| Zostera marina | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Monocots |
| Order: | Alismatales |
| Family: | Zosteraceae |
| Genus: | Zostera |
| Species: | Z. marina |
| Binomial name | |
| Zostera marina | |
 | |
| Global distribution ofZostera marina | |
Zostera marina is a floweringvascular plant species as one of many kinds ofseagrass, with this species known primarily by the English name ofeelgrass withseawrack much less used, and refers to the plant after breaking loose from the submerged wetland soil, and drifting free with ocean current and waves to a coast seashore. It is a saline soft-sediment submerged plant native tomarine environments on the coastlines of northern latitudes from subtropical to subpolar regions ofNorth America andEurasia.
This species is the most wide-ranging marineflowering plant in the Northern Hemisphere and the most widespread species in the temperate northern hemisphere of Atlantic and Pacific Oceans.[2][3] It lives in cooler ocean waters in theNorth Atlantic andNorth Pacific, and in the warmer southern parts of its range it dies off during warmer seasons.[4] It grows in theArctic region and endures several months of ice cover per year.[5] It is the only seagrass known fromIceland.[5] It can be found inbays,lagoons,estuaries, onbeaches, and in other coastal habitat. The several ecotypes each have specific habitat requirements.[citation needed] It occurs in calmer waters in thesublittoral zone, where it is rarely exposed to air.[4] It anchors viarhizomes in sandy or muddy substrates and its leaves catch particulate debris in the water which then collects around the bases of the plants, building up the top layer of the seabed.[4]
This flowering plant is a rhizomatous herb which produces a long stem with hairlike green leaves that measure up to 1.2 centimetres (0.47 in) wide and may reach over 1.0 metre (3 ft 3 in) long. It is a perennial plant, but it may grow as an annual.[6] The rhizome grows horizontally through the substrate, anchoring via clusters of roots at nodes.[4] The plant ismonoecious, with an individual bearing both male and female flowers in separate alternating clusters. The inflorescence is about 10 cm long.[7] The fruit is a nutlet with a transparent coat containing the seed. The plant can also undergovegetative reproduction, sprouting repeatedly from its rhizome and spreading into a meadow-like colony on the seabed known as agenet.[8] One meadow of cloned eelgrass was determined to be 3000 years old, genetically.[5] When undergoingsexual reproduction, the plant produces large quantities of seeds, at times numbering several thousand seeds per square meter of plants.[5] The plantdisperses large distances when its stems break away and carry the fertile seeds to new areas, eventually dropping to the seabed.[5] The seagrass is a favorite food of several species ofwaterfowl, which may also distribute the seeds.[5]
ThisZostera grows in muddy and sandy shores only at and below spring tides.[7] This plant is an important member of the coastal ecosystem in many areas because it helps to physically form the habitat and it plays a crucial role for many other species.[5][9] For example, it provides a shelteredspawning ground for thePacific herring (Clupea pallasii).[9] JuvenileAtlantic cod (Gadus morhua) hide in eelgrass beds as they grow.[10] Theblue mussel (Mytilus edulis) attaches to its leaves.[5] Thegreen algaEntocladia perforans, anendophyte, depends on this eelgrass.[11] A great many animals use the plant for food, including theisopodIdotea chelipes and the purple sea urchinParacentrotus lividus.[5] TheAtlantic brant (Branta bernicula hrota) subsists almost entirely on the plant.[10] When the eelgrass dies, detaches, and washes up on the beach, a whole newecosystem is founded; many species of insects and other invertebrates begin to inhabit the dead plant, including theamphipodTalitrus saltator, theflyFucellia tergina, and thebeetlesStenus biguttatus,Paederus littoralis, andCoccinella septempunctata.[12]
Thebacterial speciesGranulosicoccus coccoides was first isolated from the leaves of the plant.[13]
Populations of the plant have been damaged by a number of processes, especially increasedturbidity in the water; like most other plants, eelgrass requires sunlight to grow.[9] One plant may adapt to light level by growing longer leaves to reach the sun in low-light areas; individuals in clear or shallow water may have leaves a few centimeters long, while individuals in deeper spots may have leaves over a meter long.[5] Human activities such asdredging andtrawling damage eelgrass meadows; practices used inscallop andmussel harvesting in theWadden Sea have cleared much eelgrass from the sea bottom there.[5]Aquaculture operations and coastal development destroy colonies.[5]Pollution from many sources, including riversidefarms,sewage lines,[14] fish processing plants, andoil spills, damage eelgrass meadows.[10] Conservation and restoration efforts ofZostera marina habitats[15][16] have increased since their rapid decline started several decades ago.
Invasive species have been shown to have a negative effect on eelgrass and associated ecosystems. InNova Scotia, the invasive exoticgreen crab (Carcinus maenas) destroys eelgrass when it digs in the substrate for prey items,[10] or by directly eating eelgrass seeds.[17] The decline of eelgrass inAntigonish Harbour has resulted in fewerCanada geese, which feed on the rhizome, and fewercommon goldeneye, which eatinvertebrates that live in eelgrass meadows.[10]
Theslime moldLabyrinthula zosterae caused a "wasting disease" of eelgrass resulting in large-scale losses in the 1930s; localized populations are still affected by the slime mold today.[5] During this time, populations of the eelgrass-eating Atlantic brant dropped.[10] Remaining geese ate less-preferred food plants and algae, and hunters subsequently noticed that brant meat began to taste different.[10] Even today, brants no longermigrate over the Nova Scotia area.[10]
TheZostera marinagenome has beensequenced and analyzed by Olsenet al. in 2016 and the resulting article has been published inNature.[18] The approximate genome sequence ofZ. marina is 202.3 Mb and encodes approximately 20450protein-coding genes (of which 86,6% are supported bytranscriptome data). The assembled genome was found to consist of large numbers ofrepeat elements accounting for 63% of the assembled genome. The researchers revealed key adaptations at the molecular biological level that have occurred during evolution ofZ. marina, anangiosperm that has adopted a marine lifestyle. Genome analysis revealed thatZ. marina lost the entire repertoire ofstomatal genes, genes involved in volatile compound biosynthesis and signaling (such asethylene andterpenoids) as well as genes forultraviolet protection andphytochromes used for far-red sensing. Besides these gene losses, also gene gain events have been described, mostly involving the adjustment to full salinity and ionhomeostasis. Also macro-algae like cell wall components (low-methylated polyanionicpectins and sulfated galactans) have been described, unique forZ. marina compared to other angiosperms.
People have long used this plant species asroof thatching in some areas.[5] It has been used asfertilizer andcattlefodder inNorway for centuries.[19] It has also been dried and used as stuffing formattresses and furniture.[19] TheSeri hunter gatherers of Mexico eat eelgrass grains after toasting them and grinding into a paste.
Ángel León, a Spanish chef, has planted meadows ofZ. marina (described as "sea rice") in theBay of Cádiz in order to harvest the grains. The texture is described as between rice andquinoa, but with a more saline flavour. It is gluten-free and high in fibre.[20]
| National | |
|---|---|
| Other | |
