The threats to coral reefs in the Anthropocene

by Natalia Gocman – 25142142 - FYM001

As of October 2025 my news platforms and social media started to flood with rather alarming news - we have officially reached the first devastating climate tipping point. It is characterized as critical thresholds in the earth’s system, which when passed can cause sudden and dramatic changes to an ecosystem that are often irreversible (Lenton, et al., 2025). For a long time scientists have been warning about human activities having devastating effects on the Earth’s physical and chemical environment (Hoegh-Guldberg, 2011; Pearce-Kelly, et al., 2025) and their prognoses are unfortunately right. The Global Tipping Points Report of 2025 focuses on a few endangered ecosystems, with emphasis on warm water coral reefs as they are particularly vulnerable to the planet’s changing climate (Figure 1). As we approach 1.5 degrees of warming (compared to pre-industrial times), we are reaching reefs' upper thermal point (Lenton, et al., 2025) with projections estimating about 70%-90% coral loss at these temperatures (Pearce-Kelly, et al., 2025). To minimize the harm, we must critically cut greenhouse gas emissions and reach net zero by 2050, otherwise we are facing an escalation of catastrophic changes to the world that we live in (Lenton, et al., 2025). But there are many other factors impacting corals negatively that drive the biggest reef systems to extinction.

Figure 1. Graphic from The Global Tipping Points report, presenting the estimates of temperatures at which certain components of Earth’s climate are most likely to tip.

Last summer, the Great Barrier Reef faced the 5th Mass Coral Bleaching event since 2016, with the most spatially extensive coral mortality so far recorded on this reef (AIMS 2025). Coral bleaching is a process that disturbs the relation of coral with its symbiotic algae, which because of heat stress gets expelled from the animal. This process can be overturned if the water temperatures fall and algae returns, but unfortunately every year the ocean gets hotter and for a longer period which leaves coral susceptible to starvation and chronic illness (AIMS 2025). Rising carbon dioxide levels in the atmosphere also have another negative impact – it reduces the calcification rates of corals (Pearce-Kelly, et al., 2025). As the CO2 gets absorbed by seawater, it changes water’s chemical structure and makes it more acidic (Hoegh-Guldberg, 2011). The current value of pH in the open waters is 10x greater than at any time in the last 65mln years and has been only accelerating (Fabricius, et al., 2025). It is important to note that ocean acidification does not only negatively affect calcifying organisms – different invertebrates have shown metabolic depression as the pH levels decreased in their surroundings (Hoegh-Guldberg, 2011). These rapid changes to water composition will change the lively reef ecosystems that are rich in biodiversity, into eroding seascapes (Hoegh-Guldberg, 2011) or they will be replaced by different communities like urchins, soft corals and macroalgae (Pearce-Kelly, et al., 2025). The crown-of-thorns starfish outbreaks are another contributor to reefs decline; even though they’ve been going on since the 1950’s, in this century they are especially damaging as there are not enough predatory fish that keep the populations in control (Meekan, et al., 2025).

While the recent global bleaching event was execrable on Great Barrier Reef, it was way more severe on the Mesoamerican Reef (AIMS 2025). While there are some improvements when it comes to fish biomass, the reef health is still in a very poor condition (McField, et al., 2024). Aside from the usual degrading factors that worldwide warm water reefs must face in this century, pollution is detrimental to Mesoamerican Reef’s health. The Caribbean and Mediterranean Seas experience the biggest concentration of cruise ship routes in the world, and the tourism sector is the primary driver of the economies surrounding Mesoamerican Reef (Kotrikla, et al., 2021). About 90% of waste generated on the ship ends up in the ocean, and that together with poor waste management infrastructure on land causes inevitable degradation to the ocean and coastal regions (Kotrikla, et al., 2021). The Water Report, run by Cozumel Coral Reef Restoration back in 2024 discovered unacceptable levels of fecal matter such as enterococci, coliforms and Escherichia coli bacteria. All these bacteria cause serious illnesses in humans, threaten coral health and fuel macroalgae growth - an invasive algae that residues on corals and slowly suffocates them (McField, et al., 2024). Mesoamerican Reefs also face huge outbreaks of stony coral tissue loss disease which spread rapidly and could be linked to poor water quality, as the sites closer to developed areas are considerably more affected (Alvarez-Filip, et al., 2022). Without relevant policies redefining tourism carrying capacities, water treatment facilities and reduction of agricultural run-off, the future of the reef seems very bleak; but there is another major factor that needs to be elaborated, which is the participation of the communities in conservation action, land restoration and raising awareness of the importance of these vulnerable ecosystems (McField, et al., 2024).

