AsianScientist (Feb. 03, 2023) – Climate change is warming oceans, which among other things is leading to increasing instances of coral bleaching, a phenomenon wherein rising sea temperatures kill algae living inside the corals, which then leads to corals’ death because they share symbiotic relationship with each other for survival.
Scientists have been trying to understand whether it’s possible to get corals to host the species of algae that can handle higher temperatures as that could prevent or slow down bleaching. In order to figure out how that might happen, “researchers first need to understand the biology of corals and how they might react to these interventions so that we can work effectively and efficiently,” said Shelby McIlroy, an assistant research professor at the Swire Institute of Marine Science in the University of Hong Kong.
Recently out in the journal Microbiome, McIlroy’s team unraveled the reward-and-punishment relationship between corals and algae. Corals may ‘punish’ the algae that live inside them by cutting off their food supply if such algae become selfish and renege on their part of the resource-sharing deal with the coral.
In the coral-algae relationship, the two sides – the coral host, and the algal symbiont, share and recycle nutrients they cannot access on their own. But this relationship is open to abuse. Corals can host several species of symbiotic algae at the same time, but not all algal species are honest. Some take advantage of their host by keeping more nutrients for their own needs instead of passing them to the coral. In this way, the selfish algae gain an advantage over more beneficial species that grow slower because they share their nutrients more generously with corals. This cheating ultimately undermines the long-term health and growth of the coral itself. “If we think about how evolution works, there would be a chance of parasitism where partners cheat more and are benefiting themselves,” McIlroy told Asian Scientist Magazine. “Whereas for the coral to be successful, it needs to be in a true mutualism.”
Using stable isotope techniques, McIlroy was able to unravel the flow of nutrients between different species of algae and their host corals. ‘Stable isotopes combined with genetic techniques allow us to track the currency exchange between the partners. In this case, the currency is nutrients, in the form of carbon and nitrogen,’ McIlory explained.
The research team compared the back and forth exchange of carbon and nitrogen with the algae density and the type. “We wanted to know how [the flow of the nutrients] changes relative to the types of symbiont that the corals have inside of them” said McIlroy. Their data suggest that corals could sense whether the algae living inside them is good or bad. Corals need the carbon from algae’s photosynthesis and the algae needs the nitrogen from coral. “Coral can turn off access to nitrogen when a particular algae is not passing enough carbon,” McIlroy said.
Understanding how corals control and manipulate their symbiotic algae is now crucially important for coral survival.
‘We may have the ability to intervene and help corals resist bleaching by exposing them to more thermally tolerant partners. There’s no time to lose.’ McIlroy said.
Source: Swire Institute of Marine Science ; Image: Shutterstock
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