vascular plant
Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They ...
species as one of many kinds of
seagrass
Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the or ...
, with this species known primarily by the English name of eelgrass with seawrack 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 to marine environments on the coastlines of northern latitudes from subtropical to subpolar regions of North America and
Eurasia
Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelago ...
.
Distribution
This species is the most wide-ranging marine
flowering plant
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...
in the Northern Hemisphere. It lives in cooler ocean waters in the North Atlantic and
North Pacific
The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...
, and in the warmer southern parts of its range it dies off during warmer seasons.Flora of North America /ref> It grows in the
Arctic
The Arctic ( or ) is a polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenland), Finland, Iceland, N ...
Iceland
Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its s ...
lagoon
A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') ...
s,
estuaries
An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environmen ...
, on
beach
A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, shingle, pebbles, etc., or biological sources, such as mollusc sh ...
es, and in other coastal habitat. The several ecotypes each have specific habitat requirements. It occurs in calmer waters in the
sublittoral
The littoral zone or nearshore is the part of a sea, lake, or river that is close to the shore. In coastal ecology, the littoral zone includes the intertidal zone extending from the high water mark (which is rarely inundated), to coastal area ...
zone, where it is rarely exposed to air. It anchors via rhizomes 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.
Description and reproduction
This flowering plant is a rhizomatous herb which produces a long stem with hairlike green leaves that measure up to 1.2 cm wide and may reach over 1.0 m long. It is a perennial plant, but it may grow as an annual. The rhizome grows horizontally through the substrate, anchoring via clusters of roots at nodes. The plant is monoecious, with an individual bearing both male and female flowers in separate alternating clusters. The inflorescence is about 10 cm long.Parnell, J. and Curtis, T. 2012. ''Webb's An Irish Flora.'' Cork University Press The fruit is a nutlet with a transparent coat containing the seed. The plant can also undergo
vegetative reproduction
Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is any form of asexual reproduction occurring in plants in which a new plant grows from a fragment or cutting of the parent plant or spec ...
sexual reproduction
Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote th ...
, the plant produces large quantities of seeds, at times numbering several thousand seeds per square meter of plants. The plant disperses large distances when its stems break away and carry the fertile seeds to new areas, eventually dropping to the seabed. The seagrass is a favorite food of several species of
waterfowl
Anseriformes is an order of birds also known as waterfowl that comprises about 180 living species of birds in three families: Anhimidae (three species of screamers), Anseranatidae (the magpie goose), and Anatidae, the largest family, which i ...
, which may also distribute the seeds.
Ecology
This Zostera grows in muddy and sandy shores only at and below spring tides. 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.Wyllie-Echeverria, S. and M. Fonseca. (2003) Eelgrass (''Zostera marina'' L.) in San Francisco Bay, California from 1920 to the present. NOAA National Centers for Coastal Ocean Science. For example, it provides a sheltered
spawning
Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of releasing the eggs and sperm, and the act of both sexes is called spawning. Most aquatic animals, except for aquat ...
ground for the
Pacific herring
The Pacific herring (''Clupea pallasii'') is a species of the herring family associated with the Pacific Ocean environment of North America and northeast Asia. It is a silvery fish with unspined fins and a deeply forked caudal fin. The distribut ...
blue mussel
The blue mussel (''Mytilus edulis''), also known as the common mussel, is a medium-sized edible marine bivalve mollusc in the family Mytilidae, the mussels. Blue mussels are subject to commercial use and intensive aquaculture. A species with a l ...
(''Mytilus edulis'') attaches to its leaves. The
green alga
The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...
endophyte
An endophyte is an endosymbiont, often a bacterium or fungus, that lives within a plant for at least part of its life cycle without causing apparent disease. Endophytes are ubiquitous and have been found in all species of plants studied to date; h ...
, depends on this eelgrass. A great many animals use the plant for food, including the isopod '' Idotea chelipes'' and the purple sea urchin ''
Paracentrotus lividus
''Paracentrotus lividus'' is a species of sea urchin in the family Parechinidae commonly known as the purple sea urchin. It is the type species of the genus and occurs in the Mediterranean Sea and eastern Atlantic Ocean.
Description
''Paracent ...
''. The Atlantic brant (''Branta bernicula hrota'') subsists almost entirely on the plant. When the eelgrass dies, detaches, and washes up on the beach, a whole new
ecosystem
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
is founded; many species of insects and other invertebrates begin to inhabit the dead plant, including the amphipod ''
Talitrus saltator
''Talitrus saltator'', a species of sand hopper, is a common amphipod crustacean of sandy coasts around Europe. The animal's typical "hopping" movement gives it its common name, and is produced by a flexion of the abdomen. In order to do this, i ...
beetle
Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...
Coccinella septempunctata
''Coccinella septempunctata'', the seven-spot ladybird (or, in North America, seven-spotted ladybug or "C-7"), is the most common ladybird in Europe. Its elytra are of a red colour, but punctuated with three black spots each, with one further spo ...
''.
The
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
l species '' Granulosicoccus coccoides'' was first isolated from the leaves of the plant.Kurilenko, V. V., et al. (2010). ''Granulosicoccus coccoides'' sp. nov., isolated from leaves of seagrass (''Zostera marina''). ''Int J Syst Evol Microbiol'' 60 972-76.
Threats
Populations of the plant have been damaged by a number of processes, especially increased
turbidity
Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality.
Fluids ...
in the water; like most other plants, eelgrass requires sunlight to grow. 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. Human activities such as dredging and
trawling
Trawling is a method of fishing that involves pulling a fishing net through the water behind one or more boats. The net used for trawling is called a trawl. This principle requires netting bags which are towed through water to catch different spec ...
damage eelgrass meadows; practices used in scallop and mussel harvesting in the Wadden Sea have cleared much eelgrass from the sea bottom there.Aquaculture operations and coastal development destroy colonies.
