Researchers from the University of Amsterdam, SECORE International and the Carmabi Marine Research Station have for the first time successfully raised laboratory-bred colonies of the critically endangered Caribbean coral species elkhorn coral (Acropora palmata) to sexual maturity. This event marks the first ever successful rearing of such a Caribbean coral species to its reproductive age. The researchers’ findings are published in the latest issue of the scientific journal 'Bulletin of Marine Science'.
The Elkhorn coral is one of the most important reef-building corals in the Caribbean. Due to its large size and branching shape, elkhorn corals have traditionally formed vast forests in shallow reef waters that protect shores from incoming storms and provide a critical habitat for a myriad of other reef organisms, including ecologically and economically important fish species. Whereas it used to be found abundantly throughout the region, its numbers have plunged in recent decades by between 80 to 90 per cent.
Elkhorn corals reproduce only once or twice a year, generally a few days after the full moon in August. During those nights, Acropora colonies synchronously release their gametes (reproductive cells) into the water column. Traditionally, most techniques for rearing coral have centred on the ‘coral gardening’ approach, where small fragments are harvested from colonies on the reef and then grown in special nurseries to larger sizes before being returned to the reef. By using a new technique, the research team collects a small proportion of these gametes by gently placing special nets around spawning colonies to collect the floating gamete bundles. After collection, the researchers then produce coral embryos by in vitro fertilisation, mixing sperm and eggs in the laboratory. Coral embryos develop into swimming larvae within days and eventually settle onto specifically designed substrates. After a short nursery period, the substrates are outplanted with the newly settled corals to the reef.
‘We just learned that elkhorn corals can reach sexual maturity in only 4 years. This is exciting news, as we now know that offspring raised in the laboratory and outplanted to a reef can contribute to the natural pool of gametes during the annual mass-spawning of elkhorn corals within 4 years’, says Valérie Chamberland, a PhD researcher at the UvA’s Institute for Biodiversity and Ecosystem Dynamics.
According to Chamberland, the next step will be to assess whether the researchers’ methods can also be applied to reefs that are more degraded than their study site. ‘Any particular reef requires tailored solutions to address its causes of deterioration, and propagating laboratory-bred corals to a degraded reef will only aid its recovery if the major causes of degradation are minimized at the restoration site prior to outplanting. The next step is therefore to apply our techniques in a holistic way, in concert with other management tools such as fishing quotas, coastal protection and pollution regulations’.
Chamberland, VF; Petersen, D; Latijnhouwers, KRW; Snowden, S; Mueller, B and Vermeij, MJA. 2016. Four-year-old Caribbean Acropora colonies reared from field-collected gametes are sexually mature. Bulletin of Marine Science. doi: 10.5343/bms.2015.1074.