Urchin barren

An urchin barren is an area of the subtidal where the population growth of sea urchins has gone unchecked, causing destructive grazing of kelp beds or kelp forests (specifically the giant brown bladder kelp, Macrocystis). The transition from kelp forest to barren is defined by phase shifts in which one stable community state is shifted to another.[1] There is a theory that both sea urchin barrens and kelp-beds represent alternative stable states, meaning that an ecosystem can exist under multiple states, each with a set of unique biotic and abiotic conditions (i.e. barren except for urchins or flourishing with kelp). Those who argue for this theory propose several criteria: that different self-replacing communities dominate the site; each state exists longer than one complete turnover of the dominant community or species; and that following a disturbance (e.g. a storm), the system returns to the previous state.

Alternatively, another theory known as the continuous phase shift is widely accepted. This describes a transition from one ecosystem state to another where the threshold for the forward shift is at the same level as the threshold for the reverse shift back to the previous state. In other words, a kelp bed can re-establish itself when urchin grazing intensity decreases to the threshold density triggering the initial shift.

Over the past four decades, barrens have been reported along coastlines around the world, everywhere from Nova Scotia to Chile. They can either span over a thousand kilometers of coastline or occur in small patches.[2]

Sea urchins eat kelp holdfasts.[3] This can be caused by a lack of sea otters or other predators in the area,[4] which makes it extremely important to protect the ecological balance in a kelp forest. Keystone species such as the sea otter help maintain healthy kelp communities; however, because of overfishing and increased killer whale predation, their numbers are in decline.[5] Off the California coast, storm runoff, erosion and polluted water allow less light to penetrate, weakening the kelp.[6] Sea urchins then can move in and settle.

Despite their name, urchin barrens are usually abundant with marine invertebrate life, echinoderms in particular.[7] Species such as the sunflower starfishes, brittle stars, and the purple sea urchin are common. Although macrofauna such as these are aplenty, there is little primary productivity among microorganisms.[8] This makes it difficult for newly settled sea urchins (juveniles) to survive, making barrens more dangerous for juveniles than for adults.[9] Once having wiped out a kelp forest, the environment becomes unsupportive of new sea urchin settlement and adults are forced to find a new resource.

References

  1. ^ FilbeeDexter, Karen; Scheibling, Robert E. (2014-01-09). "FEATURE ARTICLE: REVIEW Sea urchin barrens as alternative stable states of collapsed kelp ecosystems". Marine Ecology Progress Series. 495: 1–25. doi:10.3354/meps10573.
  2. ^ Stewart, Nathan L.; Konar, Brenda (2012-02-28). "Kelp Forests versus Urchin Barrens: Alternate Stable States and Their Effect on Sea Otter Prey Quality in the Aleutian Islands". Journal of Marine Biology. 2012: 1–12. doi:10.1155/2012/492308.
  3. ^ Planet Earth (2006 TV series) (2006). Shallow Seas (Television production). BBC Natural History Unit.
  4. ^ Stewart, NL; Konar B (2012). "Kelp Forests versus Urchin Barrens: Alternate Stable States and Their Effect on Sea Otter Prey Quality in the Aleutian Islands". Journal of Marine Biology. 2012: 1–12. doi:10.1155/2012/492308.
  5. ^ Estes, J. A.; Tinker, M. T.; Williams, T. M.; Doak, D. F. (1998-10-16). "Killer Whale Predation on Sea Otters Linking Oceanic and Nearshore Ecosystems". Science. 282 (5388): 473–476. doi:10.1126/science.282.5388.473. ISSN 0036-8075. PMID 9774274.
  6. ^ "Purple sea urchins spoiling kelp forest". SFGate. Retrieved 2015-12-04.
  7. ^ https://www.youtube.com/watch?v=D3W4OCnHyCs
  8. ^ FilbeeDexter, Karen; Scheibling, Robert E. (2014-01-09). "FEATURE ARTICLE: REVIEW Sea urchin barrens as alternative stable states of collapsed kelp ecosystems". Marine Ecology Progress Series. 495: 1–25. doi:10.3354/meps10573.
  9. ^ Rowley, R.J. (1990). "Newly settled sea urchins in a kelp bed and urchin barren ground: a comparison of growth and mortality". Marine Ecology Progress Series. 62: 229–240. doi:10.3354/meps062229.
Amazon Reef

The Amazon Reef, or Amazonian Reef, is an extensive coral and sponge reef system, located in the Atlantic Ocean off the coast of French Guiana and northern Brazil. It is one of the largest known reef systems in the world, with scientists estimating its length at over 1,000 kilometres (600 miles), and its area as over 9,300 km2 (3,600 sq mi). Publication of its discovery was released in April 2016, following an oceanographic study of the region in 2012. Evidence of a large structure near the delta of the Amazon River dated from as early as the 1950s.

Depauperate ecosystem

A depauperate ecosystem is one which is lacking in numbers or variety of species, often because it lacks enough stored chemical elements required for life. Thus, depauperate ecosystems often cannot support rapid growth of flora and fauna, high biomass density, and high biological diversity. An urchin barren is an example of a depauperate ecosystem.

An ecosystem is a biological community of interaction organisms and their actual physical environment. In Ecology, depauerate is an area that is so poor in species quantities and diversity. It lacks in numbers or a variety of species. Basically, a plant or animal is imperfectly developed. The reasons why there are depauperate areas are because the species do not have many competitors to fight with. Also, they have fewer resources causing the species not to survive without any protein or nutrients. Because these species lack the basic life necessities that they need, it’s hard for them to continue to carry on with life. ( The ecology of Adaptive Radiation). Therefore they aren’t reproducing the way that they are supposed to. In some cases, the species will actually start inbreeding. And because of that there are the same species everywhere. Therefore, competing with themselves, which can cause them to die. So, the area ends up falling short of the natural developmental size.

