Evidence that mud seafloor serves as recruitment habitat for settling and early benthic phase of the American lobster Homarus americanus H. (Decapoda: Astacidea: Nephropidae)

Structurally complex cobble seafloor protects against predators, and is generally assumed to be the only meaningful habitat for settlement and benthic recruitment of American lobsters (Homarus americanus H. Milne Edwards, 1837). Accordingly, historical surveys on featureless substrates such as mud have found few and only older juveniles. Mud, however, is far more common than cobble across the lobster's range, and may be of increasing importance in regions where the lobster population has been growing over the past few decades. As a first step to determining whether mud seafloor serves as meaningful recruitment habitat for juvenile lobsters, we deployed artificial habitats (bio-collectors) at five locations varying from 100% mud to mostly cobble, in Maces Bay, Bay of Fundy, NB, Canada, to capture young lobsters. A broad size range of lobsters, from new settlers up to adolescents, colonized bio-collectors in all locations, suggesting that lobsters settle and spend at least some of their juvenile life on mud. Differences in body condition (length-standardized mass) of lobsters sampled from the different locations suggest that some individuals must reside on mud for at least months to years, long enough to show differential growth between habitats. The greater relative abundance of adolescents in bio-collectors on mud also suggests their net movement from densely populated cobble beds into mud habitat. We propose that mud seafloor may be a more important habitat for settlement and early survival of American lobsters than is currently appreciated, especially given the current potential saturation of scarce cobble nursery habitat by growing lobster populations and, in some regions, reduced predation on mud seafloor due to overfishing of groundfish.