The effect of pH on the larvae of two sea urchin species using different pH manipulation methods

Climate change alters ocean pH, temperature, and salinity, which presents challenges for oceanic organisms, especially those with calcium carbonate skeletons. Our research examines how decreasing pH impacts larval survivorship and calcium carbonate skeletal development of two sea urchin species, Lytechinus variegatus and Arbacia punctulata. Based on previous work in various sea urchin species, it is expected that as pH decreases, survivorship decreases and skeletal malformations increase. Both L. variegatus and A. punctulata have been used in prior studies to explore pH change on survivorship and development, but these studies incorporated various outcomes and pH manipulation methods, limiting how comparable they are. Therefore, we wanted to measure the same outcomes between species and compare the effect of different pH manipulation within species. We altered pH by either HCL addition or CO2 bubbling through seawater. Larvae, at a concentration of 3 larvae/ml, were exposed to seawater of pH 8.4, 8.0, or 7.6. For each treatment, survivorship of 30-40 larvae was measured daily for 10-14 days depending on the trial. Larval malformations were quantified for about 10 larvae from daily fixed samples. Larval arm length, body length, and body width were measured using Image J. For both methods of pH manipulation and both species, there was a statistically significant (p<0.001) decrease in survivorship as pH decreases consistent with the prediction. Preliminary analysis of skeletal deformities suggests malformations increase as pH decreases, but data are still being collected. Similar abnormalities observed between species regardless of pH manipulations include uneven or missing arms and misshapen aboral sides. The effect of pH on larval survivorship and development in L. variegatus and A. punctulata are comparable to observations in other species suggesting effects are consistent across manipulation methods and species. With this research, we can continue to fine-tune methodology and build on our understanding of how climate change-driven ocean acidification can impact species.

Miller K., 2023. The effect of pH on the larvae of two sea urchin species using different pH manipulation methods. Georgia Journal of Science 81(1): 49. Article.

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