Scientists of Marine Hydrophysical Institute of RAS and the A.O. Kovalevsky Institute of Biology of the Southern Seas of RAS developed a mathematical model demonstrating how global warming and ocean pollution threaten a key plankton species in the Black Sea. The model predicts that changes in the population of the tiny crustacean Calanus euxinus could have serious consequences for the marine ecosystem in the coming decades.
Calanus euxinus is a species of cold-water crustacean that forms the basis of the diet of many Black Sea fish. These barely noticeable organisms, called copepods, make daily vertical migrations: at night they rise to the surface to feed on microalgae – phytoplankton, and during the day they sink into the depths to avoid being eaten by predators, and spend time there in a kind of hibernation called “diapause”. The crustacean Calanus is finding it increasingly difficult to avoid its enemies, as the upper boundary of the oxygen-free zone in the Black Sea, where Calanus dives, has risen by almost 50 metres in recent decades! Viktor Melnikov, a leading researcher at the A.O. Kovalevsky Institute of Biology of the Southern Seas of RAS, explains:
“Until the 1980s, anoxic waters were at a depth of about 120 metres. Calanus hid there because its main predator, the sprat, only went down to 100 metres”.
Since the 1980s, the situation has changed. Due to pollution and climate change, oxygen levels in deep waters have decreased by 44%. The oxygen-free zone has risen to depths of 75-80 metres.
To understand the impact of these changes on the copepod population, scientists developed a mathematical model. Elena Vasechkina, Deputy Director of Marine Hydrophysical Institute of RAS, explains:
“Our model takes into account key parameters that influence the dynamics of the Calanus population and allows us to assess changes in its abundance and structure both under relatively stable conditions and under increasing predation pressure”.
The model assumes that copepods at depth in a vulnerable state of diapause, up to 75% of the total population, may be preyed upon by sprat. The transition of a part of the population from a safe hibernation state to a risk zone has an extremely negative effect on its overall abundance. The results of simulation modelling indicate that increased predation pressure on Calanus in diapause will lead to a severe degradation of the copepod population within two years.
Further reduction of the living space of Calanus may lead to serious problems in the ecosystem of the deep-water part of the Black Sea.
According to Victor Melnikov:
“The trouble for Calanus has come from below: now it can’t sleep peacefully at a depth of 70-80 metres, since voracious fish scurry around everywhere. Calanus is the base of the trophic pyramid of the entire Black Sea ecosystem. If it disappears, cascading changes will begin and this will no longer be the sea we know”.
The work of Sevastopol scientists clearly demonstrates how global warming affects specific ecosystems. The Black Sea we know today could change dramatically in the lifetime of the current generation. And the question is no longer whether we can stop these changes, but whether we are ready for their consequences.
The study has been published in the Journal of Marine Systems.
The work was carried out within the scope of the state assignment FNNN-2024-0001 “Fundamental studies of the processes that determine fluxes of matter and energy in the marine environment and at its boundaries, the state and evolution of the physical and biogeochemical structure of marine systems in modern conditions”.