Pollution
Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the ...
from many sources, including riverside
farm
A farm (also called an agricultural holding) is an area of land that is devoted primarily to agricultural processes with the primary objective of producing food and other crops; it is the basic facility in food production. The name is used ...
s, sewage lines, fish processing plants, and oil spills, damage eelgrass meadows. Conservation and restoration efforts of ''Zostera marina'' habitats have been plenty since their rapid decline started several decades ago.
Invasive species have been shown to have a negative effect on eelgrass and associated ecosystems. In
Nova Scotia
Nova Scotia ( ; ; ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. Nova Scotia is Latin for "New Scotland".
Most of the population are native Eng ...
, the invasive exotic green crab (''Carcinus maenas'') destroys eelgrass when it digs in the substrate for prey items, or by directly eating eelgrass seeds. The decline of eelgrass in
Antigonish Harbour
Antigonish Harbour is a community and harbour in the Canadian province of Nova Scotia, located in Antigonish County
, nickname =
, settlement_type = County
, motto =
, image_skyline ...
has resulted in fewer
Canada geese
The Canada goose (''Branta canadensis''), or Canadian goose, is a large wild goose with a black head and neck, white cheeks, white under its chin, and a brown body. It is native to the arctic and temperate regions of North America, and it is o ...
, which feed on the rhizome, and fewer
common goldeneye
The common goldeneye or simply goldeneye (''Bucephala clangula'') is a medium-sized sea duck of the genus ''Bucephala'', the goldeneyes. Its closest relative is the similar Barrow's goldeneye. The genus name is derived from the Ancient Greek ...
, which eat
invertebrate
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
s that live in eelgrass meadows.
The
slime mold
Slime mold or slime mould is an informal name given to several kinds of unrelated eukaryotic organisms with a life cycle that includes a free-living single-celled stage and the formation of spores. Spores are often produced in macroscopic mul ...
'' Labyrinthula 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. During this time, populations of the eelgrass-eating Atlantic brant dropped. Remaining geese ate less-preferred food plants and algae, and hunters subsequently noticed that brant meat began to taste different. Even today, brants no longer migrate over the Nova Scotia area.
Genomics and evolutionary adaptations
The ''Zostera marina''
genome
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...
has been
sequenced
In genetics and biochemistry, sequencing means to determine the primary structure (sometimes incorrectly called the primary sequence) of an unbranched biopolymer. Sequencing results in a symbolic linear depiction known as a sequence which suc ...
and analyzed by Olsen ''et al.'' in 2016 and the resulting article has been published in
Nature
Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans are ...
. The approximate genome sequence of ''Z. marina'' is 202.3 Mb and encodes approximately 20450
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
-coding genes (of which 86,6% are supported by
transcriptome
The transcriptome is the set of all RNA transcripts, including coding and non-coding, in an individual or a population of cells. The term can also sometimes be used to refer to all RNAs, or just mRNA, depending on the particular experiment. The t ...
data). The assembled genome was found to consist of large numbers of repeat elements accounting for 63% of the assembled genome. The researchers revealed key adaptations at the molecular biological level that have occurred during evolution of ''Z. marina'', an angiosperm that has adopted a marine lifestyle. Genome analysis revealed that ''Z. marina'' lost the entire repertoire of stomatal genes, genes involved in volatile compound biosynthesis and signaling (such as ethylene and
terpenoid
The terpenoids, also known as isoprenoids, are a class of naturally occurring organic chemicals derived from the 5-carbon compound isoprene and its derivatives called terpenes, diterpenes, etc. While sometimes used interchangeably with "terpenes" ...
s) as well as genes for
ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
protection and
phytochrome
Phytochromes are a class of photoreceptor in plants, bacteria and fungi used to detect light. They are sensitive to light in the red and far-red region of the visible spectrum and can be classed as either Type I, which are activated by far-re ...
s used for far-red sensing. Besides these gene losses, also gene gain events have been described, mostly involving the adjustment to full salinity and ion
homeostasis
In biology, homeostasis (British also homoeostasis) (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physical, and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and ...
. Also macro-algae like cell wall components (low-methylated polyanionic pectins and sulfated galatans) have been described, unique for ''Z. marina'' compared to other angiosperms.
Human uses
People have long used this plant species as roof thatching in some areas. It has been used as
fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
and
cattle
Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult ma ...
Norway
Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and the ...
for centuries.Alm, T. (2003) On the uses of ''Zostera marina'', mainly in Norway. ''Economic Botany'' 57:4 640-45. It has also been dried and used as stuffing for mattresses and furniture. The Seri hunter gatherers of Mexico eat eelgrass grains after toasting them and grinding into a paste.
Ángel León, a Spanish chef, has planted meadows of ''Z. marina'' (described as "sea rice") in the
Bay of Cádiz
The Bay of Cádiz is a body of water in the province of Cádiz, Spain, adjacent to the southwestern coast of the Iberian Peninsula.
The Bay of Cádiz adjoins the Gulf of Cádiz, a larger body of water which is in the same area but further offsho ...
in order to harvest the grains. The texture is described as between rice and
quinoa
Quinoa (''Chenopodium quinoa''; , from Quechua ' or ') is a flowering plant in the amaranth family. It is a herbaceous annual plant grown as a crop primarily for its edible seeds; the seeds are rich in protein, dietary fiber, B vitamins, a ...
, but with a more saline flavour. It is gluten-free and high in fibre.