| The tropical Indo-Pacific is the location of highest global foraminiferal biodiversity. However, the shallow-water hydrothermal system in Tutum Bay at Ambitle Island, Papua New Guinea, possesses some of the world's highest naturally-occurring [As]. Foraminifers were collected in this intriguing system in 2003 and 2005 as part of a larger project to examine the possible effects of As and other hydrothermal factors on benthic communities. Despite the high ambient [As], a diverse foraminiferal fauna was observed.;Foraminferal communities were examined from surface sediment and from material adhered to rubble at locations from 1-300m from venting and from reference sites, at depths from 1--28m. From this material, 159 species were identified representing 107 genera, 55 families, 30 superfamilies, and 10 orders. Species abundances exhibit a logarithmic series distribution, with two species comprising 40%, twelve species comprising two-thirds, and 20 species comprising 80% of all identified specimens. All other species individually contributed <1% to the total community. Foraminiferal abundance and diversity were analyzed across the hydrothermal field; both increase with decreasing hydrothermal influence: decreasing sediment and pore water [As] and temperature, and increasing pH and salinity. A thorough taxonomic reference of the region was compiled, consulting appropriate original descriptions, and is herein presented, and initial steps in creating an online database of all Recent foraminifers is described. Scanning electron micrographs of the most common taxa are provided.;Laboratory experiments assessed the effects of [As3+] and [As5+] on growth of Amphistegina gibbosa. Exposure to As3+ and As5+ at concentrations of 0-1000mug/kg showed that As3+ is approximately 2.2 times more toxic than As5+, that [As3+] of 600--1000mug/kg is sufficient to kill or severely impair specimens on approximately two-week timescales, and that [As5+] of 1000mug/kg or [As3+] of 200mug/kg are sufficient to retard the growth of A. gibbosa on approximately four-week timescales. Over timescales of several months, cultures with extremely low [As] (2mug/kg As5+ and 0mug/kg As), showed growth rates not significantly greater than high-[As] treatments, possibly due to antimicrobial/parasiticidal properties of low [As]. Foraminifers displayed an exponentially-decaying functional relationship to [As], halving their rate of growth with every 300mug/kg increase in [As 3+] or 600ig/kg increase in [As5+].;Measurements of foraminiferal whole-specimen [As] via SEM-EDX, AFS, and ICPMS revealed high [As] of ∼20mg/kg for specimens near hydrothermal venting declining to background values of ∼2mg/kg for distal and non-hydrothermal reference species. Laboratory-exposed specimens contain [As] of ∼6mg/kg indicating an As adsorption rate of ∼0.25mg/kg/wk. The major portion of foraminiferal As likely occurs in a reduced-toxicity organoarsenical form, such as arsenobetaine. |
