One of the things I am doing for my PhD is going back through photographs I have taken over the last six years and annotating them. I am hoping that, in the end, some patterns will emerge around the seasonality and abundance of algae. As I do that, I am also noting key coral species as they appear, one of which is the Goniopora, or flowerpot coral.
As I trawl through these photos, I keep coming across something I have always called ‘net’ coral. But should I really be noting these as flowerpots, or as something else? At first glance, they look very similar. I decided that I’d better check; this is what I found out.
Flowerpot corals (Goniopora) have 24 tentacles
These flowerpot corals have fuller-looking polyps
Some of the flowerpot coral polyps, above, are retracted, and some are extended
Alveopora – or ‘net’ coral – and flowerpot corals can look remarkably alike. Both have long, daisy-like polyps that extend out from the colony and sway beautifully in the water. But there is one very handy clue that usually separates them: Alveopora polyps have 12 tentacles, while flowerpot corals – usually species of Goniopora – have 24. That gives Alveopora a slightly neater, lighter look, while flowerpot corals often appear fuller and more crowded.
In our lagoon, Alveopora colonies also tend to be much smaller than the flowerpots. Another difference lies in the skeleton. Alveopora has a more lightly built skeleton with more porous walls, whereas Goniopora tends to have a heavier, more solid-looking corallite structure. You often cannot see that clearly underwater unless the colony is partly retracted, but it helps explain why the two can look so similar at first glance while belonging to different genera.
Here are a few photos to illustrate the differences: Goniopora, above; Alvepora, below.
Net corals (Alveopora) have 12 tentacles
On Norfolk Island, net coral colonies inside the lagoons tend to be smaller
Some of the net coral polyps, above, are retracted (right), and some are extended (above)