PARENT SESSION
OOS 4: Organisms as Ecosystem Engineers: Conceptual Progress, Limits and Challenges.
Organized by: JP Wright and CG Jones
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room E 146.

Experimental evidence for the role of biogenic habitat and productivity-diversity relationships at hydrothermal vents.

Govenar, Breea^*,1, Fisher, Charles¹, ¹ Pennsylvania State University, University Park, PA, United States

ABSTRACT- Habitat provided by foundation species plays an important role in structuring communities in a variety of terrestrial, aquatic and marine habitats. At the basalt-hosted hydrothermal vents of the East Pacific Rise (∼ 2500 m depth), the giant tubeworm Riftia pachyptila (Polychaeta: Siboglinidae) forms large and dense aggregations in a spatially and temporally variable environment where sulfide concentrations can be up to 300 M and temperatures can range from 2 to 30°C. On the surfaces of the tubes, there is a higher density and diversity of fauna than on the surrounding rock substrate. We hypothesize three mechanisms that contribute to this: provision of biogenic habitat, variability in productivity, and biological interactions with R. pachyptila. To test for the effect of these three factors on local species diversity, we deployed artificial tubeworm aggregations at three distances from R. pachyptila along a productivity gradient. After one year, all of the artificial aggregations had been colonized by endemic hydrothermal vent species. Although species richness was lowest in the artificial aggregations that were located 20 m away from any R. pachyptila, it was higher than expected, where there is no hydrothermal venting and productivity is assumed to be very low. Species richness was similar in both moderate and high productivity zones and fell within the range of species richness from natural R. pachyptila aggregations at the same site. However the species composition was different between the three treatments of the artificial aggregations and also from the natural aggregations. In this study, we show that the physical structure of R. pachyptila forms habitat islands, which support relatively high local species diversity. The results of this experiment also demonstrate that productivity and biological interactions with R. pachyptila are important factors in structuring the community.

Key words: artificial substrate, Riftia pachyptila, biogenic habitat, hydrothermal vent