Lake communities in central and southern Chile

Peñuelas is one of the few semi-natural lakes in central Chile. Originally, this shallow, mesotrophic lake1 extended over 19 km2. At the time of these studies, the planktonic community was rich in phyto- and zooplankton species. This lake was characterized by 41 zooplankton species, together with the freshwater jellyfish Craspedacusta sowerbyi Lankester, which was the first record for this species in Chile. Although rotifers constituted almost 75% of all species and 48% of total abundance, the cladoceran Daphnia ambigua  Scourfield and the copepod Diaptomus diabolicus Brehm dominated the zooplankton biomass1. Today, due to a climate change induced decline in rainfall in the central zone of Chile, lake Peñuelas practically vanished, just covering 10 - 20% of its original surface area.
Among the lakes of southern Chile, Lake Rupanco covers an area of more than 220 km2, which was an ultra-oligotrophic lake largely without environmental impacts at the time of the investigations. The zooplankton was characterized by few species dominated by the copepod Boeckella gracilipes Daday, the cladoceran Bosmina (Eubosmina) hagmanni Stingelin and the rotifer Collotheca pelagica (Rousselet)2.
Similarly, Lake Llanquihue, the second largest lake in Chile with a surface area of more than 850 km2, was oligotrophic and, consequently, also characterized by a species-poor zooplankton community. During the austral summer, densities were dominated by the rotifer species Conochilus unicornis Rousselet. In autumn, the copepod species Boeckella gracilipes Daday and Mesocyclops araucanus Loeffler, and the rotifer Synchaeta stylata Wierzejski dominated the zooplankton community2,3,4,5.
During the last decades, fish farming facilities for the salmon industry were introduced in these southern lakes. Using the lakes as smolt farms, the constant nutrient influx due to the feeding of juvenile fish has negatively affected the water quality, particularly of Lake Llanquihue. The salmon industry, together with the population increase in coastal towns of these lakes have certainly profound effects on the state of these ecosystems. However, little or no research has been conducted on the effects of the salmon industry and the effectivity of wastewater treatment plants on planktonic as well as benthic communities of these lakes.