Increasing atmospheric carbon dioxide and its dissolution in seawater have
reduced ocean pH and carbonate ion concentrations, with potential implications
on calcifying organisms. To assess the response of large Caribbean benthic
foraminifera to low carbonate saturation conditions, we analyzed benthic
foraminifers' abundance and relative distribution in surface sediments in
proximity to low-carbonate-saturation submarine springs and at adjacent
control sites. Our results show that the total abundance of large benthic
foraminifera was significantly lower at the low-pH submarine springs than at
control sites, although responses were species specific. The relative
abundance of high-magnesium, porcelaneous foraminifera was higher than that
of hyaline foraminifera at the low-pH springs due to the abundant
Archaias angulatus, a chlorophyte-bearing foraminifer, which secretes
a large and robust test that is more resilient to dissolution at low-calcite
saturation. The different assemblages found at the submarine springs indicate
that calcareous symbiont-barren foraminifera are more sensitive to the
effects of ocean acidification than agglutinated and symbiont-bearing
foraminifera, suggesting that future ocean acidification will likely impact
natural benthic foraminifera populations.</p