Answer:
In deep water the marine food web includes the population of zooplankton, phytoplankton and other species of the fishes.
If there is a significant decrease in the number of phytoplankton then other tropic levels of the marine food web will be affected.
If there is a successive less growth of phytoplankton in the marine water then the organism feeding on them will be affected.
There will be a significant decrease in the oxygen level as well and all the organisms will be at higher levels will be affected as the basic level is affected.