Has marine Antarctic ecosystem changed?-A tentative comparison of present and past macrozooplankton abundances

• Main Author: Akito Kawamura
• Format: Report
• Language: English
• Published: Faculty of Fisheries, Hokkaido University 1986
• Subjects: Antarctic; Antarctic Ocean; The Antarctic; Antarc*; Euphausia superba; Memoirs of National Institute of Polar Research; Polar Research; Copepods
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=1892; http://id.nii.ac.jp/1291/00001892/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=1892&item_no=1&attribute_id=18&file_no=1

The N70V net, a small silk ring net of 70cm in diameter which was originally designed by the Discovery Committee for collecting macrozooplankton in the Antarctic Ocean was reconstructed, and the collection with this net was made after the similar sampling procedures to the Discovery Investigations during the BIOMASS SIBEX I (1983-84) investigation. The abundances of total zooplankton biomass and of four major herbivorous copepod species were compared with the corresponding data of the Discovery Investigations 50-60 years ago when the marine Antarctic ecosystem was almost in its initial state. The total zooplankton biomass at present is well within the variation of possible sampling bias of the Discovery result, and is considered to have been almost unchanged during the past several decades. On the other hand, the abundance of three of four major herbivorous copepods, Calanus propinquus, Calanoides acutus, and Rhincalanus gigas, is remarkably poorer with the magnitudes of 1/10 to 1/100 in more than 70% of average figures of the present study than that reported in the Discovery Investigations. These results suggest that there occurred possible changes in the abundance and the relative compositions of macrozooplankton community of the Antarctic Ocean. Especially, a change in the abundance of major herbivorous copepods is noteworthy, since it must have resulted from an increase in the stock size of unconsumed krill, Euphausia superba, which perhaps caused some changes in the feeding conditions among other herbivorous animals.