Seasonal abundance of the siphonophore, Nanomia bijuga, in Monterey Bay

Quantitative video surveys, conducted in the upper 1000 m in Monterey Bay from an ROV, showed that the year-round population of the siphonophore Nanomia bijuga occupied a daytime depth range between 10 and 800 m, with the majority between 200 and 400 m. The time-series transects revealed a repeating pattern of seasonal variations in abundance, with peak abundance during the Oceanic period, about three months after the onset of regional upwelling. The seasonal pattern was consistent over a three-year period from 1993 to 1995. The abundance of N. bijuga was significantly correlated with the annual cycle of primary production in Monterey Bay. This study is based on data from the first time series of systematic mesopelagic transects conducted by an ROV.