Jane Watson has studied sea otters for decades, but it was in the 1990s that the BC ecologist observed that they had a destructive habit. As conservationists worked diligently to restore damaged seagrass prairies elsewhere in the world’s oceans, it seemed ironic that in the seagrass habitat of northern Vancouver Island, which is much healthier than others around the world, furry floats scurry and dig for clams, dislodging aquatic vegetation.
As she and others surveyed the sandy bottoms marked with clam pits, Dr Watson noted anecdotally that in places where otter populations were long established, the grass, also known as name of eelgrass, seemed to flower more frequently.
She wondered: Did these disturbing otters influence plant reproduction? She sat on the idea for decades, but her curiosity later inspired one of her undergraduate students at Vancouver Island University. Years later, that intuition was found to be correct in an article published Thursday in Science and led by former student Erin Foster, now a research affiliate at the Hakai Institute.
Research by Dr Foster and his colleagues shows that sea otters are like eelgrass elephants. Their disturbance, as they dig for clams and dislodge the roots of eelgrass, stimulates sexual reproduction among vegetation. This sexual activity, unlike reproduction by natural cloning, stimulates the genetic diversity of eelgrass and improves the resilience of the ecosystems in which both otters and eelgrass live.
The results underscore the importance of restoring extinct predators like sea otters to marine ecosystems, whose foraging cascades throughout the environment.
Mary O’Connor, a seagrass ecologist at the University of British Columbia’s Biodiversity Research Center who was not involved in the study, praised the research, saying that if the impacts genetics of major predators on other parts of ecosystems are understood in ecological theory, “it’s really hard to see, and they made it clear.
Eelgrass, says Dr. Foster, has two modes of reproduction. It can reproduce asexually, by cloning from roots. Or eelgrass can reproduce sexually, producing flowers which are pollinated and produce seeds. Sexual reproduction, producing unique combinations between distinct plants, is like playing the genetic lottery. Cloning, on the other hand, makes each offspring genetically identical.
While pursuing her doctorate at the University of Victoria, Dr. Foster devised a sophisticated test to determine if sea otters were influencing eelgrass reproduction. Working with Dr Watson and 11 other ecologists, evolutionary biologists and geneticists, Dr Foster examined the genetic signatures of eelgrass, taking plant tissue samples from three types of sites along the coast of the Great Rainforest. Bear and western Vancouver Island.
At some sites, sea otters had been absent for over a century, a long-term consequence of the fur trade in Europe. In others, reintroduced otters had been present for decades. And in a third subset of survey sites, otters had been present for less than 10 years. By painstakingly collecting eelgrass shoots for DNA analysis, Dr Foster predicted that eelgrass grasslands with a longer-term presence of otters should have higher levels of genetic diversity.
She also tested the impacts of latitude, depth, grassland size and temperature. But she found that the most influential factor for the genetic diversity of eelgrass was the length of occupation of sea otters. Digging sea otters increased the possibilities of seedling germination, increasing the genetic diversity of the sea. eelgrass up to 30 percent.
The team notes that otters are not the only driver of eelgrass genetic diversity. In the past, eelgrass bloom may have been aided by the now extinct or rare megafauna, or by the traditional indigenous harvest of eelgrass. rhizomes and seeds, a practice that declined with European colonization.
Seagrass meadows provide rich food and protective habitats for marine life around the world. The seagrass patches that support otters on these remote British Columbia shores are unusually pristine, but elsewhere many are threatened by agricultural runoff, boating and coastal development. By better understanding the factors that could make this underwater carpet essential for genetically healthier life, said Chris Darimont, co-author of the study also at the Hakai Institute, this sea otter research shows “a another way for a predator to hedge our bets against an uncertain future.