INFLUENCE OF A SHALLOW-WATER HYDROTHERMAL VENT SYSTEM AT AMBITLE ISLAND, PAPUA NEW GUINEA, ON BENTHIC FORAMINIFERAL ASSEMBLAGES
During field studies in 2003 and 2005, foraminiferal assemblages from sediment and cobble samples were examined along a transect starting at one of the hydrothermal vents and extending out to a distance of more than 300 m seaward; diffuse venting occurred intermittently along the first 150 m of the transect. Sediments were devoid of foraminiferal shells and other carbonate fragments to a distance of >60 m along the transect. In contrast, live foraminifers were commonly found on cobble and phytal substrates, even in close proximity to focused venting, and Assilina ammonoides were observed living abundantly in a diffuse vent field away from the transect line, though dead shells were absent. In total, 159 species were identified, all previously reported in the western Pacific region; no taxa specific to the vent system were found. Two species, Calcarina defrancii and Amphistegina lessonii, comprised 40% of all identified specimens, with C. defrancii common on cobbles within the vent field. In 2005, live larger benthic foraminifers were experimentally deployed for five days in small mesh bags along the transect. Mortality was only seen in specimens deployed within 15 m of the vent mouth, where water temperatures of 40-60° C and pH values of ~6 were recorded; some specimens of C. defrancii and A. lessonii survived the five days at 60° C. However, shells of specimens that died during deployment exhibited substantial dissolution. Thus, we found that some larger benthic foraminifers can live in corrosive environments where their dead shells dissolve. Our observations provide insight into persistence of benthic foraminiferal species through extinction boundaries marked by carbonate depositional hiatuses.