Food or Habitat: Drivers of Diporeia sediment preference on a Lake Superior transect

Abstract

The amphipod Diporeia remains the dominant macroinvertebrate in Lake Superior despite population declines throughout the other Laurentian Great Lakes. Diporeia is most abundant at water depths between 30- and 125-meters. It has been hypothesized that this region is preferred because there are higher rates of both primary production and deposition, resulting in more food availability. This study used 120-hour preference-avoidance bioassays to determine Diporeia sediment preference from different water depths. Diporeia strongly preferred sediment from 30- and 60-m depth. Sediment from these two depths had significantly different chemical characteristics and the only variable consistent between depths was sediment grain size, with both sites classified as medium silt and very poorly sorted. This suggests that physical habitat may have a stronger influence on Diporeia habitat preference than food availability alone and that dreissenid mussel’s role as ecosystem engineers altering sediment grain size may contribute to Diporeia population decline.