Date of Award

Summer 8-21-2020

Level of Access

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Marine Biology

Advisor

Ian Bricknell

Second Committee Member

Carrie Byron

Third Committee Member

Heather Hamlin

Additional Committee Members

Gayle Zydlewski

Damian Brady

Abstract

The salmon louse Lepeophtheirus salmonis is a parasitic copepod that infects wild and farmed salmonids throughout the northern hemisphere. L. salmonis represents the largest economic hurdle of the Atlantic salmon (Salmo salar) industry, with an estimated annual cost of nearly $1 billion globally due to production losses and anti-parasitic control measures. Salmon farming in Maine has existed for decades and is a critical economic driver, yet the region is underrepresented in global sea lice research. The aim of this work was to examine parasites in the context of animal trophic transfer and characterize physiological condition by quantifying the flow of stable isotopes and seasonal energy reserves in sea lice, respectively.

A meta-analysis of fish host-parasite stable isotopes was conducted, as well as stable isotope analysis in a case study of farmed and wild S. salar in Maine and their respective parasites, L. salmonis and Argulus foliaceus. Across the literature, endoparasites were depleted in d15N relative to their hosts, ectoparasites demonstrated a range of d15N enrichment patterns, and

d13C enrichment varied extensively across taxa. L. salmonis and A. foliaceus demonstrated contrasting d15N and d13C enrichment patterns relative to their hosts, and none were in agreement with current animal standards. Results suggest that parasites do not conform to traditional predator-prey standards, and that, even among closely related ectoparasites, there does not appear to be a universal enrichment pathway.

To quantify lipid and thermal energy reserves in sea lice embryos, histology and differential scanning calorimetry were respectively employed. Both reserve types exhibited seasonal patterns, with peak lipid quantities in the spring and lower levels in colder seasons, and the highest thermal energy content (via specific heat capacity, Cp) in the summer. Daily changes in Cp varied between months, although values generally declined between initial and final sampling days. Collectively, maximal lipid reserves and energy content aligned with the beginning of typically observed annual infection surges on farms and optimal conditions for L. salmonis development. With the earliest opportunity for population forecasting at the understudied embryo stage, these indicators of condition may contribute to more accurate infection models that inform pest management.

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