Acropora tenella is one of the lesser known ‘deep water’ or ‘naked’ style Acros, and it can be quite beautiful and colorful too. However a recent observation of this species in the coral obliterates the maximum known depth for this genus in the Coral Sea.
The Tenella Acro is not particularly rare but it does prefer living at moderate depth and we’ve actually seen some beautiful colonies of a red form we call the Red Devil at around 60 feet in Kwajalein Atoll. However very large stands of this species are sometimes seen in clear oceanic water at a depth of around 100 feet where other Acros would struggle in the low light.
The flattened tubular branches of A. tenella are actually quite attractive, sometimes with neon green polyps on colorful tissue. This semi-tabling growth form is especially well adapted to collecting light in deeper environments but no one could have imagined how deep it was recently found.
The Coral Sea is well known for the clarity and visibility of its water and this is certainly one of the factors that allowed a colony of A. tenella to be found living and growing at a depth of 110 meters, or around 360 feet!
This depth record ties the observed depth of 110 meters for an Acropora longicyathus in the Marshall Islands, where the light level is around 1% of what is available at the surface. This just goes to show you that although we tend to think of Acropora as light loving SPS coral species, there’s definitely a subgroup of these which are well adapted to very low light. [Springer]