Seasonal Variations In Trophic Links Between Microzooplankton And Nanoflagellates In A Coastal Ecosystem

Abstract

Using incubation experiments with size-fractionated coastal waters, this study calculated the growth and loss rates of nano flagellates in a coastal ecosystem of the subtropical western Pacific along a rocky shore in northeastern Taiwan. Samples were taken monthly from September 2014 to August 2015. Seasonal variations in growth rates of heterotrophic nanoflagellates (HNF) and pigmented nanoflagellates (PNF) ranged from 0.17 to 1.13 d(-1) and 0.05 to 1.21 d(-1), respectively. This study found that grazing had a significant impact on nanoflagellate community (PNF: 0.14 to 0.39 d(-1); HNF: 0.12 to 0.52 d(-1)), accounting for about 15-30% for PNF and 18-60% for HNF growth during the warmer periods. However, during colder period, grazing was not found to have an impact on the mortality of nanoflagellates in this subtropical coastal ecosystem. Furthermore, an interesting phenomenon in this study, composition of nanoflagellates 5-10 mu m and > 10 mu m size class showed a more pronounced increase in < 20 mu m treatments at the end of experiments during the warmer study periods. We suggest that at least two trophic levels within the nanoflagellate community: small nanoflagellates and large nanoflagellates.