Vertical change of living siliceous radiolarians and their responses to water masses in the tropical Southeast Indian Ocean in spring
摘要
Due to scarce in-situ research, little is known about planktonic biodiversity in deep sea and their environmental characteristics. The water masses in upper 3 000 m of the tropical Southeast Indian Ocean were sampled with the Maxi Multi Plankton Sampler and the containing Radiolaria species were identified, from which the vertical spectra of the species composition were clarified. Radiolarians displayed a classic shallow subsurface abundance maximum of 1 428–1 635 inds./m3 in 50–100 m, followed by a steep decline with increasing depth. Variance partitioning analysis indicated that temperature was the principal driver of vertical community structure, followed by silicate concentration. Nonetheless, water masses with different salinity modulated the vertical compression or expansion of radiolarian assemblages within a confined depth range. Cluster analysis and ordination analysis showed that radiolarian communities in two regions exhibited four depth-specific assemblages. In the euphotic layer, Dictyocoryne muelleri, Dictyocoryne truncatum, Didymocrytis tetrathalamus, Spongaster tetras, Tetrapyle spp., Acanthodesmia vinculata, Botryocyrtis scutum, and Zygocircus microporus were dominated and controlled by high temperature and adequate light. Anthosphaera minuta, Xiphatractus aff. trachyphloius, and Anthocyrtidium zanguebaricum were dominant species in Persian Gulf Water (200–500 m), while Amphisphaera umbilicata, Spongopyle aff. osculosa, Spongotrochus vitabilis, Lamprotripus hirundo, and Sethoconus sp. A were typical in the Red Sea Water (500–2 000 m) and could tolerate relatively lower dissolved oxygen (approx. 50 µmol/kg). The nutrient-rich Indonesian Intermediate Water could increase the growth of Actinomma eriosperma below 1 000 m. Amphisphaera aff. xiphydrion and Dictyophimus platycephalus reflecting rich silicate were probably influenced by the Circumpolar Deep Water.