Ingestion and Clearance of Microplankton and Particulates by

Krill Furcilia on NBP02-04

Scott Gallager, Gustavo Thompson, Philip Alatalo, and Kendra Daly

The objective of this study is to quantify microplankton and particle ingestion by early stages of krill furcilia as a function of particle size and type. Both natural particulates and fluorescent polystyrene beads were used to quantify size selection and ingestion as a function of particle concentration. A functional response curve was developed to allow clearance to be estimated at each station where furcilia were observed and relate this to observed levels of microplankton. On NBP01-04, we used natural particulates to estimate ingestion by both particle depletion, and direct observation in the guts using fluorescence microscopy. It was clear from those experiments that furcilia scavenged most particles very effectively within a size range of 10 to 200 microns. Clearance rate on natural particulates increased from a mean of 20 to over 50 ml/individual/h as particle concentration increased to 2x ambient levels, and then decreased as concentration continued to increase. Ingestion rate increased from 2 to over 10,000 cells/individual/h over the same prey concentration range. Preliminary conclusions regarding the impact of furcilia feeding on the microplankton community across the survey grid suggest a strong top-down control on microplankton abundances by krill furcilia.