No Easy Answers: Dramatic shifts in American lobster habitat and demography in the Gulf of Maine
Date:
Abstract: The American lobster, Homarus americanus, naturally prefers to occupy shelters and populations have historically been concentrated in shelter-providing boulder habitat. However, this paradigm has shifted. From 1997 to 2019, population densities in shallow zones (~10 m) of coastal Maine declined over 66% in boulder habitats but increased 202% in relatively featureless habitats, and lobsters found using rocky shelters declined 30%. This represents a fundamental change in their behavior, ecology, and distribution; particularly with boulder being rarer than featureless habitats. A decline in predatory fishes decreasing the need for lobsters to use shelters might provide a simple explanation, but predators already declined to non-functional levels by the 1990s. Further investigation targeted the dramatic phase shift from kelp to filamentous turfs and expansion of nonnative algae species in these areas. This led to the hypotheses that low oxygen, resulting from the breakdown of algal detritus, or chemical compounds from new species could cause the observed changes in the lobster population. Laboratory shelter selection experiments showed no selection preference of lobsters between shelters with low oxygen and ambient oxygen levels nor between shelters filled with algae and those without it present. Additional work will be necessary to identify drivers of this behavioral change.
Authors: Jarrett, R., Steneck, R.
Ph.D. Dissertation Research at the University of Maine