COMPOSITION AND DISTRIBUTION OF MACROINVERTEBRATES ASSOCIATED WITH <i>LUBOMIRSKIA BAIKALENSIS</i> SPONGES (SPONGILLIDA, LUBOMIRSKIIDAE) DURING AN ECOLOGICAL CRISIS IN LAKE BAIKAL

Abstract

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 family Lubomirskiidae. Sponges play important roles in biotic communities of the rocky littoral of the lake, ensuring water purity and serving as a specialized habitat for a variety of organisms. In the last decade, mass disease and mortality of sponges were reported in different areas 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, such as amphipods and gastropods, living on diseased branched Lubomirskia baikalensis sponges in three basins of Lake Baikal (2015, 2020, 2021, 2022) and made historic comparisons. The taxonomic richness of amphipods, including 35 species or subspecies, as well as further 5 taxa identified only to genus, increased and had 20 taxa more than 30 years ago. A total of 22 gastropod species or 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 areas as 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 (grazers, scrapers and filter feeders) providing a 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.