Time-series feeding rates of the euphausiid Thysanoessa raschii in a temporally patchy food environment

• Main Author: Sam Mcclatchie
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1986
• Subjects: Thysanoessa raschii
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.420.8443; http://www.aslo.org/lo/toc/vol_31/issue_3/0469.pdf

A flow-through system was used to measure grazing rates of Thysanoessa raschii under conditions simulating encounters with gradients of phytoplankton concentration. Ingestion rates of krill fed Chaetoceros gracilis, measured over 1 O-min intervals, closely tracked changes in phytoplankton concentration. The relationship between ingestion rates and pigment concentration was linear from 0.5-9 fig pigment liter-‘, and zero ingestion was predicted at 0.25 pg pigment liter- ’ (intercept significantly different from zero, P < 0.05). Clearance rates were almost constant (15.4+ 3 ml krill-1 h-l) at all concentrations. This indicated that the changes in ingestion rate resulted from changes in food concentration, rather than as an active response of the krill to the food gradient. The results do not support the hypothesis that krill elevate their feeding rates in response to encounters with high concentrations of phytoplankton in patches or layers. The strategy of krill may be to remain within food concentrations encountered in the field, rather than to feed faster. Zooplankters live and feed in a spatially heterogeneous environment, where food sources are often distributed in patches or layers. Many laboratory feeding studies suggest that they must exploit fine-scale concentrations of food to meet their intake requirements