LINKING LARVAL TEMPERATURE TOLERANCE IN THE LAB TO SETTLEMENT AND PERFORMANCE IN THE FIELD IN THE AMERICAN LOBSTER

American lobster (Homarus americanus) populations in the Gulf of Maine are settlement driven and our research focuses on how temperature tolerance of planktonic larvae shapes patterns of settlement. We defined physiological thresholds of thermal tolerance for the planktonic postlarval stage through laboratory experiments quantifying growth and mortality, scope for activity and gene expression. We related these thresholds to performance in the field by deploying wild postlarvae in cages at depths of approximately 10, 40 and 80 m for two months and quantifying settlement over the same depth range.  Mean bottom temperature for caged larvae was 9 °C at 80 m and 14 °C at 10 m and was well within the critical temperature range of 4-27 °C determined in our laboratory assays. Mortality was less than 5% at all depths. However, larvae deployed at 80 m for two months had significantly reduced carapace length and molt increment than those deployed at 10 m. Larval settlement in the field decreased significantly with depth and decreasing temperature, and was 60-fold lower at 80 m than at 10 m. Our results suggest larvae can successfully settle across the entire depth range sampled but sublethal effects may provide a selective pressure to settle in shallower, warmer depths.  Moreover, there is an apparent disconnect between physiologically defined thermal tolerance and the vertical distribution of settlement in the field.  The proximate determinate of depth of settlement is likely due to behavioral rather than physiological responses to decreasing temperature with depth.

Presentation Preference: Oral

Primary Presenter: Eric Annis, Hood College (annis@hood.edu)

Authors:

Eric Annis, Hood College  (annis@hood.edu)

Christina Shaner, Hood College  (cms45@hood.edu)

Aubrey Jane, University of New England  (ajane@une.edu)

Jesica Waller, Maine Department of Marine Resources  (Jesica.D.Waller@maine.gov)

Markus Frederich, University of New England  (mfrederich@une.edu)

Douglas Rasher, Bigelow Laboratory for Ocean Sciences  (drasher@bigelow.org)