There are more hydrogen atoms on living organisms than any other atom, but oxygen is more abundant in terms of mass. why is this statement true

Hydrogen has a much much smaller mass.  Oxygen is like 16 times more dense.

above statement is not a true statement about the open ocean because the open ocean has low levels of nutrients. most of the photosynthetic activity on earth occurs in the open ocean within the photic zone. organisms in the deep ocean are exposed to frigid temperatures and total darkness but it does not begin at the low-tide mark.