Continuous and Nocturnal Feeding of the Marine Planktonic Copepod Calanus Helgolandicus

Grazing and ingestion rates of continuously and nocturnally feeding late copepodids and adult females of Calanus helgolandicus were determined at 15°C. Grazing rates decreased with time when the copepods fed on chain-forming diatoms but remained constant when particles of uniform size were offered as food. Grazing and ingestion rates of female C. helgolandicus raised in the laboratory, a deep tank, and originating from the Pacific Ocean differed little when fed the same phytoplankton species at concentrations close to those found in the Pacific Ocean off La Jolla. Continuously and nocturnally feeding specimens of different origin increased their grazing rates when food concentrations decreased. The differences between mean ingestion rates of continuous and nocturnal feeders were insignificant.