Date of Award

Summer 8-18-2023

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Oceanography

Advisor

Jeffrey Runge

Second Committee Member

Lee Karp-Boss

Third Committee Member

Rachel Lasley-Rasher

Additional Committee Members

Catherine Johnson

Abstract

The Gulf of Maine (GoM) harbors a productive ecosystem that supports a wide variety of marine life, providing services upon which local communities rely. The GoM ecosystem supports many important commercially harvested species, including the American lobster (Homerus americanus) which is the most valuable fishery in the US, Atlantic herring (Clupea harengus) and a variety of groundfish. The GoM is also home to the critically endangered North Atlantic right whale (Eubalaena glacialis), which has historically been known to feed in the eastern GoM and Bay of Fundy during the summer and fall months. In recent decades, the Gulf of Maine has experienced a rate of warming that is among the highest across the globe. Changes in circulation possibly originating from atmospheric CO2 increase have altered the external sources of supply and physical properties of the water in the GoM. The changes in the GoM ecosystem are being described in the literature as a “regime shift” occurring around the year 2010. The 2010 oceanographic shift has been linked to changes in the biological components of the ecosystem including fisheries closings and declines in the populations of endangered species. Zooplankton represents an important link in energy transfer from lower to higher trophic levels in the marine environment as they control the abundance and composition of phytoplankton and are a food source for consumer from pelagic forage fish to baleen whales. The objective of this study is to examine whether there were changes in the characteristics of the mesozooplankton community in the western GoM following the 2010 shift. Data from two long-term time series stations were assessed; one in Wilkinson Basin, a primary overwintering habitat for C. finmarchicus and an historically important feeding ground for the NARW, and one at the western margin of the MCC, an important source of advective supply and transport of zooplankton to Wilkinson Basin. This study investigates the effects on the overall mesozooplankton biomass, seasonal and longer-term change in biodiversity and community structure. The data were assessed in a time period of 5 years before and 6 years after the shift, corresponding to the availability of data in the time series. The changes observed in the mesozooplankton biomass and community structure in the western GoM support the idea that a regime shift has occurred in the GoM around the year 2010. These changes seem to be climate related and are strongly seasonal.

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