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.