Thursday, September 30, 2010

September 30, 2010 : Tigerfish


Tigerfish 

Tigerfish is the common name for a variety of species from several different families of fish, usually on account of their colouration or otherwise fearsome appearance.

Several species in the genus Hydrocynus of the family Alestiidae are called "tigerfish" and are particularly prized as gamefish. These African fish are found in many rivers and lakes on the continent and are fierce predators with distinctive protruding teeth.

The two most common species are probably most recognizable in Southern Africa. The first is the Goliath Tiger (Hydrocynus goliath), which is found in the Congo River system, the largest of the family. The second-largest, and the southernmost species, is the Tigerfish (Hydrocynus vittatus), commonly found in the Zambezi River and in the two biggest lakes along the Zambezi, Lake Kariba in Zambia, Zimbabwe, and Cabora Bassa in Mozambique and Jozini dam in South Africa.

The name "tigerfish" has occasionally been used for species of cichlid in the genus Rhamphochromis. These are large, silver-colored fishes that may have one or two black horizontal lines running the length of the body. These fish are native to Lake Malawi in Africa. They can measure up to 2 meters (6 ft. 7 in.) in length and weigh up to 50 kg (105 lbs.) They also have very sharp teeth that can rip through skin easily; however, they are not known to eat humans.

Tigerfish can be considered Africa's equivalent of the South American piranha, though they belong to a completely different family, as they are famous for their ferocity when hunting. They have razor-sharp teeth that are interlocking, along with streamlined, muscular bodies built for speed. Tigerfish are aggressive predators. A tigerfish has a gas-filled sac in its body that it uses as a sound receiver. This transmits vibrations from the water, enabling it to detect any animals nearby and respond accordingly. A school of juveniles can tackle animals of almost any size, including any land animals that stray too close to the water's edge. Adults tend to travel in smaller groups of four or five, but they are no less dangerous. Even an individual can take down prey as large as itself. When food is scarce or the competition for food is too great, tigerfish may resort to cannibalism. This is particularly common in the dry season. Tigerfish have also been known to attack humans, these attacks can be devastating owing to their sharp teeth and aggressive hunting tactics.

Wednesday, September 29, 2010

September 29, 2010 : Sengeal Birchir


Senegal Bichir

The Senegal Bichir, Polypterus senegalus, also known as the Gray Bichir and Cuvier's Bichir, is sometimes called the "dinosaur eel" at many local pet chains - a misnomer, as the creature is not an eel. It is a fish, a prototypical species of the Polypterus genus, meaning most of its features are held across the genus.

The body is long and about as deep as it is wide. A serrated dorsal fin runs along most of the body until it meets the caudal fin. The pectoral fins attach just behind and below the gill openings and are the primary means of locomotion, providing a slow, graceful appearance. P. senegalus is smaller than its brethren, reaching about 35.5 cm (14").

The head is small and lizard-like with a gaping mouth and small eyes on either side. Since its eyesight is poor the bichir primarily hunts by smell. External nostrils protrude from the nose of the fish to enable this.

The fish has a pair of primitive lungs instead of a swim bladder, allowing it to periodically gulp air from the surface of the water. In the aquarium bichirs can be observed dashing to the surface for this purpose. Provided the skin remains moist, the creature can remain out of the water for near indefinite periods of time.

This bichir's skin serves as a particularly effective armor.

Bichirs are predatory fish and in captivity will take any live or dead animal that can be swallowed or broken apart and then swallowed. The only thing preventing a bichir from emptying an aquarium of smaller fish is its speed; the pectoral fins only allow for slow cruising, and while it can achieve amazing bursts of speed, it can't catch fish of average speed. Given enough time, any fish that can fit in the bichir's mouth will be eaten; this fish should not be kept with any other fish smaller than three inches.

Tuesday, September 28, 2010

September 28, 2010 : Ocean Gyre


Ocean Gyre

A gyre in oceanography is any large system of rotating ocean currents, particularly those involved with large wind movements. Gyres are caused by the Coriolis Effect; planetary vorticity along with horizontal and vertical friction, which determine the circulation patterns from the wind curl (torque). The term gyre can be used to refer to any type of vortex in the air or the sea, even one that is man-made, but it is most commonly used in oceanography, to refer to the major ocean systems.

The following are the five most notable gyres: North Atlantic, South Atlantic, Indian Ocean, North Pacific and South Pacific.

Tropical gyres are less unified and tend to be mostly east-west with minor north-south extent. These include the Atlantic Equatorial Current System, Pacific Equatorial Current System and the Indian Monsoon Gyres.

The center of a subtropical gyre is a high pressure zone. Circulation around the high pressure is clockwise in the northern hemisphere and anticlockwise in the southern hemisphere, due to the Coriolis effect. The high pressure in the center is due to the westerly winds on the northern side of the gyre and easterly trade winds on the southern side of the gyre. These cause frictional surface currents towards the latitude at the center of the gyre. The build-up of water in the center of the gyre creates equatorward flow in the upper 1,000 to 2,000 m (3,300 to 6,600 ft) of the ocean, through rather complex dynamics. This equatorward flow is returned poleward in an intensified western boundary current.

The intensified western boundary current of the North Atlantic Gyre is the Gulf Stream, in the North Pacific it's the Kuroshio Current, in the South Atlantic it's the Brazil Current, in the South Pacific it's the East Australian Current, and in the Indian Ocean it's the Agulhas Current.

Subpolar gyres form at high latitudes (around 60°). Circulation of surface wind and ocean water is anticlockwise in the Northern Hemisphere, around a low-pressure area, such as the persistent Aleutian Low and the Icelandic Low. Surface currents generally move outward from the center of the system. This drives the Ekman transport, which creates an upwelling of nutrient-rich water from the lower depths. 

Subpolar circulation in the southern hemisphere is dominated by the Antarctic Circumpolar Current, due to the lack of large landmasses breaking up the Southern Ocean. There are minor gyres in the Weddell Sea and the Ross Sea, the Weddell Gyre and Ross Gyre, which circulate in a clockwise direction.

Monday, September 27, 2010

September 27, 2010 : Basilosaurus (Extinct)


Basilosaurus

Basilosaurus ("King Lizard") is a genus of cetacean that lived from 40 to 34 million years ago Its fossilized remains were first discovered in the southern United States (Louisiana), and were initially believed to be some sort of reptilian sea monster, hence the suffix -"saurus", but later it was found that was not the case. Fossils from at least two other species of this taxon have been found in Egypt and Pakistan.
in the Late Eocene.Basilosaurus averaged about 18 meters (60 ft) in length, and is believed to have been the largest animal to have lived in its time. It displayed an unparalleled degree of elongation compared with modern whales. Their very small vestigial hind limbs have also been a matter of interest for paleontologists. The species is the state fossil of Mississippi and Alabama in the United States.

