Acropora horrida
Dana, 1846
This species shows wide geographic variation.
Description: Colonies are usually open branched, becoming bushy on upper reef slopes and in shallow lagoons. Main branches of colonies in turbid water have irregular branchlets; those in shallow clear water have compact branchlets, giving colonies a bushy appearance. Corallites are irregular and the surface of branches is rough. Tentacles are usually extended during the day.
Color: Usually pale blue (which may photograph pink or purple), sometimes dark blue or pale yellow or brown. Polyps are pale blue or white.
Habitat: Turbid water around fringing reefs.
Abundance: Usually uncommon.
Similar Species: Acropora tortuosa. See also A. vaughani, which has widely spaced corallites and a smooth coenosteum.
Taxonomic note: This species is divisible into several smaller semi-distinct taxonomic units. Source reference: Veron (2000). Taxonomic references: Veron and Wallace (1984), Wallace (1999). Identification guides: Veron (1986), Nishihira and Veron (1995).
The typically twisted appearance of branches. This colour is mostly due to artificial light. Great Barrier Reef, Australia Photograph: Charlie Veron
Branch detail. Great Barrier Reef, Australia Photograph: Ed Lovell
Bushy branches. Papua New Guinea Photograph: Charlie Veron
Skeletal detail. Axial and radial corallites.
Branch tips of a reef slope colony. Flinders Reef, Coral Sea Photograph: Charlie Veron