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Introduction

You may have heard Australian hobbyists referring to something called the “Dallas Acro”, “Acropora dallaswarreni” or “The Green Weed”. What are they talking about? Or may be you even a frag of it yourself. So, what is the story with this coral? Where did it come from? What species is it? Why do so many people have this coral? 

Origin

The origin of this coral is nothing out of the ordinary. My reef tank was set up at the start of 1997 and by the middle of the year was trying out various Acropora spp. with mixed success. At that time there was a number of stores within Melbourne that I frequented. One of them was quite close to where I lived, Coburg Aquarium, so I spent most of my time visiting it and therefore purchased a number of corals from there. In August 1997 I picked up a small Acropora sp. fragment that was brown with green highlights for AUD$35. It was a fork shaped colony about 8 centimetres long with three branches.

Original colony about one month after addition to the tank. Photograph taken by Dallas Warren, 1998.

Note that you may find some references in online discussion in the last couple of years that the coral came from Mentone Aquarium. However, that was a mistake on my part and I have check my records and confirmed that it did infact come from Coburg Aquarium.

Growth and Behaviour

Within 6 months the coral was starting to amaze me with how fast it was growing and the fantastic deep green colouring with bright green highlights that it developed. At this time there was three main colonies within my tank and a number of frags to start distributing it to other hobbyists. The original colony at this point was now about 15 cm long with about 7 major branches developing. The second colony, which ended up being the nicest after another year, started as a single branch fragment about 3cm long from the original colony. By the begining 1998, it was 8cm long with four major branches. One of the major fingers developed into a number of smaller / thinner branches that developing out from the underside and commenced to grow along and out from underneath. The third colony took on the most unusual growth form, as it was located about 10 centimetres from the top surface of the tank. Rapidly one of the branches grew the 7 or so centimetres up to the water surface. Once the axial polyp reached the surface it only grew as far as where the water swelled over it, keeping it wet. The swelling was caused by the current from a pump outlet located near the water surface on the opposite end of the tank. If it grew up about 5mm further then it would break the water surface and remain totally dry. It did not managed do this, as the tissue at the tip died off. Most likely the lighting intensity was too high in the top couple of millimetres of the water and has killed the tissue attempting to grow that close to the water surface. Even though the tip died, the branch continued to increasing in thickness. When this colony was fully developed there was at least 10 branches teminating at the water surface, forming a very interestingly shaped colony.

Original colony after approximately 4 months of growth. Photograph taken by Dallas Warren, 1999.

 Common to all three of these first colonies is how they encrusted over the rock surface at an incredible rate, in addition to the fast branch growth rate. All of three encrusted for nearly a year at about a rate of 1cm per month is most directions. Of course the encrusting was limited in some cases by the rock curving down and under, so they didn't grow there because of the lack of light. The encrusted surfaces did not reach a large enough size to start branches as the main section of the colonies shaded it out.

Identification

The identification of this species has been difficult. At this point in time the following is know for sure:

• Phylum: Cnidaria
• Class: Anthozoa
• Subclass: Zoantharia
• Order: Scleratinia
• Family: Acroporidae

My own initial identification was A. micropthalma, which is part of the horrida group. This indentification was performed using Veron's Corals of Australia and the Indo-Pacific. Over the years a number of people have attempted identification down to the species level using either Veron's Corals of the World or Wallace's Staghorn Corals of the World”. But nothing has been found that more than a couple of people have been happy with. This difficulty is compounded by the vast array of different growth forms that fragments of the same colony can form in a different system.

Colony number 2, branch structuring of small section of colony after approximately 6 months of growth from small fragment. Photograph taken by Dallas Warren, 1999.

Then around November 2001, Gavan Harrison took a tissue sample and performed some DNA testing. The DNA was then matched up against a database with a number of different species of Acropora by performing a sequence based similarity search of GenBank with a partial PaxC DNA sequence.. The closest match for the coral was A. valida, part of the nasuta group, and it had quite a number of different genetic patterns to that of A. micropthalma present within the database. Not all Acropora sp. were present within the database, but Gavan believes that the match is close neough to believe that this is in fact the correct species identification. The outward appearence of A. valida within both Veron and Wallace is different to the coral of interst. A. valida forms caespitose-corymbose colonies, where as the coral of interest are typically arborescent in captivity. But growth form is not a very good indicator as within a single species there can be a wide variation in growth forms.

 

Colony number 2, close up of corallites. Photograph taken by Dallas Warren, 1999.

So, where does that leave us? In a state of contention I think personally. Until further sequencing is performed we can't be totally sure of the species that it is. But that doesn't really matter anyway, it is a great captive coral that will grow in under wide range of conditions.