During the early 19th century in the American South, Basilosaurus cetoides fossils were so common (as well as large) that they were regularly used as furniture. Vertebrae were sent to the American Philosophical Society by a Judge Bly of Arkansas and Judge John Creagh of Clarke County, Alabama. Both fossils ended up in the hands of the anatomist Dr. Richard Harlan, who requested more examples from Creagh. With some reservation, Harlan speculated that the fossils belonged to a (50 m [166 ft] long) marine reptile, for which he suggested the name Basilosaurus, meaning “King reptile”.

When the British anatomist Sir Richard Owen studied the spine, mandibular fragments, arms, and ribs (more recently found) he proclaimed them to be mammalian. Owen proposed renaming the find to Zeuglodon cetoides (“whale-like yoke teeth”), which is now a junior synonym; though the latter is considered by many to be a more fitting name, the first-published name always takes precedence. The name Zeuglodon refers to the double rooted teeth typical of marine mammals.

In 1845, “Dr.” Albert Koch heard stories of giant bones in Alabama, and went down to cobble together a full skeleton. He eventually created a huge 114-foot (35 m) skeleton of a “sea serpent” he called "Hydrarchos", which he displayed in New York City, and later Europe. It was eventually shown to have come from 5 different individuals, some of which were not Basilosaurus. The remains were eventually destroyed in the Great Chicago Fire.

Fossil finds of another species, Basilosaurus isis, have been found in the aptly named Valley of the Whales in Egypt. The fossils were very well preserved, hind limbs included, and were rather numerous. Paleontologist Philip Gingerich, who organized several expeditions to the valley, speculated that Egyptian crocodile worship may have been inspired by the huge skeletons that lay there. Fossil remains of another species, Basilosaurus drazindai, have been found in Pakistan. Another fossilized species named Basiloterus husseini was its closest known relative, but was not as large or elongated.

Sunday, September 26, 2010

September 26, 2010 : Seven-arm Octopus


Seven-Arm Octopus

The Seven-arm Octopus (Haliphron atlanticus) is the largest known species of octopus based on scientific records, with a total estimated length of 4 m and weight of 75 kg. However, there have been disputed claims of even larger octopuses of the species Enteroctopus dofleini.

The Seven-arm Octopus is so named because in males the hectocotylus (a specially modified arm used in egg fertilization) is coiled in a sac beneath the right eye. Due to this species' thick gelatinous tissue, the arm is easily overlooked, giving the appearance of just seven arms. However, like other octopuses, it actually has eight.

In 2002, a single specimen of giant proportions was caught by fisheries trawling off the eastern Chatham Rise, New Zealand. This specimen, the largest of this species and of all octopuses, was the first validated record of Haliphron from the South Pacific. It had a mantle length of 0.69 m, total length of 2.90 m, and weight of 61.0 kg, although it was incomplete.

The type specimen of H. atlanticus was collected in the Atlantic Ocean at 38°N 34°W. It is deposited at the Zoologisk Museum, University of Copenhagen.

Saturday, September 25, 2010

September 25, 2010 : Sea Squirt


Sea Squirt 

Tunicates, also known as urochordates, are members of the subphylum Tunicata or Urochordata, a group of underwater saclike filter feeders with incurrent and excurrent siphons that is classified within the phylum Chordata. While most tunicates live on the ocean floor and are commonly known as sea squirts and sea pork,others – such as salps, doliolids and pyrosomes – live above in the pelagic zone as adults. 

Most tunicates feed by filtering sea water through pharyngeal slits, but some are sub-marine predators such as the Megalodicopia hians. Like other chordates, tunicates have a notochord during their early development, but lack myomeric segmentation throughout the body and tail as adults. Tunicates lack the kidney-like metanephridial organs, and the original coelom body-cavity develops into a pericardial cavity and gonads. Except for the pharynx, heart and gonads, the organs are enclosed in a membrane called an epicardium, which is surrounded by the jelly-like mesenchyme. Tunicates begin life in a mobile larval stage that resembles a tadpole, later developing into a barrel-like and usually sedentary adult form.

Tunicates apparently evolved in the early Cambrian period, beginning c 540 million years ago. Despite their simple appearance, tunicates are closely related to vertebrates, which include fish and all land animals with bones.

Most tunicates are hermaphrodites. The eggs are kept inside their body until they hatch, while sperm is released into the water where it fertilizes other individuals when brought in with incoming water.

Some larval forms appear very much like primitive chordates with a notochord (stiffening rod). Superficially, the larva resemble small tadpoles. They swim with a tail, and may have a simple eye, or Ocellus, and balancing organ, or Statolith. Some forms have a calcereous spicule that may be preserved as a fossil. They have appeared from the Jurassic to the present, with one proposed Neoproterozoic form, Yarnemia.

The larval stage ends when the tunicate finds a suitable rock to affix to and cements itself in place. The larval form is not capable of feeding though it may have a digestive system, and is only a dispersal mechanism. Many physical changes occur to the tunicate's body, one of the most interesting being the digestion of the cerebral ganglion, which controls movement and is the equivalent of the human brain. From this comes the common saying that the sea squirt "eats its own brain". In some classes, the adults remain pelagic (swimming or drifting in the open sea), although their larvae undergo similar metamorphoses to a higher or lower degree.

Once grown, adults can develop a thick covering, called a tunic, to protect their barrel-shaped bodies from enemies.

Tunicates are suspension feeders. They have two openings in their body cavity: an in-current and an ex-current siphon. The in-current siphon is used to intake food and water, and the ex-current siphon expels waste and water. The tunicate's primary food source is plankton. Plankton gets entangled in the mucus secreted from the endostyle. The tunicate's pharynx is covered by miniature hairs called ciliate cells which allow the consumed plankton to pass down through to the esophagus. Their guts are U-shaped, and their anuses empty directly to the outside environment. Tunicates are also the only animals able to create cellulose.

Tunicate blood is particularly interesting. It contains high concentrations of the transition metal vanadium and vanadium-associated proteins as well as higher than usual levels of lithium. Some tunicates can concentrate vanadium up to a level one million times that of the surrounding seawater. Specialized cells can concentrate heavy metals, which are then deposited in the tunic.

Friday, September 24, 2010

September 24, 2010 : Glass Sponge


Glass Sponge 

Hexactinellid sponges are sponges with a skeleton made of four- and/or six-pointed silaceous spicules, often referred to as glass sponges. They are usually classified along with other sponges in the phylum Porifera, but some researchers consider them sufficiently distinct to deserve their own phylum, Symplasma.

Glass sponges are relatively uncommon and are mostly found at depths from 450 to 900 metres (1,480 to 3,000 ft) although the species Oopsacas minuta has been found in shallow water, while others have been found much deeper. They are found in all oceans of the world, although they are particularly common in Antarctic waters. 

