Restoring Baikal’s vital underwater ecosystem through innovative cultivation methods Baikal's sponge population crisis triggers exploration of advanced methods, from larvae to primmorphs, in a bid for salvation.
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Restoring Lake Baikal’s vital underwater ecosystem through innovative cultivation methods

Baikal's sponge population crisis triggers exploration of advanced methods, from larvae to primmorphs, in a bid for salvation.

Almost two-thirds of Lake Baikal’s distinctive wildlife consists of native species. The Lubomirskiidae family of freshwater sponges found there differs greatly from other types, resembling tall trees underwater. These sponges, reaching over a meter in height, are key elements in the lake’s aquatic systems. They filter water, removing algae, microorganisms, and some pollutants, which helps maintain the lake’s water purity, particularly along the shoreline.

In recent years, the situation on Lake Baikal, according to many experts, has been characterised as catastrophic, primarily in the littoral zone.

Numerous reports highlight a worrying trend of depressed and dying Baikal sponges, with up to 100% affected in some areas, according to recent studies. The slow growth rate of the Lubomirskiidae family, averaging just 1 cm annually, exacerbates concerns over their survival. Without action, the loss of these sponges could significantly impact the lake’s natural water filtration system, risking the disappearance of associated symbiotic organisms. This raises questions about the urgency of implementing environmental restoration measures for Baikal’s endemic species, particularly the Lubomirskiidae.

When seeking ways to revive Baikal’s sponge population, experts often refer to studies on Porifera reproduction for biotechnological and commercial applications. We conducted a comprehensive review of global sponge cultivation methods, exploring their potential for Baikal’s sponges. Four main approaches to growing sponges ex-situ and in situ are described in most detail in the literature: 1) from larvae; 2) from primmorphs (sponge cell cultures); 3) from resting stages (gemmules and reduction bodies); 4) from explants (fragments of living tissue separated from the mother’s body) (Figure 1).

Figure 1. Advantages and drawbacks of methods and approaches for the recovery of Porifera populations.
Credit. Author

Growing sponges in situ

Explant cultivation

Explants, a widely-used technique for sponge farming, involve fragments of the organism grown to desired sizes. Cultivating explants in natural underwater conditions, known as “in situ,” shows promise. However, lab cultivation, or “ex-situ,” requires precise environmental control, resulting in slower growth rates compared to natural settings. Currently, many different designs are used for in situ cultivation of sponges. These leashes fix a sponge fragment, mesh bags, stainless steel mesh containers, fastening explants on nylon cords stretched between two cables, etc.

This method is relatively simple and cheap. A significant disadvantage of growing sponges from explants, both in situ and ex-situ, is the long cultivation period. At the same time, in laboratory conditions, it is difficult to select conditions for cultivation, and in real conditions, such a crop is quite difficult to control.

Growing ex-situ sponges

Larvae

Cultivating sponges from larvae shows potential, with studies assessing colonization, morphological changes, and survival rates of various species under controlled conditions. While lab cultivation proves preferable for early-stage survival, variations in larval development across species pose challenges. Further research is needed, particularly regarding Baikal’s sponges, to address this gap and advance conservation efforts.

Primmorphs

Porifera possesses a unique ability to regenerate into complete organisms from cell accumulations called perimorphs. These spherical aggregates of sponge cells, cultivated in lab settings, precede the formation of fully functional sponges. This process involves complex cellular transformations under specific environmental conditions, marking a crucial stage in sponge regeneration research. Studies have focused on several sponge species, including Clathria prolifera, Ephydatia fluviatilis, and Spongilla lacustris, to understand reaggregation and regeneration processes. While promising, research on cultivating primmorphs into mature sponges is in the early stages, primarily aimed at modeling culture and obtaining useful compounds.

Researchers have conducted various studies on obtaining primmorphs of Baikal sponges in laboratory conditions. Primmorphs of L. baikalensis, for instance, were obtained and remained viable for over 10 months. Subsequent research detailed the ultrastructure of these primmorphs and identified symbiotic microalgae.

The cultivation of sponges, including Baikal endemics, from the culture of primmorphsis particularly promising. The relative simplicity and low cost of the method evidence this. In addition, using the example of Sycon ciliatum, it was shown that development from primmorphs at the transcriptomic level is very similar to natural development from larvae. This confirms the potential for sponges formed ex-situ to adapt to real conditions.

Gemmules and reduction bodies

Gemmules, the internal buds of freshwater sponges, act as cellular reservoirs, shielding themselves with layers of polysaccharides and scleroproteins. Unique to Baikal, these sponges also produce external buds called reduction bodies, enabling them to endure harsh conditions, including temperature fluctuations. Research documents successful sponge cultivation from gemmules, including those of Ephydatia fluviatilis and Spongilla lacustris, shedding light on their resilience amidst challenges. However, long-term experiments reveal limited and conflicting data on sponge development, presenting a challenge for further understanding.

The most promising of the techniques considered in this review for the cultivation and restoration of Baikal endemic sponges is the culture of primmorphs and explants. In the future, they may form the basis of recommendations for the restoration and maintenance of the unique sponge fauna of the lake.

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Journal reference

Topchiy, I. A., Stom, D. I., Tolstoy, M. Y., Ponamoreva, O. N., Stom, A. D., Saksonov, M. N., & Kupchinsky, A. B. (2023). Some Approaches to the Recovery of Baikal Sponge Populations: A Review. Contemporary Problems of Ecology16(1), 1-7. https://doi.org/10.1134/S1995425523010092

(Doctor of Biological Sciences, Professor, Honoured Worker of the Higher School of the Russian Federation) – chief researcher at the Baikal Museum of the SB RAS, professor, and head of the laboratory of aquatic toxicology at Irkutsk State University. He has many years of research experience in hydrobiology and ecotoxicology, including on organisms of Lake Baikal. Specialises in the detection and assessment of the level of danger of pollutants, the study of their effect on organisms, wastewater treatment, waste disposal, and bioremediation of contaminated environments. Author of more than 400 publications, 80 patents, leader and participant in more than 30 scientific projects and grants.

Alexander Kupchinsky, a candidate in biological sciences, is the director of the Baikal Museum of the SB AS. Specialist in the field of ichthyology, biochemistry, and hydrobiology, author and co-author of more than 80 scientific papers and three patents for inventions, leader and participant in more than 10 scientific projects and grants.