Ocean Acidification and Marine Biodiversity

Abstract

Ocean acidification -- the ongoing decline in seawater pH resulting from absorption of anthropogenic CO2, with mean surface ocean pH having fallen from 8.21 to 8.10 since pre-industrial times and projected to fall to 7.95-7.75 under RCP 4.5-8.5 by 2100 -- represents one of the most pervasive and chemically certain stressors on marine biodiversity. The biological consequences of acidification operate through three primary pathways: dissolution of calcium carbonate structures in calcifying organisms (corals; molluscs; echinoderms; pteropods); physiological stress from reduced seawater carbonate ion concentration affecting acid-base regulation; and behavioural disruption from altered chemosensory signalling in fish and invertebrates. This comprehensive review and meta-analysis synthesises 247 experimental studies of ocean acidification effects on marine organisms across 84 taxonomic groups, covering calcification rates, survival, growth, reproduction, and behaviour under current and projected future pH conditions (pH 7.6-8.1). The overall meta-analytic effect of acidification on calcification was strongly negative (Hedges' g = -1.14 +- 0.38; p < 0.001 across all calcifying taxa). Coral calcification showed the largest effect (g = -1.84) followed by pteropods (g =-1.47) and bivalves (g = -1.24). Fish behaviour showed significant disruption at pH 7.8 (-0.74) but recoverable physiological effects at pH 8.0. Biological sensitivity was strongly predicted by mineralogy: aragonite-forming taxa (more soluble) showed 47.4% larger effects than calcite-forming taxa (partial R2 = 0.54; p < 0.001)