Meeting Abstract
Coastal organisms reside in highly dynamic habitats. Global climate change is expected not only to alter the mean of the physical conditions experienced in these habitats, but also the frequencies and/or the magnitude of fluctuations of these environmental factors. One such factor is pH of the ambient water. There is an increasing number of studies that investigate if diel variations in pH would alleviate the impact of ocean acidification. However, no study to date has studied the role of frequencies and initial conditions of the fluctuations on organismal performance. Here, we exposed larval sea urchin Heliocidaris crassispina to constant and fluctuating pHs. Consistent with published results, reduced pH alone (pH 7.3) did not affect larval mortality but reduced the growth of larval arms in the static pH treatment . The relative negative impact of changes in pH, computed as Log Response Ratio, on larval arm was smaller when larvae were exposed to pH fluctuations, especially when the pH change is not frequent (48 hr vs 24 hr cycle). Our observations further highlight that larval urchin are particularly sensitive to changes in pH during the first 24 hours of development: such that larvae exposed to the control condition (pH 8.0) during the first day performed better than those first experienced the low pH (pH 7.3). Our observations suggest that larval responses to climate change stress could not be easily predicted only from exposure to mean conditions. Instead, further work on understanding the rate of physiological response as well as the real-time environmental conditions along the dispersive pathway is key to predicting organismal responses in the future ocean.