They are more-or-less cup-shaped animals, ranging from 10 to 30 centimetres (3.9 to 12 in) in height, with sturdy lattice-like internal skeletons made up of fused spicules of silica. The body is relatively symmetrical, with a large central cavity that, in many species, opens to the outside through a sieve formed from the skeleton. Unlike other sponges, they tend to be present as individuals, rather than forming large fused colonies. They are generally pale in colour. 

Much of the body is composed of syncitia, extensive regions of multinucleate cytoplasm. In particular, the epidermal cells of other sponges are absent, being replaced by a syncitial net of amoebocytes, through which the spicules penetrate. Unlike other sponges, they do not possess the ability to contract. 

One ability they possess is a unique system for rapidly conducting electrical impulses across their bodies, making it possible for them to respond quickly to external stimuli. Glass sponges like "Venus' Flower Basket" have a tuft of fibers that extends outward like an inverted crown at the base of their skeleton. These fibers are 50 to 175 millimetres (2.0 to 6.9 in) long and about the thickness of a human hair. They work as optical fibers somewhat similar to those used in modern telecommunication networks.

These creatures live for a very long time, but the exact age is hard to measure; one study based on modelling gave an estimated age of a specimen of Scolymastra joubini as 23,000 years, which is thought impossible, but is the basis for a listing of ~15,000 years in the AnAge Database.

Thursday, September 23, 2010

September 23, 2010 : Kaleidoscope Jellyfish


Kaleidoscope Jellyfish
 

Haliclystus auricula is a stalked jellyfish found in the Northern hemisphere. It is the type species for its genus.

In 2010, Natural England, The Guardian and the Oxford University Museum of Natural History ran a competition asking members of the public to provide a common name for this species. The name Kaleidoscope jellyfish was eventually chosen. Runner-up names included Fractal flower jellyfish and Mermaid's trumpet jellyfish.

H. auricula is 2-2.5cm tall with the stalk accounting for half of the height of the organism. The remainder of the organism is shaped like a funnel, the colour of which varies across the species from grey/green to red/brown. It has eight arms which radiate out from a central mouth. Each arm is tipped by clusters of up to 100 tentacles and connected by a thin membrane. Primary tentacles known as anchors are located on the membrane margin between the arms. The kidney-shape of these appendages is a key distinguishing feature of this species.


H. auricula is one of ten species of
Haliclystus found in the Northern hemisphere. It is very sensitive to pollution. The populations along the British coastline are in decline. 

This species lives in shallow water that has adequate circulation on marine eelgrass and other algae. H. auricula is able to move location by attaching a specialised tentacle to the substrate as an anchor, detaching its base and 'cartwheeling' into the new position.

This species reproduces by sexual means. H. auricula is most abundant in a given location in midsummer. Like all stalked jellyfish, a single H. auricula individual is believed to live for only one year.

Wednesday, September 22, 2010

September 22, 2010 : Marine Snow


Marine Snow

In the deep ocean, marine snow is a continuous shower of mostly organic detritus falling from the upper layers of the water column. Its origin lies in activities within the productive photic zone. Consequently, the prevalence of marine snow changes with seasonal fluctuations in photosynthetic activity and ocean currents. Thus marine snow is heavier in spring, and the reproductive cycles of some deep-sea animals are synchronized to take advantage of this occurence.

Marine snow has a composition which includes: dead or dying animals and plants (plankton), protists (diatoms), fecal matter, sand, soot and other inorganic dust. The "snowflakes" (which are more like clumps or strings) are aggregates of smaller particles held together by a sugary mucus, transparent exopolymer particles (TEPs); natural polymers exuded as waste products by bacteria and phytoplankton. These aggregates grow over time and may reach several centimetres in diameter, travelling for weeks before reaching the ocean floor.

However, most organic components of marine snow are consumed by microbes, zooplankton and other filter-feeding animals within the first 1,000 metres of their journey. In this way marine snow may be considered the foundation of deep-sea mesopelagic and benthic ecosystems: As sunlight cannot reach them, deep-sea organisms rely heavily on marine snow as an energy source. The small percentage of material not consumed in shallower waters becomes incorporated into the muddy "ooze" blanketing the ocean floor, where it is further decomposed through biological activity.

Tuesday, September 21, 2010

September 21, 2010 : Freshwater Mussels


Freshwater Mussels 

Generally unable to move of their own accord, the parasite larva or glochidium can do little more than clamp down on the first thing that brushes by its cute little jaws, sometimes equipped with vicious fangs and an adhesive tongue. Once attached, the host's skin will grow to encase the tiny hitchhiker, which remains for days or weeks until ready to drop off and settle down as a young mussel. Other species even allow themselves to be swallowed, and settle in the digestive tract where they may absorb nutrients until they are excreted. Usually only compatible with a single fish species, they rely on their parents to infect the right host with all manner of devilry.
 

Read the full article

Monday, September 20, 2010

September 20, 2010 : Furcacauda (Extinct)


Furcacauda

According to the Systema Naturae 2000 Taxonomic classification, Furcacauda is a genus within the family of Furcacaudidae, within the order Thelodonti, the Class Agnatha, and the Subphylum Vertebrata. Canadian fossils give rise to the Furcacaudiformes during the Devonian and Silurian time periods. Furcacaudiformes were deep water jawless vertebrates with symmetrical fork and lobed-finned tails and smaller than typical loganellid and nikoliviid thelodonti scales.

Furcacaudiformes are noted to having a laterally compressed body, large anterior eyes, slightly posterior, lateral, and vertical to a small mouth, and a condensed curved row of branchial openings (gills) directly posterior to the eyes. Many but not all had laterally paired fins. Wilson and Caldwell also note the presence of a caudal peduncle and a long caudal fin made of two large lobes, one dorsal and one ventral separated by 8 to 14 smaller intermediate lobes, giving the appearance of a striated half-moon shaped tail resembling the tail of a heterostracan
. A large square cavity within the gut connecting a small intestine to a anal opening lead many to believe that it is this genus that exhibits the first vertebrate stomach.

According to Wilson and Caldwell their discovery, based on sediment infillings of fossils of the
Furcacauda heintze, gives credence to the evolutionary development of stomach before jaws.

Sunday, September 19, 2010

September 19, 2010 : Elephantfish


Elephantfish

The family Mormyridae, sometimes called "elephantfish" (more properly freshwater elephantfish), are freshwater fish in the order Osteoglossiformes native to Africa. It is by far the largest family in the order with around 200 species. Members of the family are popular, if challenging, aquarium species. These fish are also known for having large brain size and unusually high intelligence.

They are not to be confused with the Australian ghost shark (Callorhinchus milii) which is sometimes referred to as the "elephantfish", but is better known as the elephant shark in the scientific community.

The elephantfishes are a diverse family, with a wide range of different sizes and shapes. The smallest are just 5 centimetres (2.0 in) in adult length, while the largest reach up to 1.5 metres (4.9 ft). They do, however, have a number of unique features in common. Firstly, the cerebellum (part of the brain) is greatly enlarged, giving them a brain to body size ratio similar to that of humans. This is likely to be related to the interpretation of bio-electrical signals. Secondly, the semicircular canals in the inner ear have an unusual structure and are associated with a gas-filled bladder entirely separate from the main swim bladder.

