57.那么多的物种生活在河口

so many species live in estuaries

56.通过旅游业和渔业为经济做贡献contribute to the economy through tourism and fishing

55.为研究各种生命提供情报无尽的机会

　have endless opportunities to study a variety of life

54.在海滩上嬉戏 have fun on the beach

53.为人类提供休闲和教育的场所provide both recreation and education for human beings

52.保护动物免遭风暴和洪水

protect animals and plants

51.对环境污染很敏感

be sensitive to environmental pollution

50.吸收营养物质和污染物

absorb nutrients and pollutants

49.海洋哺乳动物　 marine mammals

48.生物的密集度

　the density of living creatures