Scientific study finds laboratory-grown corals proved resistant to bleaching during the 2023 Caribbean marine heatwave
SECORE International’s Coral Seeding programme utilises laboratory-bred corals for reef restoration, and a new peer-reviewed study has shown that the method has proven successful in reducing Caribbean coral’s susceptibility to bleaching
Coral seeding involves the laboratory fertilisation of gametes collected from wild corals in a laboratory, breeding the resulting larvae in special enclosures in the ocean and then replanting them on damaged reefs once they have matured sufficiently.
The programme – now present in nine Caribbean nations – increases the genetic diversity of the local corals, thus improving their chances of survival through changing ocean conditions.
The new study has found that young corals bred through the seeding programme remained healthy during the marine heatwave of 2023, which proved fatal to many corals in the Caribbean Basin as a sustained increase in water temperature precipitated a mass bleaching event across the region.
Coral bleaching occurs when elevated water temperatures cause the coral’s symbiotic, nutrient-providing zooxanthellae – a type of algae – to be ejected from the coral’s polyps, returning them to their natural translucence and exposing the white coral exoskeleton beneath, giving them the appearance of being ‘bleached’.
Bleaching is survivable if temperatures return to normal or the coral acquires more heat-resistant zooxanthellae, however, as the elevated water temperatures persisted across the Caribbean during the summer of 2023, many weakened corals died.
During a routine health check of out-planted corals in Mexico, SECORE scientists found that the young corals they had grown appeared to be completely healthy amidst the other corals on the reef, which had bleached.
Similar observations were made across 15 sites by SECORE teams in Curaçao, Bonaire, Dominican Republic and St Croix, in the US Virgin Islands, confirming that lab-grown ‘Assisted Recruits’ of six reef-building coral species have proven substantially more resistant to extreme heat stress than their wild counterparts.
‘We were excited to observe this pattern showing another benefit of using assisted coral recruits in restoration,’ said Dr Margaret Miller, SECORE’s Research Director and lead author of the new study. ‘These results provide a lot of encouragement and confirmation that restoration using assisted coral recruits can play an important role in orchestrating coral persistence into our warmer future.’
Most coral restoration programmes involve collecting pieces of broken coral and growing them in protected coral nurseries before returning them to damaged reefs. The problem with this method is that it creates genetically identical clones of the existing colonies, which remain susceptible to the same stressors as before.
Sexual reproduction, however, increases the genetic diversity of a species meaning that there is a greater chance that individual colonies will survive events that threaten others. The new SECORE study is the first scientific evidence that coral restoration utilising this method creates more resistant colonies than those created through fragmentation.
‘I am excited about the very positive results of this large study since it shows that our Coral Seeding approach is an important contribution to help coral reefs deal with climate change,’ said Dr Dirk Petersen, SECORE’s Founder and Executive Director. ‘Our investment over the past five years to build a large network for coral restoration in the Caribbean has paid off.
‘This network not only produces and outplants tens of thousands of corals every year but could also immediately assess how these corals responded to this unprecedented heat wave. Our priority is now to further scale efforts to the ecosystem level.’
The study ‘Assisted sexual coral recruits show high thermal tolerance to the 2023 Caribbean mass bleaching event’ (Miller et al, 2024) is published in the peer-reviewed journal PLOS ONE.