Some species possess modifications of the mouthparts to facilitate feeding upon small invertebrates buried in muddy substrates. The shape and structure of these leads to the popular name of "elephant nosed fish" for those species with particularly prominent mouth extensions. The extensions to the mouthparts usually consist of a fleshy elongation attached to the lower jaw. They are flexible, and equipped with touch, and possibly taste, sensors.

Among those members of the family lacking extended mouthparts, the body shape and general morphology of the fishes has led to some being known among aquarists by the name of "baby whale", despite the fact that true whales are mammals. Other "mormyrid mammalian misnomers" include the term "dolphin fishes", in reference to certain members of the Genus Mormyrops.

Elephantfishes are notable for their ability to generate weak electric fields that allow the fishes to sense their environment in turbid waters where vision is impaired by suspended matter. The generation of these electric fields and their use in providing the fishes with additional sensory input from the environment is the subject of considerable scientific research, as is research into communication between and within species.

Electric discharges are most often pulsatile, with Gymnarchus niloticus being an exception to this rule, discharging its electric organ near approximately 500 Hz, giving it a near-sinusoidal like discharge. The electric organ is developmentally related to muscle, as in Gymnotiform electric fish, as well as in electric rays and skates. There is a surprising degree of convergent evolution between the South American Gymnotiforms and the African Mormyridae, particularly in the sensory apparatus for detecting and processing electrical signals involved in electrolocation and electrocommunication.

Saturday, September 18, 2010

September 18, 2010 : Giant Pacific Octopus


Giant Pacific Octopus

The North Pacific Giant Octopus (Enteroctopus dofleini) is a large cephalopod belonging to the genus Enteroctopus. It can be found in the coastal North Pacific, usually at a depth of around 65 meters (215 ft). It can, however, live in much shallower or much deeper waters. It is arguably the largest octopus species, based on a scientific record of a 71 kg (156.5 lb) individual weighed live. The alternative contender is the Seven-arm Octopus based on a 61 kg (134 lb) carcass estimated to have a live mass of 75 kg (165 lb). However, there are a number of questionable size records that would suggest E. dofleini is the largest of all octopus species by a considerable margin.

The North Pacific Giant Octopus, or the Giant Pacific Octopus, are distinguished from other species by their sheer size. Adults usually weigh around 15 kg (33 lb), with an arm span of up to 4.3 m (14 ft). However, there are highly questionable records of specimens up to 272 kg (600 lb) in weight with a 9 m (30 ft) arm span. The mantle of the octopus is spherical in shape and contains most of the animal's major organs. By contracting or expanding tiny pigment-containing granules within cells known as chromatophores in its tissue, an octopus can change the color of its skin, giving it the ability to blend in to the environment.

This species of octopus commonly preys upon shrimp, crabs, scallops, abalone, clams, and fish. Food is procured with its suckers and then crushed using its tough "beak" of chitin. They have also been observed in captivity catching Spiny dogfish (Squalus acanthias) of up to 3-4 feet in length. Additionally, consumed carcasses of this same shark species have been found in Giant Pacific Octopus middens in the wild, providing strong evidence that these octopuses prey on sharks in their natural habitat.

Marine mammals such as Harbor Seals, Sea Otters, and Sperm Whales depend upon the North Pacific Giant Octopus as a source of food. The octopus is also commercially fished in the United States.

The North Pacific Giant Octopus is considered to be short-lived for an animal its size, with life spans that average only 3-5 years in the wild. To make up for its relatively short life span, the octopus is extremely prolific. It can lay up to 100,000 eggs which are intensively cared for by the females, who die protecting the eggs. Hatchlings are about the size of a grain of rice, and only a very few survive to adulthood.

Friday, September 17, 2010

September 17, 2010 : Sea Lice


Sea Lice 

Sea louse (plural sea lice) are copepods within the order Siphonostomatoida, family Caligidae. There are 36 genera within this family which include approximately 42 Lepeophtheirus and 300 Caligus species. Sea lice are marine ectoparasites (external parasites) that feed on the mucus, epidermal tissue, and blood of host marine fish. This article focuses on the genera Lepeophtheirus and Caligus which parasitize marine fish, in particular those species that have been recorded on farmed salmon. Lepeophtheirus salmonis and various Caligus species are adapted to saltwater and are major ectoparasites of farmed and wild Atlantic salmon. Several antiparasitic drugs have been developed for control purposes. Since L. salmonis is the major sea louse of concern and has the most known about its biology and interactions with its salmon host, this review will focus on this species. Caligus rogercresseyi has become a major parasite of concern on salmon farms in Chile, and studies are under way to gain a better understanding of the parasite and the host-parasite interactions. Recent evidence is also emerging that L. salmonis in the Atlantic has sufficient genetic differences from L. salmonis from the Pacific, suggesting that Atlantic and Pacific L. salmonis may have independently co-evolved with Atlantic and Pacific salmonids, respectively.

Most of our understanding of the biology of sea lice, other than the early morphological studies, is based on laboratory studies designed to understand issues associated with sea lice infecting fish on salmon farms. Information on sea lice biology and interactions with wild fish is unfortunately sparse in most areas with a long-term history of open net-cage development, since understanding background levels of sea lice and transfer mechanisms have rarely been a condition of tenure license for farm operators.

Many sea louse species are specific with regards to host genera, for example L. salmonis which has high specificity for salmonids, including the widely farmed Atlantic salmon (Salmo salar). Lepeophtheirus salmonis can parasitize other salmonids to varying degrees, including brown trout (sea trout: Salmo trutta), arctic char (Salvelinus alpinus), and all species of Pacific salmon. In the case of Pacific salmon, coho, chum, and pink salmon (O. kisutch, O. keta, and O. gorbuscha, respectively) mount strong tissue responses to attaching L. salmonis, which lead to rejection within the first week of infection. Pacific L. salmonis can also develop, but not complete, its full life cycle on the three-spined stickleback (Gasterosteus aculeatus L.). This has not been observed with Atlantic L. salmonis.

Thursday, September 16, 2010

September 16, 2010 : Giant Sea Bass


Giant Sea Bass

The giant sea bass (Stereolepis gigas) is a fish native to the northern Pacific Ocean. Considering its conspicuous size and its curious nature, it is surprising that relatively little is known about its biology or behavior.

There are published reports of giant sea bass reaching a size of 2.5 m (8.2 feet) and a weight of up to 255 kg (562 lbs). However in Charles F. Holder's book The Channels Islands published in 1910, the author claims specimens taken from the Gulf of California attained 800 pounds (360 kg). In the eastern Pacific its range is from Humboldt Bay, California to the Gulf of California, Mexico, most common from Point Conception southward. In the western Pacific it is found in the sea around Japan. It usually stays in relatively shallow water, near kelp forests, drop offs or rocky bottoms.

