Increase in air CO₂ is causing concurrent increase in oceanic CO₂ value, leading to a drop in seawater pH, known as Ocean Acidification (OA). OA specially affects calcareous species such as corals and mollusks. Many previous studies examined the OA impacts on tropical species such as corals, whereas its effects on cold-current species are not well understood yet. This study aims to examine the OA effects on calcareous sessile epifauna in a seagrass bed of Akkeshi-ko estuary, Hokkaido, where cold-current Oyashio affects its oceanography.

Three abundant calcareous sessile epifauna in Zostera marina bed, two spirorbid polychaete Neodexiospira brasiliensis and Circeis spirillum, and one bryozoan species were used. During five weeks of experiment, each species were kept under three different conditions, “Extreme”, “High” and “Control” with approximate pCO₂ value of 3000, 1000 and 700 ppm respectively, then analyzed for a variation in survival, growth and recruitment rate for evaluation.

The responses to CO₂ enrichment varied substantially among different species and among objective variables. Mostly they showed negative responses, but some even showed positive responses. The observed variation may be related to their differences in shell mineral composition, physiology and life traits.