The science of sustainable seafood, explained

Ocean Optimism?

How about a shot of good news to temporarily alleviate the universal despair of the present?

According to new research published last week in Nature, plants and animals in the ocean have a chance to recover within a generation.

Using different indicators of life, like animal populations and habitat degradation, scientists describe a hopeful path forward for living things in the ocean, but the scale and magnitude of climate change looms.  

Key takeaways:

  • Policy measures to protect and rebuild animal populations are working (but the work isn’t done)
  • Pollution and habitat indicators are a mixed bag, but real solutions exist.
  • Though many indicators offer hope, they stand little chance if decarbonization does not happen soon. Climate change policy is the Goliath that will truly determine what life in the ocean is like in 2050.

Rebuilding ocean life

The study chronicled the history and politics of several threats to ocean life over the course of modern society and concluded that if the right policy actions are taken, life in the ocean can fully recover by 2050.

Timeline of threats to the ocean. Figure 1 from Duarte et al 2020.
Many human pressures commenced well before the industrial revolution; a number of those pressures peaked in the 1980s and are slowing down at present (with great regional variation), with the notable exceptions of pollution and climate change. Initially, hunting and fishing were followed by deforestation, leading to excess sediment export and the direct destruction of coastal habitats. Pollution (synthetic fertilizers, plastic and industrial chemicals) and climate change represent more-recent threats. Hunting of megafauna has been heavily regulated or banned and fishing is now progressing towards more-sustainable harvests in many regions, and regulatory frameworks are reducing some forms of pollution. Climate change—caused by greenhouse gas emissions that have accumulated since the onset of the industrial revolution—became considerable compared with background variability in the 1960s, and is escalating as greenhouse gases continue to accumulate. As a net result of these cumulative human pressures, marine biodiversity experienced a major decline by the end of the twentieth century. From Duarte et al. 2020

Animal populations

Threats to animals appear to have peaked in the late 20th century. The rise of ocean conservation groups during that time pushed policies forward and laid the foundation for the current recovery: since 2000, the proportion of marine animals officially listed as threatened has fallen from 18% to 11%. Yet, work remains. Peak threat does not mean end of threats.

However, whales are an encouraging example of how rebuilding populations can progress. Hunting for whales and other marine megafauna peaked in the early 20th century and recovery has been strong.

marine megafauna recovery. Figure from Duarte et al. 2020
Recovery for several marine species. Units are adjusted to a common scale. From Duarte et al. 2020

The authors describe some remarkable comeback stories:

Some large marine species have exhibited particularly notable rebounds, even from the brink of extinction. Humpback whales migrating from Antarctica to eastern Australia have been increasing at 10% to 13% per year, from a few hundred animals in 1968 to more than 40,000 currently. Northern elephant seals recovered from about 20 breeding individuals in 1880 to more than 200,000 today, and grey seal populations have increased by 1,410% in eastern Canada and 823% in the Baltic Sea since 1977. Southern sea otters have grown from about 50 individuals in 1911 to several thousand at present. While still endangered, most sea turtle populations for which trends are available are increasing in size, with increases in green turtle nesting populations ranging from 4 to 14% per year.

International policies like the Convention on International Trade of Endangered Species (CITES) in 1975 and the global Moratorium on Commercial Whaling in 1982 have helped tremendously.  

The authors pointed to global fisheries as another success-in-progress story. Overfishing peaked in the late 1980s and early 1990s and fishery management has been improving ever since. On average, scientifically-assessed fish populations around the world are healthy or improving. Right now, a third of fisheries are overfished while two thirds are sustainably fished. There are several data-deficient fisheries in Asia and West Africa that are probably overfished, but building scientific and enforcement capacity in those places would quickly put them on a path to sustainability.

Fish populations recover quickly once fishing pressure is reduced to sustainable levels—generally within 10 years.

Pollution and coastal habitats

Pollution harms coastal ecosystems like coral reefs, kelp forests, and seagrass meadows. There have been several different kinds of pollution threats over the past century—many have been eliminated or are improving, while others are emerging and peaking.

Improved sewage treatment in the U.S. and Europe in the 1970s has reduced coastal eutrophication and improved water quality. International agreements like the Stockholm Convention and the MARPOL convention have reduced and phased out harmful pollutants: “Time-series analyses show that legacy persistent organic pollutants have declined even in marine environments that tend to accumulate them.” For example, after a global push to switch to unleaded gasoline in the 1980s, lead levels in the ocean have reversed to baseline levels. Despite recent high-profile oil spills, safety regulations have been improving for decades: the 1970s saw 24.7 large oil spills per year, while 2010-2019 saw only 1.7 per year, a 14-fold improvement.

Regulations and international agreements work, but several types of pollution still need to be addressed.

