The world’s oceans constitute over 90% of the habitable space on Earth. They are home to millions of marine species, from fish to squid to plankton. By 2100, without significant changes to mitigate climate change, more than half of the world’s marine species may stand on the brink of extinction.
The 2015 Living Planet Index from the World Wildlife Fund reported a nearly 50% decline in marine life populations between 1970 and 2012. Many of these species are vital food sources for many countries, especially for poorer nations that rely primarily on the fish population for food. Populations of locally and commercially fished species have also fallen by half. The tuna and mackerel populations, for instance, have seen a nearly 75% decline. Meanwhile, Bluefin tuna in the Pacific are on the brink of extinction.
"The ocean is a renewable resource that can provide for all future generations if the pressures are dealt with effectively. If we live within sustainable limits, the ocean will contribute to food security, livelihoods, economies, and our natural systems,” Marco Lambertini, director-general of WWF International, said.
The researchers identified two main factors for the decline: the decline in fish habitats and pollution. According to CNN, an American news-based pay television channel owned by AT&T's WarnerMedia, many of the mangroves and seagrasses have been lost while the oceans' tropical reefs have decreased by half and could all be lost by the year 2050. Also, humans dump tons of plastic in the oceans, harming all marine species.
The Marine Megafauna
Marine megafauna, the largest animals in the oceans, serve key roles in ecosystem functioning. They play a critical role in the health of our oceans’ vast ecosystems, and thus the survival of all marine life. This group of large ocean creatures is important in ocean ecosystems by eating smaller organisms, transporting nutrients via waste and connecting habitats during long migrations. Previous studies show that they live not only in oceans but also mangrove forests, seagrass meadows, and saltmarshes. Green turtles and manatees, for instance, are known to eat seagrass, and dolphins hunt in mangroves.
A study published in the journal Trends in Ecology and Evolution revealed that far more megafauna species use coastal wetlands than we thought. According to The Conversation, a network of not-for-profit media outlets that publish news stories written by academics and researchers, this includes 80% of dugongs and manatees, 57% of sea turtles, 35% of crocodiles and alligators, 28% of dolphins and porpoises, 26% of otters, minks, and seaks, and 11% of sharks and rays.
Unfortunately, just like other species, marine megafauna are also on the brink of extinction. In 2017, researchers discovered that around a third of marine megafauna disappeared about two to three million years ago. The team investigated fossils of marine megafauna from the Pliocene and the Pleistocene epochs (5.3 million to around 9,700 years BC) for this study. This extinction event has affected marine mammals, which lost 55% of their diversity. The findings revealed that as many as 43% of sea turtle species, 35% of sea birds, and 9% of sharks were lost.
Marine Megafauna Extinction Will Lead to Huge Loss in Functional Diversity
A recent study revealed that marine megafauna is most at risk from climate change. According to Daily Mail, a British daily middle-market newspaper published in London in a tabloid format, 1 in 5 of the world’s large marine animals go extinct in the next 100 years. "The extinction crisis challenges scientists to better measure biodiversity: how will the total variety of life on Earth be affected as human activities lead to the losses of more-and-more species?" the researchers said.
The largest ocean animals, while they have a stronger way to protect themselves, face high levels of threat from human activities such as fisheries and climate change. In this study, the researchers ran two different extinction scenarios to understand the extent of ecological functions they perform in marine systems. The first one required the team to look at the extinction probability of the species based on their current IUCN (International Union for Conservation of Nature) status. In the second, they assumed all species listed as threatened, around 40% had gone extinct.
The findings showed that an estimated 18% of marine megafauna could go extinct in the next century, reducing the functional richness of global ecosystems by 11%. If all threatened species went extinct, functional richness fell by 48% across the world. According to Newsweek, an online site that provides in-depth analysis, news and opinion about international issues, technology, business, culture and politics, the researchers discovered that sharks would be hit hardest, with greater losses in terms of functional richness.
"We already knew that sharks are one of the most threatened groups in the ocean. They are also very vulnerable due to their large size and low reproductive rate. Our results show that future extinctions would be selective against the most functionally unique and specialized shark species, resulting in greater projected losses,” the researchers said.
Researcher Douglas McCauley from the Marine Science Institute at the University of California Santa Barbara said that sharks appear to be more vulnerable because they are already undergoing significant declines and local extinctions in many regions. Several factors also contribute to them being especially susceptible to extinction. Their extinction would be a major blow in conservation efforts because of their unique and irreplaceable roles in ecosystems.
In their previous study, the researchers found out that marine megafauna had suffered an unusually intense period of extinction as sea levels oscillated several million years ago. Today, they face an even larger threat from human pressures. According to Phys.org, an internet news portal that provides the latest news on science, the findings showed not only a diverse range of functional traits held by marine megafauna but also how the current extinction crisis might affect their functional diversity.
"Our results show that among the largest animals in the oceans, this so-called "redundancy" is very limited—even when you roll in groups from mammals to mollusks. If we lose species, we lose unique ecological functions. This is a warning that we need to act now to reduce growing human pressures on marine megafauna, including climate change while nurturing population recoveries,” co-author Dr. John Griffin said.