Giant sea bass were once a relatively common inhabitant of Southern California waters, yet in the 1980s it was facing the threat of local extinction off the California coast. Beginning in the late 1800s, the species supported both a commercial fishery taking hundreds of thousands of pounds annually, and a sport fishery that also landed hundreds of fish each year. Spear fishermen also exploited the giant sea bass, first as free divers, and then after the mid 1950s using scuba gear. Often the divers would target the species when they moved into shallow water during the summer months to spawn. By the late 1970s, biologists with the California State Department of Fish and Game, recognized that the local population of giant sea bass was in serious trouble. Actions were taken, resulting in protection from commercial and sport fishing that went into effect in 1982. Yet for almost two decades encounters with giant sea bass were scarce. The giant sea bass reproduces slowly with a population doubling time of more than 14 years and is still listed as critically endangered.

Due to its size and carnivorous nature it can pose some threat to humans.

Wednesday, September 15, 2010

September 15, 2010 : Sea Butterfly


Sea Butterfly  

Sea butterflies, also known as Thecosomata or flapping snails, are a taxonomic suborder of small pelagic swimming sea snails. These are holoplanktonic opisthobranch gastropod mollusks in the informal group Opisthobranchia. They include some of the world's most abundant gastropod species. 

This group is included in the pteropods, with its sister group the Gynmosomata. The validity of this clade is not unanimously established; whilst it had fallen out of favour, recent molecular evidence suggests that the taxon should be resurrected. The word pteropod applies both to the sea butterflies in the clade Thecosomata and also to the sea angels in the clade Gymnosomata. Most Thecosomata have a calcified shell, whereas mature Gymnosomata do not.

These snails float and swim freely in the water, and are carried along with the currents. This has led to a number of adaptations in their bodies. The shell and the gill have disappeared in several families. Their foot has taken the form of two wing-like lobes, or parapodia, which propel this little animal through the sea by slow flapping movements. They are rather difficult to observe, since the shell (when present) is mostly colorless, very fragile and usually less than 1 cm in length. Although their shell may be so fine as to be transparent, it is nevertheless calcareous; their shells are bilaterally symmetric and can vary widely in shape: coiled, needle-like, triangular, globulous.

The shell is present in all stages of the Cavolinioidea (euthecosomata) life cycle, whereas in the Cymbulioidea (pseudothecosomata), adult Peraclididae bear shells, Cymbuliidae shed their larval shells and develop a cartilaginous pseudoconch in adulthood, and Desmopteridaen adults lack any rigid structure.

Tuesday, September 14, 2010

September 14, 2010 : Great Pacific Garbage Patch


Great Pacific Garbage Patch

The Great Pacific Garbage Patch, also described as the Pacific Trash Vortex, is a gyre of marine litter in the central North Pacific Ocean located roughly between 135° to 155°W and 35° to 42°N. The patch extends over a very wide area, with estimates ranging from an area the size of the state of Texas to one larger than the continental United States; however, the exact size is unknown. This can be attributed to the fact that there is no specific standard for determining the boundary between the “normal” and “elevated” levels of pollutants and what constitutes being part of the patch. The size is determined by a higher-than normal degree of concentration of pelagic debris in the water. Recent data collected from Pacific albatross populations suggest there may be two distinct zones of concentrated debris in the Pacific.

The Patch is characterized by exceptionally high concentrations of pelagic plastics, chemical sludge, and other debris that have been trapped by the currents of the North Pacific Gyre. Despite its size and density, the patch is not visible from satellite photography since it primarily consists of suspended particulates in the upper water column. Since plastics break down to ever smaller polymers, concentrations of submerged particles are not visible from space, nor do they appear as a continuous debris field. Instead, the patch is defined as an area in which the mass of plastic debris in the upper water column is significantly higher than average.

Like other areas of concentrated marine debris in the world's oceans, it is thought, the Great Pacific Garbage Patch formed gradually as a result of marine pollution gathered by oceanic currents. The garbage patch occupies a large and relatively stationary region of the North Pacific Ocean bound by the North Pacific Gyre (a remote area commonly referred to as the horse latitudes). The gyre's rotational pattern draws in waste material from across the North Pacific Ocean, including coastal waters off North America and Japan. As material is captured in the currents, wind-driven surface currents gradually move floating debris toward the center, trapping it in the region.

The size of the patch is unknown, as large items readily visible from a boat deck are uncommon. Most debris consists of small plastic particles suspended at or just below the surface, making it impossible to detect by aircraft or satellite. Instead, the size of the patch is determined by sampling. Estimates on size range from 700,000 square kilometres (270,000 sq mi) to more than 15,000,000 square kilometres (5,800,000 sq mi) (0.41% to 8.1% of the size of the Pacific Ocean), or, in some media reports, up to "twice the size of the continental United States." Such estimates, however, are conjectural based on the complexities of sampling and the need to assess findings against other areas.

Related Articles
: Pacific Munitions Dump

Monday, September 13, 2010

September 13, 2010 : Doryaspis (Extinct)


Doryaspis 

Doryaspis ("Dart Shield") (also known by its synonym, "Lyktaspis") is an extinct genus of primitive jawless fish that lived in the Devonian period. Fossils have been discovered in Spitsbergen.

The animals had a canteen-shaped body armor, and had large branchial plates that extended out and curved downward in a triangular shape, very similar to those of the pycnosteids. An element of the median oral plates (that would correspond to the lower lip or chin in gnathostomes) extends out in a long rod-shaped appendage, called the "pseudorostrum." The tail is long and slender, and has large rows of thick scales.

In the type species, D. nathorsti, the lateral edges of the branchial plates and of the pseudorostrum are serrated. The second species, D. arctica, is smaller, and does not have any serrated edges.

Sunday, September 12, 2010

September 12, 2010 : Halosaur


Halosaur 

Halosaurs are eel-shaped fishes found only at great ocean depths. As the family Halosauridae, halosaurs are one of two families within the order Notacanthiformes; the other being the deep-sea spiny eels. Halosaurs are thought to have a worldwide distribution, with some seventeen species in three genera represented. Only a handful of specimens have been observed alive, all via chance encounters with remotely operated submersibles.

From the Greek hals meaning "sea" and sauros meaning "lizard", halosaurs look like living fossils from some throwback era. Their greatly elongated bodies end in a whip-like tail; their scales are large. There is one small dorsal fin close to the sharply pointed, mostly scaleless head. The tail fin is greatly reduced, with the anal fin being the largest fin. Their pecotral fins are slender and also greatly elongated. The mouth is somewhat large, with the lower jaw shorter than the upper jaw. The gas bladder is absent.

