ACE Spotlight: Anushka Rajagopalan

Anushka Rajagopalan is a Master's students at the University of Edinburgh, and a member of the Changing Oceans research group. Here she shares some insight into her research on cold water corals.

Author: Francesca Roberts

Editor: Anushka Rajagopalan

What do you picture when you hear the word ‘coral reef’? What colourful images from the shores of Australia, the Maldives or the coasts of Indonesia come to mind? What warm tropical waters do you imagine?

Do you also think of cold depths of up to a thousand meters? Reefs off the coast of Norway or North Scotland? No? Well, I am not surprised if not.

Many people do not know that cold-water corals (CWCs) exist, let alone that they are vital for supporting marine life and maintaining ocean health. Corals are colonial marine animals composed of individual polyps. Coral species can vary based on location, structure, growth forms and more. CWCs are found at much deeper depths than their tropical cousins; they can inhabit anywhere from two hundred to one thousand metres in depth.

Also, unlike their tropical cousins, they are greatly understudied, mainly due to the difficulties involved in accessing them. Many people, therefore, do not realise the great threat that these keystone species are under.

Anushka Rajagopalan, a Master's student in Marine Systems and Policies at the University of Edinburgh and a member of the Changing Oceans Research Group, is working to understand how a changing climate will impact these understudied organisms.

How do corals grow, and what is the aragonite saturation horizon?

Anushka: Many species of coral grow a calcite or aragonite (both forms of calcium carbonate) skeletal base precipitated from carbonate ions in the water. Live tissue can then grow on top of this carbonate skeleton. This rigid structure forms a foundational framework, supporting a vast range of both marine fauna and animals; corals can act as refuges, nurseries, breeding grounds and ecosystem engineers.

In the water column, seawater transitions from being undersaturated to saturated with calcium carbonate ions; this border is known as the aragonite saturation horizon (ASH). Calcium carbonate needs to accumulate and precipitate for coral to grow their skeletons. Under the ASH, calcium carbonate is undersaturated, so there is a greater chance for skeletal dissolution and lower habitat complexity.

How are the oceans affected by rising CO2 levels?

Anushka: The ocean acts as a great sink for carbon dioxide; CO2 dissolves in the water and in doing so, releases hydrogen ions, lowering the pH.

Between 1950-1965, it was recorded that 1.6 billion tonnes of oil were used per year. By 2015, this rate increased by more than seven times. As a result of using these fuels, 2024 marked an all-time high of 37.4 billion tonnes of global carbon dioxide emitted. The emissions that remained in the atmosphere contributed to a record CO2 concentration of 422.8 ppm that year. These values are 50% higher than pre-industrial levels.

An increase in the global atmospheric carbon dioxide concentration means the ocean is taking in an unprecedented amount of carbon dioxide. This is making our oceans more acidic.

There is a natural carbon cycle that occurs from atmosphere to ocean. The problem is that there are a lot of external drivers putting this cycle in excess. It’s not a balance anymore.

How does this affect CWCs?

Anushka: Increased ocean acidity reduces the availability of carbonate ions, crucial for corals to grow and survive. Over time, this causes the ASH depth to rise; the carbonate skeleton of corals below this horizon starts to dissolve, leaving the live tissue vulnerable to collapse. This phenomenon is known as coral-porosis.

Put simply, the depth at which corals can survive is decreasing dramatically each year.

Scientists have predicted that in the North Atlantic, the ASH level will rise from 2000 metres to just 115 metres by the end of the century, and in the North Pacific, the ASH level will rise from 140 metres to the surface. In other words, if emissions continue as normal, all coral below 115 metres depth in the North Atlantic Ocean and below the surface in the North Pacific, will be at risk of dissolution by the end of this century.

What are you investigating?

Anushka: The study aims to examine how end-of-century ocean acidification scenarios affect the structural dissolution of CWC species Lophelia pertusa, by making real-time observations on how L. pertusa reefs degrade. Lophelia pertusa is a species common to the Norwegian margin and offshore Scottish waters.

I am using both individual fragments and colony-sized pieces of recycled L. pertusa skeletons. Paraffin wax is used as a new methodology technique to mimic the live tissue component. In each of the tanks there’s a batch of 0%, 50%, and 90% wax treatments, referring to the percentage of the skeleton that is covered by paraffin wax.

This method prevents the need for a fieldwork period and is more sustainable; live animal samples do not need to be extracted. It also allows the study to be more biologically realistic than solely experimenting on bare skeletons or using computational modelling. The colony-sized samples are especially important, as they serve as ‘mini-reef’ projections where dissolution can be observed on a relevant size scale.

This study will facilitate realistic coral dissolution using more ethical and short-term methods. The pH treatments used (7.2, 7.6 and a control of 8.1) are purposely extreme to reach an accelerated point of acidification that translates to an end-of-century situation.

What have you observed so far?

I have observed some whitening of exposed skeleton compared to what is shielded from paraffin wax, which could be an initial indicator of dissolution.

I am planning to analyse the change in growth rate of the samples, and use electron scanning microscopy and a new 3D photogrammetry interface known as PolyCam to visualise these colouration changes.

coral fragments side by side — Both have 50% wax treatment, bottom half of skeleton is exposed, top half is covered in paraffin wax. Left: control treatment, pH 8.1. Right: acidic treatment, pH 7.2. The part of the skeleton not protected by paraffin wax appears whiter in the fragment exposed to the acidic environment. Whitening is one of the first indicators of dissolution.

Why does this matter?

Anushka: Coral is a keystone species, meaning if it disappears, the home for thousands of other marine species also disappears. Both tropical and cold-water corals support at least one quarter of all marine life. In 2013, Lophelia pertusa alone was found to support an estimated 1,800 other species.

Human beings are deeply reliant on the ocean for our survival. For example, many people rely on various fish populations to support their subsistence and economic needs. Fish themselves rely on coral reefs for their own habitats, so once a whole CWC framework collapses, that transcends to other trophic levels, and eventually, humans.

What needs to change?

Anushka: Humans are committing countless anthropogenic activities: trawling, dredging, plastic pollution, fossil fuel burning, deforestation… we are directly contributing to the degradation of these reefs.

Policy is the first step. There needs to be more fully protected marine areas established, whether in the UK or in international waters. In areas of the ocean without national jurisdiction, having agreements such as the High Seas Treaty ratified is really important. This would be a legally binding entity that can directly incorporate more protective measures to be enacted for CWC reefs. We need to be educating ourselves about what our politicians and elected representatives stand for, and if they can contribute to their member state ratifying something like High Seas.

Incorporating more eco-friendly activities in our lives can also be significant, for example, composting, reducing our plastic consumption, waste, car usage, and involving ourselves in local environmental restoration projects.

We’re at a time when people may not have much hope for conservation strategies, but it all starts at the individual level. If all 8 billion of us are saying I’m just one person, I can’t do anything, we’re not going to get anywhere.

Anushka hopes to continue her experiment over the summer and is aiming to publish her findings by next year. Her innovative and new methodology of using paraffin wax may also be used in further research at the university. The research may help other scientists find mitigative and restorative strategies as the threat of acidification persists.

Anushka’s work is demonstrating how important it is that now, more than ever, we make changes as a society to redirect the course we’re on. Her work displays how ‘business as usual’ is not only not sustainable, it is detrimental and could lead to the extinction of coral reefs, the foundational framework of the ocean, by the end of this century.

This article was published on 2025-06-23