Acropora ID mini-class

[Julio]

This is a gret thread already with out the class even starting.

[EricHugo]

ok...so tomorrow we do radials..and then its time to get out the books and see what we have.

[firefish15]

Hi Eric,
I took your Coral Biology class over at Reefs.org last year. I didn't have my tank set up at that time so could not do any of the labs. This is a great opportunity for me. The coral I'm trying to identify is a " Fancy Acropora" I bought at as a lfs. It was mostly brown at the time but changed into a real beauty after a few weeks. It's a small colony about 3" x 4" so I'm not sure of the growth form. It looks similar to yours which you describe as digitate and clump-like.

[firefish15]

After 3 months.

[firefish15]

branch.

[firefish15]

Here's a view from the top showing axial and radial corallites.

[firefish15]

Closup of axial corralite. 6 primary and 6 secondary septa. I don't have the measurements yet. I'll try tomorrow.

[piercho]

Firefish those are excellent photographs of the coralites. Can I ask for a simple description of how you are getting them?

[MiddletonMark]

How did you get those pictures? They're great.

Time to get on board.

Purple-Tip Acro, acquired by frag, not given species name [though likely what's often called A. nana]. If I had a photo of the mother colony [many years old] it probably would help a lot.

Anyway, photo of mother colony below:



With a small piece, it's hard to tell growth form ... but I'm thinking it looks like Wallace's `H' ... caespitose-corymbose.

Bleached frag is here [hopefully I don't need to frag again to get something more, but oh well, it'll just grow]:

Need to pick up batteries for my calipers tonight, jump on the corallites with even more added information to swim through

[EricHugo]

Nice to see some more vicitims here.

So, as mentioned radial corallites typically form as buds from the axials and lie between and around them. By comparison with axials, radials are quite variable. Wallace notes that the terminology for them stems from Dana in 1846 and makes significant use of anatomical terms. The wall of the radials can be complete and tubular, or they can be incomplete, as though an incipient tube-like corallite was chopped off. In contrast to axials with their normally round openings, radials can have round, oval oblique or have an extra bit of skeleton lost at the outer and upper edge (dimidiate) or an extra bit added to the outer and upper edge. The latter case produces nose-like or nariform radial corallites. Additionally, the angle of the radials against the corallum or axial wall can vary from perpendicular (sticking straight out) to totally appressed. The shape of the corallites is also variable as will be seen in the idealized drawing below. As if this isn't enough, numerous variations may occur along a branch and within a colony. Gradations are common along a branch in many species. Radial corallites can also be dimorphic, with more that one type/size occurring on a colony. Finally, one must again consider the septa in each type of radial corallites, the same as with the axials.

It is probably helpful to look at many colonies to become more familiar with all the different sizes, shapes, types, and variations.

Whew. Now, let me post the image of radial corallites from Wallace, Carden C. (1999) Staghorn Corals of the World, CSIRO, Queensville. p. 55.

[EricHugo]

Here is a list of terms:

tubular : tube-like
cochleariform : ear-like
nariform : nostril- or nose-like
labellate : lip-like (can be flaring or straight)
conical : the distal end tapers from a wider base
rounded tubular : berry- or keg-like
appressed : angled so that the inner edge lies against the corallum
sub-immersed : barely sticking out from the corallum with little ridges of wall showing
immersed : totally flat against the corallum
oblique : the opening appears as though a tube was cut at an angle
round: the opening is rounded when viewed from the end
oval : the opening is oval when viewed from the end
dimidiate : the wall forming the opening is incompletely developed

So, in a nutshell:

1. determine how many basic types of radial corallites exist on your colony
2. assess the angle - see if any gaps exist completely around the corallite, or if part of the corallite touches and remains connected with the rest of the corallum (appressed)
3. determine the opening shape
4. detemine the corallite shape
5. Measure the average corallite length, outer and inner diameter
6. Assess the septa as with the axials (how many, in how many cycles, and the degree as an approximate percentage of the radius with which they project into the opening).

Fortunately, we really don't have to address the variations along the septa as is required for many other corals. That makes is so much easier, doesn't it?

[davejnz]

Just got my branch and will be geting some photos tonight of mother colony so i'll be with ya soon

[JB NY]

Here is the best closeup of the axial corallite I could get.


I count primary six septa. No secondary.

Trying to add it little more that I can observe.

Septal lenght is mostly equal
Cycles of septal: One cycle
Septal height: not exsert
septal dentition: forms comb rows (not 100% on this as it's hard to see)
Paliform structures: absent

Hopefully I'll get a caliper today.

[EricHugo]

So, for my coral, I have a big mess.

I seem to have two primary types of radials

One set is mostly immersed with some sub-immersed towards the branch ends, with round openings ( I'll measure and assess septa under the scope later)

The other set is pretty much everything but the kitchen sink....I'll point this out in the figures attached.

[EricHugo]

and again

[EricHugo]

and the last

[EricHugo]

now...knowing this, and having come this far (though we have a ways to go yet), go back and look at an Acropora in your tank and try to evaluate it.

Tomorrow we will do the coenosteum, and then we are finished with the morphology.

