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#oceanography

2 public questions tagged with this topic.

ECOSYSTEM TYPES

What describes the neritic zone?

The neritic zone is the shallow marine water extending from the low-tide margin to the edge of the continental shelf. Its exact offshore width varies because continental shelves may be narrow or hundreds of kilometres broad, but depth commonly remains below about 200 metres. Sunlight can reach much or all of this water column, while rivers, coastal runoff, sediment resuspension, and upwelling often supply nutrients. These conditions support phytoplankton, seaweeds, seagrasses, benthic invertebrates, fishes, and many commercial fisheries. The neritic zone is not simply the shoreline: the intertidal region is periodically exposed, whereas neritic water remains marine and overlies the shelf. Beyond the shelf break lies the oceanic zone over deep open ocean. “Deep ocean” therefore describes neither its position nor typical depth, and “open sea” is too broad. By linking a horizontal marine region to the underlying continental shelf, the definition also explains its generally high productivity: shallow illumination and land-derived or mixed nutrients are more available than in many offshore surface waters.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 2-3

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ECOSYSTEM TYPES

What zone in oceans is also called the twilight zone?

The mesopelagic zone is widely called the twilight zone because it receives weak, diminishing sunlight but not enough for net photosynthesis. It generally extends from about 200 to 1,000 metres below the ocean surface, with boundaries varying according to water clarity and latitude. Blue wavelengths penetrate farthest, producing dim illumination that can support vision, counterillumination, and daily vertical migration but little primary production. Many fishes, squids, crustaceans, and gelatinous organisms rise toward surface waters at night to feed and descend by day, transferring carbon to depth. Above it, the epipelagic zone is the sunlit layer where phytoplankton photosynthesis occurs. Below it, the bathypelagic zone is essentially dark, and the abyssopelagic lies deeper still. This light gradient, rather than pressure alone, explains the name “twilight.” Mesopelagic animals often possess large eyes, sensitive photoreceptors, dark coloration, or bioluminescent organs suited to low-light conditions. The ecological identity of this zone therefore follows from its intermediate illumination between the bright surface and the permanently dark deep ocean.

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 2-3

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