Irkutsk scientists conducted an expedition to study the Baikal sponges

The route of the ship is from south to north of Lake Baikal. This expedition of Limnological Institute SB RAS is dedicated to a phenomenon that scientists find extremely concerning - the mass morbidity and death of the Baikal sponge, one of the lake`s most unusual inhabitants.

It is easily identified at the bottom by its long, branching green trunks. Despite this, there are other species. However, the endemic's primary characteristic is its capacity to pump tens of liters of water through itself every day. This is a complex living organism and a kind of natural filter of the purest water in the world.

“In this case, morbidity has ragged edges. The same thing – necrosis occurs.”

The sick sponges are also immediately visible. They can lose their color, develop stains and emit a foul odor. According to Igor Khanaev, sponges have started to suffer from a mass disease 15 years ago. He directs the diving research and underwater monitoring group of Limnological Institute. The divers were the first to notice that something was wrong with the Baikal endemic. Since then, Irkutsk scientists continue observing.

Unfortunately, the situation is not improving annually. The number of sponges has decreased. Igor Khanaev, the head of the diving research and underwater monitoring group at Limnological Institute SB RAS, states that there are no healthy sponges in some zones of Listvyanka settlement.

Every year, limnologists evaluate the sponge`s health in prearranged locations on board the ship. With a metal frame, divers circle the bottom, divide it into squares, and carefully count. This time, the so-called transects in various areas of Lake Baikal were examined, along with two underwater sites and eleven special sites. Additionally, a number of stations were set up to keep an eye on the lakeёs bottom layerёs temperature regime. Because sponges dislike warm water, it may also cause negative processes.

Over 250 samples of sponges at different depths up to 35 meters were gathered by scientists from the bottom. Fixing sick specimens is the responsibility of the biologists already on board. They also identified several other diseases, such as biofilm fouling, black spot formation, and coat, in addition to necrosis.

“This is how a sick sponge looks like. This dark spot is necrosis. That is, in this place, the sponge's tissue died off,” says correspondent Natalia Salnikova.

“Photofixation of samples and species identification are done in the ship`s laboratory. In this manner, we fix species that could not be identified on board in the form of tiny tissue fragments. Alena Yakhnenko, a junior researcher at Limnological Institute SB RAS, explains, “And then we carry out identification by the elements of the skeleton, which are called spicula.”

What is the reason for mass morbidity of the Baikal sponges? Researchers have several hypotheses, among them are climate change, an increased amount of methane in the water, and a lack of silicon, which is the main building material of the endemic skeleton. The anthropogenic load on the lake could also aggravate the situation. Another reason is that cyanobacteria form a biofilm on the sponge, so scientists are also investigating it.

However, there are also moments of encouragement. In an experiment, scientists replaced a sick sponge's dead branch with a new one. And growth was noted a year later. Additionally, divers started to come across fields of young sponges in some areas of Lake Baikal. It has been observed that Baikal endemics occasionally recover from the illness.

Original material: https://vk.com/wall-35929536_234477