Context – Tipping Points- Coral Reefs Die-Off

Contents:

Overview
Impacts
Recent Posts and News Articles

(Article Note –All references used in the article are indicated and directly linked in the article. Emphasis highlighted in maroon – Direct quotations are indicated in italics.)

1. Coral Reef Die-off: Overview

Source: Thresholds- Temperatures and Timeframes (from McKay et al, Science (2022)):

Type – Multiple Positive Feedbacks, Abrupt Tipping Point

Threshold – Estimated temperature rise of 1.5 degrees C (minimum – 1 degree C, maximum – 2 degrees C).

Timeframe-Estimated time-frame to reach tipping point is 10 years

Mechanism

i) Positive Feedbacks – corals have a narrow temperature range in which they can survive. As sea temperature rises, this causes the symbotic relationship between the coral structure and the zooxanthellae to break down; the coral bleaches as the zooxantellae, which gives corals their distinctive colour departs and the coral dies.

This is compounded by the acidification of ocean waters, caused by carbon dioxide emissions dissolving which further weakens the coral structure. Overfishing is a further driver of the destabilization of the corals as a healthy fish herbivore population are essential to remove harmful algae from the algae.

ii) Tipping Points? – Corals can and do recover from heating events (marine heatwaves) but as elevated sea temperatures become more frequent and last longer, coral mortality rates increase. This proceeds until a tipping point is reached where mass bleaching events occur where massive swathes of coral die such as happened along Australia’s great barrier reef in 1998, 2002, 2016, 2017, 2020 and 2022; as can be seen from the years in which this occurred, the frequency of such events are increasing.

As described in the 2022 ClimateCodeRed report, ‘Climate Dominos’ :

The bottom line: If severe bleaching events occur regularly at shorter than 10–15 year intervals, then reefs face a death spiral of coral mortality followed by inadequate recovery periods: “The time between recurrent events is increasingly too short to allow a full recovery of mature coral assemblages, which generally takes from 10 to 15 years for the fastest growing species and far longer for the full complement of life histories and morphologies of older assemblages.” (p17).

As reported by Carbon Brief in its Tipping Point Explainer: A 2020 study in Nature Communications suggests that, once tipped, Caribbean coral reefs could collapse within 15 years. Such “decadal timescales” are “coherent with the observations that coral cover across the Caribbean declined by 80% from 1977 to 2001 and may completely disappear by 2035, depending on rates of further overfishing, climate change and ocean acidification”, the authors note.

2. Coral Die-off – Impacts

– Regional Impacts

Carbon Brief in its Tipping Points Explainer explains that this ocean heat stress has the same destructive impact on seaweed such as kelp. These seaweeds and corals are critical nurseries for a whole range of marine species.

Coral reefs have been described as the rainforests of the sea. It is estimated that the provide an essential habitat for over 1 million species or 25% of marine species although they only cover less than 1% of the ocean.

Apart from the devastation that this will cause to key marine ecosystem, the impact on coastal fishing industries would also be of a catastrophic scale. The UN estimates that approximately 1 billion people depend for their livelihoods and food security on coral reefs. The International Union for Conservation of Nature (IUCN)puts the figure at 500 million but that is those that are directly dependent on coral reefs for daily subsistence, mostly in poor countries.

Other Impacts –

Noted by the Reef-World Foundation are:

Coastlines would take a battering –

Coral reefs don’t just work their magic underwater. It’s a little-known fact that they have a pretty important job of protecting coastlines too by providing a natural buffer against powerful waves and extreme weather. Without them, shorelines would be vulnerable to erosion and rising sea levels would push coast-dwelling communities out of their homes.

Nearly 200 million people rely on coral reefs to safeguard them from storms. This means that reefs already play an important (and naturally cost-effective) role in protecting human lives. The cost of building sea walls for the same level of protection would be in the trillions!

Medical breakthroughs would grind to a halt –

Did you know coral reefs are often referred to as the ‘medicine chests of the sea’? That’s because the plants and animals that live within the reef hold the key to new treatments for a whole bunch of diseases and ailments. By researching the corals’ natural chemical defenses, scientists are able to develop medicines to treat all sorts: from cancer and arthritis, to Alzheimer’s and heart disease. This means the health of our coral reefs is directly tied to our own health. When you put it like that, losing them all is a very scary prospect.

Diving would be a LOT less interesting –

According to PADI, one million new scuba divers are certified each year and millions more go snorkelling on reefs around the world. There’s a reason why corals draw such a huge fanbase in the diving community. Anyone who’s been on a reef dive will tell you that it’s a spectacular, visceral and, often, moving experience. The rainbow of colours and life that you find on a healthy reef are out of this world. Diving just wouldn’t be the same without them.

The sea would be a whole lot slimier-

When toying with this hypothetical (but, let’s face it, not altogether unrealistic) scenario of a reef-less world, some scientists have suggested the ocean bed would eventually become dominated by algae. As the skeletal structures of the limestone reefs slowly break away, microbial life would soak up the sun’s energy, producing slime. Lots of slime. Oh, and plenty of jellyfish to graze on the buffet of microbes. So, jellyfish and slime? Yay!

There’d be less oxygen –

Everyone knows that trees play a major role in producing oxygen in our atmosphere. That’s why the Amazon rainforest is known as the ‘lungs of the Earth.’ But did you know that around 50-80% of oxygen production on our planet comes from our oceans? Most of this oxygen is produced by plankton and other photosynthesising bacteria. In turn, this oxygen is consumed by marine life and by humans too in the air we breathe. The moral or the story? For a healthy atmosphere, we need a healthy ocean. And a healthy ocean needs healthy coral reefs.

MCL – February 2025 (next update schedule: Spring 2028; more regular updates in the ‘Recent News Section’).

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3. Corals – Recent News

Climate Junction

Posts – Coral Reefs Collapse