Holdfast (biology)

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Holdfast torn from the sea floor by a storm Giant kelp (Macrocystis pyrifera) holdfast.jpg
Holdfast torn from the sea floor by a storm
Eocrinoid holdfasts on an Ordovician hardground in Utah. Ordovician hardground Utah.jpg
Eocrinoid holdfasts on an Ordovician hardground in Utah.

A holdfast is a root-like structure that anchors aquatic sessile organisms, such as seaweed, other sessile algae, stalked crinoids, benthic cnidarians, and sponges, to the substrate. [1]

Holdfasts vary in shape and form depending on both the species and the substrate type. The holdfasts of organisms that live in muddy substrates often have complex tangles of root-like growths. These projections are called haptera and similar structures of the same name are found on lichens. The holdfasts of organisms that live in sandy substrates are bulb-like and very flexible, such as those of sea pens, thus permitting the organism to pull the entire body into the substrate when the holdfast is contracted. The holdfasts of organisms that live on smooth surfaces (such as the surface of a boulder) have flattened bases which adhere to the surface. The organism derives no nutrition from this intimate contact with the substrate, as the process of liberating nutrients from the substrate requires enzymatically eroding the substrate away, thereby increasing the risk of organism falling off the substrate.

The claw-like holdfasts of kelps and other algae differ from the roots of land plants, in that they have no absorbent function, instead serving only as an anchor. [2]

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<span class="mw-page-title-main">Kelp</span> Large brown seaweeds in the order Laminariales

Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera. Despite its appearance, kelp is not a plant - it is a heterokont, a completely unrelated group of organisms.

<span class="mw-page-title-main">Brown algae</span> Large group of multicellular algae, comprising the class Phaeophyceae

Brown algae, comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown algae are the major seaweeds of the temperate and polar regions. They are dominant on rocky shores throughout cooler areas of the world. Most brown algae live in marine environments, where they play an important role both as food and as a potential habitat. For instance, Macrocystis, a kelp of the order Laminariales, may reach 60 m (200 ft) in length and forms prominent underwater kelp forests. Kelp forests like these contain a high level of biodiversity. Another example is Sargassum, which creates unique floating mats of seaweed in the tropical waters of the Sargasso Sea that serve as the habitats for many species. Many brown algae, such as members of the order Fucales, commonly grow along rocky seashores. Some members of the class, such as kelps, are used by humans as food.

<span class="mw-page-title-main">Reef</span> A shoal of rock, coral or other sufficiently coherent material, lying beneath the surface of water

A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic (non-living) processes such as deposition of sand or wave erosion planing down rock outcrops. However, reefs such as the coral reefs of tropical waters are formed by biotic (living) processes, dominated by corals and coralline algae. Artificial reefs such as shipwrecks and other man-made underwater structures may occur intentionally or as the result of an accident, and are sometimes designed to increase the physical complexity of featureless sand bottoms to attract a more diverse range of organisms. Reefs are often quite near to the surface, but not all definitions require this.

<span class="mw-page-title-main">Thallus</span> Undifferentiated vegetative tissue of certain organisms

Thallus, from Latinized Greek θαλλός, meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms were previously known as the thallophytes, a polyphyletic group of distantly related organisms. An organism or structure resembling a thallus is called thalloid, thallodal, thalliform, thalline, or thallose.

<span class="mw-page-title-main">Kelp forest</span> Underwater areas with a high density of kelp

Kelp forests are underwater areas with a high density of kelp, which covers a large part of the world's coastlines. Smaller areas of anchored kelp are called kelp beds. They are recognized as one of the most productive and dynamic ecosystems on Earth. Although algal kelp forest combined with coral reefs only cover 0.1% of Earth's total surface, they account for 0.9% of global primary productivity. Kelp forests occur worldwide throughout temperate and polar coastal oceans. In 2007, kelp forests were also discovered in tropical waters near Ecuador.

<i>Hormosira</i> Species of Phaeophyceae

Hormosira banksii, also known as Neptune's necklace, Neptune's pearls, sea grapes, or bubbleweed) is a species of seaweed native to Australia and New Zealand. The genus Hormosira is monotypic.

Rhizoids are protuberances that extend from the lower epidermal cells of bryophytes and algae. They are similar in structure and function to the root hairs of vascular land plants. Similar structures are formed by some fungi. Rhizoids may be unicellular or multicellular.