The most immediate threat to life in the ocean is terrestrial food production. Fertilizer use and runoff, which researchers say is currently at maximum threat level, has not yet peaked. Fertilizer and livestock manure runoff cause eutrophication in the ocean, a situation where too many nutrients in the water prompt an algae bloom that deoxygenates the water, suffocating life. Reducing fertilizer use and shifting diets away from terrestrial animal protein (especially cow) is crucial.

Cow production is also the main driver of deforestation. Deforestation loosens soil and sediment which then washes into the ocean and also suffocates coastal ecosystems. Terrestrial woodlands, especially coastal ones like mangroves, play a vital role in marine habitat health.

The authors of the paper highlighted several mangrove restoration projects around the world as important progress, but we continue to lose more mangrove than we gain. An optimistic outlook is that global loss has slowed to just 0.11% per year and reversal is imminent.

Plastic is also mentioned as a modern issue, but plastic seems to be more ugly than dangerous. Yes, some seabirds, whales, and turtles are killed by plastic pollution, but the numbers killed by plastic pale in comparison to other anthropogenic threats.

More good news from the authors:

The recovery of coastal habitats after the removal of stressors or following active restoration of the habitat typically occurs on a similar timescale as fish stock recovery: less than a decade for oyster reefs and other invertebrate populations, and kelp-dominated habitats; between one to two decades for saltmarsh and mangrove habitats; and one to several decades for seagrass meadows. Deep-sea corals and sponges grow more slowly and recovery times from trawling disturbance or oil spills may range from 30 years to more than a century.

Marine protected areas (MPAs) can be a good way to protect and restore these coastal habitats. The authors point to the steady rise in MPAs around the world as progress, but MPAs are controversial and do nothing to prevent the greatest threat to life in the ocean: climate change.

Climate change threatens everything

In the above passage, the authors mention several different kinds of ocean habitat, but coral reefs are conspicuously absent. That’s because coral reef health is the worst it has been in human history and getting worse. Runoff and sedimentation have certainly crippled coral reefs, but the major threat is carbon emissions.

Excess carbon in the atmosphere causes ocean acidification and ocean heating. Coral can’t grow as fast in low pH water while too much heat causes them to bleach, a process that 50% don’t recover from. Coral reefs completely protected and isolated from anthropogenic impacts suffer just like any other under warmer and more acidic water.

In the 20th century, global bleaching events happened every few decades, but, due to unusually warm water caused by climate change, there have been 3 in the past 5 years. The only direct action to save coral reefs is to limit carbon emissions. If carbon emissions are not stopped, they will end coral reefs within the 21st century.

Carbon emissions are also a major threat to ocean animals and other habitat. As the ocean warms, organisms will be forced to migrate toward the poles—areas they were not evolved for. There will be massive shifts in habitat location and abundance. Kelp forests are sensitive to warm water while sea level rise can harm mangroves. Marine animals are especially vulnerable to climate-induced extinction.

In 2016, the world attempted to enact a global policy to limit climate change induced global warming to 2 degrees above pre-industrial levels. The Paris Agreement was signed by nearly every country in the world, but Earth is still on track for 2.6-4.5 degrees of warming (the planet is currently 0.8-1° warmer than pre-industrial levels). The latest IPCC report on climate change suggested that warming needs to be limited to 1.5° to save coral reefs. Stronger policies are needed.

The threat and magnitude of climate change cannot be overstated. It is, by far, the largest threat to life in the ocean and the most important threat to address. According to the authors of the paper, it is “the critical backdrop against which all future rebuilding efforts will play out.”

Overall, the societal benefits that would accrue from substantially rebuilding marine life by 2050 will depend on the mitigation of greenhouse gas emissions and on the development of efficient CO2 capture and removal technologies to meet or, preferably, exceed the targets of the Paris Agreement.

If only there was a momentous global moment where humanity began heeding expert advice and flattening the (global emissions) curve.

Ocean Optimism

Climate change is the most important ocean conservation issue of our time. The scale can seem overwhelming, but there are plenty of reasons to be hopeful. Most importantly, any amount of reduced warming is enormously beneficial. The target is 1.5°, but 2° is still orders of magnitude better than 3° which is orders of magnitude better than 4°. Every bit matters.

Though our time is running out, we still have a legitimate chance at 1.5°. Large-scale decarbonization can happen with the right political leaders and policy prescriptions (i.e. elections have consequences). For example, in the U.S. a “Green New Deal” policy to rapidly decarbonize the country has quickly become popular.

Hope is not lost, we have the blueprint to restore life in the ocean—we just need to execute it.

The most impactful actions you can take:

  1. Advocate, campaign, and vote for policies and leaders that favor the ocean

Other good actions:

  1. Reduce your dietary impact. Read our guide to eating for the planet.
  2. Get your electricity from renewables.
  3. Fly less.
Picture of Max Mossler

Max Mossler

Max is the managing editor at Sustainable Fisheries UW.

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