As the earth heats up, the oceans, the source of all life, are undergoing rapid, ominous changes capable of dramatically altering the context of human existence.
We begin with a briefing from the World Bank:
Billions of people worldwide —especially the world’s poorest— rely on healthy oceans to provide jobs and food, underscoring the urgent need to sustainably use and protect this natural resource.
According to the OECD, oceans contribute $1.5 trillion annually in value-added to the overall economy. The FAO estimates that around 60 million people are employed in fisheries and aquaculture, with the majority of those employed by capture fisheries working in small-scale operations in developing countries. In 2016, fisheries produced roughly 171 million tons of fish, with a “first sale” value estimated at US$362 billion, generating over US$143 billion in exports. Moreover, fish provided about 3.2 billion people with almost 20 percent of their average intake of animal protein, even more in poor countries [emphases added].
Healthy oceans, coasts and freshwater ecosystems are crucial for economic growth and food production, but they are also fundamental to global efforts to mitigate climate change. “Blue carbon” sinks such as mangroves and other vegetated ocean habitats sequester 25 percent of the extra CO2 from fossil fuels and protect coastal communities from floods and storms. In turn, warming oceans and atmospheric carbon are causing ocean acidification that threatens the balance and productivity of the oceans.
While ocean resources have the potential to boost growth and wealth, human activity has taken a toll on ocean health. Fish stocks have deteriorated due to overfishing — the share of fish stocks outside biologically sustainable levels rose from 10 percent in 1974 to 32 percent in 2013, while in the same year approximately 57 percent of fish stocks were fully exploited. Fish stocks are affected by illicit fishing, which may account for up to 26 million tons of fish catches a year or more than 15 percent of total catches. . . Fish habitats are also under pressure from pollution, coastal development, and destructive fishing practices that undermine fish population rehabilitation efforts.
Oceans are also threatened by marine plastic pollution and each year, an estimated 8 million tons of plastic enter the oceans, with microplastics becoming part of the food chain. Five countries produce the highest volumes of plastic waste and researchers estimate that a 75 percent reduction in plastics pollution in just China, Indonesia, the Philippines and Vietnam could reduce the flow of plastic into the ocean globally by almost 45 percent.
Threats from over-fishing
The World Wildlife Fund’s Living Planet Report 2018 notes that “Zones of moderately heavy to heavy fishing intensity now wrap around every continent, affecting all coastal areas and many parts of the high seas. This implies that fishing activities have exposed shallow coastal marine ecosystems to potential long-term damage, notably by trawling.” The report cites the particularly heavy intensification in the global South and East over the past six decades, with the greatest intensification in South East Asia.
This map from the report reflects the changes globally [click on the image to enlarge]:
Coral reef bleaching levels hit new heights as seas warm
AVERAGE ANNUAL CATCHES OF THE WORLD’S MARITIME FISHING COUNTRIES IN THE 1950s COMPARED TO THE 2000s.
Blue indicates zero or very minute catches, and yellow indicates light or no fishing. Zones of moderately heavy [ orange] to heavy fishing intensity [red] now wrap around every continent, affecting all coastal areas and many parts of the high seas.
Almost 6 billion tons of fish and invertebrates [e.g. crustaceans and molluscs] have been extracted from the world’s oceans since 1950. Annual catch increased dramatically from 28 million tons in 1950 to more than 110 million tons in 2014. However, since peaking in 1996 at about 130 million tons, catch has been decreasing at an average rate of 1.2 million tons per year.
Marine coral reef bleaching may be the greatest immediate threat, as rising temperatures upset the balance of the delicate reefs which serve as breeding grounds for much of the fish so vital to the lives and livelihoods of some of the world’s poorest peoples. [Also see our previous posts on the subject]
From the National Oceanic and Atmospheric Administration, a look the recent escalation of the crisis and what it might mean:
Historically, global-scale coral bleaching has been associated with El Niño events, which generally raise global temperatures. The first mass coral bleaching was observed during the strong El Niño in 1983, and the first truly global event coincided with the strong El Niño of 1998. The world’s tropical reefs were stressed again during a moderate-strength 2010 El Niño.
The coral-bleaching event of 2014–2017 was unusual not just for its long duration, experts say, but also because it wasn’t entirely due to El Niño. Though an El Niño was anticipated in 2014, it didn’t really materialize until March 2015, yet bleaching-level heat stress was already well underway by that time. A strong El Niño arrived in 2016, and heat stress occurred at 51 percent of the world’s coral reefs into early 2017, when a La Niña was in place.
The 36-month heatwave and global bleaching event were exceptional in a variety of ways. For many reefs, this was the first time on record that they had experienced bleaching in two consecutive years. Many reefs—including those in Guam, American Samoa, and Hawaii—experienced their worst bleaching ever documented. In the Northern Line Islands in the South Pacific, upwards of 98 percent of the coral at some reefs were killed. Reefs in the northern part of Australia’s Great Barrier Reef that had never bleached before lost nearly 30 percent of their shallow water corals in 2016, while reefs a bit farther south lost another 22 percent in 2017.
