Nekton

Nekton or necton refers to the aggregate of actively swimming aquatic organisms in a body of water. The term was proposed by German biologist Ernst Haeckel to differentiate between the active swimmers in a body of water, and the passive organisms that were carried along by the current, the plankton. As a guideline, nektonic organisms have a high Reynolds number (greater than 1000) and planktonic organisms a low one (less than 10). However, some organisms can begin life as plankton and transition to nekton later on in life, sometimes making distinction difficult when attempting to classify certain plankton-to-nekton species as one or the other. For this reason, some biologists choose not to use this term.

History

The term was first proposed and used by the German biologist Ernst Haeckel in 1891 in his article Plankton-Studien where he contrasted it with plankton, the aggregate of passively floating, drifting, or somewhat motile organisms present in a body of water, primarily tiny algae and bacteria, small eggs and larvae of marine organisms, and protozoa and other minute consumers. Today it is sometimes considered an obsolete term because it often does not allow for the meaningful quantifiable distinction between these two groups. Some biologists no longer use it.[1][2]

Definition

As a guideline, nekton are larger and tend to swim largely at biologically high Reynolds numbers (>10³ and up beyond 10⁹), where inertial flows are the rule, and eddies (vortices) are easily shed. Plankton, on the other hand, are small and, if they swim at all, do so at biologically low Reynolds numbers (0.001 to 10), where the viscous behavior of water dominates, and reversible flows are the rule. Organisms such as jellyfish and others are considered plankton when they are very small and swim at low Reynolds numbers, and considered nekton as they grow large enough to swim at high Reynolds numbers. Many animals considered classic examples of nekton (e.g., Mola mola, squid, marlin) start out life as tiny members of the plankton and then, it was argued, gradually transition to nekton as they grow.

Oceanic nekton

Oceanic nekton comprises animals largely from three clades:

There are organisms whose initial life stage is identified as being planktonic but when they grow and increase in body size they become nektonic. A typical example is the medusa of the jellyfish.

See also

  • neuston (the organisms, typically microscopic, that float near the surface of the water)
  • pleuston (all organisms that float near the surface of the water)
  • plankton (the organisms that float and drift within the water)
  • benthos (the organisms at the bottom of a body of water)

References

  1. ^ Aleyev, Yu. G. (1977). Nekton. doi:10.1007/978-94-010-1324-6.
  2. ^ Haeckel, E. 1891. Plankton-Studien. Jenaische Zeitschrift für Naturwissenschaft 25 / (Neue Folge) 18: 232-336. BHL.

External links

  • Stefan Nehring and Ute Albrecht (1997): „hell und das redundante Benthon: Neologismen in der deutschsprachigen Limnologie“. In: Lauterbornia H. 31: 17-30, Dinkelscherben, December 1997 E-Text (PDF-Datei)
Bathyscaphe Trieste

Trieste is a Swiss-designed, Italian-built deep-diving research bathyscaphe, which with its crew of two reached a record maximum depth of about 10,911 metres (35,797 ft), in the deepest known part of the Earth's oceans, the Challenger Deep, in the Mariana Trench near Guam in the Pacific. On 23 January 1960, Jacques Piccard (son of the boat's designer Auguste Piccard) and US Navy Lieutenant Don Walsh achieved the goal of Project Nekton.

Trieste was the first manned vessel to have reached the bottom of the Challenger Deep.

Benthos

Benthos is the community of organisms that live on, in, or near the seabed, river, lake, or stream bottom, also known as the benthic zone. This community lives in or near marine or freshwater sedimentary environments, from tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths.

Many organisms adapted to deep-water pressure cannot survive in the upperparts of the water column. The pressure difference can be very significant (approximately one atmosphere for each 10 metres of water depth).Because light is absorbed before it can reach deep ocean-water, the energy source for deep benthic ecosystems is often organic matter from higher up in the water column that drifts down to the depths. This dead and decaying matter sustains the benthic food chain; most organisms in the benthic zone are scavengers or detritivores.

