Biodiversity

Coral reefs exist on only 0.2% of the Earth's ocean surface, but they are home to more than a third of all fish and invertebrates in the oceans. But they are not only the most species-rich ecosystems of the oceans. They are also the source of most species. These in turn migrate into other ecosystems or are drifted by currents, so that the biodiversity of other habitats is also influenced by coral reefs. Download

Copyright/source: Heinz Krimmer / www.ICRS2020.de

Coral cemetery

The elkhorn corals of this massive reef wall are completely dead. The decline of this tropical coral reef began in the 1970s. In the Caribbean, 80% of the coral population has been lost in the last 40 years. The picture was taken in August 2016. Caribbean, American Virgin Islands, Buck Island Reef. Download

Copyright/Source: Richard Ross / Secore international / www.ICRS2020.de

Climate change

Due to climate change, El Niños are becoming ever stronger. The last El Niño in 2016 led to a prolonged temperature increase in the oceans of the tropics worldwide. Not only the Great Barrier Reef in Australia was severely affected. Large-scale coral bleaching occurred worldwide, as here in American Samoa in the Pacific. The picture of the same reef section before (left side) and after (right side) shows impressively that the complete reef top is bleached. USA, American Samoa, 2016. Download

Copyright/Source: The Ocean Agency / www.ICRS2020.de

Climate change

The bleached corals (picture left) taken in March 2016 are not dead yet. They have ejected their symbiotic algae because they produce toxins (oxygen radicals) when temperatures are too warm. But the high temperatures lasted too long, so that they could not absorb any more symbiotic algae and finally died until May 2016 (right picture). Algae began to overgrow them. Australia, Lizeard-Iceland, Great Barrier Reef, 2016. Download

Copyright/Source: The Ocean Agency / www.ICRS2020.de

Extinction of species

Many fish but also invertebrate species in the coral reefs depend on one or a few coral species. They have specialised in certain ecological niches. If these coral species disappear as a result of human activities such as CO2 emissions, physical destruction or pollution by sediment, toxins or nutrients, then this will also mean the end for the species that depend on them. Download

Copyright/Source: Heinz Krimmer / www.ICRS2020.de

Overfishing

Overfishing is one of the major local stress factors that endanger coral reefs. In particular, the removal of herbivorous species, such as this caught surgeon fish, damages the reef. Stony corals and algae fight in every reef for settlement sites. If the algae are not grazed by herbivorous fish, the corals lose the battle and the reefs become algae. Egypt, Sinai, Dahab, Red Sea, gillnet on the top of the reef. Download

Copyright/Source: Heinz Krimmer / www.ICRS2020.de