[JB NY]

1 One type of radial corallite
2 Radial corallites are 'appressed'.
3. radial corallite opening is dimidiate.
4. radial corallite shape is nariform.
5 & 6 I'm having poor luck finding a caliper to measure such small amounts (mm).

[ReefDiver]

WOW! I have been following this thread but do not happen to have an Acroporid available for ID at this time. Talk about a putting a puzzle together? Very interesting, to say the least. I wonder, after all is said and done, what the accuracy of this endeavor is? It obviously would vary depending on the person doing the examination procedure, would it not? So, if we took a colony of the same species and had three different examiners go through this and each come up with an ID, what would be the interexaminer error? Eric, what about a species that exhibits different growth forms and is found on different parts of the reef? If one were to take samples of these different growth forms and perform this evaluation would it be expected that they would key out as the same species? Or, would the variations in growth form lead to different results? Considering that one must use all of this sequencing to perform an ID, how really accurate is the process? I guess if a coral taxonimist is doing the ID, then his/her results should be fairly accurate and reproducible by another examiner. Not trying to be difficult here just had some questions related to this very interesting topic.

Thanks for putting this together and giving us your time. As usual, you have outdone yourself!

[MiddletonMark]

Steve, if you'd be interested in a branch to look at ... I could probably get you one ... somewhat of a small one [1.5" or a little more], but that's all my coral has right now [as my purple-tip shudders in fear ]
If you want to join the befuddled masses ... watching from the peanut gallery might be more fun.

-- And great questions. I think part of this exercise is to make very clear that the `observer' is an important part of the ID, never mind that we may not have `representative' specimens in our tanks.

[davejnz]

heres a pic of the branch i have

[davejnz]

and here's the colony from the LFS that it was broken off of.It was sold as a blue-tipped Acro.I would say its closest to E arborescent according to Wallace
I'll be taking measurements and septa counts later this evening and will post back

[JB NY]

Eric, on your branch you labeled a few corallites on your branch as "not appressed, tubular". I would assume that when a new axial corallite forms it takes this look before it becomes more distinct as an axial corallite. How do you differentiate between a radial corallite and a newly formed axial corallite?

[piercho]

To repeat the history of mine, it was a fragmented from a larger colony 3 months ago. When it was placed in my aquarium, it was oriented on its side. Instead of starting new growth from the upper side (like I've seen A. youngei do) the original axial tips continued to grow, but bend upward as they grow.

When I look at a branch with 3 axials, the radial coralites are fairly consistent, within zones. I am calling these the zones of my piece:
Axial, upwards.
Axial, lower.
(below the) Branch, upwards.
Branch, lower.

Axial, upwards: radials are appressed tubular, becoming more submersed as you go from the axial tip toward the branch. Septa are similar to axials described earlier.

Axial, lower: radials are appressed tubular, but more submersed than the axial, upwards radials. Occasional tubular with round opening on lower side. I think these are probably incipient axials. The septa seem more distinct in the tubular with round opening corallites.

Branch, upwards: Very submersed appresed tubulars. Denser (more numerous per unit area) than the branch, lower radials. Corallites appear smaller than the radials on the axials.

Branch, lower: Nearly emmersed radials. These coralites appear to be the smallest. Septa are very indistinct.

Measurements are not possible with the calibers I have. Maybe it's time to break out for a new instrument...

[EricHugo]

Nicely done guys:

Steve: Charlie Veron gives a talk where he describes the speciation problem in corals using a eucalyptus example...the eucalypt he knows from Townsville changes as you go towards Melbourne, and by timeyou get there, if he saw the tree without seeing the variations along the path, he would not know it as the same eucalypt. Same thing here. You will expect great variation across a range, and that is why when ID'ing these corals you need to be familiar with the variations, some of which are available by personally knowing/collecting/ID'ing them, some of the variations shown in photos like in Wallace and the early Veron Scleractinia of E. Australia. Tank conditions change it, too. And yes, bias by the person working the samples. And yes, maybe the morphological characters are too deceptive.

But, all of that is part of the excercise. We are seeing how to do it, even if only theoretically or technically, and then if we do arrive at a species designation, this variation will be part of the lesson, even as in mine...within the same colony. So, long and short is that everyone is learning how to identify to species, seeing how it is not possible to see a living coral, a fragment, or a photo and say this is A. blahblahensis for the vast majority of cases. And, doing this really does bond you more to what you are keeping in the tank, knowing what it is, therefore knowing more about where it comes from, what conditions are ideal, etc. Plus, its just sort of fun.

JB - that is exactly right, and also what I suspect is happening in my coral...it is a developmental thing. But, given the numbers of variations and the gradient between types, what is "average" or "characteristic" of this colony? I don't know yet. I suspect as we get to the key part, I will have more choices to ponder than some of you.

For you guys having difficulty measuring...do your best. If you find there are parts of the identification you cannot accomplish, then you know the limitations you have and is valuable information in and of itself. You may be able to get to species without the measurements, or it might be critical in distinguishing between two or more. Time will tell.

So tomorrow, its the coenosteal features. Then time to hit the books.