The term benthos, coined by Haeckel in 1891, comes from the Greek noun βένθος "depth of the sea". Benthos is used in freshwater biology to refer to organisms at the bottom of freshwater bodies of water, such as lakes, rivers, and streams. There is also a redundant synonym, benthon.

Gérard Lopez (businessman)

Gérard López Fojaca (born 27 December 1971) is an entrepreneur-investor and an active Luxembourgish-Spanish businessman that invests in new technologies, energy sector and in the sports industry.

In the 1990s, Lopez cofounded Mangrove Capital Partners, one of the top three Tech investor in Europe. Alongside Éric Lux, he created The Genii Group. From 2009 to 2015, Lopez was President of the Formula 1 Lotus F1 Team and is still one of its minority shareholder and administrator. He is chairman of Genii Capital and is also CEO of Nekton, an investment company in the energy sector, where he spends most of his time. Lopez has been the President of Luxemburg CS Fola Esch football club since 2007.

IRobot Ranger

The Ranger is a man-portable Unmanned underwater vehicle (UUV) that supports technology development related to mine warfare, expeditionary warfare, homeland defense, underwater surveillance / reconnaissance and other missions, made by the Massachusetts robotics firm iRobot. Ranger is also designed for ocean research and commercial applications related to search and survey, such as oceanography.

Unlike the iRobot Seaglider which is propeller-less and motor-less, the Ranger has a propeller and is meant for shorter range missions.

Ranger weighs less than 20 kilograms (44 lb), travels at speeds up to 15 knots (17 mph) and is programmed via Ethernet or Wi-Fi. It can carry a variety of sensors for different kinds of data monitoring.

Ranger was initially developed by Nekton Research, Inc. in Durham, North Carolina. iRobot acquired Nekton Research in September, 2009.

IRobot Transphibian

The iRobot Transphibian is a man-portable, fin-powered AUV and bottom-crawler that can autonomously insert itself into the water and operate in a very shallow area. The fins enable the robot to navigate with 6 degrees of freedom, even in surge, to avoid obstacles and maneuver in tight spaces. In military operations the robot is more usually referred to as a UUV.

The Transphibian can carry a wide array of payloads and is designed for mine detection, harbor defense and surveillance. It employs a hybrid navigation system that allows it to operate in both shallow surf zones and in deeper waters.

The Transphibian was initially developed by the Nekton Corporation in Durham, North Carolina. iRobot acquired Nekton in September, 2008.

MOCNESS

MOCNESS is the acronym for Multiple Opening/Closing Net and Environmental Sensing System and is a net system for plankton in the ocean. The system is towed behind a research vessel with a speed of up to 2.5 knots and consists of five to twenty nets with a mesh size from 64 µm to 3 mm and an area of 0.25 to 20 m2 (although the last one is a 2x10 m systems) which are opened and closed computer controlled at desired depth. The net enables biologists to catch zooplankton and nekton in various depth horizons typically anywhere in the upper 6000 m of the oceans. All MOCNESS systems are capable of sampling to 6000 meters depth (10,000 psi). The system includes SeaBird probes to measure salinity and temperature at sampling depths, as well as optional dissolved oxygen, PAR (photosynthetically available light), transmissometry and fluorescence sensors.

Meroplankton

Meroplankton is a wide variety of planktonic organisms, which spend a portion of their lives in the benthic region of the ocean. These organisms do not remain as plankton permanently, rather, they are planktonic components in transition, which eventually become larger organisms. After a period of time in the plankton, meroplankton either graduate to the nekton or adopt a benthic (often sessile) lifestyle on the seafloor. Meroplankton consists of larval stages of organisms such as sea urchins, starfish, and crustaceans. Success of meroplankton populations depends on many factors, such as adult fecundity, fertilization success, growth and larval stage duration, behaviour, dispersal, and settlement. Mortality depends on many factors, such as predation, competition, disease, parasites, and physiological stresses. Survival and mortality of meroplankton has a direct effect on adult population numbers of many species. Many of the common, well-known animals found on the Great Barrier Reef spend time as free-swimming meroplankton, bearing little or no resemblance to the adult they will become. The differences between the appearance of larval and adult stages led to much confusion in the past when larval forms were often believed to be completely different species from the adults. Larvae spend varying amounts of time in the plankton, from minutes to over a year. However, just how long these tiny animals can be considered truly planktonic is under some debate.

