Abstract:

Zooplankton collodarians with symbiontes play important roles in the organic carbon cycle and silicon cycle in the oligotrophic waters. However, studies on the collodiarian geographic distribution were few. In this study, the biodiversity, biogeography and seasonal variation of collodarians in the surface water of the northern Indian Ocean (NIO), the Malacca Strait (MLS) and the South China Sea (SCS) are revealed for the first time by using the ship-board plankton net to collect samples and using the Rose Bengal stains to distinguish between “living” and “dead” specimens. Totally, the 17 species of collodarians occurred in spring, with 27 species in winter. The collodarian diversity in NIO and MLS is generally less than that in SCS in spring, while in the winter, the former is higher than the latter, indicating that the regional biodiversity from NIO to the SCS is considerably affected by the East Asian monsoon. Moreover, the changes of collodarian community structure have biogeographic differences under the influence of East Asian monsoon. For example, the family Collosphaeridae is obviously dominant both in spring and winter, while the family Sphaerozoidae is dominant only in winter; the composition of dominant species is also different between the spring and the winter, suggesting the collodairian community in surface water is significantly affected by the seasonal changes. Under the influence of East Asian monsoon, the mixing of surface water enhanced, resulting in obvious changes in the compostion of collodarian species, which indicates that seasonal changes are the main factor that controls the community structure of collodarians in the study sea area. The abundance of collodarians is closely related to the regional environment. For instance, the collodarian abundance is very low in spring and winter from MLS to the Sunda Shelf, followed by SCS, and is high in NIO, reflecting their adaptability to specific marine environment. It is assumed that the influence of habitat on a large scale is higher than the control of monsoon change. Therefore, the biodiversity and abundance of collodarians can reflect the different ecological environmental signals, which further provides important observation data and a basic reference for the reconstruction of palaeooceanography and palaeoenvironment by using the collodarian substitution indexes in the future.

Key words: living Collodaria, northern Indian Ocean-South China Sea section, biodiversity, biogeography, seasonal variation