Pontoporeia hoyi—a Direct Trophic Link between Spring Diatoms and Fish in Lake Michigan
Several lines of evidence suggest that the Lake Michigan benthic amphipod, Pontoporeia hoyi (an important fish prey in large, temperate, low-nutrient lakes), may obtain a large portion of its annual energy directly from the spring diatom bloom: 1) Energetic considerations suggest that P. hoyi must assimilate a large fraction of energy from incoming organic material, but that summer input rates are not sufficient to support observed annual production of P. hoyi. 2) The weight-specific lipid content of P. hoyi at some locations in Lake Michigan doubles within a few weeks after the spring diatom bloom. 3) Lipids accumulate in P. hoyi primarily as the storage products, triglycerides. 4) P. hoyi feeds intermittently and can survive for months without food. 5) The dominant spring diatom in Lake Michigan, Melosira, is not significantly cropped by zooplankton and settles rapidly through the water column in the spring and early summer. 6) After the spring diatom bloom, the phytoplankton changes to a dominance of flagellates that are mostly eaten by pelagic zooplankton and therefore largely unavailable to benthic organisms.
The ability of P. hoyi to rapidly accumulate and store energy from spring diatom blooms may help explain why this amphipod thrives in many temperate, oligotrophic/mesotrophic lakes. This apparently direct trophic linkage between spring diatoms and P. hoyi is energetically important because it involves a minimum of trophic energy loss between primary production and fish.
KeywordsBiomass Phytoplankton Sedimentation Assimilation Stratification
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