Growth characteristics and reproductive capability of green tide algae in Rudong coast, China

Since 2007, green tides have occurred along the coast of the Yellow Sea, China. The green tide extended to 50,000 km² (floating area) within 2–3 months and the calculated covering area was about 400 km² in 2010. These facts implied that the growth and reproduction of the dominant species Ulva prolifera were stimulated. We observed that 1 cm² blades (single layer) released 2.84–6.62 × 10⁶ spores or 1.14–2.65 × 10⁷ gametes and that 91.6–96.4 % of them germinated into younger seedlings. This means that, in theory, 1 g (fresh weight) of blades was able to produce about 2.8 × 10⁸–2.7 × 10⁹ new younger seedlings. From 2009 to 2011, the growth rate of green tide algae was measured in situ in enclosure experiments in Rudong coast, Jiangsu Province and the growth curve of the algae was divided into four phases: lag phase, accelerated phase, stationary phase, and decline phase. Usually, the average daily specific relative growth rate was about 23.2–23.6 % d⁻¹ for a whole growth period, and it reached up to 56.2 % d⁻¹ in the accelerated phase. Correspondingly, the morphology of green tide algae in enclosures also showed periodic variation as follows: blades presented new filamentous branches from old thallus in the lag phase, longer filamentous branches in the accelerated phase, tubular and cystic blades in the stationary phase, and folded blades in the decline stage. Those studies may be useful for understanding the green tide blooming mechanism.