How to Take a Benthic Core Sample for Resource Assessment
Core sampling is a highly accurate resource assessment tool. Use it to conduct shellfish surveys and to determine the effectiveness of management activities.
DEI provides science-based leadership to help shellfisheries adapt to the changing marine environment. Our immediate emphasis is on the crises caused by the predatory milky ribbon worm and invasive green crab. Our applied marine research provides valuable insights in how our communities can adapt to the warming ecosystem.
The Problem: Warming Temperatures are Changing Ocean Ecology
Since the early 1980’s, Gulf of Maine (GoM) Sea Surface Temperatures (SST) have been rising faster (0.03 °C/year) than the global mean rate of 0.01°C/year (Pershing et. al 2015). Since 2004, SSTs in the GoM have increased faster than in 99% of the world’s oceans, and scientists predict seawater temperatures will continue to rise. Maine winters have become milder and shorter (Fernandez, et al. 2015), with winter icing becoming less and less common.
The increased temperatures have led to many negative consequences for fisheries, as explained below.
Higher Temperatures Correspond with Increases in Green Crab Abundance:
In the early 1950’s, Maine experienced warmer seawater, which correlated with an explosion of green crab populations in northern New England (Glude 1955, Ropes 1968, Welch 1968, Grosholz & Ruiz 1996). Recent research by Downeast Institute (Beal et al. 2020a, Beal et al. 2020b, Beal et al. 2018, Beal et al. 2016) and others (McClenachan et al. 2015) shows that Maine green crab populations are strong, especially along the mid-and southwestern coast where seawater temperatures tend to be highest.
Since the 1980’s Maine’s Soft-Shell Clam Fishery Has Declined
Over the past 40 years, during the same period of time the GoM has been warming, Maine’s commercial production of soft-shell clams, Mya arenaria, has decreased nearly 75%. Since then clam landings continue to set new low records. In 2017 statewide clam landings were the lowest since 1933 and in 2020 they declined even further, with only 6,542,197 pounds landed.
The graph below shows the statewide decline in Maine soft-shell clam landings, as well as rising winter sea surface temperatures in the Gulf of Maine from 1940 to 2018.
Rising Ocean Temperatures are Associated with Higher Levels of Predation on Clams (and other species):
Graph showing 1940- 2021 Maine clam landings and the average minimum winter temperature (January through March). Average minimum temperature from ME DMR Boothbay Harbor records.
Green crabs are biologically adapted to warmer seawater. Locally, their populations have increased with warming waters and are expected to continue to rise with additional ocean warming.
Green crabs are invasive, which means they did not evolve within our ecosystem and foodweb and have no natural predators to keep their populations in check, although ducks, fish, and other crustaceans will eat them opportunistically. In Europe, green crab populations are regulated by both biotic and abiotic factors; hence, their overall effect on creating crashes in shellfish populations is moderated, compared to their effect on similar populations here in North America.
Rising seawater temperatures cause an increase in the metabolic rates of green crabs and most other predators, resulting in hungrier, more active predators during the spring through fall.
DEI’s large-scale applied marine research provides ecological information intended to inform shellfish management policies and suggest techniques to help the fishery adapt to warming oceans.
Update Shellfish Management Tools: Many of Maine’s shellfish management techniques have remained the same for over 55 years (Dow & Wallace 1961, Hanks 1963). The exception was the establishment of a minimum clam size limit of two-inches in 1984. Results from DEI’s extensive and repeated field experiments indicate that updating traditional shellfish management tools to reflect the changing environment would benefit clam survival. For example:
Clam Conservation Efforts Can Apply Lessons DEI Has Learned From Over 30 Years of Research:
Some of the techniques are explained in this editorial by DEI’s Director of Research Dr. Brian Beal and Maine Clammers Association President Chad Coffin.
DEI provides science-based leadership to adapt to a changing marine environment.
DEI has produced hundreds of millions of seed clams for coastal communities.
DEI assists fishermen and other entrepreneurs create new marine economy-based opportunities.
DEI’s marine education program makes relevant scientific exploration part of pre-K to 12 grade education.
Celebrate our community of marine innovation at our annual festival in Beals.