History of Colonization of Jeju Island (Republic of Korea) by the Water Fleas (Crustacea: Cladocera) Is Reflected by the Seasonal Changes in Their Fauna and Species Associations

Abstract

The aim of this paper is to study the species composition, structure and seasonal dynamics of the cladoceran fauna and species associations in inland water bodies of Jeju Island (Republic of Korea). Only 47 taxa were found in 199 samples. Such faunal paucity could be explained by the existence of only a few types of aquatic environments on Jeju Island as compared to continental China and the Far East of Russia, with their great diversity of water types. We have demonstrated a high significance of the tropical species on Jeju. Our data confirm seasonal faunistic changes in the continental waters of Jeju Island. The rate of tropical taxa is highest in September, after the monsoon season, while the Far Eastern endemic taxa are more common in winter. At the same time, the contribution of Boreal taxa to the fauna of the island is low even in winter. Species associations have been revealed based on binominal distribution; they change significantly from summer to winter. However, a contribution of Boreal taxa to the species associations also is minimal (even in winter), whereas tropical taxa contribute to them greatly (including in winter). We can propose a rough scheme of faunal formation exploring the whole set of obtained information. Initially, at the earlier stages of the island formation, its fauna was consisted of some pre-Pleistocene taxa. Then, during the Pleistocene time, Jeju Island was secondarily interconnected with more southern territories, and tropical species have colonized it. Recent Boreal cladoceran invaders arrived at the island water bodies later when they were already inhabited by formed associations, and for this reason only few of them were able to settle down there. Such a scheme is a hypothesis which needs to be checked by the future phylogeographic studies.

The Role of Old Relicts in Structuring the Boreal/Tropical Transitional Zone: The Case of East Asian Planktonic Cladocera (Crustacea)

“…During the last decade, it was shown that the species composition of faunistic complexes of the Cladocera undergoes seasonal changes-even in the same water body [62]. In addition, we found that, in different lakes, similar functional associations (planktonic, phytal, and benthic) are represented by different taxa, and that the portion of endemics is significantly higher among the taxa involved in these associations.…”

“…Note that even in a previous study it was shown that latitude alone, not longitude, is the main factor shaping the species composition in the region [36]. Furthermore, substantial seasonal differences in the cladoceran species abundance and association composition [62] forced us to use the samples collected at summer months only. As a result, we included in our analysis 422 qualitative samples from 343 water bodies taken in 2002-2021, from late June to earlier September.…”

“…Some specimens in these samples were re-identified based on new data obtained after the revisions of some genera [18]. Newly collected samples were analyzed following the protocol described in our previous publications [36,62]. All specimens identified up to the genus level (juveniles, ephippia of the Anomopoda, deformed specimens, separate body parts) were excluded from our analysis.…”

“…The aforementioned phylogeographic studies confirmed the relict status of the endemic Far Eastern cladocerans. These old relicts (endemic to the region, EA) had a significant advantage compared to other faunistic complexes in the colonizing of new water bodies due to the strong climate de-aridification in the Late Pleistocene/Holocene [62,63]. As a result, they monopolized at least some of the habitats in the water bodies of this region, preventing the dispersion of boreal taxa towards the south and tropical taxa towards the north [63].…”

Influence of environmental factors on the formation of zooplankton communities in a large lake system in Uzbekistan

“…The samples were put in 40% formalin, so that the concentration of the sample was 4%. The samples were identified with the help of trinocular and binocular microscopes, using generally accepted guides [9][10][11].…”