Hybrid reef animals are a very common sighting and it is especially well documented in the marine angelfish, clownfish, butterflyfish, surgeonfish, and basically many different families of fish but it is much less well documented or studied among the corals. We know that coral hybrids can occur because it’s been discovered and proven with genetic studies but it’s much less well understood because seeing a coral and recognizing it as a hybrid is much less straightforward.
Part of the reason for this uncertainty towards unusual coral genetics and pedigree is that a single coral species can occur in many different colors and strains and the appearance can change dramatically based on environment, especially depth dependent light intensity and exposure to water motion. One species which is notoriously variable is Pocillopora damicornis which even reefers will have noticed can grow into thick, clubby branches like a Stylophora under the strongest light and water flow or into to very graceful delicate branches that are easily broken like the closely related Seriatopora.
But what reefers might not know is that not all thin-branched Pocillopora are the quasi ubiquitous P. damicornis as there is one species which is readily idientified if you know how to recognize it. Pocillopora acuta is the thinnest branching species of this popular group of fuzzy polyped corals and it can be distinguished by its sharper more pointed tips to the branches, which are usually crowded with corallites that are more oval than they are round, a feature which may be hard to spot with the naked eye but is more apparent under the microscope or with an aquarium mesoscope.
We started down the rabbit hole of understanding the range of Pocillopora growth forms when we spotted the photograph below on Corals of the World’s page about mesophotic corals which captioned this image as ‘unusual open growth form of Pocillopora damicornis 33m deep Yap Micronesia’. Clearly this coral is not a typical P. damicornis and it really has some Seriatopora birdnest coral vibes about it with branches that are sharp ended like P. acuta, but they are also quite straight and more orderly like a birdnest coral.
Our hybrid-reef-animal radar definitely got some signals when we did our visual analysis of this particular coral and as we’ve seen with the Lazy’s Blue Zing birdnest hybrid, it is possible for these brooding corals to cross within the species so perhaps it’s also conceivable that a birdnest and a Pocillopora could also hybridize in a similar manner. For sure we are biased towards wanting this scenario to be possible, this unusual looking colony is most likely a very odd growth form of Pocillopora acuta growing like this in a deeper habitat sheltered from water flow, but the reefer in us would love to grow this coral in a higher energy environment to observe how its morphology might change.
Pocillopora may not be part of the ‘it coral’ crowd these days but they are very hardy, come in a wide range of colors, and have the kind of perennial polyp extension that reefers can only dream of seeing in their other small polyped stony corals. Even the fast growing P. damicornis can come in a wide range of shapes and colors and we’re confident that several of the thinnest branching strains probably represent the sharp tipped P. acuta so next time you spot some pieces of Pocillopora colonies or frags for sale or in a tank, take a closer look to see if you can spot the differences between the thinner branching species.