Past President's Address: Protists of the Mesopelagic and a Bit on the Long Path to the Deep Sea

• Published in: Journal of Eukaryotic Microbiology
• Main Authors: Dolan, John, Ciobanu, Maria, Coppola, Laurent
• Other Authors: Laboratoire d'océanographie de Villefranche (LOV), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut de la Mer de Villefranche (IMEV), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2019
• Subjects: Amphisolinidae; Deep > Sea; Phaeogromidae; Plankton; Time > series; Tintinnida; [SDV.MP]Life Sciences [q-bio]/Microbiology and Parasitology; North Atlantic
• Online Access: https://hal.sorbonne-universite.fr/hal-02188066; https://hal.sorbonne-universite.fr/hal-02188066/document; https://hal.sorbonne-universite.fr/hal-02188066/file/Dolan%20et%20al.%20-%20Past%20President%27s%20Address%20Protists%20of%20the%20Mesopela.pdf; https://doi.org/10.1111/jeu.12744

International audience The deep sea has long been a mysterious and attractive habitat for protistologists. However logistical difficulties severely limit sampling opportunities. Consequently, our knowledge of the protists in the deep sea, (arguably the largest habitat on earth), is relatively sparse. Here we present a unique time-series concerning 3 different protist taxa that share only the characteristics of being relatively large, robust to sampling, and easily identifiable to species level using light microscopy: tintinnid ciliates, phaeogromid cercozoans (e.g. Challengerids) and amphisolenid dinoflagellates. We sampled a near-shore deep water site in the N.W. Mediterranean Sea at 250 m depth over a two-year period at approximately weekly intervals from January 2017 to December 2018. To our knowledge, no previous studies have employed sampling on a similar time scale. We found taxa that appear to be restricted to deep waters, distinct seasonal patterns of abundance in some taxa, and in others non-seasonal successional patterns. Based on data from sampling following a flash flood event, the Challengerid population appeared to respond positively to a pulse of terrigenous input. Some of the distinct mesopelagic tintinnid ciliates and amphisolinid dinoflagellates were also found in 2 samples from the North Atlantic mesopelagic gathered from near the Azores Islands in September 2018. We conclude that there are a variety of protist taxa endemic to the mesopelagic, that the populations are dynamic, and they may be widely distributed in the deep waters of the world ocean.