Coral gardening — a distracting “solution” to reef decline
Replanting projects will not provide a long-term solution for coral reefs.
Coral reef gardening has been hailed as a conservation tool that could help to preserve our coral reefs despite rising ocean temperatures. It means exactly what it sounds like — coral species are cultivated and cared for by humans, in floating nurseries, before being planted back onto the reef. It’s an ecosystem intervention that has already seen some success — which is why it’s been applauded as a potential solution for coral reef destruction.
Coral reefs are widely accepted as the marine ecosystem that is most susceptible to climate change — they have been bleaching in response to warming oceans since 1998. So it’s clear that innovative solutions are needed to tackle this. But is coral reef gardening really the answer?
One of the main advantages of coral gardening is that gardeners can “select” parent plants that are more likely to survive warmer temperatures. Much like gardeners and farmers breed plants to be more resistant to disease, scientists can pick parent plants that have genes for higher heat tolerance, in a bid to produce a fresh crop of coral that can withstand a warming ocean.
The problem is that genetics are rarely so straightforward.
Corals are often extracted from reefs by a process known as “fragging” — where small pieces of coral can be broken off and will grow and thrive, given the right conditions. But reproducing corals asexually like this leads to a problem: too many similar corals will lead to a lack of genetic diversity, which would render them more vulnerable when faced with environmental changes or unexpected events.
Although corals naturally have the ability to reproduce asexually, this is generally not the dominant reproductive strategy seen on a wild reef. An effective reef restoration effort needs to incorporate sexual reproduction too[1]. But that’s more complicated, usually requires specific expertise and comes with an added cost — whereas fragging is far less expensive and much simpler[2].
In addition, by breeding corals that are more tolerant of heat, the same gene that codes for heat tolerance might also make corals more susceptible to a particular disease, 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.
Some researchers say that if we don’t select for heat, replanted corals will be more likely to bleach, die and ultimately not be able to reproduce and rebuild the reefs at all[3], since the biggest threat facing corals today is warming water.
That’s why they argue that focusing on thermal tolerance is a crucial weapon in coral reef restoration’s artillery2. It might be worth the potential future genetic risk — it might be a trade-off we have to make.
But more than two-thirds of all coral reef restoration projects have lasted for 18 months or less, meaning that the long-term effects of such projects are not well understood[4]. Most projects have been carried out over small areas — often 100km2 or less3.
And the cost of coral restoration is much more than for the restoration of other coastal ecosystems, like saltmarshes and seagrass meadows — costing on average US $2 ,915, 087 per hectare, significantly higher than the average price tag of US$1, 600 000 for marine restoration projects[5]. Success of a restoration project is not correlated with financial investment, which suggests what we’ve already said — that a lot more research needs to be done before coral reef gardening can be considered a tried-and-tested conservation method.
Coral reef gardening does not cool the oceans, nor reduce the levels of carbonic acid in the water, nor replenish the fish stocks around the reef. It’s not that we shouldn’t do this type of reef restoration — it’s more that it should be still considered as a scientific experiment requiring more research, rather than a blanket conservation measure to be rolled out across every reef in the world. The amount of money currently being funnelled into such projects could be better spent elsewhere, at least until coral gardening can be shown to work at scale and cost-effectively.
Moreover, coral reef restoration as a whole, while a vital part of our reef preservation strategy, should not be considered as an alternative to tackling climate change. Despite coral gardening, warming seas will continue to cause mass bleaching of coral, and only the most robust will survive. While breeding heat-tolerant coral will help some individuals to hold out in the short term, it will only delay the inevitable. For this reason, corporations should not be able to claim that their backing of coral reef restoration projects allows them to offset carbon emissions.
The future looks bleak for coral reefs, but there are two actions that could truly make a difference: reducing carbon dioxide emissions, and creating and enforcing marine protected areas.
Marine protected areas that are completely free from human activities can give coral reefs the space and the time needed to recolonise and recover what they have lost, including much of the genetic diversity and biodiversity of the original reef[6]. Coral fish species play important functions in the ecosystem, eating seaweed species that would otherwise overrun the reef, and coral reef fish poop contains the symbiotic algae that corals need to survive. Their impact on the coral reef ecosystem was reflected in the UN’s 5th Global Biodiversity Outlook report, which referred to overfishing as “the most pervasive and immediate” threat to reefs[7].
To have the best impact, marine protected areas should be no-take, well-enforced, large and isolated[8]. They should also be well-connected — giving marine species safe corridors to move through[9].
It’s difficult to protect an area of the ocean, however. It’s expensive to fund patrols and security to both detect and protect against intruders. Corruption can hamper efforts. So can a lack of resources — in many cases, only daytime patrols are funded and fishing vessels just glide right on in after nightfall, unchecked. Other marine protected areas are known as “paper parks” — meaning that they are protected in name only.
Multinational companies and governments alike are currently pouring funding into coral gardening and reef restoration projects. But that funding could be redirected towards enforcing marine protected areas, which would have a bigger impact on marine biodiversity and ocean health as a whole.
That said, marine protected areas will not be enough on their own. High temperatures and ocean acidification will result in bleached corals even if the reef is protected. Coral reefs are likely to decline by 70–90% by 2050 thanks to ocean warming even if the Paris climate goals are reached.[10] That’s why fast action is needed now to curb fossil fuel emissions and keep us well below that 1.5°C mark.
The writing is on the wall for coal and other fossil fuels; but some countries are not willing to let these dirty energy resources die.
If we truly want our coral reefs to survive and thrive, we must combat the source of the problem. Companies and governments should not look the other way, pointing to colourful pictures of coral gardens on their corporate websites. 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 the coral ecosystem. Everything else is a distraction.
Reference list:
[1] https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1526-100X.1995.tb00091.x
[2] https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0226631
[3] https://www.frontiersin.org/articles/10.3389/fmars.2021.632027/full
[4] https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0226631
[5] https://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/15-1077
[6] https://umaine.edu/news/blog/2018/05/09/study-finds-marine-protected-areas-help-coral-reefs/
[7] https://www.cbd.int/gbo/gbo5/publication/gbo-5-en.pdf
[8] https://onlinelibrary.wiley.com/doi/full/10.1111/ddi.12838
[9] https://link.springer.com/article/10.1007%2Fs00338-009-0470-3
[10] https://sci-hub.st/https://www.sciencedirect.com/science/article/pii/S016953471830226X
