Mechanistic understanding of the role of diatoms in the success of the Arctic complex and implications for a warmer Arctic

Lead Research Organisation: British Antarctic Survey


Copepod species of the genus Calanus (Calanus hereafter) are rice grain-sized crustaceans, distant relatives of crabs and lobsters, that occur throughout the Arctic Ocean consuming enormous quantities of microscopic algae (phytoplankton). These tiny animals represent the primary food source for many Arctic fish, seabirds and whales. During early spring they gorge on extensive seasonal blooms of diatoms, fat-rich phytoplankton that proliferate both beneath the sea ice and in the open ocean. This allows Calanus to rapidly obtain sufficient fat to survive during the many months of food scarcity during the Arctic winter. Diatoms also produce one of the main marine omega-3 polyunsaturated fatty acids that Calanus require to successfully survive and reproduce in the frozen Arctic waters. Calanus seasonally migrate into deeper waters to save energy and reduce their losses to predation in an overwintering process called diapause that is fuelled entirely by carbon-rich fat (lipids). This vertical 'lipid pump' transfers vast quantities of carbon into the ocean's interior and ultimately represents the draw-down of atmospheric carbon dioxide (CO2), an important process within the global carbon cycle. Continued global warming throughout the 21st century is expected to exert a strong influence on the timing, magnitude and spatial distribution of diatom productivity in the Arctic Ocean. Little is known about how Calanus will respond to these changes, making it difficult to understand how the wider Arctic ecosystem and its biogeochemistry will be affected by climate change.
The overarching goal of this proposal is to develop a predictive understanding of how Calanus in the Arctic will be affected by future climate change. We will achieve this goal through five main areas of research:
We will synthesise past datasets of Calanus in the Arctic alongside satellite-derived data on primary production. This undertaking will examine whether smaller, more temperate species have been increasingly colonising of Arctic. Furthermore, it will consider how the timing of life-cycle events may have changed over past decades and between different Arctic regions. The resulting data will be used to validate modelling efforts.
We will conduct field based experiments to examine how climate-driven changes in the quantity and omega-3 content of phytoplankton will affect crucial features of the Calanus life-cycle, including reproduction and lipid storage for diapause. Cutting-edge techniques will investigate how and why Calanus use stored fats to reproduce in the absence of food. The new understanding gained will be used to produce numerical models of Calanus' life cycle for future forecasting.
The research programme will develop life-cycle models of Calanus and simulate present day distribution patterns, the timing of life-cycle events, and the quantities of stored lipid (body condition), over large areas of the Arctic. These projections will be compared to historical data.
We will investigate how the omega-3 fatty acid content of Calanus is affected by the food environment and in turn dictates patterns of their diapause- and reproductive success. Reproductive strategies differ between the different species of Calanus and this approach provides a powerful means by which to predict how each species will be impacted, allowing us to identify the winners and losers under various scenarios of future environmental changes.
The project synthesis will draw upon previous all elements of the proposal to generate new numerical models of Calanus and how the food environment influences their reproductive strategy and hence capacity for survival in a changing Arctic Ocean. This will allow us to explore how the productivity and biogeochemistry of the Arctic Ocean will change in the future. These models will be interfaced with the UK's Earth System Model that directly feeds into international efforts to understand global feedbacks to climate change.

Planned Impact

The major beneficiaries will be fisheries policy makers, biogeochemical modellers, climate scientists and political bodies concerned with the health and management of the Arctic ecosystem. Improved understanding of Arctic fisheries is important for understanding the food security and provision of protein and nutrition for many nations, including the UK. Our work will also be of benefit to academics interested in understanding trophic interactions and the biogeochemistry of marine ecosystems. The involvement of PhD students and early career scientists will ensure that we contribute to training the next generation of research scientists.
Understanding how the abundance and lipid content of Calanus is likely to change is central to understanding how the productivity of fish and higher trophic levels will be affected by future environmental change. This understanding is therefore of central importance to fisheries and ecosystem managers throughout the Arctic. Knowledge of zooplankton mediated carbon sequestration is required for accurate model parameterisation and validation, and thus of benefit to biogeochemical and climate modellers: New parameterisation of the spatio-temporal distribution of copepod abundance will ready for coupling to MEDUSA, the biogeochemical model adopted by NERC and the UK Met Office to provide marine biogeochemistry in UKESM1, the UK community Earth System Model being used in phase 6 of the Coupled Model Intercomparison Project (CMIP6) that will feed into IPCC Assessment Report 6. More accurate predictions of Calanus distributions will provide more detailed insight into the knock-on effects for the composition and abundance of Arctic fish communities. In turn, this will provide more realistic assessments of food security and the provisioning of marine protein and essential omega-3 polyunsaturated fatty acids.
We will maximize the visibility and accessibility of our research to Arctic policy makers and fisheries scientists by presenting our program and its findings at Arctic Frontiers conferences (, the annual gathering of academics, politicians and business with interests in the Arctic. Our program has been designed with the involvement of ecosystem and biogeochemical modelers from the outset. On-going, 2-way dialogue between the observational/experimental and modeling components of our work will enable the effective uptake of our data products. Involvement of NEMO-MEDUSA in CMIP6 will ensure that our work contributes to the broader political process via the reports of the IPCC. We are also working directly with US and Norwegian modelling groups that are developing seasonal and multidecadal forecasts for the benefit of management and policy regarding high-value fisheries like Alaska pollock and marine mammal conservation. This simultaneous integration of multiple, well-tested copepod models into three internationally prominent oceanographic models will, to our knowledge, constitute the most complete ensemble experiment in understanding and predicting the future of Arctic zooplankton to date.
Description 1) We have compiled the occurrence records for three Calanus species - C. finmarchicus, C. glacialis and C. hyperboreus - on a pan-Arctic scale. This novel database of over 100,000 records from 90 inividual datasets includes metadata such as the coordinates, depth, date, and life stage (CIV, CV, female, male) per record. This builds on previous databases (available via OBIS or the NSF Arctic Data Center) by including more recent cruise data and adding relevant environmental variables, such as depth- and season-specific ice, temperature and chlorophyll data, to each sampling location. This database will be an important update on our knowledge of Calanus spatial and temporal distributions in the Arctic and will be a useful resource and point of reference to share with other researchers and policy makers. This data is being published and archived in an online repository, making it Findable, Accessible, Interoperable and Reusable to end users, in line with FAIR guiding principles for data management.

