Community patterns in geothermally influenced sediments

This study examined the previously unknown macrofaunal of a deep-sea cold seep and two shallow hydrothermal vents. In Chapter I, I investigate a deep-sea cold seep ( Clam Field , 950m depth) located in Monterey Bay, California. In chapter II, I report upon shallow vents that were located in Bahia Concepcion (12m depth), Mexico, and in White Point (8m depth), California. I tested whether the infaunal community compositions in these systems were different from the surrounding communities, and if the observed differences were related to the abundance of food in the deep-sea and the chemosynthetic production of the cold seep. In Chapter II, my hypotheses relate the influence of the abiotic variables and the life-history of infaunal species. Microfaunal, gain size and pore water samples from the top 5cm of the sediment were collected at locations within the venting zones and 1-5m away. Clam Field data indicated that elevated hydrogen sulphide concentration was the most significant parameter related to the abundance of infauna, which was also revealed at White Point. At the Bahia Concepcion vent the temperature inside zones of venting was significantly elevated over the outside temperature, and was the most significant parameter related to the abundance of infauna. At all sites, there was no difference in grain size between seep or vent sediments and the surrounding areas. The pH and salinity or pore waters at all three study sites also exhibited similar patters, with decreases inside venting zones and with sediment depth. As in shallow areas, the infaunal community of the deep-sea cold seep differed in species composition between the seep and outside zones; a number of species were exclusive to the seep zone. However, there was no evidence for chemosynthetic strategies amongst the shallow vent infauna, unlike previous reports at deep-sea hydrothermal vents and cold seeps. Chemosynthetic bivalves were identified among the Clam Field infaunal species. Physiological and behavioral mechanisms were discussed to explain the presence of benthic infauna in the seep and vents. The species composition of the shallow vents was a sub-set of the surrounding community, but at the Clam Field contained a high number of unique species, and therefore the cold seep fauna was considered more isolated from the outside community