Microbial loop

The microbial loop describes a trophic pathway in the marine microbial food web where dissolved organic carbon (DOC) is returned to higher trophic levels via its incorporation into bacterial biomass, and then coupled with the classic food chain formed by phytoplankton-zooplankton-nekton. The term microbial loop was coined by Farooq Azam and Tom Fenchel et al. to include the role played by bacteria in the carbon and nutrient cycles of the marine environment.

In general, dissolved organic carbon (DOC) is introduced into the ocean environment from bacterial lysis, the leakage or exudation of fixed carbon from phytoplankton (e.g., mucilaginous exopolymer from diatoms), sudden cell senescence, sloppy feeding by zooplankton, the excretion of waste products by aquatic animals, or the breakdown or dissolution of organic particles from terrestrial plants and soils (Van den Meersche et al. 2004). Bacteria in the microbial loop decompose this particulate detritus to utilize this energy-rich matter for growth. Since more than 95% of organic matter in marine ecosystems consists of polymeric, high molecular weight (HMW) compounds (e.g., protein, polysaccharides, lipids), only a small portion of total dissolved organic matter (DOM) is readily utilizable to most marine organisms at higher trophic levels. This means that dissolved organic carbon is not available directly to most marine organisms; marine bacteria introduce this organic carbon into the food web, resulting in additional energy becoming available to higher trophic levels. Recently the term "microbial food web" has been substituted for the term "microbial loop".

Oceanic physical-biological process

Due to the higher density of sea water (1,030 kg m−3) than air (1.2 kg m−3), the force exerted by the same velocity on an organism is 827 times stronger in the ocean. When waves crash on the shore, the force exerted on littoral organisms can be equivalent to several tons.

Oyster reef

The term oyster reef refers to dense aggregations of oysters that form large colonial communities. Because oyster larvae need to settle on hard substrates, new oyster reefs may form on stone or other hard marine debris. Eventually the oyster reef will propagate by spat settling on the shells of older or nonliving oysters. The dense aggregations of oysters are often referred to as an oyster reef, oyster bed, oyster bank, oyster bottom, or oyster bar interchangeably. These terms are not well defined and often regionally restricted.

Plankton

Plankton are the diverse collection of organisms that live in large bodies of water and are unable to swim against a current. The individual organisms constituting plankton are called plankters. They provide a crucial source of food to many large aquatic organisms, such as fish and whales.

These organisms include bacteria, archaea, algae, protozoa and drifting or floating animals that inhabit—for example—the pelagic zone of oceans, seas, or bodies of fresh water. Essentially, plankton are defined by their ecological niche rather than any phylogenetic or taxonomic classification.

Though many planktonic species are microscopic in size, plankton includes organisms over a wide range of sizes, including large organisms such as jellyfish.

Technically the term does not include organisms on the surface of the water, which are called pleuston—or those that swim actively in the water, which are called nekton.

Pleuronectidae

Pleuronectidae, also known as righteye flounders, are a family of flounders. They are called "righteye flounders" because most species lie on the sea bottom on their left sides, with both eyes on their right sides. The Paralichthyidae are the opposite, with their eyes on the left side. A small number of species in Pleuronectidae can also have their eyes on the left side, notably the members of the genus Platichthys.Their dorsal and anal fins are long and continuous, with the dorsal fin extending forward onto the head. Females lay eggs that float in mid-water until the larvae develop, and they sink to the bottom.They are found on the bottoms of oceans around the world, with some species, such as the Atlantic halibut, Hippoglossus hippoglossus, being found down to 2,000 m (6,600 ft). The smaller species eat sea-floor invertebrates such as polychaetes and crustaceans, but the larger righteye flounders, such as H. hippoglossus, which grows up to 4.7 m (15 ft) in length, feed on other fishes and cephalopods, as well.

They include many important commercially fished species, including not only the various fish called flounders, but also the European plaice, the halibuts, the lemon sole, the common dab, the Pacific Dover sole, and the flukes.

