Acropora ID mini-class

[EricHugo]

By the way....I'm sure many of you have read descriptions of Acroporid features before and sort of skimmed over them. Now, in a matter of days, you guys are basically able to do the same.

You would describe your colony of Acropora as, say, ceaspito-corymbose with axials having one cycle of equal-sized immersed septa, primary septa extending 75% of the radius, radial corallites appressed nariform to dimidiate, without radial dimorphism. Now that's a real description, not like "blue table with a cream base"

way to go!!

[firefish15]

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

Howard,
The pictures were taken with a Nikon cooplix 990 attached to a Leica GZ6 zoom microscope.
Paul

[davejnz]

looks like i'm gonna have to sit this one out,I tried with a 6x magnifying lens and with my poor eyesight it has been unsuccesful.thanks eric,this thread has been quite informative

[Julio]

How much do corals change in captivity to be calssified as a new species if much at all?

Great detail pics!!

[firefish15]

Axial corallite of my coral is approximately 2.5mm outside diameter and 0.8 inside diameter. These are rough estimates using a ruler. Here's a picture of the corallite next to the ruler.

[firefish15]

Originally posted by EricHugo
I would call my colony digitate and clump-like

Eric,
Your picture shows small branches at the top of some of the branches. Is this still considered to be digitate?
Paul

[EricHugo]

Later I amended that because it is small yet, and the clump-like part takes into account the branching, and I also said it might become more caespitose or corymbose over time. But, also, as mentioned, the definitions and sketches are idealized, and a number (in fact whole groups) of clump-like Acropora that stay smallish and have some branching at the ends are described as digitate. They don't all look like the classic A. humilis/gemmifera/monticulosa etc.

also, great job on the axial of yours.

[EricHugo]

Coenosteum is a term used to describe the skeletal material between polyps on corals. In Acropora, the coenosteum consists of the skeletal material formed by layering of synapticular material around the axial and radial corallites. Becuase it has different polyps types creating different corallite types, the coenosteum may be very different around and between corallites. However, this is not always the case, and it can be quite uniform.

There are relatively few terms used here, although a great degree of variation. The costae on coral skeletons are defined as the radial elements outside the corallite wall. A good example can be seen on an average Favia, where these radial skeletal elements are nearly continuous as the move over the wall of a corallite, forming the septa as they converge towards the center of the corallite.

In Acropora, similar radial elements can appear as parallel or nearly parallel raised bands of skeleton. The top edges of the bands can be smooth, or they can have jagged edges that appear like regular "teeth." These "teeth", or dentititons, are also called spinnules. Spinnules means "small spines." Spinnules have various degrees of development, and can be simply little points or shark-like teeth, or can be globular, highly ornately branched, forked, , labellate, lobed, etc. The spinnules tend to be quite regular, although again variation can exist. Finally, the coenosteum can be rather homogenous, forming a net-like appearance whereby it is termed reticulate. There can be a simple or elaborate reticulate structure. There are some excellent photos of examples in Wallace (1999) on p. 57 for those of you who have this book. Many of the photos posted here also have some nice views of coenosteum. The coenosteum very well might be among the most distinct characters on a species, and when coupled with the other characters already assessed, provides a pretty strong morphological description of the coral. Because of the variation in coenosteum, it is hard to describe in words, and often this is a place where comparison to photos becomes useful. It is also the least easily observed in living corals, being mostly to completely obscured by living tissue. It also becomes dificult sometimes where the base of the radial coenosteum joins the axial coenosteum, and this continuous structure sometimes becoomes a gradient of forms if the two have very distinct coenosteal morphologies. In other cases, it can be nearly continuous with very little distinction between the two. This seems to be more common with a simple costate or reticulate coenosteum.

Photos coming soon.

[ReefDiver]

Eric:

This is a little off topic but I was wondering how the directional growth patterns of the skeletal structure is laid down? If the polyp lays down the Ca matrix via the calicoblastic epithelium, then how is the girth or thickness of the main branches & corallites produced? I also notice in the cross sections of the corallites that between the inner and outer walls, there are many reticular "holes" (for lack of a better term} seen. Therefore, I would assume that the skeletal structure is far from solid. Do these "holes" serve as any connection for transport of nutrients, etc... or am I way off course here? Are these holes filled with tissue? Just trying to get a handle on the structural aspects. Thanks!

