In the depths of the oceans, a climate crisis of its own is occurring: more and more animals are moving away from the equator towards the poles. This mass migration even has a name: the shift to the tropics, and it has dire consequences for ecosystems and biodiversity. It could even have an impact on the global economy.
Scientists reach this conclusion after analyzing 215 studies on this topic, published over the past 20 years. The migration of marine life to colder waters is a global trend, but is particularly prevalent in areas with strong currents from the equator toward the poles, such as the Kuroshio Current in the western Pacific, which has caused corals and fish to move from the Pacific. The tropics moved to Japan’s more temperate waters.
But it also occurs in other areas. A prime example is mangroves, which expand northward along the Florida coast as winter temperatures rise. These trees are very sensitive to freezing, but can now survive at higher latitudes.
There is no guarantee on food
Transition to the tropics, i.e. the climate becoming more tropical in a place causing species to migrate, is a very broad phenomenon. From coral and algae to sea snails, reptiles and even mammals, they all move from the equator to places where the weather is less warm. Easier said than done. After all, who guarantees that animals elsewhere can live equally beautiful lives and find, for example, enough food? It is no coincidence that not all species stay away. This mainly concerns plants and animals that spread easily and can eat many different things. For example, reef fish with a wide-ranging diet are better able to settle in new areas, because they can easily find suitable food again.
More mangroves
Now you may be thinking: How bad is the movement of animals and plants? Wouldn’t it be nice if mangroves also grew in the northern regions, for example? It may not seem dangerous, but it can have a lot of disadvantages for species and even entire ecosystems. Suppose a fish that eats algae finds a new place where it eats algae again. Then there would be room for more coral reefs there, which in turn would contribute to greater flatness. As tropical sea turtles move south along the west coast of Australia, for example, their consumption is likely to increase pressure on already vulnerable seagrass beds.
new friends
This does not apply to all animals. Some people control their behavior. Take tropical Damsel, or damselfish, which swims away from the equator towards southeastern Australia. This type of fish will form schools containing more temperate fish instead of blending in with their usual group of tropical fish. This change in behavior will likely cause them to live longer and increase in size.
More tourism, less fish
Only recently has more been known about the genetic and evolutionary consequences of tropicalization. Temperate species may be pushed out and new species may take their place. This can lead to a loss of unique genetic diversity, which may make populations less able to adapt to changes in the future. Meanwhile, some temperate species are already beginning to adapt to their new tropical neighbors. For example, volcanic barnacles found in the waters off the coast of the Mexican state of Baja California actually bend to better repel tropical snails.
Whether the consequences of leveling are positive or negative depends mainly on the location and animals involved. But what is clear is that the large-scale movement of marine life is already affecting global fisheries. More tropical fish are already being caught in parts of the western Pacific. But the shift to the tropics is also leading to the loss of commercially important temperate species and an increase in the number of animal species accidentally caught in fishing nets.
Carbon storage
However, there are also advantages. Because not only is it nice to have more mangroves growing, but they also provide more carbon storage, compared to the salt marshes they replace. The expansion of attractive tropical species, such as coral reefs and the colorful marine life they harbor, can help local economies by increasing tourism.
But all consequences need much better planning, because the consequences may reach much further than what is known so far. Because leveling is a global phenomenon that is already happening now. This can have an impact on many ecosystems and economies.