2) Chlorophyll measurements have been made during three DIAPOD research cruises (JR16006, JR17005, and JR18007), and these chlorophyll measurements have been compared with data from satellites (both OC-CCI, and OLCI data). Cloud cover has been found to be significant and limits the number of match ups between in situ and satellite derived measurements. In order to estimate the contribution of diatoms to the chlorophyll concentrations, NEODAAS have provided an output of estimates of chlorophyll size fraction (from Brewin et al. 2017) for the periods over which in situ data were collected as part of the DIAPOD project. Overlapping data for JR18007 of size fractionated chlorophyll, reveal that the Brewin 2017 model does an ok job at estimating the chlorophyll associated with nanoplankton. However, during JR18007 we observed much higher concentrations of chlorophyll in the picoplankton size fraction, and lower in the microplankton size fraction, than would be predicted by the Brewin 2017 model.

3) We have analysed Calanus finmarchicus life-cycle data and found new evidence that this boreal species, which is expatriated to Arctic regions, is now capable of completing its life-cycle in the Arctic Fram Strait region. This evidence of the changing community structure of Arctic Ocean regions is likely driven by ocean warming and ice retreat in such Arctic regions. Such changes will impact the stability of Arctic marine foodwebs and the capacity of these oceanic regions to sequester carbon to deep ocean layers and mitigate anthropogenic carbon emissions.
Exploitation Route Calanus are a major dietary item for commercially fished species. We are parameterising their life-cycle and examining their physiology to improve predictions of how these species may alter in abundance and distribution in the future. This is of use to fishery managers. It will also help paramterise Earth System Models in terms of the biogeochemical impact of these species in polar systems.
Sectors Agriculture, Food and Drink,Environment

Description We have published two articles for young readers. The first (Mayor et al "Marine copepods, the Wildebeest of the Oceans") reveals how important copepods are to foodwebs in the world's oceans, particularly the polar regions. The second (Freer and Hobbs "The World's Biggest Game of Hide-and-Seek") looks at the behaviour of pelagic organisms in what is the biggest daily migration on Earth. Both articles are reviewed by the young readers themselves and have an international distribution.
First Year Of Impact 2021
Sector Education,Environment
Title Range-wide occurrence records of the subarctic copepod Calanus finmarchicus and associated environmental predictor variables 
Description This dataset contains occurrence records and associated metadata for the zooplankton species Calanus finmarchicus that were compiled from multiple open access databases. A file containing the corresponding background points is provided, along with gridded environmental variables for each season (Jan-Feb-Mar, Apr-May-Jun, Jul-Aug-Sep, Oct-Nov-Dec) and era (1955-1984, 1985-2017) that were assessed in this study. Together these data were used as input files for the MaxEnt ecological niche model within the peer reviewed article: Freer JJ, Daase, M, Tarling GA, (2021) Modelling the biogeographic boundary shift of Calanus finmarchicus reveals drivers of Arctic Atlantification by subarctic zooplankton, Global Change Biology. Finally, an R Markdown document is provided to enable data users to replicate the model optimisation and prediction steps using the input data files within this repository. Funding was provided by: UKRI Natural Environment Research Council (NERC): DIAPOD (NE/P006213/1) NERC and the German Federal Ministry of Education and Research (BMBF): CHASE (NE/R012687/1) Norwegian Research Council: Deep Impact project (300333). 
Type Of Material Database/Collection of data 
Year Produced 2021 
Provided To Others? Yes  
Impact Not applicable