Figure 2. Dr German Mendez during coral reef awareness workshop for visitors from a cruise ship. The workshop included a presentation about coral reefs, mangrove seed planting, and snorkeling session.

It has been proven that biodiversity conservation is working, and it is slowing rates of decline, as compared to places where protection efforts were not implemented (Langhammer, et al., 2024). Involving local communities does not only benefit the ecosystem but also improves health and mental well-being of the participants (Sebastian, et al., 2024). I had the pleasure of joining the Cozumel Coral Reef Restoration Programme in December 2024 (Figure 2), and while seeing degraded reefs firsthand was incredibly upsetting, I must admit that the effort this organization puts into preserving what is left is impeccable. Yes, we urgently need to cut greenhouse gas emissions and tackle the pollution crisis, but at the same time, we need direct action to enhance the resilience and recovery of the remaining reefs. The only persisting problem with conservation efforts is their very little scale, and lack of funding (Langhammer, et al., 2024) - but the aftermath of the extreme weather events is way more costly; The World Meteorological Organization assessed that the total economic cost of climate change from the 1970 to 2021 was about 4.3 trillion dollars (Greenpeace, 2024). While this sum is enormous, if we continue with business as usual it will only carry on growing. It is time to act now, or we will face widespread loss of biodiversity and drive a catastrophic economic collapse that is going to displace millions of people.

The future of warm water coral reefs is inauspicious and there is no doubt that the damage we are causing to the oceans is catastrophic – but writing coral’s obituary at this moment would diminish all the hard work that scientists and conservation organizations are doing to preserve them. Fortunately, the public and political awareness of these issues is growing; now we must work together and put pressure on governments to achieve a great systematic change if we want to carry on living on this beautiful, blue planet.

References:

Alvarez-Filip, L., González-Barrios, F.J., Pérez-Cervantes, E., Molina-Hernández, A. and Estrada-Saldívar, N. (2022) 'Stony coral tissue loss disease decimated Caribbean coral populations and reshaped reef functionality', Communications Biology, 5, 440. https://doi.org/10.1038/s42003-022-03398-6

Kotrikla, A.M., Zavantias, A., Kaloupi, M. (2021) 'Waste generation and management onboard a cruise ship: A case study', Ocean & Coastal Management, 212, 105850. https://doi.org/10.1016/j.ocecoaman.2021.105850

Australian Institute of Marine Science (2025) ‘AIMS Long-term monitoring program report: Coral status of the Great Barrier Reef 2024-2025 (Final report)’, Australian Institute of Marine Science. https://www.aims.gov.au/sites/default/files/2025-08/AIMS_LTMP_Report_GBR_coral_status_2024_2025_ final_web.pdf

Fabricius, K. E., Brown, A., Collier, C., Pineda, M-C., Robson, B., Uthicke, S., Waterhouse, J. (2025) 'The seven sins of climate change: A review of rates of change, and quantitative impacts on ecosystems and water quality in the Great Barrier Reef', Marine Pollution Bulletin, 219, 118267. https://doi.org/10.1016/j.marpolbul.2025.118267

Greenpeace (2024) ‘Paying the price’, https://www.bing.com/ck/a?!&&p=65ac1ad808a58c10b2c993f527c142458a12b16d5b53ae4615d41dd192 6e97d9JmltdHM9MTc2MjgxOTIwMA&ptn=3&ver=2&hsh=4&fclid=21ec04e2-849d-661c-3ee3-127c85ac6 7b7&psq=greenpeace+paying+the+stamp+out+poverty+briefing+document&u=a1aHR0cHM6Ly93d3cuZ 3JlZW5wZWFjZS5vcmcvc3RhdGljL3BsYW5ldDQtaW50ZXJuYXRpb25hbC1zdGF0ZWxlc3MvMjAyNC8x MS9lNGRlMjc1ZS1wYXlpbmctdGhlLXByaWNlLnBkZg

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