Response of Aquatic Organisms Communities to Global Climate Changes and Anthropogenic Impact: Evidence from Listvennichny Bay of Lake Baikal

SIMPLE SUMMARY: Lake Baikal is ranked first among the world’s lakes in terms of freshwater reserves (23,000 km(3)). It is a UNESCO World Heritage Site, and its biota is represented by unique fauna and flora, with endemics accounting for more than 60%. What is happening in the Baikal ecosystem in recent decades due to global climate change and anthropogenic impacts? In this paper, we studied this issue on the example of one of the few open bays on the western shore of Lake Baikal, as well as of some remote areas. It has been found that the plankton composition is dominated by thermophilic species; the role of endemic species in the formation of total biomass is decreasing, which confirms the ecosystem’s response to climate warming. As a result of human activity, filamentous algae bloom suppresses endemic algae species and reduces mollusk proportion. The coastal zone of Lake Baikal is taking on the features of common shallow freshwater lakes due to the predominance of cosmopolitan and widespread Palearctic species. It is necessary to monitor the Baikal ecosystem in the changing climate and to strengthen control over human activities on the shores of the lake. ABSTRACT: Recent studies have revealed how the freshwater biota of Lake Baikal responds to climate change and anthropogenic impacts. We studied phyto- and zooplankton, as well as phyto- and zoobenthos, in the open coastal waters of the southern basin of the lake and of Listvennichny Bay. A total of 180 aquatic organism taxa were recorded. The response of the Baikal ecosystem to climate change can be traced by changes in the species composition of planktonic communities of the lake’s open coasts in summer. The key species were thermophilic the Anabaena lemmermannii P. Richt. (F(ij) = +0.7) blue-green algae, the Asplanchna priodonta Gosse (F(ij) = +0.6) rotifers in 2016, the Rhodomonas pusilla (Bachm.) Javorn. (F(ij) = +0.5) cold-loving algae, and the Cyclops kolensis Lilljeborg (F(ij) = +0.9) copepods in the past century. The proportion of Chlorophyta decreased from 63% to 17%; the Cyanophyta increased from 3% to 11% in the total biomass of phytoplankton; and the proportion of Cladocera and Rotifera increased to 26% and 11% in the biomass of zooplankton, respectively. Human activity makes an additional contribution to the eutrophication of coastal waters. The Dinobryon species, the cosmopolitan Asterionella formosa Hass. and Fragilaria radians Kütz., dominated phytoplankton, and filamentous algae, Spirogyra, dominated at the bottom in the area with anthropogenic impact. The trophic level was higher than at the unaffected background site: the saprobity index varied from 1.45 to 2.17; the ratio of eutrophic species to oligotrophic species ranged from 1:2 to 3:1, and the ratio of mesosaprobiont biomass to endemics biomass ranged from 2:1 to 7:1. Currently, the boundaries of eutrophication zones of shallow waters in Lake Baikal are expanding, and its coastal zone has acquired features typical of freshwater bodies of the eutrophic type.