SS4.07 Lipids/Fatty Acids in Ecological Research
Date: Tuesday, June 11, 2002
Time: 4:00:00 PM
Location: Saanich
 
NalepaTF, Great Lakes Environmental Reseach Lab, NOAA, Ann Arbor, MI, USA, nalepa@glerl.noaa.gov
Fanslow, D, L, Great Lakes Environmental Research Lab, NOAA, Ann Arbor, MI, USA, fanslow@glerl.noaa.gov
 
DECLINES IN THE BENTHIC AMPHIPOD DIPOREIA IN LAKE MICHIGAN AND CORRESPONDING CHANGES IN ITS PHYSIOLOGICAL CONDITION
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The glacial-relict amphipod Diporeia is the dominant benthic macroinvertebrate in offshore waters of the Great Lakes and a keystone species in the offshore food web. This species has been declining in all of the lakes except Lake Superior since the zebra mussel became established in the late 1980s. In Lake Michigan, lake-wide populations have declined 68 % between 1994-95 and 2000, and large areas of the lake are now completely devoid of this species. A common theory is that mussels are outcompeting Diporeia for available food resources. Diporeia is a burrowing detritivore that relies heavily on settling diatoms, while mussels filter-feed at the sediment surface and likely intercept this material before it settles to the bottom. We examined the food-limitation theory by measuring the relative condition of amphipods before and during a population decline at two 45-m sites in Lake Michigan. Over a 5-year period, the population declined from 10,000 m-2 to < 500 m-2 at both sites. At one site, lipid levels were initally low (20% of dry weight), but then increased to 25-30% as the population declined. At the other site, lipid content remained at 25-35% over the entire period. Also, no changes were observed in growth or length-weight. While this seems to question the food-limitation theory, other reasons for the decline are not immediately apparent.