ABSTRACT
In recent decades, the central Arctic Ocean has been experiencing dramatic decline in sea ice coverage, thickness and extent, which is expected to have a tremendous impact on all levels of Arctic marine life. Here, we analyze the regional and temporal changes in pan-Arctic distribution and population structure of the key zooplankton species Calanus glacialis and C. hyperboreus in relation to recent changes in ice conditions, based on historical (1993-1998) and recent (2007-2016) zooplankton collections and satellite-based sea ice observations. We found strong correlations between Calanus abundance/population structure and a number of sea ice parameters. These relationships were particularly strong for C. glacialis, with higher numbers being observed at locations with a lower ice concentration, a shorter distance to the ice edge, and more days of open water. Interestingly, early stages of C. hyperboreus followed the same trends, suggesting that these two species substantially overlap in their core distribution area in the Arctic Ocean. Calanus glacialis and C. hyperboreus have been historically classified as shelf versus basin species, yet we conclude that both species can inhabit a wide range of bottom depths and their distribution in the Arctic Ocean is largely shaped by sea ice dynamics. Our data suggest that the core distribution patterns of these key zooplankton are shifting northwards with retreating sea ice and changing climate conditions.
Subject(s)
Copepoda , Ice Cover , Animals , Arctic Regions , Oceans and Seas , ZooplanktonABSTRACT
Two new species of the calanoid copepod family Augaptilidae are described from specimens collected from bathypelagic depths of the Arctic Ocean. The female of Euaugaptilus verae sp. nov. can be distinguished from other congeneric species by 1) the Md tooth arrangement, 2) the structure of Mx1, and 3) the lack of external spines on Re2 and 3 of the female P5. The female of Alrhabdus antjeboetiusae sp. nov. can be distinguished from the only species of this genus, A. johrdeae Grice, 1973, by 1) the shape of the rostrum, 2) absence of paired spinal protrusions at the posterior corners of the last pedigerous somite, 3) position of spermatheca on the genital double-somite, 4) the Md tooth arrangement, and 5) P5 endopod 1-2 lacking modified medial setae. Both species were collected in the deepest regions of the Eurasian and Canadian Basins of the Arctic Ocean in the water layers between 1000 m and the seafloor.
Subject(s)
Copepoda , Female , Animals , Water , Canada , Arctic RegionsABSTRACT
The structure of the female reproductive system of the calanoid copepods Calanus glacialis and Metridia longa from the White Sea was studied using light microscopy, scanning and transmission electron microscopy, as well as confocal laser scanning microscopy. For the first time, we applied also the method of 3D reconstructions from semi-thin cross-sections to visualize the general plan of the reproductive system in both species. The application of a combination of methods provided novel and detailed information on the genital structures and muscles located in the genital double-somite (GDS) as well as structures used for the reception and storage of spermatozoa, fertilization and release of eggs. An unpaired ventral apodeme and associated muscles located in the GDS are described for the first time for calanoid copepods. The role of this structure in copepod reproduction is discussed. Stages of oogenesis and the mechanism of yolk formation in M. longa are studied using semi-thin sections for the first time. A combination of non-invasive (LM, CLSM, SEM) and invasive techniques (semi-thin sections and TEM) applied in this study substantially improves our understanding of the functioning of the genital structures in calanoid copepods and could be recommended as a standard set of methods for future research in the reproductive biology of copepods.