ulva

例句：

1. 1. Ulva is a type of green alga that grows in freshwater environments.
   水藻是一种生长在淡水环境中的绿色藻类。
2. 2. The phytoplankton population in the ocean has been declining due to pollution.
   海洋中的浮游生物数量因污染而下降。
3. 3. Algae are important sources of food for many marine organisms.
   藻类是许多海洋生物的重要食物来源。