Contrasting deep‐water macrophyte communities in two highly transparent New Zealand lakes and their possible association with freshwater crayfish,Paranephrops spp

Abstract

Lakes Wanaka and Taupo are both large, deep lakes of comparable water clarity (highly transparent) but composition and depth limit of their deepest rooted macrophyte communities contrast markedly. The macrophyte community in Lake Taupo has a depth limit of 16 m and comprises characean meadows; the macrophyte community in Lake Wanaka has a depth limit of 50 m and comprises a mixed assemblage of bryophytes. A survey of other New Zealand lakes suggested that this deep bryophyte community only occurred in the absence of freshwater crayfish populations. Freshwater crayfish are present in Lake Taupo but not in Lake Wanaka. Bryophytes collected from a depth of 35 m in Lake Wanaka and charophytes collected from a depth of 15 m in Lake Taupo were all successfully established and grown on submerged platforms (which excluded freshwater crayfish) at a depth of 35 m in Lake Taupo. It is suggested that in lakes, such as Taupo which have dense crayfish populations, browsing and mechanical damage by crayfish exclude the deep bryophyte community and limit the characean algae to depths shallower than their light compensation point.