Why is there no boundary at about 1000 meters in the benthic environment but a significant one at about the same depth in the pelagic environment? think of what the main control on the benthic organisms might be that the pelagic organisms would not have to contend with, and vice versa.
why do the dissolved nutrients drop in the spring?
why does the spring phytoplankton bloom start in the spring and die out in the early summer?