Seagrass - AbsoluteAstronomy.com

Flowering plant

The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...

s from one of four plant families (Posidoniaceae, Zosteraceae

Zosteraceae

Zosteraceae is a family of marine perennial flowering plants found in temperate and subtropical coastal waters, with the highest diversity located around Korea and Japan. Most seagrasses complete their entire life cycle under water, having filamentous pollen especially adapted to dispersion in an...

, Hydrocharitaceae

Hydrocharitaceae

Hydrocharitaceae is a flowering plant family that includes a number of species of aquatic plant, broadly called the Tape-grasses, and includes the well known Canadian Waterweed and Frog's Bit.The family includes both fresh and marine aquatics...

, or Cymodoceaceae), all in the order Alismatales

Alismatales

Alismatales is an order of flowering plants including about 2500 species. Pleants assigned to this order are mostly tropical or aquatic.-Description:...

(in the class of monocotyledon

Monocotyledon

Monocotyledons, also known as monocots, are one of two major groups of flowering plants that are traditionally recognized, the other being dicotyledons, or dicots. Monocot seedlings typically have one cotyledon , in contrast to the two cotyledons typical of dicots...

s), which grow in marine

Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

, fully saline

Saline water

Saline water is a general term for water that contains a significant concentration of dissolved salts . The concentration is usually expressed in parts per million of salt....

environments.

Ecology

These unusual marine flowering plants are called seagrasses because in many species the leaves are long and narrow, and these plants often grow in large "meadow

Meadow

A meadow is a field vegetated primarily by grass and other non-woody plants . The term is from Old English mædwe. In agriculture a meadow is grassland which is not grazed by domestic livestock but rather allowed to grow unchecked in order to make hay...

s" which look like grassland: in other words many of the species of seagrasses superficially resemble terrestrial grass

Grass

Grasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae family, as well as the sedges and the rushes . The true grasses include cereals, bamboo and the grasses of lawns ...

es of the family Poaceae

Poaceae

The Poaceae is a large and nearly ubiquitous family of flowering plants. Members of this family are commonly called grasses, although the term "grass" is also applied to plants that are not in the Poaceae lineage, including the rushes and sedges...

.

Like all autotrophic plants, seagrasses photosynthesize

Photosynthesis

Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...

so are limited to growing in the submerged photic zone

Photic zone

The photic zone or euphotic zone is the depth of the water in a lake or ocean that is exposed to sufficient sunlight for photosynthesis to occur...

, and most occur in shallow and sheltered coastal waters anchored in sand or mud bottoms. Most species undergo submarine pollination

Pollination

Pollination is the process by which pollen is transferred in plants, thereby enabling fertilisation and sexual reproduction. Pollen grains transport the male gametes to where the female gamete are contained within the carpel; in gymnosperms the pollen is directly applied to the ovule itself...

and complete their entire life cycle underwater. There are about sixty species worldwide.

Seagrasses form extensive beds or meadows, which can be either monospecific (made up of a single species) or in mixed beds where more than one species coexist. In temperate

Temperate

In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...

areas, usually one or a few species dominate (like the eelgrass Zostera
Zostera
Zostera is a small genus of widely distributed seagrass, commonly called marine eelgrass or simply eelgrass . The genus Zostera contains sixteen species.-Ecology:Zostera is found on sandy substrates or in estuaries submerged or partially floating...

marina in the North Atlantic), whereas tropical

Tropics

The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...

beds usually are more diverse, with up to thirteen species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

recorded in the Philippines

Philippines

The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

.

Seagrass beds are highly diverse and productive ecosystem

Ecosystem

An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....

s, and can harbor hundreds of associated species from all phyla

Phylum

In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....

, for example juvenile and adult fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

, epiphytic

Epiphyte

An epiphyte is a plant that grows upon another plant non-parasitically or sometimes upon some other object , derives its moisture and nutrients from the air and rain and sometimes from debris accumulating around it, and is found in the temperate zone and in the...

and free-living macroalgae

Seaweed

Seaweed is a loose, colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...

and microalgae, mollusks, bristle worms, and nematode

Nematode

The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...

s. Few species were originally considered to feed directly on seagrass leaves

Leaf

A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....

(partly because of their low nutritional content), but scientific review

Review

A review is an evaluation of a publication, a product or a service, such as a movie , video game, musical composition , book ; a piece of hardware like a car, home appliance, or computer; or an event or performance, such as a live music concert, a play, musical theater show or dance show...

s and improved working methods have shown that seagrass herbivory

Herbivore

Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...

is a highly important link in the food chain, with hundreds of species feeding on seagrasses worldwide, including green turtles, dugong

Dugong

The dugong is a large marine mammal which, together with the manatees, is one of four living species of the order Sirenia. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's sea cow , was hunted to extinction in the 18th century...

s, manatee

Manatee

Manatees are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows...

s, fish

Fish

, geese

Goose

The word goose is the English name for a group of waterfowl, belonging to the family Anatidae. This family also includes swans, most of which are larger than true geese, and ducks, which are smaller....