<span class="mw-page-title-main">Coralline algae</span> Order of algae (Corallinales)

Coralline algae are red algae in the order Corallinales. They are characterized by a thallus that is hard because of calcareous deposits contained within the cell walls. The colors of these algae are most typically pink, or some other shade of red, but some species can be purple, yellow, blue, white, or gray-green. Coralline algae play an important role in the ecology of coral reefs. Sea urchins, parrot fish, and limpets and chitons feed on coralline algae. In the temperate Mediterranean Sea, coralline algae are the main builders of a typical algal reef, the Coralligène ("coralligenous"). Many are typically encrusting and rock-like, found in marine waters all over the world. Only one species lives in freshwater. Unattached specimens may form relatively smooth compact balls to warty or fruticose thalli.

<span class="mw-page-title-main">Fucales</span> Order of brown algae

The Fucales (fucoids) are an order in the brown algae. The list of families in the Fucales, as well as additional taxonomic information on algae, is publicly accessible at Algaebase.

<i>Postelsia</i> Species of kelp

Postelsia palmaeformis, also known as the sea palm or palm seaweed, is a species of kelp and classified within brown algae. It is the only known species in the genus Postelsia. The sea palm is found along the western coast of North America, on rocky shores with constant waves. It is one of the few algae that can survive and remain erect out of the water; in fact, it spends most of its life cycle exposed to the air. It is an annual, and edible, though harvesting of the alga is discouraged due to the species' sensitivity to overharvesting.

<span class="mw-page-title-main">Seaweed</span> Macroscopic marine algae

Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of Rhodophyta (red), Phaeophyta (brown) and Chlorophyta (green) macroalgae. Seaweed species such as kelps provide essential nursery habitat for fisheries and other marine species and thus protect food sources; other species, such as planktonic algae, play a vital role in capturing carbon, producing at least 50% of Earth's oxygen.

Holdfast most often refers to:

<span class="mw-page-title-main">Choristocarpaceae</span> Family of algae

Choristocarpaceae is a family in the order Discosporangiales of the brown algae. The family contains a single genus, Choristocarpus. The species is mostly located in the cold waters of the Northern hemisphere. A type of seaweed, Choristocarpaceae attaches itself to rocky substrate in places that are near continental shelves and the shore. Due to the species having morphological similarity, they were classified in closer relation with D. mesarthrocarpum. But due to many other differing characteristics Choristocarpaceae were put into their own family with a single genus and a single species of brown algae.

<i>Chorda filum</i> Species of brown algae

Chorda filum, commonly known as dead man's rope or sea lace among other names, is a species of brown algae in the genus Chorda. It is widespread in the temperate waters of the northern hemisphere. The species has numerous other common names related to its physical appearance. These include mermaid's tresses, cat's gut or sea-catgut, bootlace weed, sea-twine, and mermaid's fishing line.

Lobophora variegata is a species of small thalloid brown alga which grows intertidally or in shallow water in tropical and warm temperate seas. It has three basic forms, being sometimes ruffled, sometimes reclining and sometimes encrusting, and each form is typically found in a different habitat. This seaweed occurs worldwide. It is the type species of the genus Lobophora, the type locality being the Antilles in the West Indies.

<span class="mw-page-title-main">Frondose</span> Property of organism shaped like a frond

Frondosity is the property of an organism that normally flourishes with fronds or leaf-like structures.

<i>Dictyota binghamiae</i> Species of alga

Dictyota binghamiae, commonly known as mermaid's glove, is a species of brown algae found in the eastern Pacific Ocean from British Columbia to Baja California. This species was named in honor of phycologist Caroline Bingham.

Saccharina dentigera is a species of brown algae, in the family Laminariaceae. It is native to shallow water in the northeastern Pacific Ocean from the Gulf of Alaska to Baja California.

<i>Dictyota dichotoma</i> Species of brown algae

Dictyota dichotoma is a species of Brown algae found in the temperate western and eastern Atlantic Ocean, the Mediterranean Sea, the Black Sea, the Red Sea and the western Indian Ocean.

References

  1. D. N. Thomas (2002). Seaweeds. Natural History Museum, London. ISBN   978-0-565-09175-0.
  2. Attenborough, D.1984. The Living Planet. p. 232 & 235. Collins BBC ISBN   0-563-20207-6