The Lau back arc Basin, a hydrothermally active area between Tonga and Fiji, is the site of one of the United States’ Integrated Study Sites (ISS).  The ISS concept fosters multidisciplinary scientific research, integrating geological, chemical and biological studies of the oceanic spreading center system. Research activities have been focused at three selected sites, the 9-10 degree North area of the East Pacific Rise, the Endeavour segment of the Juan de Fuca ridge, and along the Eastern Lau Spreading Center and Valu Fa Ridge. The EPR and JdF sites have a long history of research and general patterns were well known, enabling selection of central “bulls eye” locations on which to focus research.  The Lau area was less well known, and required further survey prior to selection of a “bull’s eye.”

Characteristics in the Lau Basin area grade from the north to the south as the spreading axis approaches the Tofua volcanic arc.  The crust thickens, the flat axis shifts to shallow peaked volcanic highs, spreading rate decreases, faults become smaller and closer together, and hydrothermal activity decreases.  Hydrothermal fluid H2S and H2 concentrations decrease, and CH4 increases to the south.   Rock type shifts from basalt in the north to andesite in the south.

The four investigated vent fields are, from north to south, Kilo Moana, TowCam, ABE, and Tui Malila.  Two other vent fields, Mariner and Vai Lili, were investigated but did not host abundant animals and so large scale photomosaics were not created in these fields.  At the four investigated Lau hydrothermal sites, the dominant megafauna near vents is molluscan; there are two snails, Alviniconcha hessleri, Ifremeria nautilei, and a mussel, Bathymodiolis brevior. Further away from active venting, two sponge species (Phelloderma bruuni and Asbestopluma sp.), and seven species of anemones (Zoanthidea sp., Amphianthus sp., Actinostolidae sp., Cyananthea sp. nov., Actinoscyphiidae sp. nov., Chondrophellia sp. nov., and Sagartiogeton sp. nov.) dominate.  These qualitative observations suggest that the biological communities around the Lau vents are zoned.  Creation of photomosaics enabled us to describe the zonation patterns of the animal communities and compare zonation within and between vent fields.