Your Questions Answered: What Do Larval Lobsters Eat?

We all have to eat, even the smallest among us. Take a tiny lobster larva, for example. Just hatched after long months attached to its mother’s tail, afloat on the ocean’s surface and tugged by tides and currents wherever they take it. It’s hungry, but for what?

By using eDNA researchers have a better understanding of what larval lobsters prefer to eat. DMR image.

Answering that question has taken Alex Ascher, a post-doctoral researcher, a good many years. Ascher started looking at lobster larvae stomachs when he was a Ph.D. student at the University of Maine. He studied lobster larvae survivorship and how it relates to larval recruitment and settlement. Part of his research focused on lobster larvae diet.

Imagine peering through a microscope at the stomach contents of a one-centimeter creature whose stomach is the size of a pinhead. Not easy.

Enter eDNA. Environmental DNA (eDNA) is the genetic material shed by living creatures in the ocean. It is extracted from water samples and, through various processes, can identify the family, genus and even specific species of organisms found there.

Lobster are crustaceans. Unfortunately for Ascher, they eat other crustaceans, like tiny crabs or mussels. It turns out that it is very difficult to discern whether the DNA found in a larval lobster’s stomach is from its prey or is just its own.

Ascher and fellow researchers at the Bigelow Laboratory for Marine Sciences in East Boothbay created a “blocker” that filtered out the DNA of the lobster, leaving the prey DNA behind. But even that did not give Ascher and colleagues the degree of specificity they were looking for.

So they came up with another, more precise molecular technique. A DNA probe (similar to what is used in over-the-counter Covid tests) was created that is tuned to a specific species’ DNA. When it encounters that DNA, it lights up.

Using the probe, the researchers could determine exactly what these minute lobsters were consuming. Ascher, now at the Quahog Bay Conservancy and Woods Hole Oceanographic Institution, and co-authors showed in an article published this summer that larval lobsters consume the tiny zooplankton Calanus finmarchicus at a higher proportion than expected given the availability of other prey options in the wild.

Calanus finmarchicus is a butterball of a zooplankton and is an important foundational species in the Gulf of Maine food web. However, it prefers cold water; in the Gulf it is at the southern-most extent of its range. As the Gulf of Maine has warmed, Calanus densities have decreased.

In recent years juvenile lobster settlement in the Gulf also has taken a downward turn, though that trend has modified in certain areas. At the same time lobster landings have remained high; adult female lobsters continue to produce abundant eggs and larvae. Lobster researchers wondered if part of the reason larval lobsters aren’t surviving long enough to settle on the seafloor might be related to a change in their diet.

“The finding that Calanus are a preferred food of lobster larvae provides important insight into the future of the lobster fishery,” said co-author David Fields, a senior research scientist at Bigelow Laboratory and one of Ascher’s Ph.D. advisors.

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