Effects of hypoxia on Darwanian fitness traits and physiologies of larvae of the marine invertebrate Crepidula onyx

Crepidula onyx is found in great abundance in intertidal and subtidal waters over large geographic areas along the Pacific coast of North and South America, China, Japan and Hong Kong. Using C. onyx as a model species, we investigated how hypoxia affected the Darwinian fitness traits of marine invertebrate larvae, including survival, growth and metamorphosis as well as their physiologies, including filtration and respiration. The filtration rate of this filter feeder was not affected by a dissolved oxygen level as low as 3 mg O₂ l^-1. Nevertheless, the respiratory rate was significantly reduced even by a very weak hypoxic condition of 5 mg O₂ l^-1. Furthermore, we found that 3 mg O₂ l^-1 treatment significantly decreased larval survivorship and growth rate. By the time the control larvae reared under normoxic condition reached metamorphic competency with 100% metamorphic rate, the larvae in this hypoxic treatment had a significantly reduced body size and only ca. 60% of them successfully metamorphosed into juveniles. A weaker hypoxic condition of 4 mg O₂ l^-1 also decreased larval growth rate and percentage of metamorphosis. Since Darwinian fitness traits are of utmost importance in determining the sustainability of a species, the adverse effects of hypoxia on the fitness of this important gastropod species may implicate major ecological consequences over large coastal areas.