Eric R. Annis

Date of Award

8-2004

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Oceanography

Advisor

Robert S. Steneck

Second Committee Member

David W. Townsend

Third Committee Member

Neal R. Pettigrew

Abstract

The connectivity of marine populations and the degree to which they are considered open or closed has important implications for the ecology, management, and resilience of commercially harvested species. Larval exchange is a primary determinant of the level of connectivity between populations, and this thesis examines the intrinsic and extrinsic factors influencing larval transport and the distribution of larvae of the American lobster (Homarus americanus). The potential for larval transport is directly proportional to the planktonic larval duration. Our field data suggest development times in situ were up to three times faster than previous laboratory development times, indicating that potential for transport is less than previously reported. Observation of postlarvae in sitzi 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 self-recruiting, 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.

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