, swan

Swan

Swans, genus Cygnus, are birds of the family Anatidae, which also includes geese and ducks. Swans are grouped with the closely related geese in the subfamily Anserinae where they form the tribe Cygnini. Sometimes, they are considered a distinct subfamily, Cygninae...

s, sea urchin

Sea urchin

Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from across. Common colors include black and dull...

s and crab

Crab

True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...

Environmental services

Seagrasses are sometimes labeled ecosystem engineer

Ecosystem engineer

An ecosystem engineer is any organism that creates or modifies habitats. Jones et al. identified two different types of ecosystem engineers:...

s, because they partly create their own habitat

Habitat (ecology)

A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant or other type of organism...

: the leaves slow down water-currents increasing sedimentation

Sedimentation

Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained, and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration...

, and the seagrass root

Root

In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...

s and rhizome

Rhizome

In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...

s stabilize the seabed.
Their importance for associated species is mainly due to provision of shelter (through their three-dimensional structure in the water column), and for their extraordinarily high rate of primary production

Primary production

400px|thumb|Global oceanic and terrestrial photoautotroph abundance, from September [[1997]] to August 2000. As an estimate of autotroph biomass, it is only a rough indicator of primary production potential, and not an actual estimate of it...

. As a result, seagrasses provide coast

Coast

A coastline or seashore is the area where land meets the sea or ocean. A precise line that can be called a coastline cannot be determined due to the dynamic nature of tides. The term "coastal zone" can be used instead, which is a spatial zone where interaction of the sea and land processes occurs...

al zones with a number of ecosystem goods and ecosystem services

Ecosystem services

Humankind benefits from a multitude of resources and processes that are supplied by natural ecosystems. Collectively, these benefits are known as ecosystem services and include products like clean drinking water and processes such as the decomposition of wastes...

, for instance fishing grounds, wave protection, oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

production and protection against coastal erosion

Erosion

Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...

. Seagrass meadows account for 15% of the ocean’s total carbon storage. The ocean currently absorbs 25% of global carbon emissions.

Uses

Historically seagrasses were collected as fertilizer

Fertilizer

Fertilizer is any organic or inorganic material of natural or synthetic origin that is added to a soil to supply one or more plant nutrients essential to the growth of plants. A recent assessment found that about 40 to 60% of crop yields are attributable to commercial fertilizer use...

for sandy soil. This was an important use in the Ria de Aveiro

Aveiro Lagoon

The Aveiro lagoon is a lagoon in Portugal. It is located on the Atlantic coast of Portugal, south the municipalitiy of Espinho and north of Mira . Its average area covers approximately 75 km². It is named after the city of Aveiro, which is the chief urban centre located nearby the lagoon...

, Portugal

Portugal

Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...

, where the plants collected were known as moliço

Moliço

Moliço is thePortuguese word for the submerged aquatic vegetation collected for use in agriculture. This word was derived from the Latin mollis, used for expressing the quality soft.-Meaning:...

.

In the early 20th century, in France, and to a lesser extent the Channel Islands

Channel Islands

The Channel Islands are an archipelago of British Crown Dependencies in the English Channel, off the French coast of Normandy. They include two separate bailiwicks: the Bailiwick of Guernsey and the Bailiwick of Jersey...

dried seagrasses were used as a mattress (paillasse) filling, and it was in high demand by French forces during World War I

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

. It was also used for bandages and other purposes.

Currently seagrass has been used in furniture, and woven like rattan

Rattan

Rattan is the name for the roughly 600 species of palms in the tribe Calameae, native to tropical regions of Africa, Asia and Australasia.- Structure :...

Disturbances and threats

Natural disturbances such as grazing

Grazing

Grazing generally describes a type of feeding, in which a herbivore feeds on plants , and also on other multicellular autotrophs...

, storm

Storm

A storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather...

s, ice-scouring, and desiccation

Desiccation

Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...

are an inherent part of seagrass ecosystem

Ecosystem

dynamics. Seagrasses display an extraordinarily high degree of phenotypic plasticity

Phenotypic plasticity

Phenotypic plasticity is the ability of an organism to change its phenotype in response to changes in the environment. Such plasticity in some cases expresses as several highly morphologically distinct results; in other cases, a continuous norm of reaction describes the functional interrelationship...

, adapting rapidly to changing environmental conditions.

Seagrasses are in global decline, with some 30000 km² (11,583.1 sq mi) lost during recent decades. The main cause is human disturbance, most notably eutrophication

Eutrophication

Eutrophication or more precisely hypertrophication, is the movement of a body of water′s trophic status in the direction of increasing plant biomass, by the addition of artificial or natural substances, such as nitrates and phosphates, through fertilizers or sewage, to an aquatic system...

, mechanical destruction of habitat, and overfishing

Overfishing

Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....

. Excessive input of nutrients (nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

, phosphorus

Phosphorus

Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...

