Ocean Acidification: Euphausia Pacifica’s Response to Decreasing pH

Abstract:

The increasing rate of CO₂ accumulating in Earth’s oceans creates a threat to organisms that can lead to disturbances in their reproduction, survival and growth. Euphausia pacifica is the dominant species of krill in Monterey Bay, CA, and a keystone species in the bay’s food web. Previous work on the effects of ocean acidification on the survival, growth and molting of E. pacifica have shown they are fairly tolerant to increased CO₂ concentrations. However, less is known about energy costs associated with maintaining their internal pH levels which could affect food consumption, swimming behavior or growth activity.

 We hypothesized that krill exposed to high CO₂ will increase their feeding rate on local species of phytoplankton to account for increased energy costs of pH buffering activity. We exposed experimental E. pacifica to waters of pH 7.6 (the expected pH surface waters in year 2100), and pH 8.0 (control) periods.test for acclimation or longer term stress. Feeding rates were calculated as changes in phytoplankton counts over 24 hours of feeding using Frost’s equations (Frost 1972). Understanding the way E. pacifica is affected by ocean acidification is important because of the role they play as the primary food source for a variety of predators necessary to maintain the Pacific’s ecology.