Sponge Fauna of Lake Baikal in the Monitoring System: Six Years of Observations

In the last decade, the mass mortality of endemic sponges has been observed in the coastal zone of Lake Baikal. This paper presents the results of observations of the Baikal sponge fauna within the transects established throughout Baikal in 2015. The types of damage of Baikal sponges have been characterized based on visual descriptions. Between 2015 and 2020, a downward trend has been revealed for the average projective cover of healthy sponges of various body forms on the Baikal bottom. For encrusting, branched, and globular forms, the decrease in this index is 3.6, 2, and 4 times, respectively. The total area occupied by healthy and damaged sponges of various forms have reduced more than twice (from 238 to 110 m2).