Sergio Rossi - Oceans in Decline

This Copernicus imprint is published by the registered company Springer Nature Switzerland AG

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Are the oceans dying? This is a question that many people are asking themselves more and more insistently. The answer is that in no case are they dyingbut they are being transformed. Deeply. Human-induced changes across the globe affect marine more than terrestrial ecosystems. And at sea, there is a problem: because it is not our environment, it is not easy for us to see what is happening. The disappearance of large predators (whales, sharks, tuna fish, turtles, seals, swordfish, etc.), as well as the drastic reduction in many living structures on the seabed (coral reefs, algae meadows and higher plants, deep corals, etc.), has led to change in entire ecosystems to achieve a new balance on the basis of abundant small organisms and accelerated life. And there is more: persistent pollution, both chemical and biological, and the not fully understood but certain effects of climate change may be adding to the plight of our oceans as we know them. We cannot claim to know the full impact that such changes may have on the entire system, on the functioning of our planet and on our own survival.

Today, no one can ignore the fact that human beings have essentially impacted every habitat in the biosphere. More needs to be learned about concepts such as ecological economics, the persistence of species in the system, sustainable exploitation and recoverability of what we, as a species, now dominate: the planet in general, and oceans in particular. This implies knowing more about population sizes, genetic flows and the positive or negative relationships between species. It also means learning to adapt our way of life and understanding our role in nature. We are undoubtedly most backward in our knowledge concerning the marine environment, in this list of concepts, as it the most inaccessible and unknown. The problem is partly one of focus, of perspective, of the way we understand what surrounds us. The various transformations that have taken place (and are taking place) in marine ecosystems deserve reflection, not only as a result of specific experimentation but also from observation of what was once in balance and that has now shifted, across the globe.

In this book, I try to give a vision that is as global as possible of the past, present and future of the ecosystems that cover the most surface area (70% of our planet) and volume (99% of the biosphere): those of the oceans. It is not intended to touch on every point, as I do not want to detail all the instances that are taking our ocean to a very different place from the one that our ancestors knew just a few thousand years ago. However, I do want to give four openings so that the reader understands the magnitude of the process of transformation that has taken, and is taking, place on our planet.

I begin with a brief review of the history of our seas, showing that transformations and cataclysms are the order of the day on Earth. The sea has undergone many changes since the start: the movements of continents, the rise and fall in sea level, the appearance of cyanobacteria capable of creating oxygen (poisoning any being that could not consume it), its acidification and the sudden freezing of its surface. All these disturbances have been faced by species, some disappearing, others migrating or adapting to the changing conditions. But mans intervention has changed things. The pressure that we have exerted and the profound transformation of our ecosystems began much earlier than we think. Hundreds of years ago (in some cases, even thousands), humans understood that the sea was an apparently inexhaustible source of food and began to exploit it systematically and without control. In the sea, unlike on land, large carnivores were usually coveted prey, so a hunt for large cetaceans, sharks, seals, tuna fish, cod and turtles began, and their populations were soon reduced to levels that relegated them down the food chain: mankind became the new regulator of the system, the new great predator. This first part of the book analyses in depth what this ancient and fundamental historical transformation of the sea has meant.

In the second part of this book, the focus is on industrial and other means of fishing that currently take place, and the effect that they have on the transformation of the oceans. In recent decades (even centuries), much has been written about which disturbances have affected the marine balance most. Today we can say, without a doubt, that fishing is the main disruptor of the balance between species and is the culprit behind the changes in the flows of matter and energy. It has been argued that overfishing has virtually eliminated predators and resulted in a resurgence of the Mesozoic system, dominated by jellyfish, cephalopods, echinoderms and crustaceans. Of all types of resource extraction, trawling from the early twentieth century onwards has definitely been the most damaging, and it continues to be so. Besides trawling, there are the large pelagic fisheries capable of encircling and capturing entire shoals of tuna; they are unable to escape from this technology, which does not give them a chance. Even animals as resilient as anchovies and sardines are incapable of the speed of reproduction at which we force the species to multiply, due to the eagerness of our unrestrained market. The sea is at the limit of its capacity to bear fruit, and specialists have long warned that many species are either on the verge of local extinction or are already, commercially and ecologically, extinct.