Aditee Mitra

Cardiff University | CU · School of Earth and Ocean Sciences

Photosynthetic organisms have an enormous influence on our environment through their effects on the development of other life on Earth and the way they alter the planet's geology and geochemistry. This book takes a unique approach by examining the evolutionary history of the major groups of aquatic photoautotrophs in the context of the ecophysiolog...

Transfers of energy and nutrients from producers to consumers are fundamental to ecosystem structure and functioning. A common example is the transfer of essential amino acids and fatty acids, produced by phototrophs, up through successive trophic levels. A highly specialised example is the transmission of acquired phototrophy between certain plank...

Marine plankton that are capable of photosynthesis and also predation (termed “mixoplankton”) comprise up to 50% of those organisms traditionally termed phytoplankton. Many harmful bloom species are mixoplantonic. However, marine environmental management policies issued by governments, including the MSFD by the EU, have been designed assuming a str...

Traditional interpretations of marine plankton ecology, such as that in the Indian Ocean, mirror the plant-animal dichotomy of terrestrial ecology. Thus, single-celled phytoplankton produce food consumed by single-celled zooplankton, and these are in turn consumed by larger zooplankton through to higher trophic levels. Our routine monitoring survey...

Plankton phototrophy consumes CO2, increasing seawater pH, while heterotrophy does the converse. Elevation of pH (>8.5) during coastal blooms becomes increasingly deleterious for plankton. Mixoplankton, which can be important bloom-formers, engage in both photoautotrophy and phagoheterotrophy; in theory, this activity could create a relatively stab...

Prorocentrum comprises a diverse group of bloom-forming dinophytes with a worldwide distribution. Although photosynthetic, mixoplanktonic phagotrophy has also been described. Recently, the small P. cf. balticum was shown to use a remarkable feeding strategy by crafting globular mucus traps to capture and immobilize potential prey. Here we present e...

Analysis of trait trade-offs, through which physiological traits requiring common resources are ‘traded’ to optimize competitive advantage, provides a route to simplify and more readily understand the complexities of ecology. The concept of trait trade-offs has found favour in plankton research, especially directed at phytoplankton, defined here as...

With climate change, oceans are becoming increasingly nutrient limited, favouring growth of prokaryotic picoplankton at the expense of the larger protist plankton whose growth support higher trophic levels. Constitutive mixoplankton (CM), microalgal plankton with innate phototrophic capability coupled with phagotrophy, graze on these picoplankton,...

Protist plankton are major members of open-water marine food webs. Traditionally divided between phototrophic phytoplankton and phagotrophic zooplankton, recent research shows many actually combine phototrophy and phagotrophy in the one cell; these protists are the 'mixoplankton'. Under the mixoplankton paradigm, 'phytoplankton' are incapable of ph...

Rapid virus proliferation can exert a powerful control on phytoplankton host populations, playing a significant role in marine biogeochemistry and ecology. We explore how marine lytic viruses impact phytoplankton succession, affecting host and nonhost populations. Using an in silico food web we conducted simulation experiments under a range of diff...

The dinoflagellate Dinophysis is responsible for causing diarrhetic shellfish poisoning impacting shellfish aquaculture globally. Dinophysis species are invariably plastidic specialist non-constitutive mixoplankton (pSNCM), combining phagotrophy with acquired phototrophy. Dinophysis acquires phototrophy from another pSNCM, the ciliate Mesodinium ,...

A manual for the isolation and maintenance of mixoplankton is provided that offer guidelines to assist students and scientists initiating studies of mixoplankton. The manual contains specific information on: • Facilities required, including temperature regulated rooms or cabinets, instruments and consumables • Growth media and aseptic precautions •...

Emerging knowledge of mixoplankton—ubiquitous microbes that employ phototrophy and phagotrophy synergistically in one cell—reshapes our knowledge of the flow of materials and energy, with wide-reaching impacts on marine productivity, biodiversity, and sustainability. Conceptual models of microbial interactions have evolved from food-chains, where c...

It remains unclear as to how mixoplankton (coupled phototrophy and phagotrophy in one cell) affects the estimation of grazing rates obtained from the widely used dilution grazing technique. To address this issue, we prepared laboratory-controlled dilution experiments with known mixtures of phyto-, protozoo-, and mixoplankton, operated under differe...

Projecting ocean biogeochemistry and fisheries resources under climate change requires confidence in simulation models. Core to such models is the description of consumer dynamics relating prey abundance to capture, digestion efficiency and growth rate. Capture is most commonly described as a linear function of prey encounter or by rectangular hype...

The way marine systems have historically been thought to function closely parallels that of land-based systems, where plants produce food and animals consume it. Thus, in marine systems, the traditional view is that phytoplankton (microalgae) produce food which zooplankton consume, which in turn, are consumed by larger animals through to fish. "Act...

This manual, brings together the different novel approaches developed within MixITiN for investigating marine mixoplankton activity. It comprises four sections, de facto chapters, as follows:• Section 2 Genomic sampling protocols for application to mixoplankton• Section 3 Development and validation of new methods for measuring predation rates in m...

