Influence of short-term warming and irradiance on bacterivory in different-sized heterotrophic and pigmented nanoflagellates in coastal waters

Abstract

Heterotrophic nanoflagellates (HNF) and pigmented nanoflagellates (PNF) are important grazers in the microbial food web, with substantial contributions to bacterivory in marine ecosystems. Here we investigated effects of temperature and light on ingestion by different-sized HNF and PNF along coastal waters of Fujian province, China. Ingestion rates of HNF and PNF smaller than 3 mu m increased with rising temperature, while large (6-10 mu m) HNF exhibited reduced ingestion. There was a marked interactive effect of light and temperature, where HNF and PNF ingestion rates were both significantly higher in the dark. PNF of 3-6 mu m in size were the most abundant and accounted for 33-57% of total bacterivory in the nanoflagellate community across temperature and light treatments. Our results demonstrated how different-sized HNF and PNF respond to environmental factors in a coastal water system, implying potential changes in microbial community composition and nutrient cycling in projected climate change scenarios.