Population ecology of the freshwater crayfish Paranephrops zealandicus and its effect on the community structure of a lowland bush stream

摘要: My research describes aspects of the population ecology of the freshwater crayfish Paranephrops zealandicus, its influence on the community of a lowland bush stream in Otago, New Zealand, and the ecosystem consequences of their removal. Production and longevity were assessed for a population of the crayfish in Powder Creek, a headwater stream draining a catchment of regenerating coniferous-broadleaf forest in eastern Otago. 1. Crayfish abundance was 3-4 individuals m-2 in riffles and 4-12 individuals m-2 in pools. 2. Crayfish biomass (4-33 g AFDW m-2) and production (2-11 g AFDW m-2y-1) were high in comparison to equivalent overseas studies. 3. Production was dependent primarily upon the magnitude of biomass rather than growth rate. 4. Individual crayfish were found to be slow growing and long lived in comparison to other crayfish species. Crayfish with ages estimated to be 16+ years were not uncommon. Female crayfish were not reproductively active until 6+ years. 5. Fewer than 4% of all females carried eggs, and the young remained attached to the female for a minimum period of 15 months. Enclosure experiments in Powder Creek were used to examine the influence of freshwater crayfish on the invertebrate community. 1. Changes in the structure of the stream community occurred according to whether crayfish were present or absent. 2. Enclosures without crayfish accumulated silt. 3. Crayfish of different size did not influence the stream community differently. 4. Orthocladiinae and Chironominae (Diptera: Chironomidae) larvae were negatively affected by crayfish presence, while the dominant mayfly, Deleatidium …