[piercho]

This may relate to what Steve just asked:

The cross-section of my branch where it was clipped from the colony had hollow-ish "channels" in it. There was one central channel surrounded by 5 smaller channels. The 5 smaller channels were arranged around the central channel in a relatively symmetric pattern.

Are these characteristics that are useful for specie identification? Or are they common to the genus?

[piercho]

I tried with a 6x magnifying lens and with my poor eyesight it has been unsuccesful

It is pretty comical with my 20X eye loupe and makeshift light-box. I don't know how you would get by without at least 20X magnification. I think I need what we use to call a "dissection" microscope with at least 25X magnification, a tray adjustable in 3 axis, and multi-directional illumination with intensity control. And a camera adapter so I can share what I'm talking about. And my calipers - which are pretty d*mn good for shop use - are still too clumsy for measuring anything except the outer diameter on the axials. And even then my accuracy is limited to 1/64". A digital caliper that can measure to 10ths of mm and the appropriate tips is what I need. This is interesting stuff but I don't know if I'm willing to invest in the tooling to do it properly.

[Meisen]

Eric,
Awesome thread! Just what all us acro-heads need to humble us even more lol. Is it OK to jump in to class a few days late? I just caught this thread today. I am going to bring a dead piece into my office tomorrow where I have a dissecting scope to work with. I will try to get up to speed with the morphology using what you guys have laid down already. Can I ask you to backtrack slightly if (when) I get all lost and confused?

[EricHugo]

Meisen
Is it OK to jump in to class a few days late?

Of course

Can I ask you to backtrack slightly if (when) I get all lost and confused?

definitely

piercho

It is pretty comical with my 20X eye loupe and makeshift light-box. I don't know how you would get by without at least 20X magnification.

LOL - indeed

I think I need what we use to call a "dissection" microscope with at least 25X magnification, a tray adjustable in 3 axis, and multi-directional illumination with intensity control. And a camera adapter so I can share what I'm talking about.

That's about right...because once you get it under the scope, its hard to get the right position of the corallites without clamping or propping.

And my calipers - which are pretty d*mn good for shop use - are still too clumsy for measuring anything except the outer diameter on the axials. And even then my accuracy is limited to 1/64". A digital caliper that can measure to 10ths of mm and the appropriate tips is what I need.

Hence the handiness of the scale bar in a scope lens.

This is interesting stuff but I don't know if I'm willing to invest in the tooling to do it properly.

You don;t have to...just do the best you can.


piercho

This may relate to what Steve just asked:

The cross-section of my branch where it was clipped from the colony had hollow-ish "channels" in it. There was one central channel surrounded by 5 smaller channels. The 5 smaller channels were arranged around the central channel in a relatively symmetric pattern.

Are these characteristics that are useful for specie identification? Or are they common to the genus?

The degree of interconnection is a hallmark of very porous skeletons and the polyps of corals like Acropora. It is not, to my knowledge, used in systematics.


ReefDiver Eric:

This is a little off topic but I was wondering how the directional growth patterns of the skeletal structure is laid down? If the polyp lays down the Ca matrix via the calicoblastic epithelium, then how is the girth or thickness of the main branches & corallites produced? I also notice in the cross sections of the corallites that between the inner and outer walls, there are many reticular "holes" (for lack of a better term} seen. Therefore, I would assume that the skeletal structure is far from solid. Do these "holes" serve as any connection for transport of nutrients, etc... or am I way off course here? Are these holes filled with tissue? Just trying to get a handle on the structural aspects. Thanks!

The holes are largely filled with tissue...Acropora is a reticulate network of interconnected polyps to a certain depth in the skeleton. Deeper than that, you get infilling, probably via precipitation and microbes rather than coral calcification - or possibly indirectly from calcification. There is a great schematic of the polyp network in Acropora in the Wallace book, as well.

