Macoma balthica, Baltic clam, a small marine bivalve mollusk, is the main food source of the long distant migratory shorebird species red knot in the Wadden Sea, Iceland, Northern Norway and other spring staging (refueling) areas. Rapid feeding of 1 - 2 cm specimen of Macoma balthica enables knots to build major fat reserves for their thousands of kilometers non-stop flight to the Arctic breeding grounds. Macoma balthica lives in the northern parts of both the Atlantic and Pacific oceans, and also extends to the Subarctic both in North America and in Europe.