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 pCO₂ (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°C) and pH (5.9-8.1). Foraminiferal species that differ in shell structure (porcela-neous 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 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°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.