Macroinvertebrate distribution in the littoral zone of Lake Coleridge, South Island, New Zealand-effects of habitat stability, wind exposure, and macrophytes

The macroinvertebrate community was surveyed at eight littoral zone sites in Lake Coleridge, New Zealand. Sites covered a range of conditions including exposure to prevailing winds, shore-line topography, and proximity to river inputs-which are a major source of suspended sediment to the lake. The littoral zone contained an abundant and diverse macroinvertebrate fauna (47 taxa). Three communities were identified: a shallow-water community inhabiting the wave-break zone, dominated by Trichoptera and chironomid larvae; a middle-zone community associated with macrophyte beds, with high macroinvertebrate abundance and dominated by gastropods and oligochaetes; and a community in fine sediments below the macrophytes dominated by oligochaetes. The depth distribution of these communities was related to substrate, macrophyte abundance, and shore-line profile. Superimposed on this pattern were the effects of hillside slope and exposure to prevailing north-west winds. Greatest abundance was associated with macrophytes on stable shores at 4-7.5 m depth, i.e., below the effective wavebase depth. Sediment deposition had only a localised direct effect close to where river water enters the lake. Indirect effects were mediated through the effects of suspended solids on water clarity, bottom limits, and production of macrophytes and periphyton. Estimates of the proportion of littoral macroinvertebrate biomass to whole-lake zooplankton biomass was 10:1 and for production was 1.3:1, indicating the potential importance of the littoral zone to whole-lake production.