Life ain’t easy for corals:
- collision damage due to bottom trawling (fifty-five percent of Alaskan cold–water coral that was damaged by one pass from a bottom trawl had not recovered a year later),
- over-fishing, destructive fishing practices (cyanide and blast fishing) and selective fishing (like Triton’s trumpets),
- destruction due to shipping routes, tourism and coastal development like ports,
- rising sea levels (due to climate change) affecting the amount of sunlight reaching coral reefs,
- pollution with poison, sediments, pesticides or excessive nutrients from fertilizer (due to dumping or terrestrial influx)
- and diseases
caused the dead of half of the coral reefs across the oceans between 1950 and 2014. I want to discuss some reasons further.
As mentioned here, coral reefs currently suffer again from a massive coral bleaching event.
Corals live in symbiosis with microorganisms called zooxanthellae and get up to 90% of their energy supply from them. But warmer water causes the microorganisms to produce harmful substances instead of sugar. The corals are forced to expel them, leaving the corals weak with their white skeletons visible. Previously, healthy corals were able to survive these relatively short, seasonal events, as long as the zooxanthellae got back within 8 weeks to where they were supposed to be (depending on the coral species). But now, in view of climate change and general weakness, corals need longer to recover – many decades or centuries – if at all.