Marine microalgal populations can grow explosively giving rise to plankton blooms. This has important ecological consequences: bloom biomass can stimulate life across the food web; however, blooms can also be harmful (Smayda, 2019). Each year, toxin-producing Harmful Algal Blooms (HABs) kill vast numbers of animals (including fish and mammals), with substantial health and economic impacts on human society, including major losses in the aquaculture sector (Gianella et al. 2025). In addition, climate induced changes in environmental conditions, such as nutrient availability and water temperature, have made toxic HABs more frequent. Despite recent progress, toxic HABs remain poorly understood and hard to predict (Flynn & McGillicuddy, 2018). Conditions favourable to growth, e.g., nutrients, temperature and light, are necessary but not sufficient for bloom genesis and spatio-temporal evolution (Paerl, 1988). The vast majority of toxic HAB formers belong to a group known as dinoflagellates, which swim by means of flagella and have flexible feeding strategies switching between photosynthesis and predation. Swimming, particularly in calmer waters, can be biased by environmental factors (nutrient gradients, light levels) leading to competitive advantage and the potential to dominate blooms. However, current studies treat swimming simplistically, without accounting for recent progress in the physics of microswimmers, such as dinoflagellates. In the last four decades, enormous progress has been made in this area of biophysics (Bees & Croze 2014, Elgeti et al. 2015, Ishikawa et al. 2025). However, only recently are the ecological implications of the physics swimming, and its bias by environmental cues, beginning to be explored (Grunbaum, 2009). For example, it has been shown that ‘thin plankton layers’ in the ocean arise when biased swimming algae, including the HAB former Heterosigma asakiwo, get trapped in the strong flow shear which characterises these layers (Durham et al. 2009, Durham and Stocker 2012). In this interdisciplinary project you will combine state of the art biophysics, theoretical and experimental, with algal physiology and ecotoxicology to elucidate the mechanisms of toxic HAB formation. You will work with Karenia mikimotoi – a HAB dinoflagellate of increasing global concern (Li et al. 2019). This dinoflagellate has been shown to migrate vertically in the water column, getting trapped in salinity gradients (Gentien 2007). It also has been shown to feed on bacteria and other microalgae (Zhang et. al. 2011). You will investigate its biophysics, biology and ecotoxicology, which remain largely unexplored. Through a combination of lab-based studies and controlled marine environments (microcosms) you will investigate how light and nutrient availability shape K. mikimotoi blooms and their toxic content. You will also study the link between motility and mixotrophy, the ability of toxic algae to switch between photosynthetic growth and other types of nutrient acquisition (e.g. feeding on bacteria). This has not previously been investigated. The project aims to contribute to a mechanistic understanding of toxic plankton blooms, leading to more accurate forecasting by mathematical models, informed by remote sensing data, which will also be available as part of the modelling element of the project.
For more information, see: https://iapetus.ac.uk/studentships/physics-biology-and-microbial-ecology-of-toxic-plankton-blooms/
