Silicon Deficiency and the Endemic Sponge Lubomirskia baikalensis (Pallas, 1773): What Happens With Its Skeleton in Changing Environment?

Sponges are aquatic animals highly sensitive to environmental changes. They significantly impact silicon cycling by constructing siliceous skeletons. The necessity of better understanding of both biosilification and sponge physiology inspired us to focus current work on how silicon deficiency affects spiculogenesis in the branched Baikal sponges Lubomirskia baikalensis. We employed an original method to detect newly formed silica spicules: staining with a vital fluorescent dye specific to new silica deposition. A significant reduction in spicules formation was observed when silicon levels were decreased from 32 μM (artificial Baikal water) to 10 μM or less, alongside compromised primmorphs integrity. This suggests that low silicon availability may slow sponge growth by limiting spicule production. If such reductions occur naturally, they could alter sponge appearance or abundance, highly affecting Baikal's benthic communities. Our findings, consistent with previous studies, indicate a recent shift in the silicon-to-phosphorus ratio in the coastal Baikal waters, characterized by a decrease in silicon concentration. The notable reduction in siliceous sponges coincides with this trend. Further in vivo experiments are required to test the hypothesis that silicon deficiency affects both the growth and health of sponges in nature, thereby increasing their susceptibility to environmental stressors. Additionally, we examined nitrogen and phosphorus's impact on spicule formation. Seasonal fluctuations in these nutrients are unlikely to directly affect spiculogenesis, though surprisingly, higher nitrogen levels appeared to accelerate spicule growth. Our observations have broader implications, given global and anthropogenic influences on biogenic element levels in the coastal zones of aquatic ecosystems.