Echinoderm

Echinoderm is the common name given to any member of the phylum Echinodermata (from Ancient Greek, ἐχῖνος, echinos – "hedgehog" and δέρμα, derma – "skin") of marine animals. The adults are recognizable by their (usually five-point) radial symmetry, and include such well-known animals as sea stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea lilies or "stone lilies". Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone.

The phylum contains about 7000 living species, making it the second-largest grouping of deuterostomes (a superphylum), after the chordates (which include the vertebrates, such as birds, fishes, mammals, and reptiles). Echinoderms are also the largest phylum that has no freshwater or terrestrial (land-based) representatives.

Aside from the hard-to-classify Arkarua (a Precambrian animal with echinoderm-like pentamerous radial symmetry), the first definitive members of the phylum appeared near the start of the Cambrian. One group of Cambrian echinoderms, the cinctans (Homalozoa), which are close to the base of the echinoderm origin, have been found to possess external gills used for filter feeding, similar to those possessed by chordates and hemichordates.The echinoderms are important both ecologically and geologically. Ecologically, there are few other groupings so abundant in the biotic desert of the deep sea, as well as shallower oceans. Most echinoderms are able to reproduce asexually and regenerate tissue, organs, and limbs; in some cases, they can undergo complete regeneration from a single limb. Geologically, the value of echinoderms is in their ossified skeletons, which are major contributors to many limestone formations, and can provide valuable clues as to the geological environment. They were the most used species in regenerative research in the 19th and 20th centuries. Further, it is held by some scientists that the radiation of echinoderms was responsible for the Mesozoic Marine Revolution.

Habitat

In ecology, a habitat is the type of natural environment in which a particular species of organism lives. It is characterized by both physical and biological features. A species' habitat is those places where it can find food, shelter, protection and mates for reproduction.

The physical factors are for example soil, moisture, range of temperature, and light intensity as well as biotic factors such as the availability of food and the presence or absence of predators. Every organism has certain habitat needs for the conditions in which it will thrive, but some are tolerant of wide variations while others are very specific in their requirements. A habitat is not necessarily a geographical area, it can be the interior of a stem, a rotten log, a rock or a clump of moss, and for a parasitic organism it is the body of its host, part of the host's body such as the digestive tract, or a single cell within the host's body.

Habitat types include polar, temperate, subtropical and tropical. The terrestrial vegetation type may be forest, steppe, grassland, semi-arid or desert. Fresh water habitats include marshes, streams, rivers, lakes, and ponds, and marine habitats include salt marshes, the coast, the intertidal zone, estuaries, reefs, bays, the open sea, the sea bed, deep water and submarine vents.

Habitats change over time. This may be due to a violent event such as the eruption of a volcano, an earthquake, a tsunami, a wildfire or a change in oceanic currents; or the change may be more gradual over millennia with alterations in the climate, as ice sheets and glaciers advance and retreat, and as different weather patterns bring changes of precipitation and solar radiation. Other changes come as a direct result of human activities; deforestation, the plowing of ancient grasslands, the diversion and damming of rivers, the draining of marshland and the dredging of the seabed. The introduction of alien species can have a devastating effect on native wildlife, through increased predation, through competition for resources or through the introduction of pests and diseases to which the native species have no immunity.

Light This City

Light This City is an American melodic death metal band from the Bay Area of San Francisco, that has been active from 2002. The band is notable for the aggressive vocal approach of front-woman, Laura Nichol.

Regime shift

In ecology, regime shifts are large, abrupt, persistent changes in the structure and function of a system. A regime is a characteristic behaviour of a system which is maintained by mutually reinforced processes or feedbacks. Regimes are considered persistent relative to the time period over which the shift occurs. The change of regimes, or the shift, usually occurs when a smooth change in an internal process (feedback) or a single disturbance (external shocks) triggers a completely different system behavior. Although such non-linear changes have been widely studied in different disciplines ranging from atoms to climate dynamics, regime shifts have gained importance in ecology because they can substantially affect the flow of ecosystem services that societies rely upon, such as provision of food, clean water or climate regulation. Moreover, regime shift occurrence is expected to increase as human influence on the planet increases – the Anthropocene – including current trends on human induced climate change and biodiversity loss.

Sea urchin

Sea urchins or urchins () are typically spiny, globular animals, echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal to 5,000 metres (16,000 ft; 2,700 fathoms). Their tests (hard shells) are round and spiny, typically from 3 to 10 cm (1 to 4 in) across. Sea urchins move slowly, crawling with their tube feet, and sometimes pushing themselves with their spines. They feed primarily on algae but also eat slow-moving or sessile animals. Their predators include sea otters, starfish, wolf eels, and triggerfish.

Like other echinoderms, urchins have fivefold symmetry as adults, but their pluteus larvae have bilateral (mirror) symmetry, indicating that they belong to the Bilateria, the large group of animal phyla that includes chordates, arthropods, annelids and molluscs. They are widely distributed across all the oceans, all climates from tropical to polar, and inhabit marine benthic (sea bed) habitats from rocky shores to hadal zone depths. Echinoids have a rich fossil record dating back to the Ordovician, some 450 million years ago. Their closest relatives among the echinoderms are the sea cucumbers (Holothuroidea); both are deuterostomes, a clade which includes the chordates.

The animals have been studied since the 19th century as model organisms in developmental biology, as their embryos were easy to observe; this has continued with studies of their genomes because of their unusual fivefold symmetry and relationship to chordates. Species such as the slate pencil urchin are popular in aquariums, where they are useful for controlling algae. Fossil urchins have been used as protective amulets.

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