Discrimination Between Algae and Detritus by Freshwater and Marine Zooplankton
A dual-label radioisotope technique was used to investigate discrimination between live and dead algae by zooplankton from a lake in northern Germany and the Baltic Sea. In contrast to a nonselective cladoceran (Daphnia), four calanoid copepods selectively ingested live algal cells in preference to heat-killed cells of the same species. The degree of selection, however, depended on four factors: (1) copepod species, (2) kind of algae, (3) colonization of algae by bacteria, and (4) food concentration. A freshwater copepod, Eudiaptomus, was the most selective feeder, whereas coexisting marine taxa included highly selective (Pseudocalanus), intermediate (Acartia), and weakly selective (Temora) forms. Sterile dead diatoms were more strongly discriminated against than dead diatoms colonized by bacteria or dead flagellates. Consistent with optimal foraging theory, copepods which were starved or acclimated to low food levels were often less selective than well-fed individuals. Differences in the sensitivity of discrimination between algae and detritus can significantly reduce dietary overlap among species of calanoid copepods and between calanoids and other groups of zooplankton.
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Document Type: Research Article
Publication date: 1988-11-01
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