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Phytoplankton diversity at one station in Lastovo archipelago (southern Adriatic)

Phytoplankton community diversity was studied during stratification period at one station in the southern side of island Lastovo (Cape Struga). Phytoplankton was sampled every 12h from 13th - 21st July 2021 with Niskin bottles. Samples were analyzed (n=59) by Utermöhl method on inverted light microscope Zeiss Axiowert 200. A total of 95 taxa has been determined, of which: 58 diatoms, 27 dinoflagellates, 6 coccolithophores, and 4 other autotrophs which included chlorophyceae, chrysophyceae and cryptophytes. The microphytoplankton community was dominated by diatoms (37.03%), and dinoflagellates (3.3%) and coccolithophores (0.57%) contribuded less. Nanophytoplankton was comprised by dinoflagellates (38.31%), coccolithopores (6.92%) and other autotrophs (14.35%). Dominant species, defined as species or groups with abundance >500 cells L-1, and the frequency of occurrence in samples >40 %, were Cylindrotheca closterium, Guinardia flaccida, G. striata, Gyrodinium fusiforme, Hemiaulus chinensis, Leptocylindrus danicus, Proboscia alata, Pseudo- nitzschia delicatissima, Rhizosolenia imbricata, Scrippsiella sp., and Thalassionema frauenfeldii. Maximal recorded cell abundance was 1.3 x105 cells L-1, and species richness 10.22. Pielou’s evenness (J’=0.58) indicates phytoplankton species not evenly distributed in the community, which can be explained by overall higher nanophytoplankton abundances. Shannon-Weiner (H’) is 2.67, and Simpson diversity index (1- ​λ') is 0.84, showing community does not have high diversity.

community structure, diversity indices, dominant species, phytoplankton counts

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