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Sampling new waters: using plankton to understand ocean health in the South Atlantic

Plankton, the microscopic organisms that drift with the ocean’s currents, play a vital role in sustaining almost all marine life. By monitoring plankton communities, we are able to understand the health of our oceans, and how they are changing in response to drivers such as climate change.

The Continuous Plankton Recorder (CPR) Survey is a large-scale plankton monitoring programme based at the Marine Biological Association (MBA, UK). In operation for over 90 years, and having covered more than 7 million nautical miles of ocean, the CPR Survey provides unrivalled information on the state of the marine environment.

As part of the AtlantECO project, the CPR Survey has helped set up a new plankton monitoring route between South Africa and Brazil, with the first successful tow achieved in October 2021. This area of the South Atlantic has been little sampled historically - one of the aims of this project is to gain a better understanding and management of the Atlantic Ocean and its ecosystem services, and the tried and tested CPR is ideally suited for this purpose.

Setting up new CPR tows requires careful consideration, planning and problem solving. Each tow route is carefully coordinated, from identifying suitable ships to tow CPRs, training crew to deploy and recover CPRs, right through to the analysis of the plankton samples and providing open access to resulting data. This tow was one of the longest yet at approximately 3,600nm, and, due to the Covid-19 pandemic and a number of other challenges, was coordinated remotely. The success of this inaugural tow was due to the dedication and support of the crew and owners of the LODUR ship which towed the CPR, colleagues in Brazil and South Africa as well as staff at the MBA.

CPRs are simple mechanical instruments that have been used to collect plankton samples all over the world. Designed to be towed behind ships of opportunity (e.g. passenger ferries, cargo ships etc.), CPRs are torpedo shaped metal boxes, approximately 1m long, that filter seawater through a fine silk mesh as they are pulled through the water. The silks are continuously wound on a roller inside and fixed in a preservative, collecting plankton along transects hundreds of nautical miles in length.

A Continuous Plankton Recorder (CPR). These sampling instruments collect plankton across hundreds of miles of ocean at a time. ©Marine Biological Association

For this project, the CPR tows from Brazil to South Africa will be repeated every 3 months, with the plankton samples being analysed by a team of analysts based at the Federal University of Rio Grande (FURG), Brazil.

Location of sampling deployments (tows) along the Brazil and South Africa (BSA) survey line. A total of eight sampling deployments were carried out (1BSA-8BSA), each representing a tow of ca. 450 nautical miles.

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