The largest species, the 90 centimeter (3 feet) long abyssal halosaur (Halosauropsis macrochir) is also one of the most deep-living fish, recorded at depths of 3,300 meters (11,000 feet). Halosaurs have developed certain adaptations to life at these extreme depths, where no light penetrates. Their lateral line system is highly developed; this is a system of pores running the length of the fish's body, lending it a sort of "sixth sense" by detecting nearby vibrations. Some species are also known to hold their elongate pectorals erect and forward, possibly providing a further means of detection.

Halosaurs are benthic fish, spending their time cruising over or resting on the sea floor where temperatures may be just 2-4 degrees Celsius. They propel themselves with rhythmic undulations of the body, not unlike snakes. Halosaurs are thought to prey mainly on benthic invertebrates, such as polychaete worms, echinoderms and crustaceans such as copepods.

In life, most halosaurs are a grey to bluish black in colour. Like other notacanthiform fish, halosaurs are able to regenerate their tails easily if lost. This adaptation can be likened to certain terrestrial reptiles such as the glass lizard, which sacrifices its tail in order to evade predators.

Saturday, September 11, 2010

September 11, 2010 : Cabezone


Cabezone

The Cabezone or Cabezon, Scorpaenichthys marmoratus, is a sculpin native to the Pacific coast of North America. Although the genus name translates literally as "scorpion fish," true scorpionfish, i.e., the lionfish and rockfish, belong to the related family Scorpaenidae.

The cabezon is a scaleless fish with a broad bony support extending from the eye across the cheek just under the skin. Normally it has 11 spines on the dorsal fin. The cabezon also has a stout spine before the eye, an anal fin of soft rays, and a fleshy flap on the middle of the snout. A pair of longer flaps are just behind the eyes. The mouth is broad with many small teeth. The coloring varies, but is generally mottled with browns, greens and reds. >90% of red fish are males, whereas >90% of green fish are females  It reaches a weight of up to 25 pounds. As the Spanish-origin name implies, the fish has a very large head relative to its body.

Cabezon are found from northern British Columbia to southern California. They frequent kelp beds from shallow to moderate depths.

Friday, September 10, 2010

September 10, 2010 : Sea Mouse


Sea Mouse

The sea mouse, Aphrodita aculeata is a marine polychaete worm found in the North Atlantic, the North Sea, the Baltic Sea and the Mediterranean. The sea mouse normally lies buried head-first in the sand. It can live in muddy sea floors down to around 1000m.

Its body is covered in a dense mat of chaetae (hairs), from which the name "sea mouse" derives. Its scientific name is taken from Aphrodite, Greek goddess of love. This is because, when viewed ventrally, the sea mouse resembles a human female's genitalia. They may grow up to 20 cm and are active carnivores, chiefly eating other polychaetes, such as Nereis, which may be up to three times the length of the sea mouse.

The iridescent threads or setae that emerge from its scaled back are one of its unique features. Normally, these setae have a red sheen, warning off predators, but when the light shines on them perpendicularly, they flush green and blue. The setae are made of millions of submicroscopic crystals that reflect and filter the faint light of the ocean depths.

Thursday, September 9, 2010

September 9, 2010 : Whale Shark


Whale Shark

The whale shark, Rhincodon typus, is a slow-moving filter feeding shark, the largest living fish species. The largest confirmed individual was 12.65 metres (41.50 ft) in length. The heaviest weighed more than 36 tonnes (79,000 lb), but unconfirmed claims report considerably larger whale sharks. This distinctively-marked fish is the only member of its genus Rhincodon and its family, Rhincodontidae (called Rhinodontes before 1984), which belongs to the subclass Elasmobranchii in the class Chondrichthyes. The shark is found in tropical and warm oceans, lives in the open sea with a lifespan of about 70 years. The species originated about 60 million years ago. Although whale sharks have very large mouths, they feed mainly, though not exclusively, on plankton, microscopic plants and animals, although the BBC program Planet Earth filmed a whale shark feeding on a school of small fish.

The species was distinguished in April 1828, following the harpooning of a 4.6-metre (15.1 ft) specimen in Table Bay, South Africa. Andrew Smith, a military doctor associated with British troops stationed in Cape Town described it the following year. He published a more detailed description in 1849. The name "whale shark" comes from the fish's physiology; as large as a whale, it too is a filter feeder.

As a filter feeder it has a capacious mouth which can be up to 1.5 metres (4.9 ft) wide and can contain between 300 and 350 rows of tiny teeth. It has five large pairs of gills. Two small eyes are located towards the front of the shark's wide, flat head. The body is mostly grey with a white belly; three prominent ridges run along each side of the animal and the skin is marked with a "checkerboard" of pale yellow spots and stripes. These spots are unique to each individual and are useful for counting populations. Its skin can be up to 10 centimetres (3.9 in) thick. The shark has a pair each of dorsal fins and pectoral fins. Juveniles' tails have a larger upper than lower fin while the adult tail becomes semi-lunate (crescent-shaped). Spiracles are just behind the eyes.

Wednesday, September 8, 2010

September 8, 2010 : Narwhal

Narwhal

The narwhal (Monodon monoceros) is a medium-sized toothed whale that lives year-round in the Arctic. One of two species of whale in the Monodontidae family, along with the Beluga whale, the narwhal males are distinguished by a characteristic long, straight, helical tusk extending from their upper left jaw. Found primarily in Canadian Arctic and Greenlandic waters rarely south of 65°N latitude, the narwhal is a uniquely specialized Arctic predator. In the winter, it feeds on benthic prey, mostly flatfish, at depths of up to 1500 m under dense pack ice. Narwhal have been harvested for over a thousand years by Inuit people in Northern Canada and Greenland for meat and ivory and a regulated subsistence hunt continues to this day. While populations appear stable, the narwhal has been deemed particularly vulnerable to climate change due to a narrow geographical range and specialized diet.

Male narwhals weigh up to 1,600 kilograms (3,500 lb), and the females weigh around 1,000 kilograms (2,200 lb). The pigmentation of the narwhal is a mottled black and white pattern. They are darkest when born and become whiter in color with age.

The most conspicuous characteristic of the male narwhal is its single 2–3 meter (7–10 ft) long tusk. It is an incisor tooth that projects from the left side of the upper jaw and forms a left-handed helix. The tusk can be up to 3 meters (9.8 ft) long—compared with a body length of 4–5 meters (13–16 ft)—and weigh up to 10 kilograms (22 lb). About one in 500 males has two tusks, which occurs when the right incisor, normally small, also grows out. A female narwhal may also produce a tusk, but this occurs rarely, and there is a single recorded case of a female with dual tusks.

The most broadly accepted theory for the role of the tusk is as a secondary sexual characteristic, similar to the mane of a lion or the tail feathers of a peacock. This hypothesis was notably discussed and defended at length by Charles Darwin, in The Descent of Man, and Selection in Relation to Sex (1871). It may help determine social rank, maintain dominance hierarchies or help young males develop skills necessary for performance in adult sexual roles. Narwhals have rarely been observed using their tusk for fighting or other aggressive behavior or for breaking sea ice in their Arctic habitat.

