Living Hermatypic Coral Assemblages at Huon Peninsula, Papua New Guinea

Abstract

Recent coral reefs are well-developed along the coast of Huon Peninsula. Most of them are of the fringing type, although reefs with narrow lagoons are found at Sialum and Gitua. We studied the hermatypic coral assemblages with SCUBA at the reef of Sialum and the fringing reef of Hubegong about 30 km southeast of Sialum.
Sialum reef has a typical lagoon and reef crest with a narrow channel across the crest. The lagoon is about 3 km in length, and about 200 m in width. Its bottom is flat and shallower than 12 m. The crest is partly emerged up to a few meters at the central part of the barrier, while the other parts are almost at mean sea level. A reef slope has a groove and spur structure, and inclines steeply with several terraces to a depth of 20m.
No lagoon and reef crest are developed on the Hubegong coast. We made topographic profiles on the reef slope from 0 to 21 m in depth. The slope inclines at an angle of about 25°. Small terraces were recognized at depths of 3 m and 15 m. Groove and spur morphology is not formed in this area. Hermatypic corals are very abundant in the shallower part (0-5 m), but rare in the deeper. Coarse-grained detritus and boulders derived from the coral patches cover the deeper slope. Hermatypic corals disappear at depths deeper than 30 m.
Forty-three coral genera (including sub-genera) and 80 species were identified at Sialum and Hubegong. These numbers are not as large as might be expected for typical Indo-Pacific reef assemblages. This is due not only to the poorness of the actual assemblage but also to shortness of time available. Species identified in this region are similar to those of typical IndoPacific assemblages.
Coral coverage is very high in the coral thicket but almost 0% on the bottom of the lagoon and on the reef crest. It exceeds 30% in the shallower forereef and decreases to 0% in the deeper part.
We define 4 assemblages on the basis of the transect survey and other data, as follows.
Lagoon Assemblage : The assemblage is distributed inside of the lagoon from 0 to 10 m in depth. It is characterized by the presence of A. formosa, A. pulchra, M. digitata, and P. cylindrica.
Shallow Reef Slope Assemblage : It is distributed on the shallow part of the reef slope from 0 to 3 m in depth, and is defined by such species as A. hyacinthus, A. monticulosa, and A. humilis.
Middle Reef Slope Assemblage : The habitat of this assemblage ranges from 3 to 5m in depth on the reef slope. A. palifera is the diagnostic species.
Deep Reef Slope Assemblage : This assemblage inhabits the deeper reef slope from a depth of 5 to 30 m. As L. scabra, the representative of the assemblage is rare, massive Faviidae corals are more conveniently used for the assemblage definition.