Coral gardening projects are more popular than ever to help reefs recover from the effects of a warming ocean, but they are a distraction away from the real solutions, says Catherine Collins
2 February 2022
CORAL reefs in Australia are set to experience another mass bleaching event due to ocean temperature rises – the fourth in seven years – according to a forecast released by the US National Oceanic and Atmospheric Administration. Reefs need serious efforts to help them to cope and survive, but our endeavours are currently misplaced, focusing on the glamorous rather than the effective.
Coral gardening projects, where coral species are cultivated and cared for by humans in floating nurseries before being planted back onto the reef, are popping up around the world. While there are some advantages to this approach – we can choose parent corals that are more likely to survive warmer temperatures in a warming ocean, for example – it is riddled with problems.
For a start, genetics is rarely so straightforward. The same gene that codes for heat tolerance might also make corals more susceptible to a particular disease, for instance, or more likely to fail reproductively. Stacking the genetic odds in the coral’s favour in terms of heat tolerance might not necessarily be a winning strategy over the long term.
One of the methods used is called fragging, in which a small piece of coral is broken off the parent, much like a cutting, and grows to form a new coral. Although it can work, it is more like a quick fix. The resulting reef can easily lack genetic diversity if all the “cuttings” are genetically identical – and that means the corals could be more likely to perish in changing environmental conditions.
Most coral reef gardening projects are small, and haven’t been running for very long. More than two-thirds of all coral reef restoration projects have lasted for 18 months or less, meaning that their long-term effects aren’t well understood. And most projects have been carried out over small areas, often 100 square kilometres or less. We can’t rely on coral gardening to save reefs over large areas and the longer term.
All is not lost. There are actions that will make a difference for coral reefs and we need to prioritise them immediately.
The first is creating and enforcing marine protected areas. The UN described overfishing as “the most pervasive and immediate” threat to reefs in its 5th Global Biodiversity Outlook report in 2020. Coral ecosystems rely on the marine life that surrounds them – coral fish faeces contains algae that corals need to survive, for example, and parrot fish feed on seaweed that would otherwise suffocate reefs.
When parts of the ocean are completely free from human activities that can give coral reefs the space and the time needed to naturally recolonise and recover what they have lost, including much of the genetic diversity and biodiversity of the original reef.
But marine protected areas aren’t enough on their own. High ocean temperatures will result in bleached corals even if the area is protected. Coral reefs are likely to decline by 50 to 90 per cent by 2050 due to ocean warming even if we succeed in keeping atmospheric warming to well below 2°C above pre-industrial levels, as set out in the Paris Agreement. That is why fast action is needed now to curb fossil fuel emissions and keep us well below that 2°C mark.
If we truly want our coral reefs to survive and thrive, we must combat the source of the problem. What reefs really need is for us to drastically reduce our fossil fuel emissions immediately and protect the reef fish and biodiversity that nourish and sustain coral ecosystems. Everything else is a distraction.
Catherine Collins is a science journalist based in Brussels, Belgium
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