MEIOBENTHOS AS SEARCH INDICATORS FOR METHANE ACCUMULATIONS UNDER THE BLACK SEA FLOOR

The Black Sea basin is the largest methane (CH₄) reservoir on Earth. About 4.95–5.65 Tg of methane are annually emitted from the bottom into the water column via seepages, mud volcanoes, and due to microbial activities. As such, the basin holds great promise for providing new energy sources to surrounding countries, along with most of Europe.

The main goal of this study is to examine the relationship between concentrations of hydrocarbon gases, primarily CH₄, and the distribution of meiobenthos with hard shells (foraminifers, ostracods) and those without them (nematodes) in sediments of the northwestern Black Sea using multidisciplinary methods for possible delineation of CH₄ accumulations under the seabed.

Twenty-nine species of benthic Foraminifera, 44 species of Nematoda, and seven species of benthic Ostracoda were identified. The presence of CH₄ and its homologues in elevated concentrations suggests that they share a thermogenic origin. A decrease in the quantitative and taxonomic characteristics of foraminifers and ostracods along with an increase in these parameters among some nematode species that are identified as tolerant to elevated concentrations of CH₄ in bottom sediments allows us to outline areas of methane accumulation beneath the seabed. The influence of different concentrations of CH₄ on bottom ecosystems is significantly different and much more complicated than previously thought. It now seems that CH₄ emissions into the marine environment are particularly unfavorable for Black Sea bottom ecosystems, which appear to be quite fragile and vulnerable. It is possible that the qualitative and quantitative characteristics of meiobenthos at the bottom of the Black Sea may prove to be useful search indicators for CH₄ accumulations under the seabed. These results also enable us to assess the impact of CH₄ on marine biota, a question that is currently open because the relevant information is extremely fragmentary and contradictory. The study performed attempts to develop interdisciplinary methods in the search for accumulations of CH₄ under the seabed. Once developed, such methods might contain great socio-economic importance for the economy of not only Ukraine, but other Black Sea countries as well. It may also contribute to the sustainable development of Black Sea ecosystems.