Abiotic and Biotic Factors Affecting the Ingestion Rates of Mixotrophic Nanoflagellates (Haptophyta)

Abstract

Mixotrophic haptophytes comprise one of several important groups of mixotrophic nanoflagellates in the pelagic environment. This study aimed to investigate if phagotrophy in mixotrophic haptophytes is regulated by light or other factors in the surface (SE) and bottom (BE) of the euphotic zone in the subtropical northwestern Pacific Ocean. We estimated the rates of bacterial ingestion by haptophytes using fluorescently labeled bacteria (FLBs) and fluorescence in situ hybridization. Haptophyte diversity and abundance were also investigated in the same sampling area. The annual mean abundance of haptophytes was 419 ± 85.6 cells mL in both SE and BE. Cells 3-5 μm in size were the dominant group in all haptophytes and accounted for majority of bacteria standing stock removed by haptophytes (53%). Most haptophyte ingestion rates (IRs) were not significantly different between the two layers (average SE ingestion rate: 12.5 ± 2.29 bac Hap h; BE: 14.7 ± 3.03 bac Hap h). Furthermore, the haptophyte IRs were negatively correlated with nitrate concentrations in the SE and positively correlated with bacterial abundances in the BE, which accounts for the significantly high IRs in August 2012 and 2013. These findings imply that mixotrophic haptophytes in this region had different factors affecting phagotrophy to adapt to the ambient light intensity alterations between SE and BE.

Mixotrophic trade‐off under warming and UVR in a marine and a freshwater alga

“…Warming favored the phagotrophic over the photosynthetic machinery in both species (Fig. 6) according to our hypothesis and the studies of Wilken et al (2012) and Chan et al (2018). For Isochrysis galbana, warming also stimulated specific-PP, apparently mediated by increasing metabolic pathways (i.e., RuBisCO;Helbling et al 2011).…”

“…() and Chan et al. (). For Isochrysis galbana , warming also stimulated specific‐PP, apparently mediated by increasing metabolic pathways (i.e., RuBisCO; Helbling et al.…”

“…This dual ability is shared by most phylogenetic branches, clades, such as chrysophytes and haptophytes (Chan et al. ). All of these protists are widespread in natural communities (Unrein et al.…”

“…Mixotrophs are capable not only of photosynthesis but also of bacterial predation through phagotrophy. This dual ability is shared by most phylogenetic branches, clades, such as chrysophytes and haptophytes (Chan et al 2018). All of these protists are widespread in natural communities (Unrein et al 2007, Zubkov andTarran 2008), especially in oligotrophic waters (Modenutti 2014), presumably due to their trophic advantage of acquiring limiting nutrients through bacterial predation (Raven et al 2009, Tsai et al 2016.…”

Unusual marine cyanobacteria/haptophyte symbiosis relies on N2 fixation even in N-rich environments

“…DON utilization by E. huxleyi has been demonstrated to be an important source of N in nutrient-depleted surface ocean waters [ 52 , 53 ]. Phagotrophy may be unusual in some haptophyte lineages [ 54 , 55 ]; however, haptophytes have also been identified as important grazers in coastal systems [ 56 , 57 ]. UCYN-A haptophyte hosts have been identified as active predators of Prochlorococcus and Synechococcus in the North Pacific by Frias‐Lopez et al [ 58 ], although nothing was known about the symbiosis or the 18S rRNA gene sequences of the hosts at that time, so they were originally classified as unknown Prymnesiophycaea .…”