Shedding new light on a larval trophic bottleneck in New England’s iconic lobster fishery

Recent studies suggest declining young-of-year recruitment of American lobster (Homarus americanus), one of the most valuable single fisheries in the United States, may be linked to food limitation in the planktonic larval stage. Molecular techniques are ever-improving our understanding of trophic interactions in marine and terrestrial food webs. In this study, we applied DNA sequencing methods paired with traditional microscopy to augment our understanding of the larval American lobster diet from two coastal locations in the Gulf of Maine: off New Hampshire and Midcoast Maine. We found that stomachs of Stage I larvae were generally less full than those of Stage IV postlarvae and that diets were strikingly similar between the two locations. Microscopy revealed that crustaceans, and in particular copepods, dominated the diets of both Stage I larvae and postlarvae. Feeding experiments confirmed the importance of crustacean prey to larval growth and survival and the vulnerability of early-stage larvae to starvation relative to later stages. Metabarcoding underscored the prevalence of crustaceans in the diet, but also revealed a broader diversity of prey taxa than microscopy, including soft-bodied prey often missed by microscopy. A targeted, taxon-specific, real-time polymerase chain reaction assay revealed evidence of selective predation by both Stage I larvae and postlarvae on the lipid-rich Calanus finmarchicus, a cold-water-adapted copepod expected to contract in its range as waters continue to warm. These complementary diet analysis methodologies provide novel insight into trophic interactions of lobster larvae, essential for understanding the impact of food-limitation on lobster recruitment as key prey species shift in range and abundance.