Composition and Distribution of Macroinvertebrates Associated with the Sponges Lubomirskia baikalensis (Spongillida, Lubomirskiidae) during the Ecological Crisis in Lake Baikal

This study was carried out in the littoral zone of Lake Baikal during a large-scale ecological crisis that affected all parts of the ecosystem, including populations of endemic sponges of the Lubomirskiidae family. Sponges play an important role in biotic communities of the rocky littoral of the lake, ensuring the purity of the water and being a specialized biotope for a variety of diverse organisms. In the last decade, mass disease and mortality of sponges were reported in different basins of Lake Baikal, which can lead to irreversible changes in the structure of littoral communities. We studied the taxonomic richness, distribution, and abundance of the main groups of macroinvertebrates—amphipods and gastropods living on diseased, branched sponges Lubomirskia baikalensis in three basins of Lake Baikal (2015, 2020, 2021, 2022) and made historical comparisons. The taxonomic richness of amphipods, including 35 species and subspecies, as well as 5 taxa defined by genus, increased and had 20 taxa more than 30 years ago. Totally 22 gastropod species and subspecies were found on the sponge, 20 of them for the first time. The species composition, dominant species complex and quantitative characteristics of sponge-associated amphipods and gastropods varied in different lake basins evidenced by underwater observations. The abundance of all macroinvertebrate groups as well as dominant amphipod and gastropod groups per unit weight of sponges decreased from south to north. The abundance of the invertebrates associated with diseased sponges was similar to the records of the pre-crisis period. Baikal sponges host invertebrates from several ecological groups with different feeding strategies (collectors, grazers and filter feeders) providing temporary refuge for most of them. In order to restore the abundance of sponges and preserve the populations of key invertebrate species, we propose to set up sponge “farms” in the least polluted areas of Lake Baikal.