Effects of a Shallow-Water Hydrothermal Vent Gradient on Benthic Calcifiers, Tutum Bay, Ambitle Island, Papua New Guinea

• Main Author: Engel, Brienne E.
• Format: Thesis
• Language: unknown
• Published: Digital Commons @ University of South Florida 2010
• Subjects: ocean acidification; taphonomy; dissolution; Foraminifera; Halimeda; American Studies; Arts and Humanities; Ocean acidification
• Online Access: https://digitalcommons.usf.edu/etd/3553; https://digitalcommons.usf.edu/context/etd/article/4771/viewcontent/Brienne_E._Engel.pdf

Ocean acidification is occurring in response to rapidly increasing concentrations of atmospheric CO2. Shallow-water hydrothermal vent systems have been proposed as natural laboratories for studying the effects of elevated pCO2 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 (29.6oC-59.3oC) 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 59.3oC and low pH of 6.2 for five days, while at least one specimen of each of the seven species survived exposure to 39.9oC 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.