How climate change is affecting the marine species at the base of the food web

A new synthesis review, involving 22 leading scientists from around the world and published in Nature Communications, explores the main responses of zooplankton to ocean warming across the globe, namely shifts in seasonality, range and body size. From this, the team went on to assess the implications for the Earth’s biological carbon pump and potential impacts upon larger marine life, to help develop recommendations for future research.

Zooplankton may be tiny but they are a critical link for energy transfer between the smallest and largest of marine organisms. They are a major consumer of primary producers, such as phytoplankton that create their energy from sunlight through the process photosynthesis. Zooplankton are then eaten by larger marine creatures, which facilitates the passing of energy to animals higher in the food web, such as fish, seabirds and marine mammals.

They also influence oceanic biogeochemical cycles by playing an important role in the transfer of carbon through direct and indirect feedback loops, including feeding, excretion, respiration and even death.

Knowledge of how zooplankton are being affected by a changing climate is vital if society is to understand the impact of these changes and evaluate how best to respond.

Long-term datasets were invaluable to help identify the three “universal’ responses of zooplankton to warming:

• shifts in seasonal timing, typically towards earlier seasonal occurrence of spring or summer species and later occurrence of autumn species
• poleward shifts in geographical range and/or to deeper parts of the ocean to maintain optimum water temperature
• shifts towards smaller-sized individuals and zooplankton species in warmer conditions

These changes can have cascading impacts on the efficiency of the ocean’s carbon pump that biologically drives the “capture’ of atmospheric carbon dioxide into the ocean. The shifts can also desynchronise ecological interactions, for example, between predator and prey, and in turn impacting fisheries and climate regulation processes.

Dr Angus Atkinson, Marine Ecologist at Plymouth Marine Laboratory and co-author of the review, commented: “This is an important study that brings together the latest available knowledge of how a warming ocean is affecting zooplankton.”

“As we move into a new technological age of data collection, we can collect enormous amounts of plankton data, for example with environmental DNA or semi-automated particle imaging and classification. This review makes simple and tractable recommendations on how we can integrate these exciting new methods alongside the existing long-term datasets that are essential to understand climate change responses in the sea.”

“We are moving into uncharted territory with climate change posing threats not just from more longer timescale processes like ocean warming but from extreme events, such as storms and heatwaves that can push systems beyond their limits. This review shows just how important it is to preserve the existing and priceless long-term data sets, make past data more accessible and embrace technological developments to gain the level of understanding that we so urgently need”.

Towards an improved implementation of zooplankton monitoring to address global needs

Recommendation Additional information Protect existing and build new time series programmes Time series can be difficult to establish due to lack of long-term funding, lack of widespread understanding of the importance of long time series to the study of climate change-scale processes, and pressures for monitoring programmes to adopt new technology. Even subtle changes (for example, a slight change in net design) require a lengthy parallel intercalibration period to ensure comparability. Additionally, there are large gaps in coastal Asia, South America and much of Africa, and offshore, open-ocean regions where monitoring is crucially needed. Better integrate time series data Efforts are needed to actively engage with monitoring programmes as well as regional and global networks to better integrate time series data. This includes making existing data more easily available, encouraging group efforts to synthesise data across multiple time series, and “rescuing’ and combining old data which will allow for large spatio-temporal studies to understand climate change responses. Broaden our understanding of climate change responses Existing understanding is relatively unbalanced, often dominated by productive, mid latitude shelf ecosystems, and mostly of adult stages of dominant taxa. Copepoda is the most studied zooplankton group with the literature being focused on a few dominant species (for example, many of the Calanus species and the coastal species Acartia tonsa). Modern technology (for example, moorings, acoustics, molecular approaches, particle imaging) can be used to increase observations in poorly sampled systems, and address issues such as extreme events (responses to heatwaves or storms). A key focus should also extend observing and data collection efforts for holo- and meroplanktonic taxa (including small or gelatinous forms). Improve cross-disciplinary approaches Time series data, experimentation, and modelling in combination can provide a powerful approach to understand the mechanisms that zooplankton use to adjust to recent climate change. Particularly experiments that examine multiple climatic stressors, as this will enable better understanding of how the biological carbon pump and food web structure may be impacted. Likewise, engagement of zooplankton ecologists with working groups on resource management (for example, fisheries or conservation zones) and policy can ensure the data products are well utilised and will support the continuation of monitoring.