Factors affecting dark survival of the brown tide alga Aureococcus anophagefferens (Pelagophyceae)

Aureococcus anaphagefferens Hargraves et Sieburth is a pelagophyte responsible for the harmful brown tides in New York, New Jersey, and Rhode Island, USA. Recent reports of blooms in new areas, Maryland, USA, and Saldanha Bay, South Africa, suggest that the alga may be expanding its range, possibly through anthropogenic transport. Experiments tested the ability of A. anophagefferens to survive dark conditions, such as those that might be encountered during transport in ballast tanks or recreational boats. Laboratory cultures were stored in complete darkness for various lengths of time under different conditions. After returning cultures to optimal light and growth conditions, we recorded the time until growth resumed. Cultured A. anophagefferens was able to survive for at least 30 days in the dark. Temperature played a major role in dark survival, because cultures stored at 6degrees C and 12degrees C recovered faster than those stored at 18degrees C or 24degrees C. Growth phase at the time of storage had a minor effect on recovery, with exponential phase cultures resuming growth more quickly than stationary phase cells. Although the alga is known to have heterotrophic capabilities, the addition of low levels (1-3 muM) of organic nutrients did not appear to increase dark survival. Salinities within normal estuarine and oceanic ranges also did not affect survival. The ability of A. anophagefferens to survive dark periods could allow it to be transported by anthropogenic means to new regions, and temperature and length of storage appear to be key factors determining cell viability during prolonged darkness.