Date of Award

Summer 8-2017

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Wildlife Ecology and Wildlife Conservation

Advisor

Stephen Coghlan

Second Committee Member

Joseph Zydlewski

Third Committee Member

Hamish Greig

Additional Committee Members

Michael Kinnison

Alessio Mortelliti

Abstract

Anadromous sea lamprey Petromyzon marinus are native to Atlantic coastal systems and serve as a functional link between marine and freshwater ecosystems. Sea lamprey spend 1–2 years in the ocean parasitizing marine vertebrates before migrating into freshwaters during the spring to spawn. There they construct nests, spawn, then die shortly afterwards. Larvae hatch, bury into fine sediments and reside in streams for generally 6–8 years, but up to 14. Larvae then undergo metamorphosis, a non-feeding period characterized by a series of physical and physiological changes. The juveniles (macropthalmia) then migrate to the ocean to begin the parasitic juvenile phase.

Historically, marine and freshwater ecosystems were linked by migrating anadromous fish, including sea lamprey. However, barriers such as dams have reduced or eliminated these migrations and therefore the delivery of nutrients via metabolic waste, eggs, and carcasses to recipient freshwater systems. This thesis generally focused on characterizing the dynamics and delivery of nutrients from sea lamprey, the pathways by which these nutrients may be assimilated in stream food webs, and factors that may alter or influence these effects.

A first step to understanding the role of sea lamprey in freshwater food webs is to characterize the composition of adult tissue and subsequent dynamics of decomposition and nutrient liberation. First, the timing of decomposition and subsequent nutrient liberation of sea lamprey carcasses was characterized with a field and laboratory experiment. Elemental composition revealed lamprey carcass nitrogen:phosphorus ratios of 20.2:1 (± 1.18 SE). The experiments demonstrated that carcasses exponentially decompose over a three to four week period in the stream leaving 27% (± 3.0% SE) of the initial biomass remaining and liberating the majority of phosphorus and nitrogen. These experiments characterize the dynamics of nutrients delivered to freshwater systems and suggest that these subsidies may serve to enrich stream food webs and alleviate nutrient limitations.

The spatial and temporal dynamics of sea lamprey carcass nutrients were examined. Carcass addition experiments were conducted to examine changes in stream nutrients, primary productivity, and nutrient assimilation among consumers. Field experiments revealed 57–71% increases in algal biomass in areas with experimentally added sea lamprey carcasses compared to an upstream reference. However, broader spatial changes from multiple-site carcass addition may have been influenced by canopy cover from adjacent riparian vegetation that limit incoming sunlight to the stream. Several macroinvertebrate families including Heptageniidae, Hydropsychidae, and Perlidae assimilated carcass nutrients, as determined with stable isotopes analysis. Results from these experiments suggest that carcass nutrients may evoke localized effects on food webs, and the pathways of assimilation by organisms may be coupled to adjacent terrestrial systems.

Resource flows from sea lamprey across ecosystem boundaries may subsidize recipient communities and influence bottom-up and top-down processes in food webs. However, dams and barriers to fish passage may limit returns of spawning adult sea lamprey to freshwater streams. Carcass addition experiments tested the effects of a gradient of increasing carcass nutrients on primary producers and decomposers in stream reaches flowing through open and closed riparian forest canopies. These experiments revealed that manipulating the quantity of nutrient resources affected producers and decomposers differently and that trends were further influenced by adjacent terrestrial systems. A carcass addition experiment also revealed that larval lamprey assimilate a portion of carcass nutrients. Therefore, collectively these experiments demonstrate that sea lamprey carcasses may stimulate bottom-up trophic dynamics by alleviating nutrient limitations, and additionally these nutrients may be captured by higher trophic levels. This suggests that cross-ecosystem linkages may be mediated by subsidy quantity from donor systems and environmental characteristics from recipient systems.

Sea lamprey function as an ecosystem engineer through nest building and spawning activities and as a vector of nutrients to freshwater systems. Macroinvertebrates, an important intermediate pathway in the cycling of nutrients and transfer of energy, may be influenced by these physical and chemical perturbations. We examined the colonization of macroinvertebrate assemblages on cleaned coarse substrate designed to mimic substrate modified by sea lamprey spawning and subsequent nutrient enrichment from post-spawned sea lamprey carcasses. We found that abundance and biomass in sites receiving carcass nutrients were structured largely by Simuliidae, compared to control sites that were structured by Hydropsychidae, Philopotamidae, and Chironomidae. Environmental factors such as stream flow may further shape assemblages by physically constraining the foraging capabilities of certain macroinvertebrate families.

Larval sea lamprey reside in streams for 6–8 years to upwards of 14 years and function as a filter feeding detritivore and utilize nutrients from adult carcasses. As a result, larvae may exhibit higher growth rates during the post-spawn period of increasing temperatures and nutrient limitation. The sensitivity of life history parameters and influence of sea lamprey carcass nutrients on the age and growth of larval conspecifics was examined with a deterministic stock recruitment model. Larval populations receiving carcass nutrients demonstrated increases in larval growth and lower age-at-metamorphosis that, over time, resulted in a 3 fold increase in the numbers of returning adults to freshwaters. This model exemplifies two potential alternative ecosystem states, one in which fish populations are uninhibited during migration, and another in which fish passage is constrained by migratory barriers.

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