By the coast in the intertidal zone
The ocean floor, whether right by the coast or at the deepest point, is the benthic zone
Around coral reefs and into the open ocean is the pelagic zone
Going deeper is the photic zone
At the deepest points of the ocean is the aphotic zone
Depth, temperature, and salinity can cause marine ecosystems to vary
Nitrogen and phosphorus, important nutrients, are dense along the coast
Upwellings bring nutrients from the depth of the ocean to the surface, boosting productivity
Secondary productivity can be high in cold water where there is lots of dissolved oxygen