How Steller’s Sea Cows Impacted the Environment They Left Behind

This article comes from Hakai Magazine. It is an online publication that covers science and society in coastal ecosystems. You can find more stories like these at
A Steller's sea-cow grazed on kelp leaves in the cold waters of Russia's Commander Islands. The buoyant giant protected her calf from predators by staying close to the shore. Seabirds ate parasites from their skins while perched on their exposed backs. These giant sirenians died here 250 years ago. In 1768, the last Steller's sea cow died and was eaten by greedy fur traders who had been collecting pelts from the sea otters of the area. The ecological ghosts and giants that remained likely had devastating effects on the marine ecosystem. A new study has shown that megaherbivores had an impact on the dynamics of kelp forests in the northern Pacific Ocean.

Megafauna, which include whales and wooly mammoths are large-bodied, charismatic creatures. Megaherbivores, which can weigh over 1,000 kilograms, are typically animals that weigh more then 45 kilograms. These giants were more common in the past and left a lasting impact on the ecosystems they inhabited. Many of these giants have been driven to extinction by climate change, hunting, habitat loss, and other factors. This has had untold implications for ecosystem function.

In 1741, Georg Wilhelm Steller, a naturalist from Germany, first described Steller's sea cattle in Western science. They were extinct within 30 years. Steller's sea cattle weighed in at approximately 5,000 kg and measured more than seven metres. According to historical accounts, Steller's sea cattle could not submerge completely and were forced to graze near the surface. A significant number of people lived in the North Pacific coast, from Mexico to Alaska to Japan, before they were eradicated.

It is difficult to determine how an extinct species has affected its environment. There are many theories. Cameron Bullen, a marine ecoologist, conducted the research as part of his master’s thesis at the University of British Columbia. He analyzed Steller's observations of sea cow behavior and biology and compared them with archaeological evidence and knowledge of coastal environments. This allowed him to determine how giant sirenians might have affected ecosystem dynamics. While it is impossible to determine how megaherbivores might have affected kelp forests in the wild, he says that "it's difficult to imagine that they wouldn’t have had any impact whatsoever."

Bullen states that "[Steller’s] sea cows could have changed how other species might have interacted and increased the productivity kelp forests." The kelp's understory would have received more sunlight thanks to their consumption, which would have been beneficial for the kelps below. Sea cows could have grazed on the kelp and spores within the ecosystem, as well as to other parts.

Helene Marsh, an expert on dugongs at James Cook University in Australia, said that a modern analog to the Steller's Sea Cow is the dugong. She was not part of the study. Marsh explains that dugongs live in coastal seagrass meadows along the Indian Ocean and parts the Pacific Ocean. Marsh explains that they are ecosystem engineers and dig up seagrass meadows to eat plants and then spread seeds.

Marsh states that if dugongs were gone, it would not have any significant climate change. However, this would mean that the "community composition" of seagrasses would be drastically altered over a long period. Marsh says it is unlikely that they will disappear anytime soon. The population of dugongs in Australia is healthy, despite being vulnerable worldwide.

Paul Dayton, a marine ecologist with Scripps Institution of Oceanography, University of California San Diego, answers the question of scientists about how Steller's sea cattle would have created kelp forests. Although he was not part of Bullen's research, he was happy to see that someone was taking a serious look into the ecological significance of these extinct sea cattle. Dayton is not sure about Bullen's hypotheses but he believes that sea cows would have played a role in the thinning of the kelp canopy, increasing the productivity and diversity understory.

Bullen states that it is crucial to understand how extinct megafauna have affected the environment when trying to restore habitats. Bullen says that ecosystem changes are often compared to the past, and should not be assessed in relation to the present.

Bullen says, "We look at the kelp forests in all their wonder...but you don't see the things that might have been there if they weren't for humans or other influences." The ecological ghosts of sea cattle "is a great way to really understand these ecosystems' past and present."

This article comes from Hakai Magazine. It is an online publication that covers science and society in coastal ecosystems. You can find more stories like these at

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