AbstractLaboratory experiments were conducted with Calanus finmarchicus copepodites IV–V to examine the effects of food concentration, food type, and life stage on chromophoric dissolved organic matter (CDOM) release from copepods. Changes in CDOM absorption and fluorescence were monitored by incubating copepods in rotating bottles for 24 h in the dark with controlled diets. Copepods were fed a range of food concentrations from 800 to 15 000 cells l−1 of either Thalassiosira weissflogii and Skeletonema costatum or Prorocentrum minimum in stationary and exponential growth phases. Results from these studies indicate that diet does have an effect on the amount and type of CDOM released by C. finmarchicus. A diet of either diatoms or dinoflagellates in exponential growth will result in a release of humic-like material, while feeding on senescent cells leads to a net input of protein-like material. Only at very high senescent cell concentrations (>5000 cells l−1) can humic-like material accumulate. This could lead to seasonal cycles in the amount and type of CDOM released by copepods, such that humic-like material will be released in the spring and at the height of phytoplankton blooms, while protein-like material will be added to the water as the bloom dies. The humic-like material found in these studies is blue-shifted compared to the standard humic material (Peaks A, M, and C) measured in seawater. The role of this humic-like material in the environment is currently unknown, but it could be important in absorbing UV radiation.
Effects of food concentration and diet on chromophoric dissolved organic matter accumulation and fluorescent composition during grazing experiments with the copepod Calanus finmarchicus