While studying marine biota, a student needs
to distinguish
between biota of the pelagic and benthic zones. Aquatic ecosystems
systems have two parts: freshwater ecosystem and marine ecosystem. The marine
ecosystem has a high level of salinity and comprises two-thirds of the surface
of the Earth. The four parts of oceanic ecosystems: intertidal, pelagic,
benthic and abyssal etc. The pelagic zone constitutes the free water zone. It
includes the entire ocean water column. The benthic zone incorporates the water
layer present simply above the seabed.
The
Critical Difference Between The Benthic And Pelagic Zone Biota
●
Organisms that live in the benthic
zones are known as 'benthos'. Similarly, creatures found in the pelagic zones
are called pelagic organisms.
●
Biota present at the benthic level
can bear low levels of sunlight and low temperatures. As a result, usually, the
benthos cannot undertake photosynthesis. However, in the pelagic zone, more
organisms are autotrophic.
●
As pelagic is the uppermost layer,
it has a gradient of nutrients and provides optimum conditions for various
organisms to thrive. On the other hand, the benthic region lack resources and
harbours lesser diversity of organisms.
●
Organisms at the bottom have to
bear massive amounts of pressure on them constantly, so they adapted their body
systems as per the environment. One of the critical adaptations is the absence
of gas-filled structures in the body, like the lungs. Organisms at the pelagic
level, like fishes, have a swim bladder to maintain buoyancy.
●
The food chain at the pelagic
level starts from autotrophs. At benthic levels, scavengers, detrivores are the
starting point of the food chain.
●
Oxygen levels vary significantly
in the marine ecosystem. The top of the ocean forms a euphotic zone, where
oxygen is readily available. There are two reasons for it; the possibility of
photosynthesis and the surface in contact with air. Then come oxygen minimum
zones, wherein there is a significant lack of oxygen. The decomposition of
organic matter is the prime source of oxygen at this level. At the benthic
level, oxygen is almost absent. Any organic matter that reaches that deep gets
decomposed in the way and leaves no scope for a source of oxygen. Therefore,
the organisms at benthic levels have a slow metabolism.
●
Due to different metabolism, the
organisms at the pelagic level are faster in speed than those found at the
benthic level.
Examples
Of Pelagic Zone Biota
Pelagic organisms include pelagic
invertebrates like krill, copepods, jellyfish and rotifers. Fishes like forage
fish, tuna, whale shark, porbeagle,
megalodon, billfish etc., come under the biota of the pelagic zone.
Benthic
Zone Examples
Benthos include sea stars, worms, corals,
clams, crabs, flounder fish, flatfish, gargoyle fish, blue-spotted ribbontail
rays, crustaceans, sea urchins, lobsters, sponges, and other tiny organisms
that live in the bottom sediments.
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