link of the above image: https://www.innovationnewsnetwork.com/fighting-environmental-challenges-through-knowledge-based-actions/3926/

In 1998 a rise in sea temperatures caused by EL NINO, a periodic eastward surge of warm Pacific water, caused a mass bleaching of the world’s coral reefs, the permanent or temporary home of perhaps a quarter of all marine species. Up to 90% of the Indian Ocean’s technicolored reefs turned to skeletal waters, largely devoid of life. Had this happened to rain forests- coral’s terrestrial equivalent – a sea-change in attitudes to the environment could have been expected. But because this change occurred in the sea, the calamity drew minimal comment.

Traditional attitudes towards the sea, as something immutable and distant to humanity, are hugely out of date. The temperature change that harmed the corals was not caused by human activity, yet it was a foretaste of what man is now doing to the sea. The effects of overfishing, agricultural pollution, and anthropogenic climate change, acting in concert, are devastating marine ecosystems. Though corals are returning to many reefs, there is a fair chance that in just a few decades, they will all be destroyed as ocean temperatures rise owing to global warming. The industrial pollution that is cooking the climate could also cause another problem: CO2, absorbed by the sea from the atmosphere, turns to carbonic acid, which is a threat to coral, mussels, oysters, and any creature with a shell of calcium carbonate. The enormity of the sea’s troubles, and their implications for mankind, are mind-boggling. Yet, it is equally remarkable how little this is recognized by policymakers – let alone the public. Killer sharks are a more appealing subject than algal blooms, though they are much less deadly.

Several scientists have stated that anthropogenic stresses are changing the oceans faster than at almost any time in the planet’s history. That may be putting it too firmly. Yet, there is no quibbling with the evidence of marine horrors that the scientists present.

Take overfishing. The industrialization of fishing fleets has massively increased man’s capability to scoop protein from the deep. An estimated area equivalent to half the world’s continental shelves is trawled yearly, including by vast factory ships able to put to sea for weeks. Yet, they are scraping the bottom of the barrel: most commercial species have been reduced by over 75%, and some, like white-tip sharks, commonly skate by 99%. For all the tremendous technological improvements, British fishermen, mainly using sail power, caught more than twice as much cod, haddock, and plaice in the 1880s as they do today. By one estimate, for every hour of fishing, electronic sonar fish finders, industrial winches, dredges, and nets catch 6% of their forebears seen 120 years ago.

Overfishing eradicates the primary protein source of one in five people, many of whom are poor. It also weakens marine ecosystems, making them even more vulnerable to significant changes coming downstream. For example, there is the matter of chemical pollution, mostly from agricultural run-off. This has created over 400 dead zones, where algal tides turn the sea anoxic for all or part of the year. One of the biggest, at the mouth of the Mississippi Delta in the Gulf of Mexico, covers 20,000 km² of the ocean. An annual event mainly caused by the run-off of agricultural fertilizers in 40% of America’s lower 48 states, it makes the one-off Deepwater Horizon oil spill look modest by comparison.

Global warming is another problem. Hitherto, the sea has been a buffer against it: because the heat capacity of water is several times that of air, the oceans have sucked up most of the additional heat, sparing the continents further warming. Yet, this is now starting to change faster than almost anyone had dared imagine. One effect of the warming ocean, for example, is to increase the density difference between the surface and the chilly deep, decreasing their mixing. That means less O₂ is making it down to the depths, reducing the livability of the oceans. Off America’s west coast, the upper limit of low O2 water is thought to have risen by 100 m. Where strong winds bring this water nearer to the surface, there are mass die-offs of marine life. Such events will proliferate as the climate warms.

This is a poor lookout for already put-upon fish. Fish under temperature and O2 stress will reach smaller sizes, live less long, and must devote a more significant fraction of their energy to survival at the cost of growth and reproduction. And that is before he gets to the effects of ocean acidification, which could be very bad. Without dramatic action to reverse these processes, scientists predict a catastrophe comparable to the mass extinctions of the Palaeocene-Eocene Thermal Maximum, when CO2 levels, temperature, and ocean acidity all rocketed. Scientists believe that not for 55m years has there been oceanic disruption of comparable severity to the calamity that lies just 100 years ahead.