Abstract
Mixotrophy, understood as food ingestion and photosynthesis occurring in the same organism, is a nutrition mode relatively common in marine protists. Among these, pigmented nanoflagellates 2-20 µm in size (PNF) are now known to be responsible for a significant part of consumption of bacteria in the open ocean. However, knowledge about the importance of the mixotrophic nutrition of these organisms in coastal upwelling systems, where autotrophy prevails, is very limited. Here we compile the limited available information about mixotrophy of PNF in coastal upwelling systems, focusing on the NW Iberian upwelling, to show that this type of nutrition is relevant in these productive systems and to urge for further studies. Several indirect approaches allow inferring that mixotrophy was significant for PNF in the NW Iberian upwelling, with heterotrophy supplying seventy-five percent of the total carbon requirements in this plankton group. This new insight has major implications for our view of marine food webs in coastal upwelling regions, and must be taken into account in the construction of more accurate biogeochemical models of the transfer of matter and energy in these marine areas.
Highlights
The traditional and rather simple view of marine microbial food webs based on the autotrophicheterotrophic dichotomy is nowadays outdated (Flynn et al, 2013)
The phytoplankton carbon to chlorophyll a (Cph:Chl a) ratio was completely different in these two domains (Figure 2A), despite the photic layer being similar in both environments (34 ± 12 m and 36 ± 8 m in coastal and oceanic domain, respectively; P = 0.59, t-test for two samples)
Mixotrophy of pigmented nanoflagellates 2–20 μm in size (PNF) has been well described for oligotrophic zones of the North Atlantic (Zubkov and Tarran, 2008; Hartmann et al, 2012), where bacterivory by this plankton group can represent up to 95% of all bacterivory
Summary
The traditional and rather simple view of marine microbial food webs based on the autotrophicheterotrophic dichotomy is nowadays outdated (Flynn et al, 2013). Nanoflagellates Mixotrophy in Upwelling Systems an important advantage even in productive regions, allowing them to persist under the variable conditions of light, nutrients and food of these environments.
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