The vertical distribution of zooplankton in the upper 700 m of the water column was investigated across the Almeria–Oran front (Alboran Sea) during winter 1997/98 (Almofront 2 cruise). Eight sites corresponding to three hydrodynamic structures (the Atlantic jet, an anticyclonic gyre and the surrounding Mediterranean waters) were explored, by day and at night, using multiple-net sampling. Results are presented for the major species of copepods (>500 μm), macroplankton and microplankton. Species inhabiting the surface layer or occupying it at night extended deeper in the gyre. On the other hand, mesopelagic species (e.g. Pleuromamma borealis, Pleuromamma abdominalis, Euphausia krohni and Cyclothone braueri) were found to live deeper, at least by day for the migrants, in the Mediterranean waters compared with the two other structures. These changes in preferential depths across the front are discussed in relation to environmental features, such as light level, abundance of food and mixed layer depth. This study also documented the vertical distribution of some overwintering copepod species (Calanus helgolandicus, Eucalanus hyalinus and Eucalanus monachus).

Since the outburst of Mnemiopsis sp. in 1988–1990 in the Black Sea, two international cruises in June 1991 and in July 1992, and a subsequent survey

This review paper considers the features of the biology of cyanobacteria, their role as photosynthetics, nitrogen fixers, and producers of biologically active substances, as well as the distribution of these microorganisms in various marine ecosystems. The symbioses of marine cyanobacteria with a wide range of eukaryotic organisms are discussed.

The study aimed to investigate krill (Euphausia superba) and salp (Salpa thompsoni) populations in the Atlantic sector of the Southern Ocean in January and February 2022. Samples were obtained to measure the abundance, biomass and distribution patterns of krill and salp. Sex differences and feeding habits of the Antarctic krill were determined. The dependence of the physiological state of the studied aquatic organisms on changes in environmental parameters was analyzed. Current data on the association of the dynamics of hydrometeorological parameters and processes with the distribution of chlorophyll a, krill, and salp were obtained. It was established that, at numerous stations, the biomass of salps prevailed over krill. The result indicates the replacement of the Antarctic krill populations by gelatinous zooplankton. The obtained results allow assessment of the biological resource potential in the studied region based on the analysis of the samples collected.