Effects of chronic ammonia exposure on gonad growth and survival in green sea urchin Strongylocentrotus droebachiensis

Abstract

The effects of chronic unionised ammonia (UIA) exposure on mortality, gonad growth and feed intake (FC) in green sea urchin Strongylocentrotus droebachiensis were examined. Sea urchins with a mean (S.D.) initial weight of 58.2 (15.2) g were reared in shallow raceways (initial stocking density of 1.9 kg m −2) and exposed to four concentrations of UIA [0.0001 (control), 0.016 (low), 0.032 (medium) and 0.068 (high) mg l −1] for 42 days at 7.3 °C, salinity 33‰ and pH 8.04. Sea urchin mortality was influenced by UIA concentrations and increased with increasing levels of UIA. The mortality in the high-concentration group increased throughout the experimental period, and, ultimately, only 24% of the sea urchins survived. Compared to the control, gonad growth was significantly reduced at UIA concentrations above 0.016 mg l −1. Sea urchins from the exposed groups did not display a significant reduction in feed intake compared to the control, which suggests that the gonad growth reduction could not be attributed to a decreased feed intake. The present study demonstrates that adult green sea urchins show low tolerance to ambient unionised ammonia and are unable to maintain high gonad growth facing such conditions.