The family Acroporidae, known as 'staghorn' or 'branching' corals, are a family of hard corals forming colonies with branching structures, much like a tree, table, or bush, with the branches or finger-like growths covered in thousands of coral polyps.
These fast-growing coral branches are usually surrounded by small coral polyps known as radial coralites, and tipped with a distinctive axial polyp which is normally larger than the radial polyps.
Acropora corals come in many shapes and sizes and can be highly variable in colour and form, even within the same species.
Huge colonies can be formed, with many species being very important reef-builders. Colours and colony formation can depend on the growing conditions of the coral, depth, clarity of water, currents, and so on.
Colonies can be branched, table-top shaped, or in some cases, encrusting, and are found at all dive sites around Koh Lanta.
Identification of Staghorn Corals is difficult and requires either close examination of the corallites, or even a biochemical and genetic analysis in extreme cases.
New colonies are formed when branches break off and reattach to the substrate, known as asexual reproduction. Sexual reproduction (spawning) for Acropora corals occurs once or twice a year during a full moon, with the spawning months varying depending on species and location.
This species forms colonies of very different shapes, from arborescent (tree-like) to very dense bushes/thickets. Branches vary in length, can be long, disorderly and partially fused. Sub branches are short, tapered and very abundant.
The axial corallites are short, thick tubes with small openings. Radial corallites are sometimes arranged in rows, very close to each other, of different sizes and have thick walls with oblique, round or square openings.
Radial corallites vary from immersed to appressed, making the branches appear ragged.
This table-like species in generally uncommon and grows in semi-circular horizontal plates, usually less than 1 m in diameter. The main branches are usually straight and horizontal, with the short secondary branches curving upward and equidistant to each other.
Each secondary branch or branchlet is formed by a group of axial corallites and developing axial corallites, or only a single, large axial corallite which is long, think and swollen with a relatively small opening.
The axial corallite tip may be tapered or blunt. The radial corallites are tubular, small and appressed (their wall is directly attached to the branch from which they grow)
This species forms wide flat table-shaped colonies and tiered aggregations of small plates with short branches that curve upwards in an orderly way. The central branches are usually fused.
The axial corallites are tubular, rounded and slightly prominent. The radial corallites form rosettes, with the coralite wall attached to the branch from which it grows. Radial coralites are next to each other, and of the same size.
This species forms digitate colonies with a broad, encrusting base Branches are thick, finger-like, gradually tapering to large dome-shaped axial corallites. This coral species can be cream, green, purple or blue.
This species forms corymbose bushy colonies with thick tapered branches which are finger-like. Colonies are colourful, usually mixtures of cream, blue, purple, brown and yellow, commonly with purple branch ends and cream corallites.
The axial corallites are tubular, small and have a relatively wide edge. The radial corallites are of mixed sizes, some are long tubes with round opening, others appressed (part of their wall is attached to the branch from which they stem).
The radial corallites are large and conspicuous, and some are quite long. Branches can look ragged or rough.
This species forms corymbose colonies that can form a table-like structure with vertical branches. Branches along the outer edges are more horizontal than those in the center. The colony has a generally disorderly layout.
The axial corallites are tubular or slightly cone shaped, small and prominent. The radial corallites are lip-like/nariform with a swollen outer wall.
Some radial corallites may be slightly hooked and some may face in different directions. Radial corallites are next to each other and may be a mix of both large and small sizes.
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Allen, G., Steene, R., Humann, P., DeLoach, N. (2003) Reef Fish Identification, Tropical Pacific. Jacksonville, FL., USA: New World Publications, Inc., ISBN 1-878348-36-1.
