After a tough start to the year for our house reef and nursery here at Petite Anse, we’re happy to see that things are now looking up for corals. Yes, over the past few months our reef has been recruiting! …but perhaps not in the way you think. We don’t mean that job adverts have been posted and the reef is hiring new herbivores, no crab recruitment happening here. No, a “recruit” in coral terms means a young coral colony which has recently settled on the reef substrate.
You may know that corals, being the savvy, enterprising creatures they are, can reproduce in several ways. A coral colony can reproduce asexually by budding, where coral polyps in a colony produce clones of themselves. This way the colony builds up over time, with each new coral polyp secreting its protective calcium carbonate shell around its soft body, building up the hard structure of the coral. This photo, by Christophe Mason-Parker, is of a branch of an Acropora colony, with the individual coral polyp cups clearly showing and even some tiny ones in amongst the bigger ones – budding in action!
The second way corals reproduce is sexually and corals have several ways of doing this. One such way is spawning, a synchronised mass release of eggs and sperm into the water, this happens simultaneously to increase the chances of fertilisation and usually after a full moon and at high water. This can take place over a week, with different species releasing eggs and sperm on different nights to prevent hybridisation. Once fertilised these tiny fledgling corals float around as larvae before settling on the substrate as a new recruit. Corals can also reproduce sexually through brooding. As most corals are hermaphrodites they can fertilise eggs within individual coral polyps and then release this readily packaged larvae into the water ready to float its way to a likely looking patch of rock, fix itself down and start growing.
We’re seeing different species of recruits in our shallow reef these days and are happy to see Acropora sp. and Pocillopora sp. among them, these corals were some of the hardest hit by this year’s bleaching event, when we lost more of the established colonies of branching corals on the shallow reef. So hats off to them for pushing back!