Hydrothermal vent periphery invertebrate community habitat preferences of the Lau Basin

Abstract

The Eastern Lau Spreading Center (ELSC), located between 19°20′S and 22°45′S, is a back-arc basin containing active hydrothermal vents, and is characterized by gradients of several geological and chemical variables that follow along the north – south axis. The northern section of the ELSC spreads faster than the southern section resulting in farther distance from the Tofua Arc and vent geology and chemistry more akin to mid-oceanic ridges. In the southern section, where distance from the arc is less, substrates are more heavily influenced by water resulting in andesitic substrates as opposed to the basaltic substrates in the north. There are also north to south biological patterns; vent peripheral zone communities in the northern area are dominated by anemones, and in the southern area, by sponges. This project used a replacement type experiment to test whether the anemone and sponge community distributions are due to substrate preferences (basalt or andesite) or location effects. In September 2006, 17 basalt and 18 andesite rock blocks were set out in the peripheral vent zone at three locations in the Lau Basin; 42 months later, in May 2009, the rocks were recovered. After rock block collection, communities that had colonized them were defined by identifying all invertebrates to lowest taxonomic level possible. As expected, basalt rock blocks were smoother than andesite rock blocks, but they were also smaller, though this was ameliorated by even distribution at experimental locations. Rock type did not affect the invertebrate community, but location did; the location specific effect that impacted the invertebrate community may have been sulfide concentration. The seafloor at southern locations was more brecciated, allowing sulfide to distribute farther laterally, which could result in enhanced primary productivity, and thus influence the observed community differences. We conclude that in peripheral vent habitats, energy availability for primary production and food availability are more important in structuring communities than the type of rock substrate.