Global rise of symbiotic plankton - an international network to investigate a growing threat to marine fisheries

Life on Earth is heavily dependent on microscopic plankton that live in our oceans. These microscopic plankton can be divided between 3 types:

(1) phytoplankton: microscopic "plants" that make food and oxygen through photosynthesis by using carbon dioxide and energy from the sun
(2) protozooplankton: microscopic "animals" that eat the phytoplankton and are in turn food for small fish
(3) mixoplankton: microbes that combine "plant+animal", photosynthesising (making food and releasing oxygen) as well as eating prey

In this project we are going to explore the "lifestyle" of the plankton Noctiluca, commonly called "sea sparkle" as they can form bioluminescent blooms. Noctiluca are single-celled and 1 mm in diameter. As a globally distributed cosmopolitan microbe occurring along the coasts of all the continents (except Antarctica) they exist as an "animal" (protozooplankton), called red-Noctiluca because of their colouration. However, another form is becoming dominant in Asian waters; this is a "plant+animal" (mixoplankton) form, referred to as green-Noctiluca because it harbours hundreds of cells of a green phytoplankton. Green-Noctiluca still eats but, by capturing and "hosting" colonies of phytoplankton (a process termed symbiosis), they also photosynthesise.

Green-Noctiluca is usually found only in the warm tropical waters. But with climate change the green-Noctiluca are spreading. Over the last 20 years there have been regular blooms of green-Noctiluca in the Arabian Sea and also off SE Asia. Unlike red Noctiluca, which starves to death on exhaustion of its food, green Noctiluca blooms persist. As they are not readily eaten, their presence in the oceans blocks the normal food chain to fish. The decline in fish populations and increase in jellyfish, has affected the socio-economics of over 140 million humans who depend on previously highly productive fisheries. Blooms can also block desalination facilities as well as oil refinery water intakes. The concern is that with climate change the green-Noctiluca will start appearing alongside the red-Noctiluca in other areas; it could potentially spread with climate change into European waters, US waters and East China Sea - all areas with important fisheries.

The reason why both types of Noctiluca bloom in tropical waters is unknown. Also, not known are the factors that lead to the prevalence of the green-Noctiluca over the red-Noctiluca or vice versa. We propose that the key to this transition must lay with the plant-like phytoplankton (Protoeuglena) which the Noctiluca capture and maintain as symbionts. However, very little is known about these Protoeuglena - where they occur, how do temperature and light affect their growth and, therefore, how will climate change effect their spread in global oceans.

In this project we will explore factors affecting the growth of the Protoeuglena cells when they are free-living versus when they are in symbiosis with the green-Noctiluca. We will use state-of-the-art research methodologies developed in the UK, USA and Thailand, bringing together a team of experts with unique but complimentary skills.

Outputs from this project, in addition to scientific publications, will include information cards about the fascinating Noctiluca for anyone to freely access and download, videos explaining the physiology of Noctiluca, reports for coastal water monitoring and policy managers.

As a seedcorn project, the most important output, however, will be the establishment of an international team of scientists to confront what is a truly international problem. In this UN Decade of the Ocean, this project is a timely effort to understand the factors that govern the spread of Noctiluca and therefore, to develop tools and methodologies to predict future blooms and strive towards healthier and sustainable oceans.