Date of Award

5-2026

Rights

© 2026 Erin Anderson

Document Type

Thesis

Degree Name

Master of Science in Marine Sciences

Department

Marine Science

First Advisor

Patricia Thibodeau

Second Advisor

Gwangseok Yoon

Third Advisor

Jerome Pinti

Abstract

Zooplankton span a wide size spectrum and act as important bioindicators of ecosystem health and resilience in regions of environmental change. Within the Gulf of Maine (GoM), zooplankton represent the primary food source for many ecologically and economically important species, but their abundances are changing in part due to rapid warming in the region. This project employs weekly sampling methods in Saco Bay, GoM to quantify zooplankton community composition, phenology, and abundance throughout an almost two-year time series (2024-2026). Zooplankton were identified and enumerated using a Zooscan and community composition was analyzed with respect to seasonal variations in temperature, salinity, phytoplankton biomass, and Secchi depth. We hypothesized that seasonal temperature changes would be significantly related to zooplankton abundance shifts due to the winter-spring phytoplankton bloom, with a predicted maximum zooplankton abundance in summer months (July – September). Our results found four more chlorophyll a blooms in 2025 than in 2024 but three more mesozooplankton blooms in 2025 compared to 2024. Zooplankton abundances followed the general hypothesized seasonal trend, with the highest meso- and microzooplankton abundances observed during summer 2025. A General Additive Model showed moderate salinity (30-32) best explained higher mesozooplankton abundance due to the nonlinear and highly variable nature of zooplankton abundances. In terms of community composition, copepods dominated the zooplankton community, including Pseudocalanus spp., Paracalanus spp., Oithona spp., Centropages spp., and Acartia spp. Additionally, cladoceran taxa Evadne spp. and Podon spp. were abundant year-round, and a prominent peak in copepod nauplii was evident in March and April 2025. Biodiversity differed by season and was significantly higher in 2024 than 2025 with spring 2025 exhibiting the highest average diversity across all seasons. Our results indicate strong seasonal drivers of zooplankton abundance, diversity, and protein concentrations within Saco Bay. Salinity profiles at our study site are strongly influenced by the discharge of the Saco River (Tilburg et al., 2011), indicating a dynamic coastal and estuarine environment influenced by a plethora of outside factors. Analysis of weekly zooplankton community composition, biodiversity, and life histories overtime increases our understanding of community size structure, seasonal dynamics, and phenology in Saco Bay and how the coastal zooplankton community compares in trophic structure, taxonomic composition, and abundance to neighboring GoM communities.

Comments

Master's Thesis

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