Planktonic ciliate trait structure variation over Yap, Mariana, and Caroline seamounts in the tropical western Pacific Ocean

Abstract

Trait structure is increasingly used in plankton ecology to understand diversity and biogeography. However, our knowledge of microzooplankton (e.g. planktonic ciliates) trait structure and its variation with hydrography is limited. In this study, we analyzed planktonic ciliate trait structure in waters with different hydrography and deep Chlorophyll a maximum (DCM) layers over three seamounts: Yap, Mariana, and Caroline seamounts. Mariana seamount had a lower surface temperature than the Yap and Caroline seamounts. DCM layers over Mariana and Caroline seamounts were deeper than Yap seamount. There was a weak upwelling in upper 50 m around top of Mariana seamount. The ciliate distribution showed bimodal pattern (high abundance appeared in the surface and DCM layers) over three seamounts. At surface layer, the large size-fraction (>30 µm) abundance proportion to aloricate ciliate over Yap seamount (44.4%) was higher than Mariana (32.8%) and Caroline (36.1%) seamounts. For tintinnid abundance proportion to total ciliate, Mariana (12.0%) and Caroline (11.5%) seamounts at about 100-m depth were higher than that of Yap seamount (6.4%). Vertically, tintinnid could be divided into 4 groups over the three seamounts. At 30-m depth, group I (species occurring from surface to 100 m only) was dominant component over Yap and Caroline seamounts, while group IV (species occurring at every depth) changed into dominant component over Mariana seamount, the weak upwelling might be the reason. Salpingella faurei was the top dominant species, which corresponded to deeper DCM layers over Mariana and Caroline seamounts. Our results showed that the upwelling and the deeper DCM could influence the planktonic ciliate trait structure.