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March 14th this year marks thirty years of intensive weekly sampling within an area of the English Channel off Plymouth. This time series has now become a benchmark for detailed long-term monitoring of marine life and measurements of physical, chemical and atmospheric conditions. The Western Channel Observatory (WCO), as it is now known, provides a unique 30 year oceanographic dataset which, because of its quality, quantity and diversity, is recognised globally as of great importance in underpinning our understanding of the wider ocean and how it may be changing. 

However, this story of success could have been very different. Acting against the general, global trend in marine science funding of cutting budgets for gathering and analysing long-term environmental data, the UK’s Natural Environment Research Council subsequently took the decision to continue supporting this important work. This decision is now totally exonerated, as long-term observations reveal unprecedented changes taking place in our environment, including within the marine realm. Thirty years on from those far-sighted few who strove to keep readings, measurements and observations going, the WCO has really come into its own providing a solid baseline against which we can now compare today’s seas with those of the past and begin to predict those of the future. Against a background of rapid climate change, microplastic pollution is just the latest of a series of threats to our seas that the WCO data is key in understanding for formulating mitigation measures. As our coastal waters become more crowded, with numerous competing calls upon them, experiences learned from the WCO are helping to inform those that have to manage our seas and plan how they can be used in the future in ways that are both profitable for commerce and sustainable for marine life. It is only after three decades of concentrated efforts that the WCO data are of sufficient breadth and quality to become useable in understanding marine processes and how they may be impacted by individual or combined threats in both the short and long term.

The quantity of observations and measurements is impressive. Most weeks the research vessel RV Plymouth Quest makes the round trip of around 30 km (18.5 miles) to L(local)4, a sampling station off Plymouth, which has been sampled continuously for the last 30 years. Across the decades there have been more than 1300 such trips, often in harsh weather conditions, a total of about 38,624km (24,000 miles), that’s near enough the circumference of Planet Earth. The breadth of data generated, the regularity of visits and the longevity of the sampling are what makes the WCO so important globally. Looking at the plankton sampling at L4 gives us some idea of the scale of effort employed. Over the past three decades 1066 phytoplankton and 2634 zooplankton samples have been taken and analysed. Scientists back at the Plymouth Marine Laboratory, have spent countless hours checking the catch, counting and identifying in nearly two million individual planktonic organisms. To date nearly 300 hundred different ‘species’ of phytoplankton have been identified from the WCO, with almost 200 zooplankton ‘species’, as the next step up in the food chain at L4. Life at the seabed, the benthos, has been sampled for the last decade, recording over 800 species. These figures are likely to rise as new techniques become available; one exciting development is the use of environmental DNA (eDNA) which can pinpoint species from a single cell or loose DNA from skin, droppings and other fragments of organisms that have passed through the WCO but would never show up in the normal analyses.

Whether the methods are traditional or new, regular sampling week after week, year after year is needed to reveal the rarities and unusual events. Recently, following a spate of south westerlies the tropical oceanic plankton species Trichodesmium was recorded, and in just the last few years other phytoplankton has been spotted from time to time. Even new species, so far remaining unidentified turn up. A strange diatom (microscopic plant) which swims in a spiral motion and looks something like a potato crisp has been labelled the ‘Pringle’ even if its true identity remains a mystery. One spectacular creature turned up in a benthic sample from a mud core, this was a giant naked foraminiferan, a single-celled organism, whose relatives are usually microscopic. The ‘Mystery beast’ as it became known was many centimetres in diameter, changed shape and left distinct ‘footprints’ on the surface of the mud. It is still being analysed, but it has never been seen before in the many samples that have been taken in the same location over the decades, it may even be a species new to science. 

While new or unusual species are always exciting and add to our knowledge, the real strength of the WCO is that it allows us to understand what is causing the changes that we see. The weekly regularity of its sampling allows us to understand the system’s response to storms and other climatic extremes superimposed upon the normal seasonality. Now that it comes of age, its 30-year duration also lets us start to unravel some of the slower, longer-term changes that are taking place in the seas off Plymouth and further afield. Regular monitoring of plankton provides unprecedented detail of growing and dying blooms and bloom composition over the seasons. In turn, such information has provided a greater depth of understanding for how intricate and interdependent the ecological interactions are; both within and upon the plankton.

Another strength of the WCO is that we now make a wide series of measurements spanning the atmosphere, down through the water column and into the seabed. This has allowed us to better understand just how tightly coupled the processes occurring in the surface waters are to those in the seabed. The seabed life can feed directly on the plankton near the seabed and thus compete with the zooplankton for this important food resource. Such work has added to our understanding of how carbon can be transported from surface to sea bottom so sequestering it away from the atmosphere. The immediacy of the WCO observations has also proved especially useful in developing techniques for detecting harmful algal blooms (HABs) that can have devastating impacts on fisheries, aquaculture and people.

The WCO has grown and embraced the latest technologies over the last thirty years. Visits to L4 continue as regularly as ever but are now supplemented by autonomous measurements of a range of physical and chemical parameters, collected by sensors on state-of-the-art data buoys moored at L4 and its partner locations E(England)1, further out and influenced by oceanic rather than coastal conditions. Readings, taken every hour, are beamed to PML in almost real time, providing back up information that could not have been collected previously. Atmospheric readings, including detecting aerial pollution from passing ships, at the rate of once every one tenth of a second, have also been added to the arsenal of instrumentation at the WCO. Computer modelling has now become a powerful tool for predicting the path of future changes to our seas with the European Regional Seas Ecosystem Model (ERSEM) being a world leading example. Models are only as good as the data that powers them and enables them to approach close to real world conditions. PML took the ERSEM and refined and improved it, largely ‘feeding’ off the plethora of data generated from the WCO.

L4 is a well-established sampling site but it is also much more. The strategic locations of L4 and E1, and the stunning amount of data they have furnished towards a detailed understanding of how the seas close to the coast and further out into the ocean function, also lend them to being a test-bed for techniques and technologies. Whether these are autonomous underwater vehicles, sent on missions to further explore our waters or better sensors for more detailed and broader data collection, or in situ comparison sites for validating the accuracy and reliability of satellite sensing of the ocean, the locations within the WCO are ideally situated for putting ideas through their paces. PML cooperates with industry and academic partners in developing these test facilities with L4 and the wider WCO being central to the partnership developments in Plymouth’s SmartSound initiative.

L4’s past has been crucial to our broader understanding of the ocean; its future is no less exciting. L4 has grown over the last 30 years to become one of the key sampling sites worldwide, but looks forward to building on its legacy for the future. With improved technologies and the collection of more, better and broader data for improving our knowledge of the ocean at a time when it is facing big challenges, L4 will have a key role in improving our understanding of what is happening and how we might mitigate or live with those changes.