Oceans in Balance
Marine biodiversity is essential and it’s up to humans to restore and protect it
Reprinted from the July 2016 edition of the journal Biodiversity.
Biodiversity is essential to healthy oceans, which in turn help stabilize the planet. There’s a growing body of research showing that marine ecosystems with a wide array of species and functions have well-balanced food webs and they’re more able to adapt to climate change, the current extinction crisis and other major ecological disruptions.
Generations of overfishing and poor fishery management removed most of the large fish from the ocean and brought many whale species to the brink of extinction. Those are the most obvious impacts to the oceans’ biodiversity, but scientists have begun to develop more detailed understandings of the complex dynamics involved in this vast aquatic space.
For example, if a region loses its apex predators like sharks or bluefin tuna — or important keystone species such as sea otters — it causes cascading effects that ripple out through the entire ecosystem, impacting all the plants and animals in the area. Scientists have long understood this process, known as ‘trophic cascades’, but current research indicates the effects are more far-reaching than they thought.
“Recent research suggests that the disappearance of these animals (apex predators) reverberates further than previously anticipated, with far-reaching effects on processes as diverse as the dynamics of disease; fire; carbon sequestration; invasive species; and biogeochemical exchanges among Earth’s soil, water and atmosphere.” James Estes and 22 research colleagues wrote in a seminal 2011 paper for Science called ‘Trophic downgrading of planet Earth’.
Humans are the greatest threat to marine biodiversity, mostly notably through climate change, overfishing and pollution. Scientists say as much as one-third of marine species face extinction pressures due to human impacts. Yet we also have the power to reverse these troubling trends if we can acknowledge the problems, promote greater public awareness and marshal the will and resources to protect and enhance biodiversity in the ocean.
In fact, there’s a self-reinforcing mechanism to humans promoting a more balanced approach to the natural world. The less we deplete our ocean of its biodiversity, the more we strengthen its ability to resist the other impacts that we’ve set in motion, such as global warming and ocean acidification.
One study that established that connection — ‘Biodiversity enhances reef fish biomass and resistance to climate change’, by Emmett Duffy and four other researchers — received extensive media coverage when it was released in Spring 2016, in the months following the international climate accord reached in Paris.
At a time when ocean warming had already caused the life-draining bleaching of the Great Barrier Reef and other coral reefs, the report was another wake-up call. Studying 4556 standardised fish surveys from around the world, the researchers showed how biodiversity creates resilience in important reef ecosystems. And that’s crucial for oceans and the people who depend on them.
“Fishes are the most diverse group of vertebrates, play key functional roles in aquatic ecosystems and provide protein for a billion people, especially in the developing world. Those functions are compromised by mounting pressures on marine biodiversity and ecosystems. Because of its economic and food value, fish biomass production provides an unusually direct link from biodiversity to critical ecosystem services,” Duffy and his colleagues wrote.
They looked at 25 environmental drivers to test the importance of biodiversity to the different levels of fish biomass in reefs around the world. The strongest contributors to healthy fish populations were the richness of fish species and the diversity of functions they performed in their environments. And three factors accounted for almost half of the difference between healthy and disturbed reef communities: temperature, biodiversity and human influence.
Those three factors are closely related, particularly the last two. A 2014 research paper by Elizabeth Selig and eight other prominent ocean researchers, ‘Global priorities for marine biodiversity conservation’, concluded there was one key culprit in the crippling loss of biodiversity in the oceans: humans.
“Widespread impacts of human activities on the oceans continue to cause declines in species diversity and abundance. As recognition of the benefits that healthy marine ecosystems provide to people increases, protecting biodiversity and the essential ecosystem services it supports has become a priority for the scientific community, resource managers and national and international policy agreements, including the Convention of Biological Diversity,” Selig and her colleagues wrote.
Maintaining ocean biodiversity in a world that’s being dangerously altered by human activities — from overfishing to global warming — is a major challenge, as a pair of reports from 2015 indicates. In ‘Forecasted coral reef decline in marine biodiversity hotspots under climate change’, researchers concluded that “Coral bleaching events threaten coral reef habitats globally and cause severe declines in local biodiversity and productivity. Related to high sea surface temperature, bleaching events are expected to increase as a consequence of future global warming.”
A second paper, ‘Marine defaunation: Animal loss in global oceans’, discussed the cascading impacts of overfishing and removal of important species from the oceans. Basically, we’re out of balance, a conclusion of more recent reports showing that squid, octopi and other cephalopods in the ocean are increasing in abundance as their predator populations are reduced. Biodiversity is about balance.
Yet this paper also arrives at a hopeful conclusion that it’s still within our power to restore biodiversity in our oceans: “Wildlife populations in the oceans have been badly damaged by human activity. Nevertheless, marine fauna generally are in better condition than terrestrial fauna: Fewer marine animal extinctions have occurred; many geographic ranges have shrunk less; and numerous ocean ecosystems remain more wild than terrestrial ecosystems. Consequently, meaningful rehabilitation of affected marine animal populations remains within the reach of managers. Human dependency on marine wildlife and the linked fate of marine and terrestrial fauna necessitate that we act quickly to slow the advance of marine defaunation.”
We have a similar ability to alter the course of climate change, ocean acidification, ocean warming and other results of our overreliance on burning fossil fuels. Simply put, we must keep more fossil fuels safely in the ground, control the release of carbon dioxide and other greenhouse gases, transition rapidly to renewable energy sources and help the developing world find alternatives to taking our same destructive, carbon-intensive path to prosperity.
This year, the Obama administration will make important decisions on whether to open up federal lands and waters to more fossil fuel development and how the United States can lead the fight to reduce carbon emissions around the world to keep global temperature increases less than 2 degrees Celsius. This is an important time for addressing global climate change, and also a pivotal moment for maintaining ocean biodiversity.
The Endangered Species Act (ESA) is a powerful tool for protecting biodiversity, successfully helping 99 per cent of listed species from going extinct. Conservation groups just filed an ESA listing petition for the Pacific bluefin tuna, whose popularity with sushi lovers and sports fisherman has depleted its population by more than 97 per cent. Saving this powerful migratory fish from its own popularity is a prime example of the work we need to do.
We must reduce our emissions, stop overfishing, protect vulnerable species and recognize our responsibility to be wise stewards of the vast ocean environment on which all life depends.
Steven T. Jones is a long-time California journalist who now works for the Center for Biological Diversity in its oceans program.