Effects of Ocean Acidification on Swimming of Larval Urchins and Implications for Dispersal

Ocean acidification (OA), the reduction in pH associated with dissolution of atmospheric carbon dioxide, is threatening marine fauna. Often, the impact of acidification does not manifest as outright mortality but as sub-lethal effects; and these impacts can carry over from one developmental stage to another. One such sublethal effect is altered swimming behaviors through changes in overall morphology and hence biomechanics, metabolic activities, or neurotransmissions. Larvae of marine invertebrates play a key role in dispersal and swim to adjust their vertical positions, which shapes the environmental conditions, e.g., temperature, food abundance, and advective currents, they encounter. We tested the effect of acidification on swimming behaviors of larval urchins, Strongylocentrotus purpuratus and S. droebachiensis, reared under elevated pCO₂ levels in both still and moving water using non-invasive video tracking. Despite reduced growth rate, swimming performance, measured by vertical velocity, was not affected by acidification. This observation together with changes in overall shape highlights developmental and behavioral plasticity during acute exposure. We further tested if such swimming-size decoupling would affect transport and recruitment success with an idealized hydrodynamic model. Our results suggest impacts of OA on early life stages, though sublethal, could have significant implications for population dynamics.