In situ ingestion rates of appendicularian tunicates in the Northeast Water Polynya (NE Greenland)

Abstract

We report in situ ingestion rates of individual oikopleurid appendicularians from the Northeast water Polynya (NEW) determined by a modification of the gut pigment technique. Appendicularians were most abundant at ice edge stations and were rare at open water stations in the centre of the polynya. Gut passage time (GPT), which was determined in experiments onboard ship, was not related to body size (mean ± SD = 74 ± 23 min). Gut chlorophyll content (GCC) excluding phaeopigments (i.e. GCC = chlorophyll a + b + c), averaged 4.06 ng ind.-1, with quartiles of 1.20 to 4.73 ng ind.-1. There was no evidence of a diel feeding rhythm. GCC was higher and more variable at non-bloom (i.e. at chlorophyll concentrations <0.8 mg m-3) than at bloom stations, and was inversely related to the relative proportion of chlorophyll in particles >5 μm in size. This suggests inhibition of ingestion rates at ice edge stations with diatom blooms. The ingestion rate (IR, ng chlorophyll ind.-1 d-1) of individual appendicularians in the NEW can be predicted by IR = 2.5 BL:BT-0.41 TL2.14 (r2 = 0.43) where BL:BT is the ratio of chlorophyll a in particles >5 μm in diameter to the total chlorophyll biomass, and TL (mm) is the trunk length.