BIOLOGY AND ECOLOGY OF LARVAL LOBSTERS (Homarus americanus):
IMPLICATIONS FOR POPULATION CONNECTIVITY AND LARVAL
TRANSPORT BY Eric R. Annis B.A. Boston University, 1992
M. S. Florida Institute of Technology, 1998

http://www.library.umaine.edu/theses/pdf/AnnisER2004.pdf

Observation of
postlarvae in situ revealed changes in vertical distribution corresponding to ontogenetic
shifts in behavior and extrinsic environmental factors. Most notably, the 12°C isotherm
appeared to be a temperature threshold with postlarvae remaining in warmer waters
above. This suggests that settlement may be limited by bottom temperature with
negligible settlement occurring below the depth of the 12" isotherm.

Postlarvae spent 94% of the time above 4 m depth, reinforcing the importance of surface currents to
transport of the final planktonic stage. However, only 55-80% of the time was spent in
the top 0.5 m, indicating that abundance estimated from surface samples has been
chronically underestimated. The quality of larvae may contribute to successful larval
transport and laboratory experiments indicated that larvae from embryos of greater mass
were more resistant to periods of starvation. Thus, portions of the population producing
heavier eggs may contribute disproportionately to successfLl larval production. Patterns
of larval distribution over 300 km of coast in the northern Gulf of Maine revealed high
abundance of postlarvae at the downstream end of the study area suggesting a potential
larval sink and two potential upstream sources of newly hatched stage I larvae. Our
results are consistent with two potential source-sink models; one which is largely selfrecruiting,
and a second in which larvae are delivered from a distant source. The relative
contribution of these larval sources to recruitment is unknown and will define the degree
to which the population is open or closed.