Acid Trip: A Red Sea Urchin’s Journey Through a Low pH

Abstract

In this project, I exposed three red sea urchins to both ambient and low-pH seawater conditions and used micro-computed tomography (micro-CT) to observationally assess changes in spine structure. To lower the pH of the urchin’s tank, CO₂ was bubbled with an air stone into the water at a very low flow rate. The pH was left to stabilize for ~4 hours, measuring pH periodically to assure stabilization. A true stabilization was never truly achieved due in part to the natural pH oscillations of sea water from photosynthesis during the day and respiration at night. 3 spines per urchin were taken off the skeleton before and after treatment for micro-CT scanning (18 spines total). Urchins were planned to be in treatment for 3 days, but expired after 2. Lowest pH reading taken was 6.7, indicating this level was much too low for urchin survival. My goal was to determine whether short-term exposure to acidified seawater could compromise spine integrity. Micro CT scans clearly show degradation in the spines, even after only 2 days of treatment. After spines were thinner and exhibited more protrusions. Further studies with less time constraint should work to actually quantify change in density of spines with statistics.