John Bruno is a marine ecologist and professor in the department of biology at the University of North Carolina at Chapel Hill.
GALÁPAGOS ISLANDS, Ecuador — When you plunge into the ocean here, you quickly realize this isn’t your typical tropical destination. The water is cold — in some places, about 20 degrees Fahrenheit chillier than most tropical oceans, even though the islands sit right along the equator.
The cold water is caused by upwelling, which occurs when chilly, nutrient-rich water is drawn up from the deep ocean and by currents from the frigid Southern Ocean. This complex system creates an extraordinarily biodiverse environment — where else in the world do penguins and flamingos mingle? Marine creatures are a motley mixture, with tropical fish like the black-and-yellow striped Moorish idols and other species typically at home in more temperate environments. Although it’s about 600 miles off the coast of South America, it reminds me of the sea life off southern Australia or central California.
But as the climate warms, this ecosystem is changing. If we don’t slow the heating up of the atmosphere and oceans, climate models indicate that the waters around the Galápagos Islands will warm by about 7 degrees Fahrenheit by the end of the 21st century. So how will this affect the Galápagos’s marine ecosystem?
To answer this question, Ecuadorian marine ecologist Margarita Brandt and I are studying how water temperature affects the consumption of algae, which is a fundamental aspect of the marine food web. We’re documenting the habits of a wide range of creatures including sea urchins, marine iguanas, fish and sea turtles, all herbivores that eat Ulva, an easily-digestible leafy green seaweed.
Our work suggests that warming will fundamentally change the Galápagos’s marine food web. Some plant and animal species will likely adapt, but others may be forced to relocate to higher, cooler latitudes. New plants and animals currently restricted by the relatively cool waters will move in and colonize the waters around the islands, thriving in the warmer conditions. These processes will lead to a novel combination of marine species — some will provide new resources for their neighbors, and others, namely competitors and predators, will pose new threats.
Unlike extinction, these changes are largely hidden from view, even from scientists, who generally focus on more obvious signs of climate change: When a coral reef warms and bleaches, we rush in to document its death. But a growing body of research indicates that the great “speeding up” of marine ecosystems, though largely invisible, is equally widespread and problematic. Nearly all animals that inhabit the ocean are cold-blooded, or ectothermic, meaning their body temperatures match that of the seawater around them. The cooler the water, the colder their bodies get. When ectotherms warm up, their metabolism speeds up, meaning they do everything more quickly: grow, reproduce, hunt, escape, eat and digest.
Warming waters affect nearly every form of life, including plants. Photosynthesis speeds up, as energy flows more quickly from the sun to seaweed to herbivores, then to the large predators at the top of the food chain. Brandt and I have found that the warmer the water, the more quickly algae is consumed. But if algae’s growth also increases, does that balance out the growing demand?
This is an important question because one danger is that warming will increase the caloric demands of animals but not their food supply, which could then lead to starvation. Nature is stingy with its resources, and there is a limit to the number of animals an ecosystem can support. Current research suggests this capacity declines with warming. The Galápagos has an incredible abundance of marine mammals, including sea lions, whales and dolphins, as well as unique birds like the tiny Galápagos penguins, albatross and blue-footed boobies. They all eat small fish like sardines. But if global warming reduces the abundance of these food sources, these iconic and endangered species will almost certainly suffer.
The Galápagos is a natural laboratory for climate change research, and we expect to see these kinds of changes elsewhere. In the Gulf of Maine, for example, ocean temperatures this past summer were a whopping 11 degrees Fahrenheit above normal. In Sydney harbor, colonizing fish from the Great Barrier Reef far to the north are causing the rapid “tropicalization” of the ecosystem. Because of the unavoidable impact of temperature on the metabolism of most marine critters, it’s likely that the same speeding up is happening in ocean food webs around the world.
Ultimately, if we don’t find better ways to reduce our carbon emissions, we have little hope of staving off the social, economic and ecological impacts of what we all fear is coming.