — called nucleotides — that form each rung of a ladder-like strand of DNA. There are only four nucleotides: adenine, cytosine, guanine and thymine (which are abbreviated A, C, G and T). And adenine always pairs up with thymine; cytosine always pairs with guanine.

eelgrass  A common name for several species of saltwater plants. These grasses grow underwater in the ocean or in the brackish bays and estuaries where saltwater and freshwater mix. Eelgrass beds are important habitat for young fish and shellfish. They also help to stabilize the seafloor with their root-like masses.

genetic  Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics.

green crab   A species of crab (Carcinus maenas) that is native to the coasts of northern Europe. It has invaded areas outside its home range, both along the Atlantic and Pacific coasts. It is a voracious feeder and will eat many important species as it invades their habitats.

habitat  The area or natural environment in which an animal or plant normally lives, such as a desert, coral reef or freshwater lake. A habitat can be home to thousands of different species.

invasive species  (also known as aliens) A species that is found living, and often thriving, in an ecosystem other than the one in which it evolved. Some invasive species were deliberately introduced to an environment, such as a prized flower, tree or shrub. Some entered an environment unintentionally, such as a fungus whose spores traveled between continents on the winds. Still others may have escaped from a controlled environment, such as an aquarium or laboratory, and begun growing in the wild. What all of these so-called invasives have in common is that their populations are becoming established in a new environment, often in the absence of natural factors that would control their spread. Invasive species can be plants, animals or disease-causing pathogens. Many have the potential to cause harm to wildlife, people or to a region’s economy.

nucleotides  The four chemicals found in DNA. They are: A (adenine), T (thymine), C (cytosine) and G (guanine). A links with T, and C links with G, to form DNA.

species  A group of similar organisms capable of producing offspring that can survive and reproduce.