Middle Schoolers Track Invasive Crabs at Acadia National Park

On the rocky shores of Acadia National Park's Schoodic Peninsula, the usual sounds of warblers, wind and surf are joined during the school year by the excited shouts of middle schoolers in bright yellow vests, thrilled to find crabs scuttling under rocks and heaps of seaweed. They are taking part in the Schoodic Education Adventure (SEA), a multi-day program run by the park with support from Schoodic Institute and Friends of Acadia, which gives middle school students hands-on, curriculum-based field experience, including real scientific research.

Students in the SEA program search for crabs in the intertidal zone. NPS/Alexa Pezzano.

Their field site is the intertidal zone, the stretch of shore underwater at high tide and exposed at low tide. Along this part of Maine it supports thousands of commercial and recreational fishers and is vital to coastal ecosystems, home to everything from algae to clams and sea stars. The students collect data for the Gulf of Maine Research Institute's (GMRI) intertidal crab surveys, which enlist young citizen scientists to track how Maine's invasive and native crab populations are changing.

An ecological and economic threat

Two invasive species, the European green crab (Carcinus maenas) and the Asian shore crab (Hemigrapsus sanguineus), now live in intertidal habitats across the Gulf of Maine, causing serious economic and environmental harm.

The green crab reached the eastern United States in the mid-1800s, probably as larvae in the ballast water of ships from southern Europe. It was seen in southern Maine in 1900 and has spread up the coast since. It is a fast, aggressive predator that eats soft-shell clams and competes with lobsters for food, threatening Maine's most valuable fisheries. It also burrows, loosens sediment and snips plants, degrading eelgrass beds and salt marshes that feed and shelter many other species. A coastal biologist with the Maine Department of Marine Resources described it as the hardest problem in shellfish management because it is everywhere, able to live in almost any habitat and eat almost anything.

In the 1980s, a second, more cold-tolerant variety arrived in Canadian ports from northern Europe, spread south to Maine and began interbreeding with the southern one, producing hybrids that tolerate an even wider range of temperatures. Cold winters used to hold green crab numbers down, but with these hybrids, and with the Gulf of Maine warming faster than 97 percent of the world's oceans, the population keeps growing, making it one of Maine's costliest and most destructive invasive species. Tracking where it is most abundant helps parks plan the management and restoration of salt marshes, eelgrass beds, clam flats and other intertidal areas.

In the field

On one foggy June morning, seventh graders from Community Roots Charter School in Brooklyn, New York, arrived for three days at Schoodic Institute. SEA educators first explained invasive species, citizen science and tidepool safety, and handed out calipers for measuring crab width and quadrats, PVC frames marking a square meter to survey. Then the students crossed a field of seaweed as slippery as wet spaghetti to their survey sites along a measuring tape stretched across the cove. Some were eager; others, like one girl worried about being pinched, were nervous at first, until watching a classmate pluck a tiny crab from a rock gave her the confidence to join in. Their teacher said that pushing students a little out of their comfort zone gives them chances to try new things and connect the field to the classroom.

Students learn to measure crab width with calipers. NPS/Alexa Pezzano.

After 10 minutes searching each quadrat, students recorded the species, sex and size of every crab, from a few millimeters to about 10 centimeters across, and photographed the largest of each species. Green crabs were the most common. Despite the name, their color varies, mottled brown or green with yellow patches on top and orange or red underneath when molting, so students identified them by the five spines on each side of the eyes. They also found Asian shore crabs, first identified on the U.S. East Coast in 1988 and now found from North Carolina to Schoodic Point and still spreading north. They have three spines beside each eye and banded legs, and though far less widespread than green crabs, they also threaten native species by preying on them and competing for food. In 2019, a SEA student was among the first to document an Asian shore crab in Acadia, finding a molted shell; sightings have grown more frequent since.

Alexa Pezzano, the Acadia educator who directs SEA, called that discovery valuable, if alarming, and said students are part of a real science project whose results matter. Before uploading their data to GMRI's database, the students returned the crabs to the shore; their job is to collect data, not to control the population.

Inspiring the next generation

SEA added GMRI's crab survey protocol to its curriculum in fall 2021, and with careful supervision, students have since contributed a trove of high-quality data. Such citizen science helps researchers follow how the coast is changing with warming waters, rising seas, ocean acidification and invasive species. The students gain too: skills in collecting reliable data, emotional and scientific connections to Acadia, a sense of stewardship, and the knowledge that they can contribute to science at any age and from any background. A Schoodic Institute fellow in environmental science education noted that children who learn early that science is accessible are more likely to pursue it later. Two of the Brooklyn students, after their survey, asked where they could find a beach in New York to keep doing it.

Sources

• National Park Service, Acadia National Park, "Middle-School Citizen Scientists Track Invasive Crabs at Acadia National Park," by Nina Foster, a 2024 Scientists in Parks intern. https://www.nps.gov/articles/000/citizen-science-crabs.htm
• Schoodic Education Adventure: https://schoodicinstitute.org/education/schoodic-education-adventure/; GMRI intertidal crab surveys: https://investigate.gmri.org/project/intertidal_crabs; "Asian Shore Crab Discovered by a Middle School Citizen Scientist": https://www.nps.gov/articles/asian-shore-crab-discovered-by-a-middle-school-citizen-scientist.htm
• Remarks by participants are paraphrased. Photographs credited to individual photographers, Schoodic Institute and the Maine Department of Marine Resources are not reproduced.
• Words on this page from people and organisations outside the federal government are paraphrased; rewritten in hubnx's own words.