In 1925, zoologist Sir Alister Hardy launched a survey of plankton while he was exploring Antarctica. Almost 100 years later, I’m continuing part of that same endeavour, called the Continuous Plankton Recorder (CPR) survey. Here, aboard our research vessel, the Sepia, I’m showing how the CPR works.

The device is a metre-long metal torpedo towed off a boat. Inside, two pieces of silk on a scroll sample the water, picking up plankton between them. We’ve got data and samples that date to 1931 from tows across the North Atlantic Ocean, which show what species of plankton are present, how they change across time and any new species that emerge.

Our taxonomists can identify 800 taxa of phytoplankton and zooplankton. They examine what I call plankton ‘roadkill’, after the organisms smash against the silk at 10 metres per second.

We have routes that go from Canada to Japan, the United Kingdom to the Caribbean and even into the Arctic Ocean. With such a wide geographical and temporal span, we can look at large-scale spatial shifts in certain plankton species, such as those inhabiting cold-water zones contracting their ranges as warmer water moves polewards.

Container ships are ideal for consistently sampling from the same route every month. We can go on a limited budget, usually just biscuits and beer for the crew. They enjoy knowing that ‘fishing for plankton’ is doing something interesting for science.

Because we store every sample, other researchers can find unexpected signals in the ocean later on. For example, a pioneering study from 2004 used CPR samples to show an increase in ocean microplastics. Another researcher tracked the bacteria that caused a 2018 cholera outbreak in British Columbia, Canada, with CPR samples. It’s exciting to be sitting on this database that someone with a different eye can pick up to tell untold stories.