Pelagic zone

The pelagic zone is subdivided into five vertical regions. From the top down, these are: Epipelagic (sunlight) The illuminated zone at the surface of the sea, and the only zone with sufficient light for photosynthesis. This zone is just above the continental shelf and has the lowest atmospheric pressure on the oceans surface, at 1 atm for every 10 meters. Nearly all primary production in the ocean occurs here, and about 90% marine life is concentrated in this zone, including: plankton, floating seaweed, jellyfish, tuna, whales, sharks, dolphins, and many more diverse species. Mesopelagic (twilight) The thermocline serves as the boundary from the warmer top zone to the much colder mesopelagic zone, which is also located right under the continental shelf. Bathypelagic (midnight) The name stems . In this zone, the environment is pitch black at this depth and contains no trace of sunlight, apart from occasional bioluminescent organisms, such as anglerfish. No plants live here. Most creatures survive on detritus known as "marine snow" falling from the zones above or, like the marine hatchetfish, by preying on other inhabitants of this zone. Abyssopelagic (abyssal zone) The name is derived . The ocean floor is next to this zone, and it forms volcanos, mountains, and vents from the movement of the tectonic plates. Very few creatures live in this zone. Some of the recorded species are coelenterate, polychaetas, amphipods, echinoderms, and mollusks. ==Pelagic ecosystem==

The pelagic ecosystem is based on phytoplankton. Phytoplankton manufacture their own food using a process of photosynthesis. Because they need sunlight, they inhabit the upper, sunlit epipelagic zone, which includes the coastal or neritic zone. Biodiversity diminishes markedly in the deeper zones below the epipelagic zone as dissolved oxygen diminishes, water pressure increases, temperatures become colder, food sources become scarce, and light diminishes and finally disappears. Pelagic invertebrates Some examples of pelagic invertebrates include krill, copepods, jellyfish, decapod larvae, hyperiid amphipods, rotifers and cladocerans. Thorson's rule states that benthic marine invertebrates at low latitudes tend to produce large numbers of eggs developing to widely dispersing pelagic larvae, whereas at high latitudes such organisms tend to produce fewer and larger lecithotrophic (yolk-feeding) eggs and larger offspring. Pelagic fish Pelagic fish live in the water column of coastal, ocean, and lake waters, but not on or near the bottom of the sea or the lake. They can be contrasted with demersal fish, which do live on or near the bottom, and coral reef fish. Pelagic fish are often migratory forage fish, which feed on plankton, and the larger predatory fish that follow and feed on the forage fish. Migratory fish come up to the more dense prey areas of the pelagic zones to feed, and then descend at night to avoid predators. Pelagic reptiles Hydrophis platurus, the yellow-bellied sea snake, is the only one of the 65 species of marine snakes to spend its entire life in the pelagic zone. It bears live young at sea and is helpless on land. The species sometimes forms aggregations of thousands along slicks in surface waters. The yellow-bellied sea snake is the world's most widely distributed snake species. Many species of sea turtles spend the first years of their lives in the pelagic zone, moving closer to shore as they reach maturity. (Diomedea exulans) ranges over huge areas of ocean and can circle the globe. ==Food web==

Compared to terrestrial environments, marine environments have biomass pyramids which are inverted at the base. In particular, the biomass of consumers (copepods, krill, shrimp, forage fish) is larger than the biomass of primary producers. This happens because the ocean's primary producers are tiny phytoplankton which tend to have a fast life history (are r-strategists that grow and reproduce rapidly) so a small mass can have a fast rate of primary production. In contrast, terrestrial primary producers, such as mature forests, often have a slow life history (are K-strategists that grow and reproduce slowly) so a much larger mass is needed to achieve the same rate of primary production. Because of this inversion, it is the zooplankton that make up most of the marine animal biomass. As primary consumers, they are the crucial link between the primary producers (mainly (phytoplankton) and the rest of the marine food web (secondary consumers). If phytoplankton dies before it is eaten, it descends from the euphotic zone down through the pelagic water column as part of the marine snow, and settles into the depths of sea. In this way, phytoplankton sequester about 2 billion tons of carbon dioxide in the ocean each year, causing the ocean to become a sink of carbon dioxide holding about 90% of all sequestered carbon. In 2010 researchers found whales carry nutrients from the depths of the ocean back up the pelagic water column to the surface using a process they called the whale pump. Whales feed at deeper levels in the ocean where krill is found, but return regularly to the surface to breathe. There whales defecate a liquid rich in nitrogen and iron. Instead of sinking, the liquid stays at the surface where phytoplankton consume it. In the Gulf of Maine the whale pump provides more nitrogen than the rivers. == Observing and sampling methods ==

Exploring and learning more about the ocean is a main factor to ocean resource management, which sustainably manages how much and how fast we use the ocean’s resources. Ocean exploration also observes patterns in the ocean’s weather and climate, and the means by which they were affected. With this data, researchers are better able to understand and see natural phenomena such as earthquakes and tsunamis and react accordingly. Scientists and researchers have developed many methods to sample the ocean biome and pelagic fish. Trawling This method can be used from a boat to capture organisms like deep pelagic fish. A mesh net is dragged at different depths to collect for recording the captured organisms. This method can produce large amounts of specimen. However it is costly, time consuming, and mostly used by research groups with a lot of support and funding. There are also many fish that are able to out swim the net, which limits data. Active acoustics This method analyzes fish that are detected by sound pulses that are emitted from the surface, where the pelagic fish's biomass in the reflected signal is analyzed. This method of sampling cannot reach deep depths in the ocean. The pulses cover a broad area of the ocean and cause little harm or distress. The received data from this method is complicated to interpret due to specific variations of swim bladders in fish, such as having little gas or not having a swim bladder. Remotely operated vehicles Remotely operated vehicles (ROVs) are used for sampling and examining the deep pelagic sea in ways that other techniques cannot match. An ROV is an unoccupied machine equipped with lights, cameras, sensors, or arms, which allows for detailed and live observations of its surroundings and of pelagic organisms. It can conduct experiments and collect samples. These machine are limited in ground coverage, as well as expensive and hard to control, so few research groups use them. They can also be loud, bright, and big, causing organisms to avoid them. Additional methods Some other sampling and observation methods are: predator gut examinations, analysis of environmental DNA, organisms that get washed up on shore from upwelling, analyzing sediments cores, and pelagic longline fishing. ==References==