A polar bear carries a seal carcass along the Arctic coast. (Image credit: Shutterstock) (opens in new tab)
In coastal ecosystems ca Arctic peninsula, polar bears they have long been considered top predators. But a new study suggests starfish could be surprising contenders to rival the famous polar bears at the top of the local food web.
A food web is an extensive map of ecological relationships that combines all the different food chains in an ecosystem. Individual food chains contain primary producers that derive energy from the sun or by recycling dead organic material; primary users that feed on primary users; and then secondary or tertiary users who attack all users below them. But organisms in one food chain can also have a place in another, or multiple others, so the best way to see how an ecosystem works is to link those chains together.
In marine food webs, researchers often focus on pelagic, or open-water, food chains that range from small, surface-dwelling plankton all the way up to large predators such as polar bears (Ursus maritimus), which often stand at the top of multiple food chains. But the seafloor, or benthic kingdom, is often overlooked in marine food webs because scientists believe there are no true top predators.
But in a new study published on December 27, 2022 in the journal Ecology (opens in new section), researchers took a closer look at the coastal marine ecosystem in the Canadian Arctic and found that the benthic component of the region’s food web has been greatly underestimated. The research team created a detailed map of the various food webs around Southampton Island, at the mouth of Hudson Bay in the Canadian territory of Nunavut, and found that the benthic part of the web has just as many connections as its pelagic counterpart, as well as its own polar bear equivalent – predatory starfish.
Connected: A swarm of rainbow-colored starfish devours a sea lion carcass on the sea floor
Diagram showing the food web of Southampton Island. Blue arrows indicate pelagic interactions, brown arrows indicate benthic interactions, and green arrows indicate interactions between pelagic and benthic food chains. (Image: Amiraux et al./University of Manitoba) (opens in new tab)
“This is a shift in our view of how the coastal Arctic marine food web works,” the study’s lead author Remy Amirau (opens in new section), a marine ecologist at Laval University in Canada, who was at the University of Manitoba when the study was conducted, said in statement (opens in new tab). “We have shown that seawater-dwelling and sediment-dwelling wildlife form two distinct but interconnected sub-networks.”
The researchers analyzed data on 1,580 individual animals living in the coastal ecosystem of Southampton Island to create the new food web. They found that the benthic and pelagic components had a similar number of steps or trophic levels in their respective food chains.
Starfish were a key part of the benthic food web, occupying a variety of trophic levels, but one family, the Pterasteridae, was consistently at the top of most individual food chains. The researchers found that these starfish feed on a range of secondary consumers, including bivalves, a group of molluscs whose bodies are protected by a hinged shell, sea cucumbers and sponges. This means that Pterastidae starfish hunted on an equivalent scale to polar bears, which hunted walruses, seagulls, beluga whales (Delphinapterus leucas) and ringed seals (Pusa hispida). The main difference between polar bears and starfish was the size of their prey.
A starfish of the Pterasteridae family on the sea floor of Washington’s Olympic Coast National Marine Sanctuary. (Image: National Oceanic and Atmospheric Administration (NOAA)) (opens in new tab)
In addition to being among the most successful predators in the entire ecosystem, starfish and polar bears Pterasteridae also share the ability and desire to scavenge, which researchers say has allowed both groups to thrive in the Arctic.
Starfish opportunistically fed on dead pelagic organisms that sank to the sea floor, which meant they had to hunt less often. Similarly, polar bears can forage for whales that have been dumped dead, which can sustain them for weeks or even months, the researchers wrote in the study.
The team believes the new findings highlight the importance of seafloor food chains in many other marine food webs. Pterasteridae starfish are found in almost all marine ecosystems, and if they are as successful elsewhere as in the Arctic, they may prove to be some of the most successful predators in the ocean, the researchers wrote.
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