Allochthony in major groups of crustacean zooplankton in boreal lakes – strongly contrasting patterns across space and time

• The role of terrestrial organic carbon for recipient aquatic ecosystems is intensively researched. A multitude of studies now show that terrestrially-derived carbon supports a significant share (allochthony) of consumer biomass in many freshwaters. However, little is known about the mechanisms by which terrestrially-derived carbon is transferred to the level of metazoan zooplankton, and whether these pathways vary among taxonomic and functional groups. Here we present stable isotope-inferred allochthony in three major groups of crustacean zooplankton – Cladocera, Calanoida and Cyclopoida – measured both seasonally and across wide ranges of environmental gradients in boreal areas of Canada and Sweden. Our data show strongly contrasting patterns between taxa in the allochthony regulation. Whereas allochthony in calanoids was regulated by shortage of phytoplankton particles per se, both across space and time, allochthony in cyclopoids was related to food chains supported by dissolved organic carbon. Cladocerans showed the highest allochthony, but a more complex regulation. Terrestrial organic matter can be an important resource for cyclopoids and cladocerans on an annual basis, but it can also sustain otherwise herbivorous calanoids during low productivity conditions, e.g. in winter.

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NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

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