Zooplankton, a key component of most marine ecosystems, are rapidly responding to climate change. A new paper shows how various species are affected, and highlights that coordinated, sustained ocean observations will be essential to understand how ecosystems will continue to function in our changing environment.

Dr. Kim Bernard’s student, Giulia Wood, examining krill samples. Credit: Dr. Kim Bernard

It’s an early winter morning at Palmer Station, Antarctica. A team of researchers jump into their thermal, waterproof clothes and head down to the aquarium room that houses tanks filled with Antarctic krill – small, yet highly important marine zooplankton that are a keystone species in the food web of the Southern Ocean. The temperature in the room is around 0 degrees Celsius, it’s cold, damp and almost completely dark.

“We can only use red lights when we come down here. White light stresses the krill out at this time of year,” says Dr. Kim Bernard, biological oceanographer at Oregon State University. Having dreamt of working in Antarctica since she was a teenager, Dr. Bernard has now spent a total of 39 months in the coldest continent of our planet across several research expeditions. 

While on a research vessel on their way to Palmer Station, Dr. Bernard’s team collected thousands of live krill from the cold waters of the Southern Ocean. These were then placed in tanks in the dark aquarium room where the teams can study how these tiny animals are affected by changing environmental conditions.

“Zooplankton are an essential part of most marine food webs. If we speak about Antarctic krill specifically, blue whales, humpback whales, a whole variety of seals, penguins and other seabirds all feed on it – some of them exclusively. And if they are not feeding on krill, they are feeding on something else that does,” says Dr. Bernard. 

“Krill and other zooplankton also play a major role in various biogeochemical cycles. For example, they take carbon out of the surface waters and transfer it down to the deep sea, which is important for our climate,” she adds.

Dr. Bernard looking at a sample of Antarctic krill – tiny crustaceans that can reach a maximum length of 6 centimetres. Credit: Dr. Kim Bernard

Responses to a changing climate         

A recently published Nature Communications paper, produced as part of activities of the Global Ocean Observing System’s (GOOS) Expert Panel on Biology and Ecosystems, and which Dr. Bernard co-authored, provides an extensive review of various studies that show how zooplankton is being affected by climate change. 

A warming ocean favours some zooplankton species over others, but most of them are experiencing a set of universal responses to these changing conditions: peaks in zooplankton abundance are shifting in timing, the animals themselves are getting smaller, and their geographic range is moving either polewards or to the deeper layers of the ocean.

“It is only 50 years ago that an English fisheries scientist, David Cushing, hypothesised the importance of the match and mismatch between zooplankton and larval fish that feed on them for the growth of the adult populations of the fish we like to eat. Now the challenge is to monitor and understand what happens as zooplankton change their times and places of peak abundance out of sync with the fish, bird and mammal populations that depend on them,” says Dr. Nic Bax, one of the co-authors of the paper.

“It may not mean disaster, but we need sustained ocean information to help us manage marine ecosystems more effectively. If a species that feeds on zooplankton is under pressure due to these changes, timely knowledge about this will allow us to take action,” he adds.

Left: a zooplankton net lowered from the vessel; right: Dr. Bernard picking out krill. Credit: Giulia Wood

Zooplankton – one of the Essential Ocean Variables

Zooplankton is an Essential Ocean Variable (EOV) – a critical ocean measure that allows efficient monitoring of the state and health of the ocean, and its connection to other elements of the marine ecosystem. The key role of zooplankton in numerous marine food webs and biogeochemical cycles makes sustained observation of its abundance and diversity one of the priorities for the ocean observing community.  

The global efforts to observe this and other biological and ecological EOVs, such as phytoplankton, mangroves, sea turtles or marine mammals, are coordinated by the GOOS Biology and Ecosystems Panel, which Dr. Bernard, Dr. Bax and several co-authors of the paper contribute to.  

Yet, the paper mentions there are important gaps in our ability to observe long-term and global changes in zooplankton abundance and diversity. “Comprehensive and sustained monitoring of the marine ecosystem in general is rare, especially below the surface. In situ monitoring of zooplankton and other marine life is often not a priority for research agencies and philanthropic organisations,” says Dr. Bax. “It is only through sustained monitoring that we can measure how the marine system functions and how it is changing as a result of humanity’s actions,” he adds.

Another problem is the poor accessibility and interoperability of existing data. The findings of the paper show that 81% of zooplankton data collected from long-term monitoring programmes around the world are either only partially available, or not publicly available at all. 

“The global extent of many marine pressures such as climate warming, acidification and pollution means that as a scientific community we also need to collaborate globally. GOOS has adopted FAIR (findable, accessible, interoperable and reusable) data principles and promotes making existing data more open, so this costly resource can be used and reused. That is a critical first step in the scientific community coming together to address global issues,” says Dr. Gabrielle Canonico, co-chair of the GOOS Biology and Ecosystems panel.

Even when the data are publicly available, comparing it with other datasets is often challenging as many research groups use different techniques when sampling zooplankton. This brings attention to the importance of developing and promoting standardised best practices for zooplankton observing, a task the GOOS Biology and Ecosystems Panel is also working on.

“Increased coordination and targeted extension of the many existing observing networks will be necessary to build a sustained and comprehensive ocean observing system under the GOOS framework. One that allows us not only to understand the current state of our ocean, but also build effective and accurate forecasts of its future states. This will help our societies adapt to a changing environment and ensure sustainability,” says Dr. Karen Evans, co-chair of the GOOS Biology and Ecosystems Panel. 

Dr. Bernard’s student, Giulia Wood, gathering caught zooplankton specimens. Credit: Mike Tift

Packing up for another expedition to Antarctica

Huge progress has been made in understanding these tiny animals of massive importance, but our current knowledge is mostly based on data from the Northern Hemisphere. Much less is known, for example, about the main focus of Dr. Kim Bernard’s research team: the Antarctic krill in the Southern Ocean.

“They are the most important part of the Antarctic ecosystem. With climate change and the decrease in sea ice, their food sources are changing as well, that’s why it is so important to understand how krill is reacting to these changes,” says Dr. Bernard. Sharing these observations from sustained monitoring globally and connecting different trends in zooplankton populations around the world will enable us to better manage the ocean.

Now back in Oregon, United States, Dr. Bernard is preparing for another 5 month long visit to the research station in Antarctica. “It does get quite tiring, I won’t lie. But it’s such a beautiful place and I love it. I also get to take students with me, and that is an incredible opportunity for them.”