Indication of Possible Shifts in Copepod Species Composition in St. Pauls Inlet, a Fjordal Estuary Connected to the Gulf of St. Lawrence

Abstract

St. Pauls Inlet, a coastal brackish lake/estuary within Gros Morne National Park in Newfoundland and Labrador (Canada), is a semi-enclosed body of water with a narrow 80-m wide opening to the marine Gulf of St. Lawrence and with freshwater input from 24 streams. An initial biological survey of St. Pauls Inlet in 1977/78 during Park planning stages found dominant members of the mesozooplankton community to be copepods of genera Acartia, Calanus, Oithona, and Temora. Subsequent surveys of 2009, 2010, and 2019 found Calanus abundance to be much reduced or absent and low adult microcrustacean (copepods + cladocerans) densities. Recent data suggest that Calanus finmarchicus, a large energy-rich copepod, has declined across the Gulf of St. Lawrence and the wider Northwest Atlantic, with the zooplankton community shifting towards smaller, warm-water copepods This shift is coincident with rising surface sea-surface temperatures in the Atlantic. Mid-July temperatures in the inlet were higher in 2009, 2010, and 2019 compared with 1977. Shifting zooplankton abundances in St. Pauls Inlet, even with reduced exchange with the Gulf, may reflect wider trends in the Northwest Atlantic and be a useful indicator of a changing coastal environment in this national park.