Gut clearance and pigment destruction in a herbivorous copepod, Acartia tonsa, and the determination of in situ grazing rates

Abstract
Gut clearance rates of starving and continuously feeding Acartia tonsa were estimated. During the initial 30 min the rates were similar (0.045 and 0.048 min−1, respectively; 14°C) but thereafter starving animals expelled the remains of their gut contents at half the rate (0.019 min−1) of fed ones (0.048). Pigment destruction was estimated by (i) incubation experiments over 3–4 days, (ii) silica to pigment ratio in algae and faeces and (iii) by gut filling experiments. The incubations showed that 8% of the ingested pigments were destroyed to nonfluorescent residues during gut passage. The silica to pigment ratio method gave an average of 11 % (1 –24) destruction and gut-filling experiments showed no systematic difference between ingestion measured as gut filling rate (fluorescence) and particle reduction.

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