A helping hand for coral reefs With the temperature of the world’s oceans rising, concern is growing about the ability of coral reefs to adapt to climate change. We spoke to Dr James Guest and Dr Adriana Humanes about the work of the CoralAssist project in investigating whether selective breeding and the assisted gene flow (AGF) technique can help some coral reefs survive in the face of climate change. The world’s coral reefs
have been degraded by human activities, such as overfishing, over a long period, but this has accelerated over recent decades and rates of coral mortality have increased significantly over the last three decades. The largestscale coral mortalities that have occurred in recent years have been caused by rising sea surface temperatures, as Doctor James Guest explains. “If the sea temperature rises above what corals normally experience, and that temperature remains high for even just a week or two, then the corals will start to appear very pale. That’s because they’ve lost the symbiotic algae that occur inside their tissues. Those algae are part of a symbiotic partnership with the coral animal host, which is critical to the coral’s health,” he outlines. Some corals are better able to withstand heat stress than others, a topic of great interest to Dr Guest. “We have seen that if we put corals from a genetically diverse population under heat stress, we find some individuals which are more resistant than others,” he says. “What interests me is whether the attributes that make some corals more resistant can be passed on to their offspring.”
CoralAssist project This is a central part of the research agenda in the CoralAssist project, an ERC-funded initiative which brings together scientists from several different disciplines to investigate whether the Assisted Gene Flow (AGF) technique could be used in coral reef conservation. AGF involves the deliberate movement of individuals within or between habitats for the express purpose of increasing the frequency of better
adapted individuals to a desired condition in a population. A key step here is to identify the corals that are more resistant to heat stress. “We have tagged around 400 coral colonies on the reef, which we’ve been following for two years,” explains Dr Adriana Humanes, a post-doctoral researcher in the project. The aim is to identify which coral colonies have the highest tolerance to heat stress. “We take small fragments from these corals and bring them to the laboratory. Then we put them in tanks where we increase the temperature over a period similar to what they have experienced on reefs where there have been bleaching events,”
combining a range of different techniques, including physiology and proteomic analysis of the different corals, Dr Humanes and her colleagues aim to build a deeper understanding of the factors that affect heat-tolerance. “We’re looking at different characteristics of these coral colonies, to try and understand what gives them this higher heat-tolerance,” she explains. While a lot of research in this area has previously centered on the genes that these corals express, the project is looking at the proteins they produce rather than the genes. “These proteins actually control the traits that are expressed,” says
We have seen that if we put corals from a genetically diverse population under heat stress, we find some individuals which are much more resistant than others. What interests me is whether the attributes that make some corals more resistant than others can be passed on to their offspring. continues Dr Humanes. “So, we perform heat stress in a similar way to that seen in the natural environment, then record which fragments bleach and die and which ones survive.” Once it has been established which corals have a higher tolerance to heat stress, they can be bred together to find out if these traits are passed on to their offspring. Baby corals from these selected crosses are reared until they are adults to see if this heat tolerance persists through time - it may even be possible to see if it passes on to second or third generations. The underlying mechanisms behind these differing levels of heat-tolerance among corals are not fully understood, but this is a major topic of interest for CoralAssist. By
Dr Guest. “We’re working with proteomics specialists and protein chemists who have a lot of expertise in using mass spectrometers. That’s quite a novel part of our research.” This is a complex area, and there are many considerations to take into account when investigating coral health responses to heat stress. Alongside the coral animal itself, algae on the coral, the microbiome, and various other factors may affect heat-tolerance. “There are many areas of interest at the same time. Previous studies have suggested that in some cases, characteristics of the host coral are involved in heat-tolerance, but in other cases components of the microbiome, or the type of symbiotic algae inside the tissue may be more
Two-year old selectively bred corals being reared within an ocean nursery in Palau. Photograph by Till Roethig.
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