engleski

Seasonal variability of Sagitta lyra (Chaetognatha) vertical distribution of abundance and biomass in the open southern Adriatic (East Mediterranean)

Chaetognaths comprise a phylum of marine organisms which is considered among the most important zooplankton groups, as they are often second in abundance after copepods in the mesozooplankton. Some basic aspects of chaetognath distribution and biology particularly for meso- and bathypelagic species are not well known in the Mediterranean Sea as well as other seas and oceans. Vertical distribution of Sagitta lyra abundance and biomass were studied at open-sea stations from surface to 1200 m depth in the northern part of the South Adriatic Pit during four seasonal cruises in 2019/2020. S. lyra displayed ontogenetic vertical distributions, with older stages occurring at greater depth. They were more abundant in the upper 100 m, their abundance decreased conspicuously with depth, and were captured only rarely between 600 and 1200 m. Increase in abundance and biomss were found in early spring after winter convective events and early summer in time of intensive reproduction. Mean carbon and nitrogen content (as a percentage of dry weight) among maturity stages varied from 21.2 to 36.1% and 6.1 and 8.6% respectively. Higher values were recorded in greather depths where they consumed prey at high rates and where the contribution of older specimens increased.

zooplankton ; chaetognatha ; abundance ; biomass ; vertical distribution ; ontogenetic distribution

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