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DISSERTATION (Ph.D.) DEFENSE - FITZGERALD, CATHERINE

  • Horn Point Laboratory (UMCES) 2020 Horns Point Road Cambridge, MD, 21613 United States (map)

Name: Catherine Fitzgerald
Date: 08/01/2025
Time (EST/EDT): 12:00 pm
Location: AREL conference room
Remote Access: email: mees@umd.edu

Committee Chair: Dr. Jamie Pierson
Committee Members: Dr. Louis Plough, Dr. Ann Bucklin, Dr. Mike Roman, Dr. Ryan Woodland, Dr. Dave Richardson
Dean’s Representative: Dr. Alexandra Bely

Title: Zooplankton, larval fish, and investigative methods in the Choptank River

Abstract: Accurate predictions of recruitment are vital for stock assessments and fisheries management, however recruitment of fish larvae to adult populations is highly variable and the driving forces underlying it are complex. Physical environmental conditions such as temperature, salinity, and dissolved oxygen indirectly impact fish recruitment by altering the distribution of nutritious zooplankton prey. Studies of zooplankton and larval fish ecology have previously relied mainly on taxonomic identification via morphological features. This method comes with drawbacks that tissue metabarcoding of the gene cytochrome oxidase 1 (CO1) shows promise in overcoming. This dissertation will test the hypothesis that a novel genetic tool will clarify the connection between physical parameters of larval fish nursery grounds, seasonal zooplankton assemblages, and the subsequent diets of larval fish. It will further compare molecular and microscopy methods for zooplankton analysis, in terms of both the data that is collected and the cost and efficacy of both methods. The study location is the Choptank river, a tidal tributary of the Chesapeake Bay, and an important spawning and nursery ground for striped bass (Morone saxatilis), white perch (Morone americana), and bay anchovy (Anchoa mitchilli). The Choptank has a long history of monitoring for physical conditions, zooplankton, and juvenile fish, making it an ideal study site to test these hypotheses. Metabarcoding of the CO1 gene shows promise in detecting rare organisms and expanding our knowledge of zooplankton diversity; it is hindered by a lack of standardization and metrics directly comparable to counts. CO1 metabarcoding also shows promise as a tool to investigate larval fish diets, revealing a higher diversity of prey and ontogenic changes in feeding strategy not previously recorded using traditional methods. Zooplankton in the Choptank river respond strongly to physical forcing by season, salinity, and temperature. The abundance of zooplankton taxa found to be important as prey for larval fish was significantly different in the study years (2018-2019) from that expected based on the decadal trends revealed in the Chesapeake Bay Program monitoring data (1984-2002). This makes a strong case for continued monitoring to capture changes in zooplankton abundance and determine factors driving the observed patterns. Changes in the abundance of key zooplankton prey, associated with changes in environmental conditions, may contribute to observed declines in recruitment of larval fish.