The role of mixotrophy in plankton bloom dynamics, and the consequences for productivity

Abstract

. W. 2005. The role of mixotrophy in plankton bloom dynamics, and the consequences for productivity. e ICES Journal of Marine Science, 62: 833e840.Mixotrophy (Zheterotrophy and photosynthesis by a single individual) is a common phenomenon in aquatic ecosystems, in particular under light-or nutrient-limitation. However, it is not usually considered in mathematical models of biological populations. This paper shows how different types of mixotrophy might be usefully incorporated into a general predatoreprey model, and explores the consequences for plankton bloom dynamics and productivity. It is demonstrated, analytically and numerically, that even small levels of type III mixotrophy (a small fraction of the zooplankton also being involved in primary production) have significant effects on a system's equilibrium structure, stability, and short-term dynamics. Type III mixotrophy has a stabilizing effect on the system by reducing its excitability, i.e. its propensity to exhibit blooms. Compared with the nonmixotrophic benchmark, for a phytoplankton bloom to be triggered in a system with type III mixotrophy, a much larger perturbation is necessary. Type II mixotrophy (a small fraction of algae engage in phagotrophy) and type I mixotrophy (equal phagotrophy and phototrophy) are briefly discussed. The potential consequences for productivity are also studied. Our results indicate that the phytoplanktonezooplankton system becomes more productive in the presence of type III mixotrophy.

Mixotrophy: a widespread and important ecological strategy for planktonic and sea-ice nanoflagellates in the Ross Sea, Antarctica

“…Two modeling studies determined that primarily heterotrophic mixotrophs can have a great effect on primary production, and that this type of mixotrophy can lead to a noticeable increase in primary production even at 1% of the population (Stickney et al 2000, Hammer & Pitchford 2005. Determining the quantitative contributions of phagotrophy and phototrophy was beyond the scope of our study.…”

Modeling Plankton Mixotrophy: A Mechanistic Model Consistent with the Shuter-Type Biochemical Approach

“…Mitra and Flynn (2010) have indeed shown that descriptions integrating physiological processes, with some degree of feedback to modulate the processes of phototrophy and heterotrophy, are needed to properly represent the qualitative behavior of mixotrophs. Among existing mixotrophic models, only those of Stickney et al (2000) and the "perfect beast" of Flynn and Mitra (2009) take the interactions between the two trophic modes into account; the others rely on additive descriptions of phototrophy and heterotrophy (Thingstad et al, 1996;Baretta-Bekker et al, 1998;Jost et al, 2004;Hammer and Pitchford, 2005;Crane and Grover, 2010;Ward et al, 2011;Våge et al, 2013).…”

“…Most interest has been leveled at the potential impact of mixotrophs on the microbial food web structure and functioning, and the conditions under which mixotrophs may likely coexist with strict phototrophs and heterotrophs (Thingstad et al, 1996;BarettaBekker et al, 1998;Stickney et al, 2000;Jost et al, 2004;Hammer and Pitchford, 2005;Hood et al, 2006;Flynn and Mitra, 2009;Crane and Grover, 2010;Ward et al, 2011;Våge et al, 2013). By far the greater effort has been applied to CM organisms.…”

“…The complexity of the model structure varies widely among such studies. The simplest models describe mixotrophy as the ability to combine both phototrophy and heterotrophy without any feedbacks or trade-offs between the two nutritional modes and organisms have a fixed stoichiometry (e.g., Hammer and Pitchford, 2005). At the other extreme, the most complex model explicitly describes the main regulative processes that occur between phototrophy and heterotrophy in the mixotroph and allows for a variation of the cellular stoichiometry (Flynn and Mitra, 2009).…”

Mixotrophy stirs up our understanding of marine food webs

“…Following these efforts, and with increased awareness of mixotrophy as a nutritional strategy among many planktonic species, modelers began to investigate the consequences of different forms of mixotrophy, as described above (11), including elemental stoichiometric considerations of prey and nutrient availability (12). Subsequent mathematical analyses revealed that the inclusion of mixotrophy in models could affect the equilibrium community structure and improve stability of the biological community (13,14). This early work envisioned mixotrophs as constituitively photosynthetic organisms (i.e., predatory phytoflagellates).…”