生词积累：

           Algae:             [植]藻类；海藻

Diatom:          [植] 硅藻

 Copepod:       桡足动物

 Arctic Cod:     北极鳕鱼

 Ringed Seal:   环斑海豹

The graph gives information about the Arctic food chain. 

At the beginning of this food chain, it is the first stage called algae and it is providing food for the second stage, which is called diatoms.

Following that, the next stage is called copepods and it is mainly relying on diatoms for survival. 

After that, the fourth stage is called arctic cod and it is providing food for the next stage, which is called ringed seals. 

At the end of this food chain, it is human beings and polar bears. Human being are hunting the sea creatures and polar bears are eating the sea creatures for their survival. 

In conclusion, this food chain has six stages in total.