All told, more than 75 percent of Earth’s tropical reefs experienced bleaching-level heat stress between 2014 and 2017, and at nearly 30 percent of reefs, it reached mortality level. The scientists summarized the event in stark terms:
More than half of affected reef areas were impacted at least twice. This global event has punctuated the recent acceleration of mass bleaching. Occurring at an average rate of once every 25–30 years in the 1980s, mass bleaching now returns about every six years and is expected to further accelerate…. Severe bleaching is now occurring more quickly than reefs can recover, with severe downstream consequences to ecosystems and people.
The accompanying map reveals the sheer extent of coral reef bleaching:
Many coral reefs experienced mass bleaching back-to-back in 2015 [top] and 2016 [bottom]. The likelihood of coral bleaching depends on how high the temperatures are above the annual monthly maximum and how long the unusual heat persists. Scientists track these conditions using satellite-based estimates of Degree Heating Weeks. Alert 1 means coral bleaching is likely. Alert 2 means widespread bleaching and significant mortality of corals are likely. Severe coral bleaching was reported in areas circled in white.
And to make matters worse, yet another heat spike is expected in the coming year, one that might be even worse
Reef bleaching dramatically impacts fish behavior
Way back in out college days, an anthropology prof described the Three Fs of behavior: Feeding, Fucking, and Fighting. The three were often related, he added, as humans often fought for food and sex.
Fish, it seems, are much the same.
Professor Stéphan G. Reebs of Canada’s University of Monckton specializes in animal behavior and has written extensively about fish, including their aggressiveness, the focus of a 2008 paper:
Competition is a fact of life. It can take many forms, but biologists usually recognize two broad categories. In the first one, called exploitative or scramble competition, the contests are like races. The most food goes to the animal that eats the fastest, the best shelter is occupied by whoever reaches it first, and the largest share of eggs are fertilized by those males which produce the most sperm. There is usually little aggression displayed in such cases. However, in the second category, which is called interference or defense competition, animals fight among themselves for the right to monopolize food, to occupy alone a shelter or a territory, or to secure exclusive access to a mate.
And now we learn that coral reef bleaching has marked effects of fishy behavior, effects we suspect could have long-term cascading impacts on the world’s food supply.
From the University of Vermont:
A research team, including University of Vermont scientist Nate Sanders, found that when water temperatures heat up for corals, fish “tempers” cool down, providing the first clear evidence of coral bleaching serving as a trigger for rapid change in the behavior of reef fish.
Publishing in Nature Climate Change [$8.99 to read for non-subscribers],the researchers show how the iconic butterflyfish, considered to be sensitive indicators of reef health, can offer an early warning sign that reef fish populations are in trouble.
The international team of scientists spent more than 600 hours underwater observing butterflyfish over a two-year period encompassing the unprecedented mass coral bleaching event of 2016. Led by marine ecologist Sally Keith of Lancaster University, the team examined 17 reefs across the central Indo-Pacific in Japan, the Philippines, Indonesia and Christmas Island in the Indian Ocean.
During the initial data collection, the researchers were unaware that the catastrophic bleaching event was on the horizon. Once underway, the researchers realized that this serendipitous “natural experiment” placed them in a unique position to see how fish changed their behavior in response to large-scale bleaching disturbance.
The team sprang into action to repeat their field observations, collecting a total of 5,259 encounters between individuals of 38 different butterflyfish species. Within a year after the bleaching event, it was clear that, although the same number of butterflyfish continued to reside on the reefs, they were behaving very differently.
“We observed that aggressive behavior had decreased in butterflyfish by an average of two thirds, with the biggest drops observed on reefs where bleaching had killed off the most coral,” said Keith. “We think this is because the most nutritious coral was also the most susceptible to bleaching, so the fish moved from a well-rounded diet to the equivalent of eating only lettuce leaves—it was only enough to survive rather than to thrive.”
“This matters because butterflyfishes are often seen as the ‘canaries of the reef,'” said Nate Sanders, director of UVM’s Environmental Program and professor in the Rubenstein School of Environment and Natural Resources. “Due to their strong reliance on coral, they are often the first to suffer after a disturbance event.”
Such changes in behavior may well be the driver behind more obvious changes such as declining numbers of fish individuals and species. The finding has the potential to help explain the mechanism behind population declines in similarly disrupted ecosystems around the world.
By monitoring the fishes’ behavior, “we might get an early warning sign of bigger things to come,” said co-author Erika Woolsey of Stanford University. And the new work shows that animals can adjust to catastrophic events in the short term through flexible behavior, “but these changes may not be sustainable in the longer-term,” said co-author Andrew Baird of the ARC Centre of Excellence for Coral Reef Studies at James Cook University.
But it’s not a problem, right?
At least that’s what the White House would have us believe.