Tuesday, September 7, 2010

September 7, 2010 : St. Elmo's Fire


St. Elmo's Fire

St. Elmo's fire (also St. Elmo's light) is an electrical weather phenomenon in which luminous plasma is created by a coronal discharge originating from a grounded object in an atmospheric electric field (such as those generated by thunderstorms or thunderstorms created by a volcanic explosion).

St. Elmo's fire is named after St. Erasmus of Formiae (also called St. Elmo, the Italian name for St. Erasmus), the patron saint of sailors. The phenomenon sometimes appeared on ships at sea during thunderstorms and was regarded by sailors with religious awe for its glowing ball of light, accounting for the name.

Physically, St. Elmo's fire is a bright blue or violet glow, appearing like fire in some circumstances, from tall, sharply pointed structures such as lightning rods, masts, spires and chimneys, and on aircraft wings. St. Elmo's fire can also appear on leaves, grass, and even at the tips of cattle horns. Often accompanying the glow is a distinct hissing or buzzing sound.

In 1750, Michael Dedman hypothesized that a pointed iron rod during a lightning storm would light up at the tip, similar in appearance to St. Elmo's fire.

Although referred to as "fire", St. Elmo's fire is, in fact, plasma. The electric field around the object in question causes ionization of the air molecules, producing a faint glow easily visible in low-light conditions. Approximately 100–3000 kV per meter is required to induce St. Elmo's fire; however, this number is greatly dependent on the geometry of the object in question. Sharp points tend to require lower voltage levels to produce the same result because electric fields are more concentrated in areas of high curvature, thus discharges are more intense at the end of pointed objects.

St. Elmo's fire and normal sparks both can appear when high electrical voltage affects a gas. St. Elmo's fire is seen during thunderstorms when the ground below the storm is electrically charged, and there is high voltage in the air between the cloud and the ground. The voltage tears apart the air molecules and the gas begins to glow.

The nitrogen and oxygen in the Earth's atmosphere causes St. Elmo's fire to fluoresce with blue or violet light; this is similar to the mechanism that causes neon lights to glow.

Monday, September 6, 2010

September 6, 2010 : Sturgeon


Sturgeon 

Sturgeon is the common name used for some 26 species of fish in the family Acipenseridae, including the genera Acipenser, Huso, Scaphirhynchus and Pseudoscaphirhynchus. The term includes over 20 species commonly referred to as sturgeon and several closely related species that have distinct common names, notably sterlet, kaluga and beluga. Collectively, the family is also known as the True Sturgeons. Sturgeon is sometimes used more exclusively to refer to the species in the two best-known genera; Acipenser and Huso.

One of the oldest families of bony fish in existence, sturgeon are native to subtropical, temperate and sub-Arctic rivers, lakes and coastlines of Eurasia and North America. They are distinctive for their elongated bodies, lack of scales, and occasional great size: Sturgeons ranging from 7–12 feet (2-3½ m) in length are common, and some species grow up to 18 feet (5.5 m). Most sturgeons are anadromous bottom-feeders, spawning upstream and feeding in river deltas and estuaries. While some are entirely freshwater, very few venture into the open ocean beyond near coastal areas.

Several species of sturgeons are harvested for their roe, which is made into caviar—a luxury good which makes some sturgeons pound for pound the most valuable of all harvested fish. Because they are slow-growing and mature very late in life, they are particularly vulnerable to exploitation and to other threats, including pollution and habitat fragmentation. Most species of sturgeons are currently considered vulnerable, endangered or critically endangered.

Sturgeon and related paddlefish appeared in the fossil record approximately 200 million years ago, making them among the most ancient of actinopterygian fishes. In that time they have undergone remarkably little morphological change, indicating that their evolution has been exceptionally slow and earning them informal status as living fossils. This is explained in part by the long inter-generation time, tolerance for wide ranges of temperature and salinity, lack of predators due to size, and the abundance of prey items in the benthic environment.

Along with other members of the Chondrostei and the Acipenseriformes order, sturgeon are primarily cartilaginous, lack a vertebral centrum, and are covered with bony plates called scutes rather than scales. They also have four barbels—tactile organs that precede their toothless mouth and are dragged along often murky river bottoms. Sturgeon are distinctly and immediately recognizable for their elongated bodies, flattened rostra, distinctive scutes and barbels, and elongated upper tail lobes.

They are primarily benthic feeders. With their projecting wedgeshaped snout they stir up the soft bottom, and use the barbels to detect shells, crustaceans and small fish, on which they feed. Having no teeth, they are unable to seize prey, though larger specimens can swallow very large prey items, including whole salmon.

Sunday, September 5, 2010

September 5, 2010 : Razorfish


Razorfish
 

Aeoliscus strigatus, also known as the razorfish, is a member of the family Centriscidae of the order Gasterosteiformes. This unique fish adopts a face down, head up position as an adaptation for hiding among sea urchin spines.

The razorfish is generally found in coastal waters from the central Indian Ocean to the Red Sea to Hawaii. Its natural habitat includes beds of sea grass and coral reefs, where sea urchins are found.

The razorfish eats mainly small brine shrimp and other invertebrates. They have also been known to eat minute crustaceans in the zooplankton. In the wild they have been observed hiding in the spines of sea urchins, both as a defense mechanism and as a hunting mechanism. When threatened by larger fish, the razorfish darts away to a nearby sea urchin. The larger fish, wary of being stung by the sea urchin, which can sometimes be deadly, gives up the chase. They also hide in the spines for a completely different reason. When hunting, razorfish will hide among the sea urchin spines an wait for small invertebrates that feed on the urchins. When their prey gets close the razorfish will dart out and try to catch its dinner.

Saturday, September 4, 2010

September 4, 2010 : Moray Eel


Moray Eel
 

Moray eels are cosmopolitan eels of the family Muraenidae. The approximately 200 species in 15 genera are almost exclusively marine, but several species are regularly seen in brackish water and a few, for example the freshwater moray (Gymnothorax polyuranodon) can sometimes be found in freshwater. With a maximum length of 11.5 centimetres (4.5 in), the smallest moray is likely the Snyder's moray (Anarchias leucurus), while the longest species, the slender giant moray (Strophidon sathete) reaches up to 4 metres (13 ft). The largest in terms of total mass is the giant moray (Gymnothorax javanicus), which reaches almost 3 metres (9.8 ft) and can weigh over 36 kilograms (79 lb).
 

The dorsal fin extends from just behind the head along the back and joins seamlessly with the caudal and anal fins. Most species lack pectoral and pelvic fins, adding to their serpentine appearance. Their eyes are rather small; morays rely on their highly developed sense of smell, lying in wait to ambush prey.

The body is generally patterned. Camouflage is also present inside the mouth. Their jaws are wide, framing a protruding snout. They possess large teeth, designed to tear flesh as opposed to holding or chewing.
 

