Feeding selectivity of calanoid copepods on phytoplankton in jangmok bay, south coast of Korea

Abstract

Grazing impacts of calanoid copepods on size-fractionated phytoplankton biomass [chlorophyll (Chl)-a] were measured in Jangmok Bay, Geoje Island, Korea, monthly from November 2004 to October 2005. The ingestion rate of calanoid copepods on total phytoplankton biomass ranged between 1 and 215 ng Chl-a copepod-1 day-1 during bottle incubations. Results indicated that microphytoplankton (>20 μm) was the primary food source for calanoid copepods in grazing experiments on 3 phytoplankton size categories (>3 μm, 3-20 μm, and >20 μm). The ingestion rate on microphytoplankton showed a significant increase (r= 0.93, p <0.01) with Chl-a concentration. Nanophytoplankton (3-20 μm) showed a negative ingestion rate from June 2005 to October 2005, but the reason is not completely understood. Calanoid copepods were unable to feed efficiently on picophytoplankton (<3 μm) due to unfavorable size. Calanoid copepods removed between 0.1% and 27.7% (average, 3.6 ±15.8%) of the phytoplankton biomass daily during grazing experiments. Grazing pressure was high in winter and early spring (January-March: 15.6-27.7%), while low in summer (June-August:-33.1-0.0%) and autumn (September-November:-1.4-5.1%). Results suggest that calanoid copepods play an important role in controlling the biomass and size structure of phytoplankton in winter and early spring. © 2010 Korea Ocean Research & Development Institute (KORDI) and the Korean Society of Oceanography (KSO) and Springer Netherlands.