FAECES PRODUCTION RATE AND COPROPHAGY IN EUCALANUS SUBTENUIS (COPEPODA: CALANOIDEA), UNDER LABORATORY CONTROLLED CONDITIONS

Abstract

Twelve laboratory experiments to evaluate the egestion in short time periods at the herbivorous copepod Eucalanus subtenuis, were carried out with the aim to obtain data about the morphometry, volume, faeces production rate and coprophagy index, as well as to detect some feeding strategy. Two feeding treatments with different phytoplankton size classes (measured as chlorophyll a concentration) were applied to the copepod: 0 -25 μm (pico and nanophytoplankton) and 25-85 μm (microphytoplankton). The food source was obtained from the surface water in the Caribbean central coast region, between February and May 2001. At copepods with mean total size of 1855.45 +/- 20.50 μm, faeces length fluctuated between 66.66 and 315 μm, being longer when copepods fed with smaller phytoplankton size. The faeces diameter ranged from 12.5 to 58.3 μm and the volume from 1.3x104 and 6.3x105 μm3. The egested faeces fluctuated between 0 and 1.52 faeces cop-1 and 0 and 2.10 faeces cop-1, for the two size feeding treatments (0-25 μm and 25-85 μm), respectively, without dependence of the phytoplankton concentration. At treatments with smaller size phytoplankton, the faeces production rate was 1.65 faeces cop-1 h-1 and 2.04 faeces cop-1 h-1 for longer size phytoplankton, without significant differences between treatments, that is, the faeces rate production doesn’t depend on food concentration and size. Copepods fed with smaller size phytoplankton had a mean tolerated coprophagy index of 20.02%, while those fed with longer phytoplankton was of 36.41%, responding to a more food active search that increase the finding probability in the egestion bottle. Globally, E. subtenuis is a herbivorous species, but considering the results, could be a detritivorous copepod product of the coprophagy and a great adaptability to select and use the food.