Effects of Ocean Acidification on Late Embryogenesis, Larval Condition, and Survival in Red King Crab (Paralithodes camtschaticus)

Rising levels of atmospheric CO₂ lead not only to atmospheric changes but also to changes in the chemical properties of oceanic water as much of the CO₂ is absorbed by the ocean.  This increase in CO₂ concentrations has lead to ocean acidification (OA), resulting in. a decrease in the pH of ocean water over the last two centuries and this is expected to intensify in the future.  A decrease in pH can affect survival, calcification, reproduction, and morphology of organisms living in the water.  Species with calcified shells or exoskeletons, such as crabs may be particularly vulnerable.  It is critical to understand the effects of OA on marine species, and especially on fishery species, so that appropriate management actions can be taken.  We held ovigerous red king crab, Paralithodes camtschaticus, in acidified, pH 7.8, and control seawater for three months (out of a ~12 brooding cycle) prior to hatching.  Embryos were photographed monthly for morphometric analysis.  After hatching, larvae were collected and held in acidified and control seawater to quantify the effects of OA on larval survival and calcium content.  We crossed maternal treatment with larval treatment to examine interactions between the effects of OA at the embryo and larval stages.  Larvae were also photographed for morphometric analysis.  Embryo morphometry changed with time; embryo size and eyespot size increased and yolk size decreasing as the embryos developed.  Embryos held in acidified waters were larger, had smaller yolks and larger eyespots than embryos held in control water.  Exposure to acidified water, both as an embryo and as a larvae, decreased survival time for starved larvae.   Larvae that hatched from embryos held in acidified water were morphometrically different from those held in control water and in general were slightly larger.  Finally, larvae held in acidified water had a higher calcium content than larvae held in control water.  We conclude that OA has a substantial effect on red king crab embryos and larvae and may negatively affect the stock through decreased larval survival within a century if CO₂ levels continue to rise unabated.