Marine Domains Study Documents

‭MARINE DOMAINS‬ ‭There are basically two: the pelagic domain, the water masses with the organisms that‬ ‭populate them, and the benthic domain, the seabed and the organisms that have more or less‬ ‭close relationships with them. We can say that the further subdivisions of the marine‬ ‭environment are based on three further elements: the distance from land, the depth and the‬ ‭benthic/pelagic organisms that populate the seabed. In the image we see the two domains‬ ‭represented, pelagic and benthic; both domains in turn can be divided both vertically and‬ ‭horizontally. The pelagic domain can be divided horizontally into two regions, a neritic one,‬ ‭made up of the waters overlying the continental shelf, and the oceanic region that lies above‬ ‭the slope and above the ocean floor. Vertically the domain‬ ‭pelagic can then be further subdivided. A first subdivision is based on the penetration of light:‬ ‭photic or euphotic zone, whose lower limit coincides with the limit of light penetration and varies‬ ‭in depth depending on the transparency of the water. In the open ocean the lower limit of the‬ ‭photic zone can be placed between 100 and 200 m depth. Synonymous with the photic zone is‬ ‭the epipelagic zone, the primary production zone of the oceans. Below the photic zone is the‬ ‭aphotic zone: in the middle between the two there is a disphotic zone, in which light can still be‬ ‭found but not enough to allow photosynthesis and extends to a maximum depth of 1000 m. The‬ ‭disphotic zone coincides with the mesopelagic zone, which in the image represents the upper part‬ ‭of the aphotic zone. The lower limit of this mesopelagic zone in clear and tropical waters is‬ ‭constituted by the 10° isotherm, which can be located between 700 and 1000 m depth.‬ ‭Proceeding vertically we find the bathypelagic zone, which is located between the 10th isotherm‬ ‭and the 4th isotherm and in terms of depth, between 700/1000 m and 2000/4000 m. From this‬ ‭depth up to 6000 m the abyssopelagic zone extends, which covers the large oceanic abyssal‬ ‭plains. The water of the deep ocean trenches, from 6000 m to 11000 m, constitutes the‬ ‭hadalpelagic or hadopelagic zone. If we then move on to the subdivision of the benthic domain,‬ ‭also in this case horizontally, we can identify a coastal area (or of the continental shelf) and a deep‬ ‭area, which extends from the margin of the continental shelf to the maximum depths of the‬ ‭oceanic trenches. The deep area is also called aphytal, to underline the absence of plant forms‬ ‭associated with the seabed. This area is divided into three planes: the bathyal plane,‬ ‭corresponding to the continental slope, up to 4000 m depth, the abyssal plane, corresponding to‬ ‭the waters of the pelagic abyss, and then beyond 6000 m there is the adal plane . Corresponding‬ ‭to the neritic region, i.e. from the coastlines to the edge of the continental shelf, the seabed is‬ ‭represented by the littoral system. The coastal system is characterized by the most superficial part‬ ‭of the littoral zone, the intertidal zone, which extends between the two extreme high and low tide‬ ‭levels, and then also extends to the most superficial zone yet, affected only sporadically by sea‬ ‭water: the entire intertidal zone represents a transition zone between the marine environment and‬ ‭conditions and the terrestrial environment and conditions. Below the littoral zone we have a‬ ‭sublittoral zone that extends to the entire continental shelf.‬ ‭In this image the different components of the pelagic‬ ‭and benthic domain are represented‬ ‭three-dimensionally. Here in particular the different‬ ‭zones of the pelagic domain are highlighted in relation‬ ‭to the neritic and oceanic regions: only the epipelagic‬ ‭is always present in both regions. The upper part of‬ ‭the mesopelagic can be located in the most distal and‬ ‭also deepest part of the coastal shelf.‬