[justgettinstarted]

i am going to have to try and get in on this when i get off work tonight.... I have an acro that i would be curious to try and ID

Eric, does it matter if it has been dead for maybe a month or so but still in the tank? The frag RTN'd

thanks

Garrett

[EricHugo]

Garrett:

It depends how much the skeleton has been encrusted...most will probably be algae and easily removed with the bleach. If there is a lot of erosion or coralline or calcareous stuff on it, it willbe variably useful - from partly to not at all.

[davejnz]

Well I'll try to continue,My colony is arborescent
measurement of axial: outer 3.8mm,inner1.6mm
axial appears to have 6 primary septa that are immersed and extend to center of corallite(columella?)
radial corallites are appressed,labellate,and dimidiate
will get radial measurements later.

[davejnz]

pic of branch with calpers used to obtain measurements

[EricHugo]

OK, sounds like everyone has moved along well.

Hopefully by now you have all seen what your coenosteum looks like

Now, both Carden Wallace and Charlie Veron have grouped Acroporid species into larger subcategories. Veron lists 38 categories, Wallace has 20. I rather prefer the way Wallace lists them since they are arranged phylogenetically, while Veron separates them morphologically. It may seem easier to deal with the latter, but the descriptives of the categories require almost as much work to translate as would the species itself, and many of the terms seem a bit vague. For example, Wallace would have A. horrida in the A. horrida group, consisting of 8 species related to A. horrida. In general, the members have a lot in common, but in some cases may be quite different in appearance. Not that this really matters, given the variability we have learned about, right? In contrast, Charlie puts them in the "species with middle sized branches and irregular radial corallites" group that has four unrelated or related species in it.

I will list them all for you guys in case you do not have these references. It will be helpful for you to be able to move your coral into one of these categories.

Wallace's grops:

A. rudis group - 4 species
A. humilis group - 8 species
A. nasuta group - 7 species
A. divaricata group - 5 species
A. lovelli group - 3 species
A. verweyi group - 1 species
A. cervicornis group - 3 species
A. muricata group - 5 species ( Wallace refers to A. formosa as A. muricata - Veron disagrees, and says no basis or need exists for changing a distinct and well-recognized taxon. I agree.)
A. robusta group - 8 species
A. togianensis group - 1 species
A. selago group - 8 species
A. aspera group - 7 species
A. florida group - 2 species
A. hyacinthus group - 7 species
A. latistella group - 4 species
A. horrida group - 8 species
A. plumosa group - 1 species
A. elegans group - 7 species
A. loripes group - 12 species
A. echinata group - 8 species

then there is the Isopora subgenus, consisting of 4 species (according to Wallace).

Let's do some easy intial work using the process of elimination.

Now, you might note the discrepancy in numbers of species. It is helpful here to note especially the ones with a lot or few species. Without going any further, I would look at the list and think about reproduction and dispersal. If a coral has many relatives, it has probably had ample time to diverge, and is probably a widespread group. By contrast, those with few related members are probably more recent or have significant barriers to dispersal - either being relatively new species or really old ones on their way to the genetic glue factory. In fact, if we look at the A. togianensis group, which consists of A. togianensis, I would thinkthe name means that it is found in and around the Togian Island group of Northeast Sulawesi, Indonesia. In fact, this is the case, and it is restricted to that area. The Togian Islands are a protected area, and are also very hard to reach. It is unlikely any corals collected for the aquarium trade came from here, and so one can immediately almost cross this species and group off the list.

It is notable that using a name is not a good thing to use in making assumptions. Often, a name may indicate a place of first discovery, but the species with all its variations was later found to be very widespread. This brings up another very important aspect in identifying your Acropora corals. The range. Unless you have good reason to believe, or know, that a coral was collected elsewhere, there are relatively few areas of coral collection for the aquarium trade. Veron and Wallace both give the known ranges for the species. Thus, one can immediately eliminate the A. cervicornis group which consists of Caribbean/Tropical western Atlantic species. One can, as one looks at the invidual groups, rule out species that are only known from Australian waters, the Hawaiian islands, the eastern Pacific, the east African coast, and, likely, the Red Sea. Now, if the range goes into that wide Indian Ocean, Indo-Pacific, Central Pacific region, then it must stay in the list of possibiltiies. Mind you, this does not rule out a lot, since the vast majority of Acroporids will be found in areas where it is possible they were collected for the aquarium trade. However, geographical range is a quick a dirty way to eliminate species that yours cannot possiby be with very little work.

