SHELL DISSOLUTION IN LARGER BENTHIC FORAMINIFERS EXPOSED TO PH AND TEMPERATURE EXTREMES: RESULTS FROM AN IN SITU EXPERIMENT

Areas where CO2-enriched gases discharge into shallow-marine environments can serve as natural laboratories to study the effects of elevated pCO(2) (i.e., ocean acidification) on benthic communities. Hydrothermal vents in Tutum Bay, Ambitle Island, Papua New Guinea, occur at depths of 10 m and are surrounded by a tropical fringing coral reef. Live specimens of seven species of larger benthic foraminifers were collected from a nearby reef location, placed in small mesh bags, and deployed for five days at six different sites along a gradient of temperature (60-29 degrees C) and pH (5.9-8.1). Foraminiferal species that differ in shell structure (porcelaneous vs. hyaline) and composition (high- and intermediate-Mg calcite) were used in the experiment. Approximately 25% of the specimens, representing four of the seven species, retained normal symbiont color and exhibited minimal dissolution when exposed for five days to temperatures up to 60 degrees C and pH as low as 6.2; shells of specimens that lost symbiont color during deployment exhibited extensive corrosion. More than 80% of the specimens, representing at least one of each species, retained normal symbiont color where the temperature was approximately 40 degrees C and pH fluctuated between 5.9 and 7.4. These observations indicate that shells of reef-dwelling foraminifers can substantially resist dissolution, as long as organic matter is largely intact, under pH conditions sufficiently extreme to erase any fossil footprint.