Deep-sea heterotrophic nanoflagellates of the Eastern Mediterranean Sea: qualitative and quantitative aspects of their pelagic and benthic occurrence

Due to the significant lack of information on the community structure of deep-sea nanoflagellates and other nanofauna components as a potentially important component of deepsea matter fluxes, the aim of the present study was to check whether there is a specific deep-sea nanofauna (< 20 µm) community.Studies were carried out in the deep oligotrophic basins of the Eastern Mediterranean Sea around Greece (1249 to 4260 m depth).Direct microscopic counts and quantitative cultivation techniques were used to estimate the abundance and community structure of heterotrophic flagellates and amoebae from abyssopelagial samples and deep-sea sediments.Euglenids and bodonids were the dominant groups comprising about 2/3 of the abundance and biomass of flagellate nanofauna.Our direct counts clearly demonstrate that attention also has to be paid to species which seldom appear in crude cultures.The records of hemimastigid-like forms were remarkable in this respect.Among the 35 deep-sea nanofauna taxa identified here, 8 never appeared in cultures and 18 taxa were found only in cultures.At least 9 taxa have not been previously recorded from the deep sea.Meteora sporadica seems to be the first record of an endemic deep-sea heterotrophic nanoprotist.The variety of functional groups recorded indicates the nanofauna as part of a complex microbial food web in the deep sea.Estimates of potential maximum growth rates of fresh isolates from deep-sea waters ranged from 1 to 6.3 d -1 (Ancyromonas, Amastigomonas, Bodo, Caecitellus, Cafeteria, Kiitoksia, Massisteria, Percolomonas).There was considerable clonal variability.