If you’ve ever ordered a lobster tail from Red Lobster, there’s a good chance some of your meal can be traced back to swamp gas.

Let me explain.

Red Lobster is a major purchaser of Caribbean spiny lobster, a species that lives in coral reefs in the western Atlantic Ocean. In the 1980s, lobster fishers started constructing artificial reefs in sea grass beds throughout the Caribbean to attract these lobsters.

Before long, the fishers noticed something peculiar. They were finding “piles and piles of clams” outside their makeshift lobster shelters, said Nicholas D. Higgs, a marine biologist at Plymouth University in Britain who comes from generations of lobster fishermen in the Bahamas.

These clams, Dr. Higgs confirmed in a recent study, form a significant portion of the lobsters’ diet at these reefs. In a paper published on Thursday in Current Biology, Dr. Higgs and colleagues report that sea-grass-dwelling lucinid clams make up 20 percent of what Caribbean spiny lobsters eat in artificial reefs. What’s unusual about this situation (and where swamp gas comes in) is the way these clams get their food.

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