Effects of a shallow-water hydrothermal vent gradient on benthic calcifiers, Tutum Bay, Ambitle Island, Papua New Guinea

Ocean acidification is occurring in response to rapidly increasing concentrations of atmospheric CO 2 . Shallow-water hydrothermal vent systems have been proposed as natural laboratories for studying the effects of elevated p CO 2 on benthic communities. Hydrothermal vents occur at depths of approximately 10m in Tutum Bay, Ambitle Island, Papua New Guinea; these vents are surrounded by a typical-appearing fringing coral-reef community. Groups of live specimens of seven species of reef-dwelling, larger benthic foraminifers, along with segments of calcareous green algae broken from live thalli, were collected from a reef location, placed in small mesh bags, and deployed for five days at six different sites along a gradient of temperature (29.6°C-59.3°C) and pH (5.9-8.1) with distance from a large hydrothermal vent in Tutum Bay. Foraminiferal taxa used in the experiment included Amphisorus hemprichii , a species with Mg-calcite porcelaneous shells, three species of Amphistegina that produce hyaline calcite shells, and three species with hyaline Mg-calcite shells ( Heterostegina depressa and two Calcarina spp.). Several specimens of four of the seven foraminiferal species examined survived exposure to elevated temperatures of 59.3°C and low pH of 6.2 for five days, while at least one specimen of each of the seven species survived exposure to 39.9°C and pH 5.9. Examination of shells at 600-1000x magnification using scanning electron microscopy revealed fine-scale dissolution in specimens up to 30m from the vent. Results of this experiment, as well as previously reported observations from the study site, indicate that the calcifying reef-dwelling organisms examined can survive pH extremes that result in dissolution of their shells following death.

Engel, B. E., 2010. Effects of a shallow-water hydrothermal vent gradient on benthic calcifiers, Tutum Bay, Ambitle Island, Papua New Guinea. University of South Florida. 85 pp. Dissertation.

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