We are getting a preview of what rapid warming of the oceans will look like as tropical marine species begin to migrate to more temperate marine regions made possible by increasing surface water temperatures. As a result of this migration, certain marine species will become very vulnerable to climate change while others will thrive, but the final result will be a huge loss of the planet’s biodiversity. Tropical ocean eco-systems are much less productive then temperate marine eco-systems, which provide a large percentage of the seafood that we and other predators consume.
“By 2020, models project that global surface temperature will be more than 0.5°C (0.9°F) warmer than the 1986-2005 average, regardless of which carbon dioxide emissions pathway the world follows. This similarity in temperatures regardless of total emissions is a short-term phenomenon: it reflects the tremendous inertia of Earth's vast oceans. The high heat capacity of water means that ocean temperature doesn't react instantly to the increased heat being trapped by greenhouse gases. By 2030, however, the heating imbalance caused by greenhouse gases begins to overcome the oceans' thermal inertia, and projected temperature pathways begin to diverge, with unchecked carbon dioxide emissions likely leading to several additional degrees of warming by the end of the century”.
Kelp forests are an at risk temperate marine eco-system. These forests grow worldwide in clear, relatively shallow, and nutrient-rich water whose temperatures are between 42–72 degrees.
Climate-driven changes can profoundly alter marine communities, particularly when they impact kelp, a foundation species that is critical for a healthy and productive temperate marine system. “In marine systems, changes in herbivory and the consequent loss of dominant habitat forming species can result in dramatic community phase shifts, such as from coral to macroalgal dominance when tropical fish herbivory decreases, and from algal forests to ‘barrens’ when temperate urchin grazing increases”.
Yale Environment 360 published an article written by Alastair Bland based on a study of the Australian kelp forest’s response to warming sea temperatures that was prepared by the University of Tasmania’s Institute for Marine and Antarctic Studies.
A steady increase in ocean temperatures — nearly 3 degrees Fahrenheit in recent decades — was all it took to doom the once-luxuriant giant kelp forests of eastern Australia and Tasmania: Thick canopies that once covered much of the region’s coastal sea surface have wilted in intolerably warm and nutrient-poor water. Then, a warm-water sea urchin species moved in. Voracious grazers, the invaders have mowed down much of the remaining vegetation and, over vast areas, have formed what scientists call urchin barrens, bleak marine environments largely devoid of life.
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The Tasmanian saga is just one of many examples of how climate change and other environmental shifts are driving worldwide losses of giant kelp, a brown algae whose strands can grow to 100 feet. In western Australia, increases in ocean temperatures, accentuated by an extreme spike in 2011, have killed vast beds of an important native kelp, Ecklonia radiata. In southern Norway, ocean temperatures have exceeded the threshold for sugar kelp — Saccharina latissima — which has died en masse since the late 1990s and largely been replaced by thick mats of turf algae, which stifles kelp recovery. In western Europe, the warming Atlantic Ocean poses a serious threat to coastal beds of Laminaria digitata kelp, and researchers have predicted “extirpation of the species as early as the first half of the 21st century” in parts of France, Denmark, and southern England.
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And in northern California, a series of events that began several years ago has destroyed the once-magnificent bull kelp forests along hundreds of miles of coastline. A brief shutdown of upwelling cycles left the giant algae groves languishing in warm surface water, causing a massive die-off. Meanwhile, a disease rapidly wiped out the region’s urchin-eating sea stars, causing a devastating cascade of effects: Overpopulated urchins have grazed away much of the remaining vegetation, creating a subsurface wasteland littered with shells of starved abalone. Scientists see no recovery in sight.
A 2016 study noted a global average decrease in kelp abundance, with warming waters directly driving some losses. But the researchers said that a characteristic of kelp forest declines is their extreme regional variability. Some areas are even experiencing a growth in kelp forests, including the west coast of Vancouver Island, where an increasing population of urchin-hunting sea otters has reduced the impacts of the spiny grazers, allowing kelp to flourish. Ultimately researchers say, warming ocean waters are expected to take a toll on the world’s kelp forests. The 2016 paper, coauthored by 37 scientists, concluded that “kelp forests are increasingly threatened by a variety of human impacts, including climate change, overfishing, and direct harvest.”
Orca’s are starving in many regions, particularly in Alaska’s Aleutian islands. Their traditional foods of seal, sea lions and salmon have seen a major population decline due to climate change, overfishing, and destruction of free running rivers that allow salmon to spawn. As a result, Orca’s are now feeding on sea otters as well as other non traditional food sources. The reduction in sea otter populations, which feed on sea urchins, has allowed urchin barrens to increase even without sea temperatures being a factor. Since otters are more like a snack for an Orca than a sea lion or seal would be, a malnourished Orca must eat a lot of them to survive.
Sea Urchins are not the only species that is a threat to marine temperate environments. Migrating tropical fish can also cause enormous destruction to seaweed beds and kelp forests.
The undersea world is on the move. Climate change is propelling fish and other ocean life into what used to be cooler waters, and researchers are scrambling to understand what effect that is having on their new neighborhoods. They are finding that the repercussions of the migration of tropical fish, in particular, are often devastating. Invading tropical species are stripping kelp forests in Japan, Australia, and the eastern Mediterranean and chowing down on sea grass in the northern Gulf of Mexico and Atlantic seaboard.
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Sea grass beds and kelp forests are often known as the sea's nurseries because they have nooks and crannies filled with nutrients that feed and protect fish larvae and juveniles. The kelp and sea grass, however, are being replaced with other warm-water species such as coral that follow the arrival of tropical fish, said Vergés.
Many tropical fish species are "browsers" or "scrapers" that clean coral of algae and plants that could otherwise choke the reefs. But when the herbivorous fish move toward more temperate waters, they often find a bountiful harvest of kelp or sea grass to feed their voracious appetites.
Once a tropical fish species arrives in a new area, it can quickly mow down vegetation and algae and destroy the lush habitat that protects other species. For instance, "parrotfish are capable of eating a lot of sea grass per individual," said marine scientist Joel Fodrie of the University of North Carolina at Chapel Hill.