The thesis is devoted to the study of the systematics and distribution patterns of Atlantic marine tardigrades. Marine tardigrades belong to the phylum Tardigrada Doyère, 1840 and have representatives in the class Heterotardigrada Marcus, 1927 and the class Eutardigrada Richters, 1926. They are part of the meiobenthos (meiofauna), a group of microscopic organisms that act mainly as first-order consumers or detritophages in the food webs of aquatic communities. There is a so-called “meiofauna paradox” associated with the widespread distribution of some species, but the absence of dispersal stages in the life cycle of meiobenthos representatives. Marine tardigrades are a poorly studied group due to their microscopic size and the difficulty of identifying species-specific characteristics. Finds of marine tardigrades are primarily associated with “shallow” samples of meiobenthos and are mosaic in nature. Studies of the geographical distribution of marine tardigrades in the literature are few. All of this necessitates a study of systematics, biodiversity, and biogeography with in-depth attention to deep-sea samples, and using the most detailed methods of morphological research.
To accomplish this goal, we analyzed the marine tardigrades literature records from the Atlantic Ocean and its adjacent regions. As a result, we present a systematic list of 124 species from the study area. We also considered data on the bathymetric distribution of these species.
An inventory of materials from eight expeditions was made: PS101, IceDivA1, IceDivA2, BIODIAZ, Andeep-I, Andeep-II, Andeep-III and Andeep-Systco. Samples were collected from bathyal-abyssal depths ranging from 294 m depth (BIODIAZ) to 5194 m depth (Andeep-I). A total of 1255 individuals of marine tardigrades were analyzed.
The morphology of the specimens was studied by light microscopy (differential interference contrast) and scanning electron microscopy at the Senckenberg am Meer institute, Wilhelmshaven, Germany. In the course of this work, we adapted the methodology of making permanent microslides for both light and electron microscopy. Species identification was checked against the original descriptions, and the author's comments and notes were made.
Patterns of geographical distribution were identified using statistical methods in biogeography (cluster analysis and non-metric multidimensional scaling). A collection of marine tardigrades was created and is stored in the Senkenberg Museum (Frankfurt am Main, Germany).
As a result of the literature analysis and our own research, it was found that the fauna of the Atlantic Ocean marine tardigrades includes 134 species, which belong to 11 families of the class Heterotardigrada and 1 family of the class Eutardigrada.
The original research from the bathyal-abyssal zone of the Atlantic revealed 19 species of tardigrades: Batillipes wyedeleinorum, Coronarctus dissimilis, C. tenellus, Moebjergarctus clarionclippertonensis, Chrysoarctus briandi, Quisarctus sp, Neostygarctus oceanopolis, Angursa abyssalis, A. capsula, A. antarctica, A. lanceolata, A. lingua, Rhomboarctus aslaki, Styraconyx qivitoq, S. nanoqsunguak, S. takeshii, Tholoarctus oleseni, Tanarctus aff. gracilis, Isoechiniscoides aff. sifae sp. can.
The use of scanning electron microscopy revealed new features of the cuticle structure, claws, sensory organs and reproductive system of seven species: Batillipes wyedeleinorum, Moebjergarctus clarionclippertonensis, Angursa abyssalis, A. capsula, A. lanceolata, Tholoarctus oleseni, Isoechiniscoides aff. sifae sp. can. Quisarctus sp. and Isoechiniscoides aff. sifae sp. can. are candidates for new species due to their morphology. Six species (Moebjergarctus clarionclippertonensis, Quisarctus sp., Angursa capsula, Styraconyx takeshii, Tholoarctus oleseni, Isoechiniscoides aff. sifae sp. can.) were reported first time for the study area. It is shown that the genera Angursa and Coronarctus are distributed throughout the Atlantic Ocean abyssal zone. The species Angursa antarctica, Batillipes wyedeleinorum, Styraconyx qivitoq, Tholoarctus oleseni, as well as the genera Batillipes, Styraconyx and Isoechiniscoides and the family Echiniscoididae have a wide bathymetric distribution; they are present, in particular, in the abyssal zone.
Based on the results of the cluster analysis of the findings of marine tardigrades, two large biogeographic regions were identified: “Southern Ocean” and “Atlantic abyssal zone”.
The scientific novelty of the results obtained is the acquisition of fundamental data related to a comprehensive assessment of the biodiversity and geographical distribution of the Atlantic Ocean marine tardigrades. New species have been described and new data on the morphology of already known species have been presented. The results contribute to the understanding of the biogeography of marine tardigrades and the meiofauna paradox in general.
