IMPACT OF OCEAN ACIDIFICATION ON BENTHIC FORAMINIFERA OF TOUCARI BAY AND PURPLE TURTLE, DOMINICA

Dominica, a Caribbean island of the Lesser Antilles, has high volcanic activity and numerous CO₂ vents in shallow, nearshore environments that lower the pH locally and may mimic the future effects of ocean acidification in the global ocean. Two sites on the eastern side of the island, located just off the beaches of Toucari and Purple Turtle, were chosen to understand the influence of these vents on benthic foraminiferal abundance and diversity.

Ten sand samples taken from the seafloor surfaces of Toucari Bay and Purple Turtle Beach were analyzed for benthic foraminiferal composition and compared to pH measurements taken at each site. Toucari Bay is an area where gas frequently bubbles up from the seafloor, while Purple Turtle is a control environment with normal marine conditions. The pH at Toucari Bay (8.23) was lower than the pH at Purple Turtle (8.32). Foraminifera were nearly absent from Toucari Bay, with an average of 6.8 tests/sample. Greater numbers of tests (average = 94.6 tests/sample) and a greater foraminiferal diversity (19.6 species/sample) were found at Purple Turtle compared to 3.8 species/sample at Toucari Bay. Purple Turtle foraminifera were primarily calcareous (average = 83% calcareous tests), while Toucari Bay foraminifera were primarily agglutinated tests (average = 40% agglutinated tests).

The increased diversity and numbers of tests at Purple Turtle suggest more favorable conditions for benthic foraminifera at this location. These data suggest that these two otherwise similar nearshore environments, separated by only 4 km, are significantly different. The foraminifera of Toucari Bay are likely being influenced by the presence of these submarine fumaroles, resulting in decreased numbers of calcareous tests than would be expected for this environment. The pH of Toucari Bay indicates a greater acidity than that at Purple Turtle, yet a pH of 8.23 is not low enough to dramatically impact carbonate dissolution, therefore it is likely that factors in addition to pH are influencing the distribution and abundance of foraminifera at these sites. However, the environment of Toucari Bay may still represent the future of global ocean acidification and its impact on calcifying marine organisms.