根据 according to 在数量和种类方面in numbers and species 在最近几年 in the last few years/in recent years（完成时）
原因如下：（列举），使鱼觅食困难
There are a couple of reasons responsible for it, such as . which makes it …
为了（in order to保护（protect ）海洋，我们应该采取下列措施（take the following measures）， 在中国沿海(coastal areas)每年禁止（ban ）捕鱼两个月，以便（so that）使鱼的数量（the number of ）增加。
Besides, 详细记录（keep a record of ）污染的情况，惩罚punishing 那些those 污染海洋的工厂（用定语从句）。
如果If 人人参与do what he can 保护海洋， 我们会有一个适合我们居住的环境（我们可以有一个可以快乐生活的地球）。可用where 或which 连接
According to reports, sea plants and animals have been sharply going down both in numbers and species in recent years. There are a number of reasons responsible for this, such as pollution, which makes it difficult for sea animals to find food，over-fishing as well as global warming. In order to protect sea animals and plants, we should take the following measures. First, in some costal areas, we should ban fishing completely for about 2 months so that the number of fish can grow. Besides, the government should keep a record of the level of pollution, punishing those factories which pollute the sea. If each of us do what we can, we will have a clean environment suitable for living./where we can live comfortably.