Mixoplankton are now recognised as a major group of protist plankton, encompassing many traditionally labeled 'phytoplankton' and 'protozooplankton'. A key is given to help identify HAB species within the mixoplankton functional types.

A Simple N-based Mixoplankton Model. This work is an output of the MixITiN project (see www.mixotroph.org). It describes the construction and example deployment of a simple model describing the growth of mixoplankton for education purposes. The book is supported by a free-to-end-user model to operate on Powersim Cockpit, and an editable model in Po...

A mechanistic system dynamics description is developed of the interactions between a single lytic-virus – phytoplankton-host couple. The model has state variables for virus, uninfected and infected host biomass, and describes virus and host allometry and physiology. The model, analogous to experimental laboratory virus-host systems but more amenabl...

Different hypotheses have been proposed explaining plankton community assembly and how changes in biodiversity can impact ecosystem function. Mixoplankton (photo-phago-trophs) are important members of the plankton, but science lacks a clear understanding of their role in plankton succession. Here, we used a modelling approach to evaluate the season...

Many protist plankton are mixotrophs, combining phototrophy and phagotrophy. Their role in freshwater and marine ecology has emerged as a major developing feature of plankton research over recent decades. To better aid discussions, we suggest these organisms are termed “mixoplankton”, as “planktonic protist organisms that express, or have potential...

On land, plants make their own food by photosynthesis and animals live by eating. However, in the microscopic world in the oceans, it is not that simple. Many microscopic so-called plants (phytoplankton) can also eat like animals and many microscopic so-called animals (microzooplankton) can also photosynthesize like plants! More amazingly, some of...

Aim Most protist plankton are mixotrophic, with potential to engage in photoautotrophy and phagotrophy; however, the ecology of these organisms has been misdiagnosed for over a century. A large proportion of these organisms are constitutive mixotrophs (CMs), with an innate ability to photosynthesize. Here, for the first time, an analysis is present...

Mixotrophy is widespread among protist plankton displaying diverse functional forms within a wide range of sizes. However, little is known about the niches of different mixotrophs and how they affect nutrient cycling and trophodynamics in marine ecosystems. Here we built a plankton food web model incorporating mixotrophic functional diversity. A di...

Results from a dynamic mathematical model are presented simulating the growth of the harmful algal bloom (HAB) mixotrophic dinoflagellate Karlodinium veneficum and its algal prey, Rhodomonas salina. The model describes carbon-nitrogen-phosphorus-based interactions within the mixotroph, interlinking autotrophic and phagotrophic nutrition. The model...

Stable isotope ratios (SIR) are widely used to estimate food-web trophic levels (TLs). We built systems dynamic N-biomass-based models of different levels of complexity, containing explicit descriptions of isotope fractionation and of trophic level. The values of δ¹⁵N and TLs, as independent and emergent properties, were used to test the potential...

The traditional view of the planktonic food web is simplistic: nutrients are consumed by phytoplankton that, in turn, support zooplankton, which ultimately support fish. This structure is the foundation of most models used to explore fisheries production, biogeochemical cycling, and climate change. In recent years, however, the importance of mixotr...

Mixotrophs, tiny sea creatures that hunt like animals but grow like plants, can change everything from fish populations to rates of global warming

This first comprehensive analysis of the global biogeography of marine protistan plankton with acquired phototrophy shows these mixotrophic organisms to be ubiquitous and abundant; however, their biogeography differs markedly between different functional groups. These mixotrophs, lacking a constitutive capacity for photosynthesis (i.e., non-constit...

We explore approaches to minimise impacts of zooplanktonic pests upon commercial microalgal crops using system dynamics models to describe algal growth controlled by light and nutrient availability and zooplankton growth controlled by crop abundance and nutritional quality. Losses of microalgal crops are minimised when their growth is fastest and,...

Most biogeochemical/ecological models divide planktonic protists between phototrophs (phytoplankton) and heterotrophs (zooplankton). However, a large number of planktonic protists are able to combine several mechanisms of carbon and nutrient acquisition. Not representing these multiple mechanisms in biogeochemical/ecological models describing eutro...

Mixotrophy, i.e., the ability to combine phototrophy and phagotrophy in one organism, is now recognized to be widespread among photic-zone protists and to potentially modify the structure and functioning of planktonic ecosystems. However, few biogeochemical/ecological models explicitly include this mode of nutrition, owing to the large diversity of...

Mixotrophs are important components of the bacterioplankton, phytoplankton, microzooplankton and sometimes zooplankton, in coastal and oceanic waters. Bacterivory among the phytoplankton may be important for alleviating inorganic nutrient stress and may increase primary production in oligotrophic waters. Mixotrophic phytoflagellates and dinoflagell...

Once fixed by photosynthesis carbon becomes part of the marine food web. The fate of this carbon has two possible outcomes, it may be respired and released back to the ocean and potentially to the atmosphere as CO 2 or retained in the ocean interior and/or marine sediments for extended time scales. The most important biologically mediated processes...

