>The present concentration of co2 in the atmosphere according to Zhang, Yi Ge; et al. is the highest in 14m years. Given crabs in general have been around adapting for 145m years, I do not think the current levels will be detrimental.
It's not my field, but doesn't the rate-of-change matter even more than absolute value in time? Life can and does adjust, but it takes generations; if things change too fast, then only the quickest (smallest) life-forms can adapt.