Absorption of anthropogenic atmospheric CO2 into the ocean surface is causing ocean acidification and chemistry changes that reduce calcification in organisms that form calcium carbonate skeletons and shells. Increased acidity also affects aspects of life history other than calcification, such as sexual reproduction and recruitment. Studies of scyphozoan jellyfish abundance have not reached a consensus on the effects of ocean acidification on jellyfish populations, and few laboratory studies have looked at the effects of acidified seawater on jellyfish biology. This study examined the effect of acidity on the benthic and early pelagic stages of the scyphozoan Chrysaora colorata and the formation of a calcium sulfate sensory structure, the statolith. Researchers who model future ocean surface pH levels predict a drop of 0.3-0.5 units from pre-industrial levels by 2100 if fossil fuel consumption continues at its current rate. To understand how these conditions will affect C. colorata, treatments of acidified seawater (pH = 7.85, 7.75, 7.65, and 7.55) and a control (pH = 7.97) were used to test the effects of ocean acidification on asexual reproduction (number of podocysts formed, number of new polyps formed, number of days to begin strobilation, duration of strobilation, number of healthy ephyrae released, and percentage of ephyrae that were healthy) and statolith size. There was no effect of acidity on asexual reproduction in C. colorata, but there was a significant negative effect of acidity on statolith size—this supports previous research on the scyphozoan Aurelia labiata. This study suggests that C. colorata will be able to survive and asexually reproduce from the polyp stage through the ephyra stage in near-future ocean conditions. Previous studies have shown that a lack of statoliths results in swimming abnormalities, but the effect of smaller statoliths is unknown. To fully understand how C. colorata will be affected by ocean acidification, further research needs to be conducted on other stages of the lifecycle. C. colorata and other scyphozoans play important roles in their ecosystems, and if their abundance is negatively affected then their predators, prey, and competitors will be affected as well. However, it is possible that the effects of ocean acidification on C. colorata and other scyphozoans will be subtle and that they could benefit from declines in the abundance of predators and competitors that are more sensitive to the chemistry changes of ocean acidification.
Knowles T., 2012. Effects of acidified seawater on asexual reproduction and statolith in the scyphozoan Chrysaora colorata. MSc thesis, Moss Landing Marine Laboratories and California State University Monterey Bay, 21 p. Thesis.