Another quick and dirty technique is abundance data. When we begin using our characters, it may be helpful to see whether a species is common or rare. In general, odds are that your coral is probably not some rare coral, simply by virtue of the odds of collection. The same is true with habitat information. A rare Acroporid known only from deep current swept reef slopes or in mangrove areas is not likely to be your coral species, because collectors are unlikely to collect there, or to find it if they were. This is not a definite method of elimination, but it should be helpful.

Words of advice as we proceed, just general bits of trivia regarding preconceived notions if they haven't already been dispelled. Do not trust what the name of the coral was when you purchased it. Do not trust names you have previously associated with your specimen. As with my favorite example, everyone calls whorling or plating Montipora M. capricornis, even though this growth form is very common in Montipora and many many species exist other than M. capricornis....trust me when I say idenitfication of Montipora is hard. Similiary, the hobby tends to call any Acropora with scale-like radial corallites A. millepora, and although the radials are distinct and a good beginning, A, millepora belongs in the A. aspera group which has 7 similar species. Also, there are several others in other groups altogether that are very distinct as adult colonies, but very similar as small colonies or fragments, that have similar looking corallites. Also, do not believe if someone has told you your coral is rare. So, if you have a "rare deepwater Bali Acropora," do not begin by looking for deepwater uncommon corals where Bali is within their range. Just, throw out any preconceived notions, in general, and go from where we are now.

Tomorrow, I will list the characters for each group. Then, we will get a list of groups from each of you and begin moving in on the species.

When we are finished, I will also take you through an example using the Coral ID CD, which is a very user friendly coral identification method produced by AIMS.

I will also take you through a systematics key that is more traditional.

[firefish15]

My acropora has four types of radial corallites.
1. tubular nariform opening.
2. nariform elongate opening.
3. appressed tubular
4. immersed.
Size is quite variable. The largest being eliptical 2mm x 2.5mm outside diameter, 1 mm x 0.7 mm inside diam. The smallest circular 1 mm outside diam, 0.5 inside diam.
Eric, do these corallites change as they age? for example do appressed tubular change to nariform elongate opening then tubular nariform opening?
here's a picture of types 1 and 2.

[firefish15]

The septae are also varaible, all have2 cycles, The most nuimerous being 6 primary and 6 secondary. The least nulerous 2 primary, 4 barely visible secondary.
appressed tubular and immersed corallites.

[firefish15]

The costae around the axial and radial corallites are similar with shark-like teeth.

[firefish15]

The coenosteum seems to be a simple reticulate structure.

[EricHugo]

A. rudis group - A. rudis, A. variolosa, A. austera, A. hemprichii
growth form - large, thick-branched, simple, robust with simple, irregular branching
radial corallites - rounded tubular, evenly sized, thick sometimes swollen walls, relatively small calices
axial corallites - large, numerous synapticular rings, contribute a lot to branch thickness
coenosteum - elaborate spinules throughout
habitat - subtidal
range - Indian Ocean and Red Sea, except A. austera
notes - A. austera is the only species likely in the trade

A. humilis group - A. humilis, A. globiceps, A. gemmifera, A. monticulosa, A. samoensis, A. digitifera, A. multiacuta, A. retusa
growth form - corymbose or digitate, sturdy, conical or terete branches
Radial corallites - short, thick tubular, nariform to dimidiate openings, dense,evenly sized or two sizes, often touching
axial corallite, large and dominant, dense reticulum, contribute a lot to branch thickness
coenosteum - reticulate or reticulo-costate, with laterally flattened, blunt, or flaky irregular spinules
habitat - most restricted to shallow, intertidal, strong water flow, usually very common on reef flats
range - wider Indo-Pacific

A. nasuta group - A. nasuta, A. cerealis, A. valida, A arabensis, A. secale, A. lutkeni, A. kimbeensis
growth form - all are corymbose
radial corallites - nariform or tubular-nariform, evenly sized or in two sizes, contribute a lot to branch thickness
coenosteum - reticulate with simple spinules, sometimes spinules in rows or joined to form costae
habitat - subtidal, shallow, common
range - Indo-Pacific

