JOST, Jennifer A: The risk of freezing in an intertidal polychaete: effects of salinity and sediment depth

This study focuses on the freeze tolerance of the marine polychaete worm, Nereis virens. The risk of exposure of these worms to freezing temperatures was explored as a function of both salinity and sediment depth. By slowly bringing these worms to low temperatures in the laboratory, I found N. virens to be a freeze tolerant species. Ice crystals formed when the body temperature of the worm was below 5.5 degrees C. The worms were allowed to thaw under normal conditions (33 ppt seawater solution at room temperature), and with the exception of one group, all N. virens were living after 24 hours in the lab. However, sub-freezing temperatures in combination with a salinity increase to 50 ppt resulted in a 100% mortality rate within 24 hours. These data do not corroborate past research suggesting that cold hardiness increases with increased salinity. Possible reasons for the discrepancy are that N. virens experienced cell desiccation resulting in protein denaturation or toxic levels of organic solutes as ice formation occurred in the body tissues. I also found that sediment depth had no effect on the survivorship of N. virens following exposure to sub-freezing temperatures. However, visible ice crystals were observed only in the absence of a sediment layer, suggesting that freezing does not occur in the natural habitat.