Meiobenthos and taxocene of Nematodes under changes in ecological conditions in the coastal zone of the NorthWestern part of the Black Sea

Abstract

Based on studies conducted in June - August 2023 at two marine sites in the in front of Odessa Bay (Cape Lanzheron and Cape Maly Fontan), an assessment was made on the response of meiobenthos and nematodes to the destruction of the dam of the Kakhovka reservoir (06 June 2023) in the coastal waters of the NW Black Sea. In the sublittoral zone (0.5 m) of Cape Lanzheron, the abundance of meiofauna varied from 4000 to 169830 ind./m2, averaging 28094 ± 10982.2 ind./m2. A low occurrence of meiobenthos taxa, a species diversity index, and a high percentage of dominance of Nematoda and Oligochaeta were noted. An increase in the number of r-strategists and a predominance of non-selective detritivores were recorded. According to the values of the maturity index (MI) and the index of trophic diversity (ITD), the water area of Cape Langeron during the study period changes the status of ecological quality (EcoQ) from Good (I-III survey) to Poor (IY-Y survey). The increase in eutrophicity in the waters of Cape Maly Fontan in the sublittoral zone (1 - 5 m), caused by the consequences of the disaster, contributed to an abnormally sharp increase in the abundance of meiobenthos, especially nematodes. The density of meiobenthos varied from 114000 to 9708310 ind./m2, averaging 1753412 ± 261350.7 ind./m2. Low MI values and an increase in ITD values due to the noticeable dominance of one trophic group (1B) indicate increased stress in the area of Cape Maly Fontan. The response of nematode assemblages to environmental changes, both in terms of density and diversity, has demonstrated significant potential for persistence and recovery. The increase in the density of Harpacticoida and juvenile Bivalvia during the last survey (08/24/2023) may be evidence of their ability to quickly recover when environmental conditions improve. In general, the status of the ecological quality of the environment (EcoQ) of the study area can be classified as (Bad) in the area of Cape Lanzheron and (Poor) in the area of Cape M. Fontan.