A. divaricata group - A. divaricata, A. solitaryensis, A. kosurini, A. hoesksemai, A. clathrata
growth form - always determinate, central or side attachment, mostly very similar, often symmetrical
radial corallites - nariform, thick walls, round, oblique, or dimidiate openings, contribute a lot to branch thickness, multiple types and sizes common within colony, spaced out, often even
coenosteum - reticulate with forked or simple spinules, very dense to costate depending on habitat
habitat - often occur across wide depth range
notes: A. clathrata, A. divaricata and A. solitaryensis are commonly named in aquarist circles, and represent species thought to be fairly distinct in growth form...THEY ARE NOT! They can form plates, tables, or thinly branched caespitose to arborescent colonies with the distinction being the attachment point. Small colonies will be indistinct in growth form.

A. lovelli group - A. lovelli, A. bushyensis, A. glauca
growth form - varies
radial corallites - appressed rounded tubular, evenly sized
coenosteum - reticulate with simple spinules, spinules sometimes in rows, or costate
habitat - broad, but restricted - shallow coastal fringing reefs
range - wide, but restricted
notes: kind of an oddball, catch-all group in terms of appearances.

[EricHugo]

see if you can eliminate your species based on these five groups. I'll do another five tonight. whew.

[EricHugo]

A. verweyi group - A. verweyi
growth form - digitate or caespito-corymbose, branches 5-10mm in diameter, up to 100mmm long. Low clumps or patches, often flat topped. Whitish cream to cream brown, occasionally with orangishaxial corallites
radials - evenly distributed, equal sizes and shapes, appressed tubular with large flaring round openings, two sets of septa (primary 3/4R, secondary to 1/3R)
axials - outer diameter 2.8-3.5mm, inner 0.8-1.1 mm, two cycles (primary to 3/4R, secondary to 1/3R), a tertiary set of septa may be present
coenosteum - uniform reticulate with subcostate simple or leterally flatttened spinules
habitat - fills in spaces between other Acropora, exclusively shallow water species.
range - wider Indo-Pacific/Indian Ocean

A. muricata group - A. muricata (A. formosa), A. grandis, A. acuminata, A. valenciennesi, A. pharaonsis
growth form - open arborescent or arborescent tables with thick sturdy branches
radials - tubular, various openings, evenly spaced, variable in size, contribute equally with axials to branch thickness
axials - can become thickened and contribute to heavier sturdier branches
coenosteum - uniform reticulate with simple spinules, somewhat variable
habitat - fairly broad.
range - depends on species

A. robusta group - A. robusta, A. abrotanoides, A. palmerae, A. intermedia, A. polystoma, A. downingi, A. listeri, A. sukarnoi
growth form - variable - subarborescent, corymbose to digitate, simple sturdy branches
radials - dimorphic; long tubular with dimidiate openings and sub-immersed
axials - contribute most to branch thickness
Coenosteum - retiuclate between radials, costate on radials
habitat - shallow high-water movement environments, except A. intermedia (wider range of habitats)
range - variable, depends on species

A. togianensis group - A. togianensis
- looks like a Montipora with unusual corallites and coenosteum

A. selago group - A. selago, A. tenuis, A. eurystoma, A. striata, A. donei, A. yongei, A. loisetteae, A. dendrum
growth form - variable - corymbose, corymbose table, arborescent, hispidose, etc.
radials - cochleariform with flaring lip, evenly sized
Coenosteum - retiuclate with simple spinnules b/t radials, costate on radials
habitat - variable, but usually protected from strong water flow.

A. aspera group - A. aspera, A. pulchra, A. millepora, A. spathulata, A. spicifera, A. papillare, A. roseni
growth form - corymbose or arborescent
radials - labellate, upper edge absent, lower edge flaring lip
coenosteum - open, simple, with few simple spinules b/t radials, costate on radials
habitat - shallow water on reef flats, lagoons or shallow slopes
notes - degree of lip development is what separates species in this group. They also interbreed often, though some breeding barriers exist. Genetic differences small, hybridization common. i.e. - hard to tell apart!!

More later.