Bloom forming phytoplankton punch far above their weight; although only 1% of thephotosynthetic biomass on Earth they fix as much carbon as all terrestrial plants combined.As well as being the engines of primary productivity on which all aquatic ecosystemsdepend, these phytoplankton can cause problems when blooms release toxins or generatelarge amounts of organic matter, leading to ecological damage. Such blooms have massiveeconomic impacts on fisheries, pose a risk to public health, and can negatively affectbiodiversity and the recreational value of water bodies.

Phytoplankton encompass species ranging from cyanobacteria to green algae and diatoms,and the fundamental biology of many of theses groups is poorly understood. One largelyenigmatic aspect of phytoplankton lifecycles are resting stages, which allow species thatnormally live in the water column (pelagic algae) to persist in sediments forming a ‘seedbank’ that has potential to act as a reservoir of genetic diversity and a source of cells thatinitiate pelagic blooms. Resting stages can take the form of highly resistant cysts capable ofsurviving extreme conditions (e.g. complete desiccation); some have been revived after lyingdormant in sediments for thousands of years.

Despite the potential importance of phytoplankton resting stages in bloom formation, weunderstand little about the cellular mechanisms that allow them to persist in sediments or theenvironmental drivers and cellular mechanisms of differentiation and germination. We knowthat algal resting stages germinating from sediments can contribute to pelagic biomass, butwe don’t know whether they can be the primary seed population for blooms or whether thegenetic and phenotypic diversity harboured in the sediment is important for adaptation of thepopulation to changing conditions.2/6

This PhD project will combine the latest molecular tools with field work to improve ourknowledge of algal resting stages, focusing on Loch Leven, a large, shallow lake in lowlandScotland. The UK Centre for Ecology and Hydrology (UKCEH) has been collecting data fromLoch Leven fortnightly since 1968; these data were instrumental in guiding its restorationfrom a highly eutrophic state in the 1990s. However, recent years have seen increasingdominance of potentially harmful cyanobacterial blooms, which may be linked to increasingwater temperatures. With the lake’s temperature projected to increase by about 3°C by 2080,there is now an urgent need to understand the factors that control algal blooms in thissystem, how they might be impacted by changes in temperature and how they might becontrolled. Loch Leven is an important nature reserve, trout fishery and recreational facility,and there is strong local and national interest in creating a sustainable future of the Loch.

This project will focus on two algal groups that are often common in Loch Leven blooms: thecyanobacterial genus Dolichospermum (formally known as Anabaena) and the diatom genusAsterionella. Dolichospermum can produce toxins and are known to produce resting stagescalled akinetes, while Asterionella can form undifferentiated resting cells in lake sedimentsthat form a key part of the phytoplankton succession in years when cyanobacteria are lessabundant. The following questions will be addressed:

1. What resting cells are present in Loch Leven sediments and how does their abundancevary over the year?

2. How does the intraspecific genetic diversity of resting cells compare with that of thepelagic population? By following genetic lineages over time, can we ascertain whether or notresting cells are a major contributor to the bloom inoculum?

3. Do resting cell populations harbour phenotypic diversity that may allow populations toadapt to a changing climate?

4. What molecular mechanisms allow resting stages to survive long periods in sedimentsunder very low light, and likely near anoxic, conditions?

There will be an opportunity to focus the project on areas of particular interest to the student.These could be more ecological, for example using benthic traps to estimate the carbon fluxdue to resting stage formation, or more molecular, focusing on the cellular mechanisms ofpersistence.