Moray eels' heads are too narrow to create the negative pressure that most fish use to swallow prey. Quite possibly because of this, they have a second set of jaws in their throat called pharyngeal jaws, which also possess teeth. When feeding, morays launch these jaws into the mouth, where they grasp prey and transport it into the throat and digestive system. Moray eels are the only animal that uses pharyngeal jaws to actively capture and restrain prey. Larger morays are capable of seriously wounding humans.
 

The Morays are frequently thought of as particularly vicious or ill-tempered animals. In truth, morays hide from humans in crevices and would rather flee than fight. Morays are shy and secretive, and attack humans only in self-defense or mistaken identity. Most attacks stem from disruption of a moray's burrow (to which they do react strongly), but an increasing number also occur during hand-feeding of morays by divers, an activity often used by dive companies to attract tourists. Morays have poor vision and rely mostly on their acute sense of smell, making distinguishing between fingers and held food difficult; numerous divers have lost fingers while attempting hand feedings. For this reason the hand feeding of moray eels has been banned in some locations, including the Great Barrier Reef. The moray's rear-hooked teeth and primitive but strong bite mechanism also makes bites on humans more severe, as the eel cannot release its grip even in death and must be manually pried off. While the majority are not believed to be venomous, circumstantial evidence suggests that a few species may be.

Friday, September 3, 2010

September 3, 2010 : Yeti Crab


Yeti Crab 

Kiwa hirsuta is a crustacean discovered in 2005 in the South Pacific Ocean. This decapod, which is approximately 15 cm (6 inches) long, is notable for the quantity of silky blond setae (resembling fur) covering its pereiopods (thoracic legs, including claws). Its discoverers dubbed it the "yeti lobster" or "yeti crab." 

K. hirsuta was discovered in March 2005 by a group organized by Robert Vrijenhoek of the Monterey Bay Aquarium Research Institute in Monterey, California and Michel Segonzac of the Ifremer and a Census of Marine Life scientist using the submarine DSV Alvin, operating from RV Atlantis. The discovery was announced on 7 March 2006. It was found 1,500 km (900 miles) south of Easter Island in the South Pacific, at a depth of 2,200 m (7,200 feet), living on hydrothermal vents along the Pacific-Antarctic Ridge. Based on both morphology and molecular data, the species was deemed to form a new genus and family (Kiwaidae). The animal has strongly reduced eyes that lack pigment, and is thought to be blind.

The "hairy" pincers contain filamentous bacteria, which the creature may use to detoxify poisonous minerals from the water emitted by the hydrothermal vents where it lives. Alternatively, it may feed on bacteria, although it is generally thought to be a carnivore.

Although it is often referred to as the "furry lobster" outside the scientific literature, Kiwa hirsuta is a squat lobster, more closely related to crabs and hermit crabs than true lobsters. The term "furry lobster" is more commonly used for the family Synaxidae.

September 2, 2010 : Pyrosomes


Pyrosomes

Pyrosomes, or pyrosoma, are free-floating colonial tunicates that live usually in the upper layers of the open ocean in warm seas, although some may be found to great depth. Pyrosomes are cylindrical or conical shaped colonies made up of hundreds to thousands of individuals, known as zooids. Colonies range in size from less than one centimeter to several meters in length.

Each zooid is only a few millimeters in size, but is embedded in a common gelatinous tunic that joins all of the individuals. Each zooid opens both to the inside and outside of the "tube", drawing in ocean water from the outside to its internal filtering mesh called the branchial basket, extracting the microscopic plant cells on which it feeds, and then expelling the filtered water to the inside of the cylinder of the colony. The colony is bumpy on the outside, each bump representing a single zooid, but nearly smooth, though perforated with holes for each zooid, on the inside.

Pyrosomes are planktonic, which means that their movements are largely controlled by currents, tides and waves in the oceans. On a smaller scale, however, each colony can move itself slowly by the process of jet propulsion, created by the coordinated beating of cilia in the branchial baskets of all the zooids, which also create feeding currents.

Pyrosomes are brightly bioluminescent, flashing a pale blue-green light that can be seen for many tens of meters. The name Pyrosoma comes from the Greek (pyro = "fire", soma = "body"). Pyrosomes are closely related to salps, and are sometimes called "fire salps." Sailors on the ocean are occasionally treated to calms seas containing many pyrosomes, all bioluminescencing on a dark night.

Wednesday, September 1, 2010

September 1, 2010 : Rogue Waves


Rogue Waves
 

Rogue waves (also known as freak waves, monster waves, killer waves, extreme waves, and abnormal waves) are relatively large and spontaneous ocean surface waves that occur far out in sea, and are a threat even to large ships and ocean liners. In oceanography, they are more precisely defined as waves whose height is more than twice the significant wave height (SWH), which is itself defined as the mean of the largest third of waves in a wave record. Therefore rogue waves are not necessarily the biggest waves found at sea; they are, rather, surprisingly large waves for a given sea state. "Rogue waves are not tsunamis, which are set in motion by earthquakes [and] travel at high speed, building up as they approach the shore. Rogue waves seem to occur in deep water or where a number of physical factors such as strong winds and fast currents converge. This may have a focusing effect, which can cause a number of waves to join together."

Once thought by scientists to exist only in legends, rogue waves are now known to be a natural ocean phenomenon. Eyewitness accounts from mariners and damages inflicted on ships have long suggested they occurred; however, their scientific measurement was only positively confirmed following measurements of the "Draupner wave," a rogue wave at the Draupner platform, in the North Sea on January 1, 1995. During this event, minor damage was inflicted on the platform, confirming that the reading was valid. Satellite images have also confirmed their existence.

Freak waves have been cited in the media as a likely source of the sudden, inexplicable disappearance of many ocean-going vessels. One of the very few cases in which evidence exists that may indicate a freak wave incident is the 1978 loss of the freighter MS M√ľnchen, detailed below. In February 2000, a British oceanographic research vessel sailing in the Rockall Trough west of Scotland encountered the largest waves ever recorded by scientific instruments in the open ocean, with a SWH of 18.5 meters (61 ft) and individual waves up to 29.1 meters (95 ft). "In 2004 scientists using three weeks of radar images from European Space Agency satellites found ten rogue waves, each 25 metres or higher."

A rogue wave is not the same as a tsunami. Tsunamis are mass displacement-generated waves which propagate at high speed and are more or less unnoticeable in deep water; they only become dangerous as they approach the shoreline and do not present a threat to shipping (the only ships lost in the 2004 Asian tsunami were in port). A rogue wave, on the other hand, is a spatially and temporally localized event that most frequently occurs far out at sea.

Rogue waves may sometimes be referred to as "hundred-year waves," due to the supposed likelihood of their occurrence. They should not be confused, however, with the hundred-year wave, which is a statistical prediction of the highest wave likely to occur in a hundred-year period in a particular body of water. These predictions are typically based on wave models which do not take rogue waves into account.