Daily vertical migrations of aquatic organisms and water transparency as indicators of the potential exposure of freshwater lakes to light pollution

Light pollution, which disrupts the vital functions of organisms, including aquatic organisms, has become widespread in recent years. One of the main biological features of aquatic organisms is the presence of daily vertical migrations (DVM). However, as a result of exposure to artificial lighting, organisms become visible to predators. This leads to disruption of the DVM of aquatic organisms and, accordingly, disruption of the functioning of the reservoir ecosystem. Water transparency plays an important role in predators detecting their prey under light pollution. Based on this, it was hypothesized that the susceptibility of freshwater lakes to light pollution may be indicated by both the presence and intensity of DVM of organisms and water transparency. The study was carried out on lakes Baikal, Hovsgol and Ladoga, which differ in water transparency and the intensity of DVM of amphipods. On the lakes at night, samples were taken using a net to determine the composition of organisms located in the water column, and underwater video observations were carried out at two depths using a video system with a lighting source. As a result, the greatest migratory activity of amphipods was observed in Lake Baikal both at a depth of 0.5-1 m and at 3-6.5 m. In Lake Ladoga, migration activity at both depths was equally weak, and in Hovsgol, little activity was observed at a depth of 3-6.5 m. A comparison of sampling data and video observations showed that the studied lakes contain organisms that can either be attracted to or avoid artificial light from the video system. Since Lake Baikal, of the presented lakes, has the highest water transparency and intensity of DVM of organisms, this lake may be the most vulnerable to increasing light pollution, including those associated with the growth of tourist flows.