Oceans cover approximately three-quarters of our planet. Oceanic organisms are placed into one of two divisions, the pelagic (open waters) and benthic (ocean floor) divisions. .
The pelagic division includes the neritic province and the oceanic province. The neritic province contains a greater concentration of organisms than the oceanic province because sunlight penetrates these waters and it contains the most nutrients. Phytoplankton is food not only for zooplankton but also for small fishes. These small fishes in turn are food for commercial fishes-herring, cod, and flounder. .
The oceanic province is further divided into zones called the epipelagic, mesopelagic, and bathypelagic zones. The epipelagic zone does not have a high concentration of phytoplankton because of the lack of nutrients. These photosynthesizers, however, still support a large assembly of zoo plankton because the oceans are so large. The zooplankton are food for herrings and bluefishes, which in turn are eaten by larger mackerel, tunas, and sharks. Flying fishes, which glide above the surface, are preyed upon by dolphins. Mammalian porpoises are also present. Whales are other mammals found in the epipelagic zone. Baleen whales strain krill (small crustacea) from the water, and the toothed sperm whales feed primarily on the common squid. .
Animals in the mesopelagic zone are carnivores, are adapted to the absence of light, and tend to be translucent, red colored, or even luminescent. There are luminescent shrimps, squids, and fishes, such as lantern and hatchet fishes.
The bathypelagic zone is in complete darkness except for an occasional flash of bioluminescent light. It is the largest zone. Carnivores and scavengers are found in this zone. Strange-looking fishes with distensible mouths and abdomens and small, tubular eyes feed on infrequent prey. .
The benthic division includes organisms that live on the continental shelf, the continental slope, and the abyssal plain.