Title: UNUSUAL FEATURES OF A MESOPHOTIC HARD CORAL ASSEMBLAGE IN A LAGOON ENVIRONMENT DOMINATED BY HEAVY TERRIGENOUS SEDIMENTATION: THE BANC GAIL (SW NEW CALEDONIA)

Abstract: Mesophotic coral assemblages are most often developed on the deep fore reef slopes exposed to oceanic conditions. Less common are the mesophotic assemblages which occasionally occur within the confines of large lagoons where environmental conditions impart specific and unusual characters to the scleractinian community. Situated in the SW lagoon of the New Caledonian barrier reef system, the Banc Gail is an example of such uncommon mesophotic environment. There, between 35 and 45m deep, the lagoon floor is subjected to input in the form of periodical pulses of fine terrigenous mud originating from the nearby rivers. The terrigenous silts and clays are trapped in an eddy of the general water circulation and settle on the seabed. Such a turbid environment favours the settlement of oysters forming banks that tends to create ridges up to 3 m high on which corals settle, separated by muddy gullies Although high levels of fine particle sedimentation are proven to be detrimental to the development of scleractinians, a number of corals have adapted to such peculiar conditions, principally low light levels and high rates of fine sediment deposition. The composition of the scleractinian assemblage is examined. Although the suite of species is a subset of the general scleractinian mesophotic fauna, some key components such as the Agariciidae or species of the Acropora elegans group are uncommon or absent. Further, most species show unusual growth forms in response to the high and periodic muddy particle ingress and a high incidence of natural fluorescence has also been observed

Authors: Joannot P, Pichon M, Thomassin BA

Presentation: Oral

Session: 29

Date: 06/22/16

Time: 18:00

Location: 308 A/B

Back