A longstanding view of the Arctic food web places polar bears firmly at the top of the chain, but new research suggests a more complex picture. A study published in Ecology details how certain starfish species may also function as apex predators, notably within the often-overlooked seafloor ecosystem. This finding, based on analysis of marine life around Southampton Island in Nunavut, Canada, underscores the need to reassess traditional understandings of Arctic marine ecosystems-and the interconnectedness of life within them.
For decades, polar bears have been considered the apex predators of the Arctic. However, a new study suggests that certain species of starfish may also occupy the top rung of the local food web, particularly when considering the ocean floor ecosystem. The research, published in the journal Ecology, challenges conventional understanding of Arctic marine ecosystems.
A food web represents the complex network of feeding relationships between species within an ecosystem. These networks are built from primary producers – organisms that derive energy from sunlight or the breakdown of organic matter – supporting lower trophic levels, which in turn transfer energy up to apex predators. Understanding these relationships is crucial for assessing the health and stability of an environment, especially as climate change impacts species distribution and abundance.
Marine food web research often focuses on the pelagic zone – the open water column. In the Arctic, this traditionally starts with microscopic plankton and extends upwards to polar bears (Ursus maritimus). However, the benthic zone – the seafloor – has been comparatively understudied, often perceived as a less complex food chain with lower trophic level species.
The new research demonstrates that the benthic component of the Arctic food web has been significantly underestimated.
Two Distinct, Yet Interconnected Sub-Networks
Researchers from Université Laval analyzed 881 samples of benthic invertebrates representing 97 taxonomic groups and nine phyla, alongside 699 samples of pelagic fauna – including invertebrates, demersal and pelagic fish, seabirds, and marine mammals – representing 53 species from twelve taxonomic groups. The samples were collected in the marine waters around Southampton Island in Nunavut, Canada, located at the mouth of Hudson Bay.
The analysis revealed that both the benthic and pelagic components of the ecosystem had a similar number of trophic levels, or steps, in their respective food chains.
“This is a shift in our understanding of how the coastal marine food web functions in the Arctic,” said Rémi Amiraux, the study’s lead author. “We’ve shown that the fauna inhabiting the water column and those living in the sediments form two distinct, but interconnected sub-networks.”
Starfish at the Top
The study also found that starfish, particularly those belonging to the family Pterasteridae, play a key role in the benthic network, occupying various trophic levels. Some Pterasteridae species consistently appeared at the top of individual food chains, preying on secondary predators such as bivalves, sea cucumbers, and sponges. This means these starfish hunt at a comparable scale to polar bears, differing primarily in prey size.
Like polar bears, which will scavenge on whale carcasses when available, allowing them to survive for weeks, these starfish also opportunistically feed on dead pelagic organisms that sink to the seafloor, reducing their need to hunt frequently.
The findings underscore the importance of considering benthic food webs in Arctic ecosystem studies. Given that Pterasteridae starfish are found in nearly all marine ecosystems, researchers suggest that if they exhibit similar behavior in other environments, they could be considered among the most effective predators in the ocean. This research highlights the need for a more holistic understanding of marine ecosystems as climate change continues to reshape the planet.
