Red sea urchin

The red sea urchin (Mesocentrotus franciscanus)[1] is a sea urchin found in the northeastern Pacific Ocean from Alaska to Baja California. It lives in shallow waters from the low-tide line to greater than 100 m (330 ft) deep,[2] and is typically found on rocky shores sheltered from extreme wave action.

Red sea urchin
Strongylocentrotus franciscanus
Scientific classification
Kingdom:
Phylum:
Class:
Order:
Family:
Genus:
Mesocentrotus
Species:
M. franciscanus
Binomial name
Mesocentrotus franciscanus
(Aggasiz, 1863)
Synonyms
  • Strongylocentrotus franciscanus
  • Toxocidaris franciscana
  • Toxocidaris franciscanus

Description

Strongylocentrotus franciscanus juvenile
M. franciscanus juvenile, found at Cape Flattery, WA: This individual is about 1.5 cm in diameter.

A sea urchin's spherical body is completely covered by sharp spines. These spines grow on a hard shell called the "test", which encloses the animal. It can vary in color from red to dark burgundy. Rarely, albino specimens are found. It has a mouth located on its underside, which is surrounded by five teeth. During larval development, the body of a sea urchin transitions from bilateral to radial symmetry.

This bilaterally symmetrical larva, called an echinopluteus, subsequently develops a type of pentaradiate symmetry that characterises echinoderms. It crawls very slowly over the sea bottom using its spines as stilts, with the help of its tube feet. Scattered among its spines are rows of tiny tube feet with suckers that help it to move and stick to the sea floor.

Feeding habits

This animal has a mouth with special jaws (Aristotle's lantern) located on the bottom (oral) surface. Its preferred diet is seaweeds and algae, which it scrapes off and tears up from the sea floor. During larval development, urchins use bands of cilia to capture food from the water column.[3] Red sea urchins found in the channel adjacent to San Juan Island have been found to live a uniquely sedentary lifestyle with the heavy currents bringing an abundance of food.[4][5]

Behavior and reproduction

Sea urchins are often found living in clumps from five to ten. They have the ability to regenerate lost spines. Lifespan often exceeds 30 years, and scientists have found some specimens to be over 200 years old.[6] Red sea urchins are notoriously ravenous kelp-eaters and are implicated in devastating kelp beds[7] by forming grazing fronts. The intense grazing pressure exerted by urchins is an important link in a trophic cascade often observed along the west coast of North America in which sea otter predation influences urchin abundance, which in turn influences kelp devastation.[8] In contrast to their negatively perceived impact on community structure in open coastal kelp beds, the sedentary behavior and capture of detrital seaweed in the San Juan Islands is hypothesized to create an important habitat and energy source below the photic zone.[4] These diverse ecosystem effects of red urchins highlight their importance as ecosystem engineers in temperate rocky reef ecosystems.

Spawning peaks between June and September. Eggs are fertilized externally while they float in the ocean, and planktonic larvae remain in the water column for about a month before settling on the bottom of the sea floor, where they undergo metamorphosis into juvenile urchins. These juveniles use chemical cues to locate adults[9]. Although juveniles are found almost exclusively under aggregated adults, the adults and juveniles are not directly related[10].

