Abstract
Cape Cod Bay is a partially-enclosed water body with a productive marine ecosystem that supports a diverse assemblage of marine life. Included in this marine life are commercial fish species and shellfish, sea birds, and marine mammals, several of which are endangered. The bay has a characteristic circulation pattern leading to long residence times of water in fall and winter and isolation of the bay’s waters in summer. The effects of these circulation patterns have been studied in multiple contexts, but specific attention has not been given to the effects of this circulation on phytoplankton composition. Another distinctive characteristic of the Cape Cod Bay system is the regular development of a summer high-nutrient-low-oxygen(HNLO)pool. It is possible that the nutrient-concentrating mechanisms creating the HNLO pool might also have effects also on phytoplankton distributions. Understanding spatiotemporal differences in phytoplankton composition and abundance will help in understanding the nature of Cape Cod Bay’s productivity, which affects higher trophic levels. This thesis explores the regional and seasonal distribution of phytoplankton in Cape Cod Bay and the mechanisms, in particular, circulation, that may produce variability in phytoplankton distribution. Total phytoplankton abundance and species composition in Cape Cod Bay in 2017 generally followed the hydrological changes that accompanied the seasonal weather patterns of the Northwest Atlantic region. The year 2017 started and ended with temperatures that were above the thirty-year average, conditions which likely affected the composition of the phytoplankton community as well as the progression of species. Observations of the taxa recorded and their abundance levels were generally in agreement with historical regional studies with the exceptions of the occurrence of the athecate dinoflagellate Karenia mikimotoi and the probable occurrence of prymnesiophyte Phaeocystis globosa. Patterns in spatial variability included some compositional differences between the eastern and western portions of the bay. Additionally, upwelling, downwelling, and mixing due to wind activity may have affected the phytoplankton communities in the center and toward the south of the bay in summer and fall.