engleski

Diel vertical distribution of copepod abundances and diversity in the open South Adriatic Sea (NE Mediterranean)

Copepod community structure was investigated on a short time sampling scale during a 24-h cycle at one fixed station in the open Adriatic Sea in June 2020 and February 2021 (from 0 to 300 m) using Nansen opening-closing net (250 µm mesh size). In June, the upper oceanic waters were characterized by vertical gradients of environmental factors while in February oceanic waters showed relatively homogeneous physicochemical conditions. During the winter vertical mixing, the bulk of the copepod population remained in the epipelagic zone (0- 100 m) over the entire 24-h cycle, with calanoids remained the dominant group. An increasing trend of copepod standing stocks from midnight to early morning in the surface layer found in June is in agreement with previous records of copepod day- night variations in the Mediterranean Sea. Average Shannon-Wiener diversity index was lower in July (2.21±0.27) than in February (2.54±0.18) with the most pronounced differences in a 200-300 m layer, during the whole sampling period. Day-night differences in diversity and number of taxa of the epipelagic area were more pronounced in June, confirming the higher intensity of diel vertical migration in summer as well as deficiency of calanoids during the most intensive daylight. Although the epipelagic community was composed of numerous weak diel vertical migration species, for the majority of investigated copepod taxa migration patterns differed between the seasons suggesting significant influence of environmental conditions on their vertical positioning.

zooplankton ; copepod ; vertical migration

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