Rectangular hyperbolic type 2 (RHt2; Michaelis-Menten or Monod-like) functions are commonly used to describe predation kinetics in plankton models, either alone or together with a prey selectivity algorithm deploying the same half-saturation constant for all prey types referenced to external prey biomass abundance. We present an analysis that indic...

Ecology involves the transfer of elements between organisms and the environment. Inevitably, and as exemplified in ‘stoichiometric ecology’, imbalances in the transfer pathways have potential to disturb trophic dynamics. It is also clear, though, that those disturbances are not simply (linearly, so to speak) related to imbalances in elemental stoic...

Arranging organisms into functional groups aids ecological research by grouping organisms (irrespective of phylogenetic origin) that interact with environmental factors in similar ways. Planktonic protists traditionally have been split between photoautotrophic “phytoplankton” and phagotrophic “microzooplankton”. However, there is a growing recognit...

We propose definitions in terminology to enhance ongoing collaborations between biologists and modellers on plankton ecology. Organism "functional type" should refer to commonality in ecology not biogeochemistry; the latter is largely an emergent property of the former, while alignment with ecology is also consistent with usage in terrestrial scien...

The aim of this paper is to investigate the role of phytoplankton nutritional status in the formation of the spring bloom regularly observed at the station L4 in the Western English Channel. Using a modelling approach, we tested the hypothesis that the increase in light from winter to spring induces a decrease in diatom nutritional status (i.e. an...

Within models, zooplankton grazing is typically defined as being dependent on total prey concentration, with feeding selectivity expressed only as a function of prey size. This behavior ignores taxonomic preferences shown by the predators and the capacity of some zooplankton to actively select or reject individual prey items from mixtures. We carri...

Human activity causes ocean acidification (OA) though the dissolution of anthropogenically generated CO 2 into seawater, and eutrophication through the addition of inorganic nutrients. Eutrophication increases the phytoplankton biomass that can be supported during a bloom, and the resultant uptake of dissolved inorganic carbon during photosynthesis...

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This paper reviews progress on understanding biological carbon sequestration in the ocean with special reference to the microbial formation and transformation of recalcitrant dissolved organic carbon (RDOC), the microbial carbon pump (MCP). We propose that RDOC is a concept with a wide continuum of recalcitrance. Most RDOC compounds maintain their...

This paper reviews progress on understanding biological carbon sequestration in the ocean with special reference to the microbial formation and transformation of recalcitrant dissolved organic carbon (RDOC), the microbial carbon pump (MCP). We propose that RDOC is a relative concept with a wide continuum of recalcitrance. Most RDOC compounds mainta...

Exploring climate and anthropogenic impacts to marine ecosystems requires an understanding of how trophic components interact. However, integrative end-to-end ecosystem studies (experimental and/or modelling) are rare. Experimental investigations often concentrate on a particular group or individual species within a trophic level, while tropho-dyna...

The traditional view of the planktonic food web describes consumption of inorganic nutrients by photoautotrophic phytoplankton, which in turn supports zooplankton and ultimately higher trophic levels. Pathways centred on bacteria provide mechanisms for nutrient recycling. This structure lies at the foundation of most models used to explore biogeoch...

This report is a result of discussions of an engineer with three biologists. The original idea of figuring out how to efficiently mine scientific papers turned into realizing how the present scientific workflows of generating and publishing results is desperately obsolete in today s world of the Internet and the Digital Economy where ideas are floa...

The performance of four contemporary formulations describing trophic transfer, which have strongly contrasting assumptions as regards the way that consumer growth is calculated as a function of food C:N ratio and in the fate of non-limiting substrates, was compared in two settings: a simple steady-state ecosystem model and a 3D biogeochemical gener...

The traditional view of the planktonic foodweb describes consumption of inorganic nutrients by photo-autotrophic phytoplankton, which in turn supports zooplankton and ultimately higher trophic levels. Pathways centred on bacteria provide mechanisms for nutrient recycling. This structure lies at the foundation of most models used to explore biogeoch...

Biofuels production from microalgae attracts much attention but remains an unproven technology. We explore routes to enhance production through modifications to a range of generic microalgal physiological characteristics. Our analysis shows that biofuels production may be enhanced ca fivefold through genetic modification (GM) of factors affecting g...

The classic portrayal of plankton is dominated by phytoplanktonic primary producers and zooplanktonic secondary producers. In reality, many if not most plankton traditionally labelled as phytoplankton or microzooplankton should be identified as mixotrophs, contributing to both primary and secondary production. Mixotrophic protists (i.e. single-cell...

Ultimately, the structure and functioning of marine ecosystems is defined by the transfer of autotrophic production to higher trophic levels and selective consumption of these autotrophs by predators. Hence, feeding regulation via modification of grazing and food incorporation by predators is critical for understanding and predicting the dynamics o...

Mixotrophs are significant components of planktonic food webs, are frequently associated with harmful algal bloom events, and thus warrant inclusion in coastal ecosystem models. There are, however, insufficient quantitative data to support the construction and testing of simple empirical descriptions of mixotrophs. Here, a complex mixotroph model b...