The Overwintering Capability of Ulva prolifera Spores and Gametes in the Yellow Sea, China

Green tides caused by the bloom of Ulva prolifera have affected the Yellow Sea annually since 2007. To explore the intrinsic causes of successive blooms, field investigations and indoor simulation experiments were conducted using micro-propagules of U. prolifera. From January to February 2014, micro-propagules of various green algae, including U. prolifera, Ulva flexuosa, and Ulva linza, were prevalent in the coastal waters of Rudong, Lianyungang, and Qingdao. However, in March 2014, micro-propagules of U. prolifera were not detected in the coastal waters of Lianyungang and Qingdao. Neither the spores nor gametes of U. prolifera can germinate at temperatures below 5°C. At 2°C and 5°C, U. prolifera spores and gametes could survive for 1–3 months at a light intensity range of 0–30 µmolm−2 s−1 and for less than 1 month if the light intensity exceeded 30 µmol m−2 s−1. By integrating indoor experiments and field investigations, this study found that U. prolifera spores and gametes could overwinter in the Rudong coastal area, which is an important factor for the annual emergence of recurring green tides in the Yellow Sea.