Algae are present in nearly every body of water on the surface of the earth. These microscopic organisms produce roughly half of the oxygen on earth, and are vital to life on the planet. However, algae can also cause significant and expensive damage to their ecosystem, to human health, and to aquaculture stocks when the local environment changes and promotes the rapid growth of a large mass of algae, known as a bloom. Factors such as the concentration of nutrients, temperature, light conditions, and intentional or unintentional interventions by humans or other species all affect the dynamics of algae species and lead to the formation of harmful algal blooms (HABs). In the aquaculture context, HABs present a major health and economic hazard. Severe human health problems can arise from the consumption of shellfish which have been impacted by blooms of toxin-producing algae. These blooms also cause negative economic impacts on aquaculture through aquaculture stock mortality and through temporary site closures and bans on harvesting due to local algae prevalence. Large-scale mortalities of cultured fish due to algae blooms have been reported across the world and financial losses per large episode can range into the tens of millions of pounds. Monitoring of phytoplankton and of the toxins they produce has been undertaken in various forms in the UK for some decades but manual sampling and subsequent off-site analysis can be slow to identify areas with upcoming or rapidly-changing problems. Microscopy, the current standard for performing algae counts, requires trained personnel both in collection and particularly in analysis, and imposes a necessary delay as samples need to be preserved and transported to an analytical facility. The overall objective of this project is to develop new technology to decrease the economic losses and health risks caused by HABs by decreasing the costs of monitoring algae growth in real-time. This technology will complement and address shortcomings in existing monitoring techniques by providing low-cost, high resolution independent data. The PhytoMOPS technology is based on previous lab-based research demonstrating that algal cells could be sorted, counted, and classified using carefully-designed microfluidic channels combined with low-cost optical readouts. The sorting technique, known as "inertial microfluidics", relies on a carefully-designed channel geometry and flow rate to sort cells by shape and size. In this project, we will design a novel optical measurement section after the cell sorting region, in which the microalgal cells are counted and classfied according to their size, shape, and optical absorption properties. The technology will initially be built and evaluated in the lab where the results will be used to develop analytical methods for interpreting the data. In order to be able to make measurements directly in the water, we will adapt the National Oceanography Centre's (NOC's) water chemistry sensor platform which has already been used for long-term autonomous measurements in a wide range of harsh and inaccessible environments. We will combine the well-engineering NOC platform (including microfluidic chips, pumps, valves, and control/communication electronics) with the algae sorting technology to produce a deployable system capable of acting as a standalone, low-cost, low-power monitor of algal species dynamics for early warning of HABS formation. Lastly, this project involves initial field tests of the system. The deployments will be facilitated by two active HAB monitoring organisations who are also providing expert advice throughout the project: the Scottish Assocation for Marine Science and the Agri-Food Bioscience Institute (North Ireland). The system will will be compared directly against manual sampling and existing algal monitoring technology and will be be evaluated for its technical suitability, usability, and long-term potential.