The name of the family is derived from the Greek πλευρά (pleura), meaning "rib" or "side", and νηκτόν (nekton), meaning "swimming".

Pleuston

Pleuston are the organisms that live in the thin surface layer existing at the air-water interface of a body of water as their habitat. Examples include some cyanobacteria, some gastropods, the ferns Azolla and Salvinia and the seed plants Lemna, Wolffia, Pistia, Eichhornia crassipes and Hydrocharis. Some fungi and fungi-like protists may be also found.

Project Nekton

Project Nekton was the codename for a series of very shallow test dives (three of them in Apra Harbor) and also deep-submergence operations in the Pacific Ocean near Guam that ended with the United States Navy-owned research bathyscaphe Trieste entering the Challenger Deep, the deepest surveyed point in the world's oceans.

The series of eight dives began with two harbor dives, then a Pacific Ocean test dive at Guam, by the newly modified Trieste, which had been modified to dive far deeper than before. After two checkout dives, the first abyssal dive reached a record of 18,150 feet (5,530 m) on November 15, 1959. The series included a record deep dive to near the bottom of the Nero deep in the Mariana Trench at 24,000 feet (7,300 m), and finally culminated with a trip to the bottom of the Challenger Deep at 35,797 feet (10,911 m), on January 23, 1960.The project name was proposed by oceanographer Dr. Robert S. Dietz in early 1958, as plans to modify the Trieste bathyscaphe to go to the deepest part of the oceans were being contemplated. It is in reference to ocean life that actively swims (nekton) as opposed to the plankton organisms that only drift. The bathyscaphe Trieste to be used for Project Nekton was able to move independently, in contrast to tethered bathyspheres. The Trieste featured two electric motors, each with a propeller, of two horsepower each. These allowed it to move forward, backward and to turn horizontally. A maximum speed of one knot (1.9 km/h; 1.2 mph) was attainable over a few miles distance.

Psammon

Psammon (from Greek "psammos", "sand") is a group of organisms inhabiting coastal sand moist — biota buried in sediments. Psammon is a part of water fauna, along with periphyton, plankton, nekton, and benthos. Psammon is also sometimes considered a part of benthos due to its near-bottom distribution. Psammon term is commonly used to refer to freshwater reservoirs such as lakes.

Seston

Seston are the organisms (bioseston) and non-living matter (abioseston or tripton) swimming or floating in a water body. Bioseston can be often regarded as plankton, although it includes nekton as well. Abioseston comprises detritus as well.

The Deep (2015 TV series)

The Deep is an Australian/Canadian co-produced animated television series based on the comic book created by Tom Taylor and James Brouwer and published by Gestalt Comics. The series was optioned by Technicolor and produced by A Stark Production and the Canadian animation studio Nerd Corps Entertainment, a subsidiary of DHX Media. Commissed by ABC, it premiered on 7TWO on December 1, 2015 and began broadcasting in Canada the following month on Family Chrgd. Netflix acquired the U.S. SVOD rights to The Deep, and it began streaming in America on June 1, 2016 It also aired on Ici Radio-Canada Télé in Canada, and Universal Kids in the US.

It is set to be broadcast on CBBC (UK), RTS Deux (Switzerland), La Trois (Belgium), Ketnet (Belgium), NRK (Norway), DR (Denmark), SVT (Sweden) and YLE (Finland), Okto (Singapore) and Super RTL (Germany).On February 8, 2018, DHX Media announced that the series has been renewed for a third season.

USS Wandank (ATA-204)

The second USS Wandank (ATA-204), originally USS ATA-204, was a United States Navy auxiliary ocean tug in commission from 1945 to 1947 and again from 1952 to 1971. The ship is possibly best known for supporting scientific operations in the Marianas, in particular serving as communication relay and support ship for the bathyscaphe Trieste in Project Nekton; she towed the bathyscaphe some 260 nautical miles (482 kilometers) from Guam to the vicinity of the Challenger Deep, where, on 23 January 1960, Trieste descended to a record 37,000 feet (11,278 meters).

Aquatic ecosystems

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