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ZOOPLANKTON POPULATION STRUCTURE AND DYNAMIC IN THE SUMMER 2018 WITHIN THE WATERS OF THE ROMANIAN BLACK SEA SHELF

Mihaela Mihaela

Abstract

Zooplankton plays a significant role within the Black Sea ecosystem, contributing to the top ? down regulation of trophic web, by intermediating vital ecological processes such as the nutrients recycling (e.g., by controlling phytoplankton and bacterial aggregates development) within the pelagic and benthic habitats. It is considered an important indicator of ecosystem health, being a quality assessment element within the Water Framework Directive (2000/60/EC). Based on the 55 samples collected in the Romanian waters in the period 16 -25 August 2018 on board R/V Mare Nigrum, the authors discuss the results of assessment of mesozooplankton population parameters (abundance and biomass), its compositional structure and pattern horizontal and vertical distribution. The collecting area covers 7 longitudinal profiles distributed from the coast to about 200 m depth and from Sulina to Mangalia on latitudinal gradient. No significant differences (Mann-Whitney U test) in the total abundance distribution between the northern (under Danube influence) and the southern Romanian marine sectors have been evinced. Excepting the marking presence of freshwater cladocerans species within the former sector, the overall population structure was dominated both as abundance and diversity by copepods, thermophilous marine cladocerans and meroplankton, while Parasagitta setosa made up 78% of the total biomass. A total of 23 holoplankton species and taxa from eight meroplankton group were identified, with an average density of edible zooplankton of 3972.33 ind.m-3 and 382.23 mg.m-3 with large variations between and within the stations (Coefficient of Variation range for density (CV): 36 ? 201.73 and CV for biomass: 97.22 ? 364.45, respectively). Noctiluca scintillans reached as much as 50% dominance at its highest abundance found in one station from Constanta (CT 05) profile. Significant differences in vertical water column distribution (e.g., between upper and under the thermocline layers) of zooplankton diversity, abundance and biomass (M-W pairwise test) were highlighted, driven by the biological factors (diel migration) and physical forces gradients such as temperature, salinity, and maximum chlorophyll layer. For the first time in the Romanian waters, presence of the amphioxus larvae Branchiostoma lanceolatum (Pallas, 1774) is reported.

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DOI resolver: doi.org/10.5593/sgem2019/3.1/s15.096

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