References

  1. ^ Agassiz, A. "Mesocentrotus franciscanus". WoRMS. Retrieved 28 April 2014.
  2. ^ Britton-Simmons, Kevin; et al. (2012). "Habitat and bathymetry influence the landscape-scale distribution and abundance of drift macrophytes and associated invertebrates". Limnology and Oceanography. 57: 176–184. doi:10.4319/lo.2012.57.1.0176.
  3. ^ Richard R. Strathmann (1971). "The feeding behavior of planktotrophic echinoderm larvae: mechanisms, regulation, and rates of suspension feeding". Journal of Experimental Marine Biology and Ecology. 6 (2): 109–160. doi:10.1016/0022-0981(71)90054-2.
  4. ^ a b Lowe, Alexander; et al. (2015). "Sedentary urchins influence benthic community composition below the macroalgal zone". Marine Ecology. 36 (2): 129–140. doi:10.1111/maec.12124.
  5. ^ Whippo, R; Lowe, A; Britton-Simmons, K (2011). "Effects of the Red Sea Urchin on Benthic Invertebrate Communities: A Link to Spatial Subsidies". In: Pollock NW, Ed. Diving for Science 2011. Proceedings of the American Academy of Underwater Sciences 30th Symposium. Dauphin Island, AL: AAUS; 2011. Retrieved 2013-03-18.
  6. ^ Thomas A. Ebert & John R. Southon (2003). "Red sea urchins (Strongylocentrotus franciscanus) can live over 100 years: confirmation with A-bomb 14carbon" (PDF). Fishery Bulletin. 101 (4): 915–922.
  7. ^ Harrold and Reed (1985). "Food availability, sea urchin grazing, and kelp forest community structure". Ecology. 66 (4): 1160–1169. doi:10.2307/1939168. JSTOR 1939168.
  8. ^ Estes and Duggins (1995). "Sea otters and kelp forests in Alaska: generality and variation in a community ecological paradigm". Ecological Monographs. 65 (1): 75–100. doi:10.2307/2937159. JSTOR 2937159.
  9. ^ Nishizaki, Michael T; Ackerman, JD (2000). "A secondary chemical cue facilitates juvenile‐adult postsettlement associations in red sea urchins". Limnology & Oceanography. 50 (1): 354–362. doi:10.4319/lo.2005.50.1.0354.
  10. ^ Moberg, PE; Burton, Ronald (2000). "Genetic heterogeneity among adult and recruit red sea urchins, Strongylocentrotus franciscanus". Marine Biology. 136 (5): 773–784. doi:10.1007/s002270000281.

External links

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Astropyga radiata, the red urchin, fire urchin, false fire urchin or blue-spotted urchin, is a species of sea urchin in the family Diadematidae. It is a large species with long spines and is found in the tropical Indo-Pacific region. It was first described in 1778 by the German naturalist Nathaniel Gottfried Leske.

Biological immortality

Biological immortality (sometimes referred to as bio-indefinite mortality) is a state in which the rate of mortality from senescence is stable or decreasing, thus decoupling it from chronological age. Various unicellular and multicellular species, including some vertebrates, achieve this state either throughout their existence or after living long enough. A biologically immortal living being can still die from means other than senescence, such as through injury or disease.

This definition of immortality has been challenged in the Handbook of the Biology of Aging, because the increase in rate of mortality as a function of chronological age may be negligible at extremely old ages, an idea referred to as the late-life mortality plateau. The rate of mortality may cease to increase in old age, but in most cases that rate is typically very high. As a hypothetical example, there is a 50% chance of a human surviving another year at age 110 or greater.

The term is also used by biologists to describe cells that are not subject to the Hayflick limit on how many times they can divide.

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Kelp forest

Kelp forests are underwater areas with a high density of kelp. They are recognized as one of the most productive and dynamic ecosystems on Earth. Smaller areas of anchored kelp are called kelp beds.

Kelp forests occur worldwide throughout temperate and polar coastal oceans. In 2007, kelp forests were also discovered in tropical waters near Ecuador.Physically formed by brown macroalgae, kelp forests provide a unique, three-dimensional habitat for marine organisms and are a source for understanding many ecological processes. Over the last century, they have been the focus of extensive research, particularly in trophic ecology, and continue to provoke important ideas that are relevant beyond this unique ecosystem. For example, kelp forests can influence coastal oceanographic patterns and provide many ecosystem services.However, the influence of humans has often contributed to kelp forest degradation. Of particular concern are the effects of overfishing nearshore ecosystems, which can release herbivores from their normal population regulation and result in the overgrazing of kelp and other algae. This can rapidly result in transitions to barren landscapes where relatively few species persist. The implementation of marine protected areas is one management strategy useful for addressing such issues, since it may limit the impacts of fishing and buffer the ecosystem from additive effects of other environmental stressors.

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Oldest verified known individuals that are currently alive

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Loxechinus albus

Loxechinus albus is an echinoderm of the family Parechinidae, native to coastal southern South America, ranging from Ecuador, along the entire coasts of Peru and Chile, to Argentina, as well as the Falkland Islands. It is known as the Chilean sea urchin or red sea urchin, but the latter name is typically used for the North Pacific Mesocentrotus franciscanus and it is not the only species of sea urchin in Chile (although it is the most common and widespread large sea urchins in that country). L. albus is found on rocky reefs and shores in the intertidal and subtidal zones to a depth of 340 m (1,120 ft).

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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.

Strongylocentrotidae

The Strongylocentrotidae are a family of sea urchins in the order Echinoida.

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