) is directly toxic to seagrasses, but most importantly, it stimulates the growth of epiphytic and free-floating macro

Seaweed

Seaweed is a loose, colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...

- and micro-algae

Algae

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

. This weakens the sunlight

Sunlight

Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...

, reducing the photosynthesis

Photosynthesis

that nourishes the seagrass and the primary production

Primary production

results.

Decaying seagrass leaves and algae fuels increasing algal bloom

Algal bloom

An algal bloom is a rapid increase or accumulation in the population of algae in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically, only one or a small number of phytoplankton species are involved, and some blooms may be recognized by discoloration...

s, resulting in a positive feedback

Feedback

Feedback describes the situation when output from an event or phenomenon in the past will influence an occurrence or occurrences of the same Feedback describes the situation when output from (or information about the result of) an event or phenomenon in the past will influence an occurrence or...

. This can cause a complete regime shift

Regime shift

Regime shifts is defined as rapid reorganizations of ecosystems from one relatively stable state to another. The idea of a regime shift was first used in investigations of freshwater and terrestrial systems. It is now been used for marine and estuarine systems to describe rapid shifts between two...

from seagrass to algal dominance. Accumulating evidence also suggests that overfishing of top predators (large predatory fish) could indirectly increase algal growth by reducing grazing control performed by mesograzers such as crustacean

Crustacean

Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s and gastropods through a trophic cascade

Trophic cascade

Trophic cascades occur when predators in a food web suppress the abundance of their prey, thereby releasing the next lower trophic level from predation...

.

When humans drive motor boats over shallow seagrass areas, sometimes the blade propeller can tear out or cut the sea grass.

The most-used methods to protect and restore seagrass meadows include nutrient and pollution

Pollution

Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...

reductions, protection using marine protected areas, and restoration using seagrass transplantation

Transplanting

For botanical organ transplant, see GraftingIn agriculture and gardening, transplanting or replanting is the technique of moving a plant from one location to another. Most often this takes the form of starting a plant from seed in optimal conditions, such as in a greenhouse or protected nursery...

Genera

Family Posidoniaceae
- Posidonia
  Posidonia
  Posidonia is a genus of flowering plants. It contains two to nine species of marine plants , found in the seas of the Mediterranean and around the south coast of Australia....

Family Zosteraceae
Zosteraceae
Zosteraceae is a family of marine perennial flowering plants found in temperate and subtropical coastal waters, with the highest diversity located around Korea and Japan. Most seagrasses complete their entire life cycle under water, having filamentous pollen especially adapted to dispersion in an...
- Zostera
  Zostera
  Zostera is a small genus of widely distributed seagrass, commonly called marine eelgrass or simply eelgrass . The genus Zostera contains sixteen species.-Ecology:Zostera is found on sandy substrates or in estuaries submerged or partially floating...
- Heterozostera = Zostera
- Phyllospadix
  Phyllospadix
  Phyllospadix is a genus of seagrass or surfgrass, a flowering plant in the family Zosteraceae, comprising 5 species. Phyllospadix grows in marine waters along the coasts of the temperate North Pacific.- Species :...

Family Hydrocharitaceae
Hydrocharitaceae
Hydrocharitaceae is a flowering plant family that includes a number of species of aquatic plant, broadly called the Tape-grasses, and includes the well known Canadian Waterweed and Frog's Bit.The family includes both fresh and marine aquatics...

(Frogbit family)
- Enhalus
  Enhalus
  Enhalus is a monotypic genus of marine flowering plants. Enhalus is large seagrass native to coastal waters of the tropical Indian and Western Pacific Oceans. The strap-shaped leaves arise directly from the rhizomes and can reach 1 m in length...
- Halophila
  Halophila
  Halophila is a genus of seagrasses in the family Hydrocharitaceae, the tape-grasses. The number of its contained species, and its own placement in the order Alismatales, has been subject to revision by botanical authors....
- Thalassia
  Thalassia (genus)
  Thalassia is a marine seagrass genus comprising 2 species.-Species:T. testudinum Banks ex König is the type specimen. It is native to the Gulf of Mexico and the Caribbean with specimens found as far east as Bermuda. It has a fossil record in the Gulf to the Middle Eocene.T. hemprichii ...

Family Cymodoceaceae
- Amphibolis
  Amphibolis
  Amphibolis is a genus in the family Cymodoceaceae. It includes two species of sea grass endemic to the western and southern coast of Australia, Amphibolis antarctica and Amphibolis griffithii, commonly known as sea nymph or wire weed...
- Cymodocea
  Cymodocea
  Cymodocea is a genus in the family Cymodoceaceae. It includes four species of sea grass distributed in warm oceans....
- Halodule
  Halodule
  Halodule is a genus of plants in the family Cymodoceaceae. It includes six to ten species of sea grass distributed in warm oceans.-External links:***...
- Syringodium
  Syringodium
  Syringodium is a genus in the family Cymodoceaceae. It includes just two species, distributed in warm oceans....
- Thalassodendron

External links

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