Oceans under threat (excerpts)

Humankind has been damaging the seas for decades by discharging pollutants into the water, destroying coastal ecosystems and overexploiting fish stocks. Ocean warming and ocean acidification are new global-scale threats affecting the seas today. A precondition for sustainable ocean use will be an exact analysis of its con­di­tion so as to allow for the correct environmental policy measures to be taken from now on. (…)

Global threats

Many scientists take the view that ocean warming and ocean acidification, two of the effects of climate change, are having a global impact on the oceans. The cause of seawater becoming more acidic is the increase in atmospheric carbon dioxide (CO2), some of which enters the ocean, thus increasing dissolved CO2 in the seawater which leads, simply put, to the formation of carbonic acid. Laboratory experiments have shown that more acidic water renders calcium carbonate (CaCO3) structures of oceanic calcifying organisms, such as corals, bivalves, molluscs and sea urchins, more vulnerable to dissolution.

There are a number of naturally occurring forms of CaCO3 which differ minimally in their chemical composition, such as aragonite and calcite, two forms of CaCO3 used by a range of marine organisms at different proportions to construct their shells or exoskeletons. The experiments have shown that those animal species which primarily use aragonite are likely to be the first to be most strongly affected by ocean acidification.

In particular, the zooplanktonic pteropods may be affected in the future; these are pea-sized “wing-footed” free-swimming sea snails. Pteropods are an important food source of fish as well as whales. Their aragonitic shells are particularly delicate and marine scientists are concerned that these shells may dissolve very quickly. Studies have shown that ocean acidification is a threat even to their offspring which may perish during their growth phase. But the shells of adult pteropods also dissolve over time.

As gases such as CO2 dissolve more readily in cold water, ocean acidification proceeds most rapidly in the colder waters of higher latitudes. In cold waters, marine scientists are already seeing the first signs of the critical point slowly being exceeded at which aragonite is beginning to dissolve. For example, on expeditions conducted by the United States National Oceanic and Atmospheric Administration (NOAA) in the Pacific Ocean off the northern U.S. states of Washington and Oregon, numerous adult pteropods were caught the shells of which displayed clear signs of corrosion.

The ongoing process of ocean acidification also impacts on animal behaviour. Scientists have found that the Atlantic king scallop loses its ability to escape from predators. Normally the animals’ escape strategy involves fast shell closure and jet-like propulsion enabling them to swim out of the danger zone. With increasing acidification, however, this clapping performance weakens, thus compromising their ability to escape from predators.

What is worrying is that the two phenomena of ocean acidification and ocean warming can amplify each other. Laboratory experiments conducted by ecophysiologists studying animal metabolism have shown that some crustaceans and fish have a shortened lifespan if the water becomes both warmer and more acidic at the same time.(…)

World Ocean Review, November 2015. Article.

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