Spatial and temporal abundance patterns for the late stage copepodites of Metridia lucens (Copepoda: Calanoida) in the US northeast continental shelf ecosystem

• Published in: Journal of Plankton Research
• Main Author: Kane, Joseph
• Format: Text
• Language: English
• Published: Oxford University Press 2003
• Subjects: ORIGINAL ARTICLES; Calanus finmarchicus; North Atlantic; North Atlantic oscillation
• Online Access: http://plankt.oxfordjournals.org/cgi/content/short/25/2/151; https://doi.org/10.1093/plankt/25.2.151

The annual cycle of abundance for the calanoid copepod Metridia lucens and its interannual variability are described from 17 611 samples collected on 193 broad-scale plankton surveys of the US northeast continental shelf region from 1977 to 1999. The copepod’s seasonal distribution is illustrated with bi-monthly geographic abundance plots. Abundance of M. lucens is compared with various environmental variables, abundance of the copepod Calanus finmarchicus, density of potential predators and the North Atlantic Oscillation (NAO) index. Metridia lucens abundance increased throughout the ecosystem during spring warming and usually reached peak levels in late spring. The highest mean densities were measured in the Gulf of Maine (GOM), where the copepod is usually found year round and exhibits a weak, decreasing west to east abundance gradient. The less dense populations located on Georges Bank and within the Middle Atlantic Bight are characterized by year-round onshore to offshore gradients that strengthen during the summer months when the copepod concentrates offshore where there is a cool layer of subthermocline water, the region often referred to as the cold pool. Interannual variability in abundance showed two persistent periods: above average values from 1979 to 1982, followed by very low levels from 1983 to at least 1987. Metridia lucens abundance in the 1990s has usually been at or above time series means. None of the environmental variables measured during the surveys could be correlated to this variability. The copepod’s abundance in the GOM was not related to variation in the NAO index or to changes in predator abundance found in the region. The seasonal abundance cycle and interannual variability of M. lucens in the GOM were found to be very similar to those found for the dominant copepod, Calanus finmarchicus. Reasons for this coupling are discussed.