EFFECTS OF TEMPERATURE ON CHRONIC HYPOXIA TOLERANCE

Effects of temperature (158, 208 and 258C), O2 partial pressure (PO2 0, 1, 2, 4, and 6 kPa), and indi-vidual size (12–79 mm shell length; SL) on survivorship of specimens of the non-indigenous, marine, brown mussel, Perna perna, from Texas were investigated to assess its potential distribution in North America. Its hypoxia tolerance was temperature-dependent, survivorship being significantly extended at lower temperatures under all tested lethal PO2. Incipient tolerated PO2 was 4 and 6 kPa at 15 and 208C, respectively, with.50%mortality occurring at 258C at all tested levels of hypoxia. PO2 had less of an effect on survival of hypoxia than temperature. At 258C, survivorship was not different over a PO2 range of 0–2 kPa and increased only at 4 and 6 kPa. Survivorship was size-dependent. Median survival times increased with increasing SL in anoxia and PO2 1 kPa, but at 2, 4 and 6 kPa, smaller individuals survived longer than larger individuals. With tolerance levels similar to other estuarine bivalve species, P. perna should withstand hypoxia encountered in estuarine environments. Thus, its restriction to inter-tidal rocky shores may be due to other parameters, particularly its relatively low temperature tolerance