Aquatic ecosystems are classified broadly into marine and fresh water ecosystems. The marine ecosystem covers around 71% of the earth’s surface while freshwater ecosystems cover around 0.8% of the earth’s surface. The life in aquatic ecosystems can be variable from one place to another as well as in different depths. While many species can inhabit the surface waters or the shallow waters, relatively few species can adapt to the living in deeper waters. This article will describe the factors that limit life at different depths in relation to most aquatic life zones.
Among the factors that limit any aquatic life zone, light, nutrients and temperature are the most significant. However, when it comes to vast ecosystems such as marine life zones, there are factors which provide specific demarcations to the aquatic life zones, contrasting them from relatively smaller aquatic ecosystems.
-Availability of light
When dividing marine ecosystems into specific zones, dividing the same based on the availability of light is the most significant. Thus, in such a division, the sunlit upper part of the ocean is known as the ‘photic’ zone while the zone, which receives enough sunlight for photosynthesis, is given the name, ‘euphotic zone’. Understandably, the ‘euphotic zone’ is the closest to the ocean surface, which receives the most amount of sunlight. In contrast, the ‘aphotic zone’ is the deeper waters, which does not receive any sunlight.
-Distance from the shore
In addition to the demarcation based on light, distance from the shore is another major factor that determines marine life zones. Thus, the area in which the land and the sea overlap is given the name ‘intertidal zone’ and is characterized by the presence of rocky and sandy shores. The ‘neritic zone’ on the other hand is seawards from the low tide line, the continental shelf out to the shelf break. ‘Oceanic zone’, which is the furthest from the shore, is the zone beyond the continental shelf.
When considering aquatic life zones based on the water depth, marine life can be classified into four main zones. Among them, the ‘pelagic zone’ is the open ocean of any depth while the ‘benthic zone’ includes any sea-bottom surface. The middle zone of the ocean depth where light is dim and scanty, is known to marine experts as the ‘bathyl zone’. Lastly, the zone in which the light is non-existent and therefore dark is given the name ‘abyssal zone’. In addition to non-availability of light, its extreme depth, high water pressure and the low temperature also characterize the ‘abyssal zone’. This is in addition to the sparse life discoverable within this zone. Thus, the food sources available for the ‘abyssal zone’ would mainly be the decaying particles and the falling fragments from the higher zones in the same marine ecosystem.
However, although the zones mentioned above are mainly used in describing a marine ecosystem, other fresh water ecosystems would also be having similar demarcations and sometimes even unique factors that affects the demarcation of its aquatic life.