DIAPOD was one of the original four projects that kick started the Changing Arctic Ocean Programme. This has now grown in to 16 projects that each investigate a different aspect of the Arctic Ocean, from the food chain, to the sea ice, to the seafloor. Together, these projects will give a holistic view of how this region is responding to change. DIAPOD is interested in how ocean warming is influencing the single main food source at the bottom of the food chain – copepods! But what are copepods? And why are we interested in them?

Copepods: known and unknown

Copepods are an important part of the zooplankton community – the tiny drifting animals in the ocean that feed mainly on microscopic plants (phytoplankton). Copepods are crustaceans, are as small as a tip of a needle, and are found in many marine and freshwater environments. In the Arctic, the most abundant copepods come from the group known as Calanus – they make up 90% of the zooplankton -and they are the preferred food for many important fish and seabird species.

Calanus copepods are highly adapted to the extreme Arctic Ocean. For example, after fattening up and storing reserves in their lipid sacs over spring, Calanus copepods sink to deeper depths to escape the harsh Arctic winter and undertake a hibernation known as diapause. The length and timing of diapause can vary between species and regions, yet the direct controls of this behaviour and life cycle, whether environmental, chemical, genetic, or otherwise, remain poorly understood.

Outline of a lipid sac in a Calanus copepod -Sarah Reed

“Our project is trying to unravel the mechanisms behind one of the largest migrations of biomass of Earth, the sinking of millions of tiny organisms called copepods each autumn from surface waters to great ocean depths to hibernate over winter. We still do not know what triggers their migration to depth or what factors wake them up again to re-ascend to the surface the following spring. The DIAPOD team will be collecting samples to examine the chemical composition of the microscopic food of copepods to determine if there are key components that these organisms need before they can enter hibernation.” – Principal Investigator, Professor David Pond.

Consequences of climate change

Phytoplankton blooms help allow Calanus to dominate the Arctic zooplankton by facilitating large lipid reserves which crucial for the copepods strategy of overwintering in the deep sea. However, current data and future predictions are suggesting that phytoplankton communities are changing both in the size of the phytoplankton species present, and in the timing of their bloom. These changes could lead to a miss-match in the life-cycle calendar of Calanus which many have consequences for their reserves, their diapause, and their dependent predators.

A successful catch of copepods during an Arctic research cruise – Sarah Reed

“Continued global warming throughout the 21st century is expected to exert a strong influence on the timing, magnitude and spatial distribution of diatom [phytoplankton] 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. Hence, the need to study this area of the Arctic in situ”. – Principal Investigator, Professor David Pond.

By conducting three Arctic research cruises combined with laboratory experiments and computer models, DIAPOD aims to gain a deeper understanding of Arctic Calanus species, their life cycle events such as diapause, and how they may be affected by climate change. Moreover, because of their huge biomass in the Arctic Ocean, any changes to the abundance, size, or distribution of Calanus species will have consequences for the Arctic ecosystem too. Thus, by studying these small-but-mighty keystone species, we will not only gain insights into the impacts of climate change on Arctic biology, but also on the biochemistry and wider health of this polar ecosystem.

Midnight zooplankton nets – Sarah Reed

DIAPOD is funded by NERC and brings together scientists from Stirling University, Scottish Association for Marine Science, Liverpool University, Leeds University, The National Oceanography Centre, British Antarctic Survey and many more international partners. You can read more about our science here.