Decoding pelagic ciliate (Protozoa, Ciliophora) community divergences in size spectrum, biodiversity and driving factors spanning global five temperature zones

Abstract. Community structure of microzooplanktonic ciliate in size spectrum, biodiversity and biotic-abiotic interplay are essential components for unraveling their ecological role in marine ecosystems, yet remain challenging to elucidate on a global scale. To address this knowledge gap, we conducted field observational studies across five temperature zones (North Frigid Zone, NFZ; Sub-Arctic Zone, SAZ; North Temperate Zone, NTZ; Torrid Zone, TZ; South Frigid Zone, SFZ). Our analysis revealed that a sharply decline in ciliate abundance and biomass occurred at 100 m layer, with distinct vertical distribution patterns observed in each climate region. Moreover, ciliate size spectra exhibited a decrease trend from small to large size spectra, with steeper slopes observed in the NFZ and SFZ compared to the other temperature zones. Furthermore, an anti-phase relationship between ciliate abundance and tintinnid biodiversity was observed in latitudinal direction, with the TZ and bipolar seas characterized by the highest biodiversity and abundance, respectively. Moreover, a multivariate biota-environment analysis indicated that temperature exert a primary influence on microzooplanktonic ciliates in the global marine ecosystem, and the bottom-up control play a key role in shaping ciliate community. In conclusion, these results underscore the unprecedented divergences in ciliate trait structure among five temperature zones and can be generalised for assessing the potential effects of climate change on pelagic microzooplankton in future marine realm.