Hypoxia - a problem for aquatic environments

When I started my scientific career about forty years ago, I concentrated on the effects of increased temperature and hypoxia on oxygen transport in fish. At that time the topic was not considered to be of general interest. Things have changed since then. In 1970’s oxygen minimum zones were a peculiarity in the oceans. Today their occurrence has increased markedly making them a grave threat to the well-being of aquatic fauna. The increased occurrence of oxygen-minimum zones occurs together with climate change and ocean pollution.

Aquatic environment always requires very effective oxygen uptake, because water can contain very little oxygen – at sea level about the same amount as air in about 20 km’s height – it is hard to breathe, and the few oxygen molecules present in water move slowly. For active aquatic animals the added problem is to be able to release enough oxygen to working muscle. In the situation of hypoxia occurring together with increasing temperature, active fish and crustaceans are not able to coupe. Consequently, large areas of oceans become devoid of animals. Since those animals are the preferred foodstuff of man: salmonid species, cod, tuna, lobster, shrimp, the spreading of hypoxic areas causes the lack of seafood.

The problems with obtaining enough seafood comes at the same time as man should increasingly shift from eating cattle and sheep, i.e. homeotherms, to eating fish and other poikilotherms in order to combat climate change. Climate change itself makes doing this difficult. Also, the oceanic biodiversity is at risk, since the habitats of many species become unsuitable for them to thrive in.