Date of Award

Spring 5-5-2023

Level of Access Assigned by Author

Open-Access Thesis

Language

English

Degree Name

Doctor of Philosophy (PhD)

Department

Marine Biology

Advisor

Richard Wahle

Second Committee Member

David Fields

Third Committee Member

Peter Countway

Additional Committee Members

Jeff Runge

Andrew Pershing

Abstract

Many marine organisms exhibit bipartite life-cycles whereby reproductive adults dwell on the benthos while the larvae are pelagic. The pelagic stage is subject to mortality rates which far exceed those experienced by the organism during its benthic existence. The larval phase therefore represents an important bottleneck to larval recruitment. Small changes to survivorship in the plankton can have large consequences for subsequent year-class strength. Understanding the factors influencing successful larval recruitment is an important step towards predicting future stock abundances and maintaining healthy fisheries. The American lobster (Homarus americanus) is a large benthic crustacean which is economically and culturally important in the Gulf of Maine. In the past few decades lobster broodstock abundance and egg production has soared, but young-of-year recruitment to benthic nurseries has declined. This suggests a breakdown in the spawner-recruit relationship due to changes in the factors that control larval survival and recruitment success. In this dissertation, I have investigated potential intrinsic and extrinsic sources of variation to larval survival, which may be responsible for declining lobster benthic recruitment. Body size is an important intrinsic trait that affects both larval production and survival. Ongoing warming within the Gulf of Maine has led to earlier maturation of female lobsters at smaller sizes. Smaller females were found to produce fewer, lower quality larvae. Meanwhile, food-limitation is an important extrinsic source of larval mortality. Warming-induced changes to zooplankton regimes could put planktivorous lobster larvae at increased risk of food-limitation, as suggested by recent correlative evidence. Results presented here suggest that risk of food-limitation coupled with declining maternal size interact to lead to lower recruitment success for lobster larvae. Larval ecology is frequently termed a ‘black box’ due to the difficulties associated with studying small dispersive larvae. This dissertation seeks to surmount these difficulties through the use of mixed-methodologies and a combination of laboratory and field-based approaches. The overarching goal of this research is to further understanding of lobster larval recruitment and ecology while demonstrating the efficacy of new tools that, when paired with traditional approaches, help to shine a brighter light on the larval ‘black box.’

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