Mixotrophic and heterotrophic nanoflagellate grazing in the convergence zone east of New Zealand

Abstract

Nanoflagellate grazing was investigated in the subtropical convergence region off the east coast of the South Island, New Zealand, in the summer of 1995. Clearance rates were estimated using 0.5 pm fluorescently labelled beads and fluorescently labelled bacteria to represent bacterial populations and 1.0 pm fluorescently labelled beads representing picophytoplankton populations. Nanoflagellate grazing by mixotrophs was on average lower than heterotrophic nanoflagellate clearance rates per individual for all prey types, and both heterotrophic and mixotrophic nanoflagellates showed a preference for picophytoplankton-sized particles over bacteria-sized particles when grazing on artificial prey. Despite lower clearance rates per individual, higher numbers of rnixotrophic nanoflagellates meant that they contributed 57 % of measured grazing impact on picophytoplankton-sized particles, 40% of grazing on bacteria-sized particles and 55% of grazing on stained bacteria per day. In addition to assessing grazing rates, by identifying the major genera involved we were able to distinguish the predominate grazers in 3 water masses and investigate how changes in species composition may be linked to grazing in this region.

Relative importance of phototrophic, heterotrophic, and mixotrophic nanoflagellates in the microbial food web of a river-influenced coastal upwelling area

“…For instance, Leakey et al (1996) reported that 9 to 33% of the BP was grazed daily by HNF in the Ross Sea, Antarctica. Safi & Hall (1999) estimated that 40 to 55% of the bacterioplankton standing stock was grazed by MNF, whereas Christaki et al (1999) reported that ~40% BP d −1 was grazed by HNF and only 5% BP d −1 by MNF. Similar to these reports, bacterivory in our study also appeared to be dominated by HNF rather than MNF.…”

“…However, the use of similar FLB uptake measurements in more oligotrophic environments (Aegean Sea, NW Mediterranean Sea, East New Zealand) has revealed larger MNF abundances, from 200 to 3000 cells ml −1 (e.g. Christaki et al 1999, Safi & Hall 1999, Unrein et al 2007). …”

Seasonal and size-dependent variations in the phytoplankton growth and microzooplankton grazing in the southern South China Sea under the influence of the East Asian monsoon

“…First, the formation of freshwater cap might inhibit the migration of mesozooplankton (e.g. copepods) into the water with lower salinity and change the mesozooplankton composition in the water column in the studied waters, as similar salinity effects on mesozooplankton have been observed in estuarine and inshore waters (Grindley, 1964;Zhou et al, 2015b), which can release the mesozooplankton grazing pressure on ciliates, then through trophic cascades increase the ciliate grazing on nanoflagellates (HNF) (Chen et al, 2012), reducing the abundance of HNF -the main grazer on pico-phytoplankton (Safi and Hall, 1999) -and releasing the grazing pressure on picophytoplankton (Klauschies et al, 2012). Second, as discussed above, the impeding effect of freshwater cap on phytoplankton accesses to nutrients could lead to poor food quality of phytoplankton as prey, and thus reduce the grazing activity of microzooplankton.…”

Significant year‐round effect of small mixotrophic flagellates on bacterioplankton in an oligotrophic coastal system

“…In fact, they have been observed as major picoplankton grazers in a variety of environments. Havskum and Riemann (1996) calculated that mixotrophs were responsible for up to 86% of the total bacterial grazing in some coastal environments, whereas Safi and Hall (1999) estimated a contribution of 55% in the subtropical convergence east of New Zealand. In some freshwater lakes mixotrophs may remove more bacteria than the crustacean, rotifer, and ciliate communities combined (Bird and Kalff 1986).…”