Pollution and climate change - the state of play
Coral reefs are ecologically and economically immensely valuable. More than 500 million people are directly dependent on them. However, they are deteriorating critically at a global scale due to environmental impacts caused by man-made activities.
These effects are both direct, such as pollution, overfishing, and indirect – increasing sea surface temperatures due to climate change. The result is the impaired health of the corals, which can be described as ecosystem engineers.
It has been estimated that, globally, more than 50% of coral reefs have already been lost since the industrial revolution. Mortality has increased in frequency and intensity in the last two decades. The death of a reef often follows a mass bleaching event – the corals lose their colour – due to the rising sea temperature.
While political policy mechanisms must be used to reduce the causes of climate change, our researchers are seeking ways to conserve corals for as long as possible. To achieve this, we are investigating a number of approaches. And we are conducting research to understand more about the general ecology of corals.
What we're doing
We are working on several projects with our international collaborators. This includes:
- Creating ‘probiotics’ to improve the health of corals
- ‘Co-culturing’ corals with sea urchins to increase survival rates
- Investigating how the effect of climate change on salt levels in sea water is linked to corals’ sensitivity to temperature
Dr Michael Sweet, Associate Professor and lead principal investigator of our Aquatic Research Facility, says: “What makes our work special (in our eyes) is our close collaborations with other groups from charities, trusts, universities and even the United Nations and other policy makers. These tight collaborations span many countries and continents, including projects running in America, Australia, Maldives, Brazil and Palau.”
And Dr Till Röthig, researcher in the Aquatic Research Facility, adds: “This is exciting work on the forefront of international research. And maybe our work can help corals and their struggle with climate change at some stage – but we really need to cut carbon emissions globally.”
'Probiotics' for coral
One strand of our research focuses on the microbial communities that are associated with corals. These are the groups of microorganisms, the tiny creatures that share the corals’ living space.
As with any animal, corals host rich and diverse microbial communities, often referred to as the coral’s microbiome. Unlike most other animals, however, corals also host single-cell algae from the family symbiodiniaceae. These algae are extremely important to the corals. They provide the corals with essential nutrition – think along the lines of sugar in your coffee or tea.
Other microbes, for instance, bacteria, acquire and recycle nutrients for the coral. They are also involved in mechanisms that support the coral’s immunity. The coral microbiome therefore plays a crucial role in the health of corals. This includes when the corals are stressed due to climate change impacts.
In this context, we co-created an international network, the Beneficial Microorganisms of Marine Organisms (BMMO), to assist in the understanding of the functions of specific microbes and to investigate the potential for employing them as ‘probiotics’.
The goal is to apply microbes to corals in a similar way to humans eating probiotic yogurts to support the microbial community in your gut. This may very well offer increased resilience of some corals in the face of the ongoing environmental changes.
The manipulation of microbes has been successful in plant research, for instance to clean contaminated soil and water, and in aquaculture (the farming in water of fish, shellfish, aquatic plants etc). Coral probiotics is very much in its infancy.
However, due to improved laboratory techniques, large portions of the coral microbiome are now culturable, meaning we can cultivate them in the lab. This has led us to identify the first collection of bacterial groups which, upon inoculation of corals, increase coral resilience.
However, the enormous complexity of the coral microbiome presents a substantial challenge to identifying specific functions of certain individual key or core microbes and how they benefit their host.
Dr Röthig says: “We address important questions of evolutionary biology, for instance: how does the symbiosis between corals and their microbial partners really work?”
And the application of “microbial treatments” in the marine environment and over large areas is an unprecedented undertaking. It bears many risks which need to be taken into consideration.
Professor Sweet adds: “We really believe in the power of our tiny microbial partners and exploring how they shape and drive functionality in any given host always brings to light something exciting and novel with each and every experiment we undertake.”
Increasing survival rates
Our researchers have found one way of increasing survival rates in young corals – raising them with juvenile sea urchins. Our work with the Horniman Museum and Gardens in London found the survival rate was eight times higher if the lab-spawned corals were raised alongside the young sea urchins.
This is because algae, which can overwhelm reefs if not kept in check, is eaten by the juvenile urchins without damaging the coral. Adult sea urchins can cause damage and will even eat coral. Compared with a coral survival rate of just 5% in a tank without any urchins, researchers found that 40% of the corals survived for six months in the tank with the most urchins (18 urchins reared alongside 1,250 corals). The research was published in September 2019 in open access journal Scientific Reports.
Professor Sweet says: "This research has overcome significant challenges in terms of logistics and husbandry, to rear sea urchins to exactly the right size to graze without damaging the juvenile corals, allowing them to thrive. In addition, we highlight one possible way in which reef restoration can be self-funded, by co-culturing a commercially important species and using the profits to funnel back into methods to try and save our reefs."
Dr Jamie Craggs, lead researcher and curator at the Horniman Aquarium, says: "Low survival rates of juvenile corals are currently a barrier to effective reef restoration. This new co-culturing technique using sea urchins makes possible a major up-scaling in the number of corals that could be reared and transplanted onto damaged reefs, and we’re already getting interest from leading reef restoration organisations around the world."
An overlooked key threat
Dr Röthig is also investigating a previously overlooked threat to coral. He is researching how climate change affects the salinity of sea water and how this is linked to the thermal sensitivity of corals.
He explains: “Coral reefs are under critical decline from rising temperatures globally but low salinity seems to decrease the thermal tolerance of corals. High temperatures in particular, but also low salinity, can cause coral bleaching and mortality – the main reason why we have lost globally about 50% of coral since 2015.
“For corals to withstand rising temperatures for longer, the interactive effects with salinity may be crucial. The whole topic could have massive implications for coral restoration and conservation, and yet it is largely overlooked.”
Dr Röthig has received an international award for this research. He is the recipient of the 2019 Ruth Gates Memorial Award from the International Coral Reef Society. The award comes with a $5,000 research grant.
He adds: “The award means an international recognition of the importance of the work we are doing in the field of coral research at the University of Derby and its potential implications for the protection and regeneration of reefs across the world.”