''Zostera muelleri '' is a southern hemisphere temperate species
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 ...
native to the seacoasts of
South Australia
South Australia (commonly abbreviated as SA) is a state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Australia's states and territories ...
,
Victoria
Victoria most commonly refers to:
* Victoria (Australia), a state of the Commonwealth of Australia
* Victoria, British Columbia, provincial capital of British Columbia, Canada
* Victoria (mythology), Roman goddess of Victory
* Victoria, Seychelle ...
and
Tasmania
)
, nickname =
, image_map = Tasmania in Australia.svg
, map_caption = Location of Tasmania in AustraliaCoordinates:
, subdivision_type = Country
, subdi ...
.
[Paul Friedrich August Ascherson. 1867. Sitzungsberichte der Gesellschaft Naturforschender Freunde zu Berlin : 15. ''Zostera muelleri ''] and
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
. Today, ''Zostera muelleri'' can be found in regions of
Australia,
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
, and
Papua New Guinea
Papua New Guinea (abbreviated PNG; , ; tpi, Papua Niugini; ho, Papua Niu Gini), officially the Independent State of Papua New Guinea ( tpi, Independen Stet bilong Papua Niugini; ho, Independen Stet bilong Papua Niu Gini), is a country i ...
,
as well as areas of the eastern Indian Ocean, and the southwest and western central Pacific Ocean.
''Zostera muelleri'' is a marine angiosperm, and is commonly referred to as eelgrass or garweed.
It is a fast growing and readily colonizing species that serves as a feeding ground for wading birds
and aquatic animals,
and a breeding ground for juvenile fish
and shrimp species.
Seagrasses are a flowering plant species, not to be confused with seaweed,
which do not form flowers, fruits, and seeds to reproduce. Seagrasses are important to the marine ecosystem for many reasons. For one, they provide food, homes, and breeding grounds to a variety of marine species.
Secondly, meadows of seagrass are important carbon reservoirs or sinks,
sequestering 10-18% of the ocean's carbon accumulation for long-term storage.
Seagrasses also enhance sediment accretion,
and protect coastlines from destructive wave energy.
Taxonomy
''Zostera muelleri'' belongs to the order
Alismatales
The Alismatales (alismatids) are an order of flowering plants including about 4,500 species. Plants assigned to this order are mostly Tropical vegetation, tropical or Aquatic plant, aquatic. Some grow in fresh water, some in marine habitats.
...
. There are approximately 72 species of seagrasses.
There are three families of seagrasses,
Zosteraceae
Zosteraceae (one of the four seagrasses families, Kubitzki ed. 1998) 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 ...
,
Hydrocharitaceae
Hydrocharitaceae is a flowering plant family including 16 known genera with a total of ca 135 known species (Christenhusz & Byng 2016), that including a number of species of aquatic plant, for instance the tape-grasses, the well known Canadian ...
, and
Cymodoceaceae
Cymodoceaceae is a family of flowering plants, sometimes known as the "manatee-grass family", which includes only marine species.
The 2016 APG IV does recognize Cymodoceaceae and places it in the order Alismatales, in the clade monocots. The fam ...
.
There is some taxonomic uncertainty with this species.
''Zostera muelleri'' is synonymous with ''Z. mucronata'', ''Z. capricorni'', and ''Z. novazelandica'',
which were once separate species, but since then molecular and morphological studies have confirmed that they are members of the same species.
In 2006, Jacobs et al. (2006) suggested the final name of the species be ''Z. muelleri''.
''Zostera muelleri'' has three subspecies, ''Z. muelleri'' subsp. ''capricorni'', ''Z. muelleri'' subsp. ''mucronata'', and ''Z. muelleri'' subsp. ''muelleri''.
Habitat and geographic range
''Zostera muelleri'' is a perennial species, meaning populations of it endure year round.
They are mostly found in places such as littoral or sublittoral sand flats,
sheltered coastal embayments,
soft, muddy, sandy areas near a reef,
estuaries,
shallow bays,
and in intertidal shoals.
They aren't common on reefs because there is little space and nutrients for them to grow there.
''Zostera muelleri'' is a marine species, but it can tolerate some freshwater inputs.
It mostly occurs in mono-specific meadows, but it can grow alongside ''
Ruppia
''Ruppia'', also known as the widgeonweeds, ditch grasses or widgeon grass, is the only extant genus in the family Ruppiaceae, with eight known species. These are aquatic plants widespread over much of the world. The genus name honours Heinrich ...
'', ''
Halophila
''Halophila'' is a genus of seagrasses in the family ''Hydrocharitaceae'', the tape-grasses. It was described as a genus in 1806. The number of its contained species, and its own placement in the order Alismatales, has evolved.
Description
Th ...
'', and ''
Lepilena''.
''Zostera muelleri'' is widespread in
Southern Australia, and its also found in
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
and
Papua New Guinea
Papua New Guinea (abbreviated PNG; , ; tpi, Papua Niugini; ho, Papua Niu Gini), officially the Independent State of Papua New Guinea ( tpi, Independen Stet bilong Papua Niugini; ho, Independen Stet bilong Papua Niu Gini), is a country i ...
.
Morphology
This species has long strap-shaped leaves,
rounded leaf tips
and thin rhizomes that are <3 mm in diameter.
There are visible cross-veins in the leaf.
The rhizomes are either dark brown or yellow.
Young rhizomes are typically yellow, but the leaves of this plant can turn red if they're under high sunlight.
Because of its phenotype, ''Z. muelleri'' can be confused with ''Z. tasmanica'' and ''Z. capensis.''
The leaf width morphology is variable, so ''Z. muelleri'' with thin leaves can sometimes also be confused with ''H. uninervus''.
Adaptations to marine life
The species ''Z. muelleri'' evolved from terrestrial plants, but adapted to marine life around 140 million years ago during the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
period.
In order to adapt to life in the ocean, the ''Z. muelleri'' genome lost/modified several genes which had once helped them survive on land, such as genes for hormone biosynthesis and signaling and cell wall catabolism.
Some of the genes that were lost include genes associated with ethylene synthesis and signaling pathways, as well as genes involved in pectin catabolism.
Additionally, genes for stomatal differentiation, terpenoid synthesis, and ultraviolet resistance were lost.
The genes responsible for salinity tolerance and stress-resistance remain in the genome.
Reproduction
Seagrasses are flowering species,
but they can reproduce both sexually and asexually.
Reproducing sexually increases genetic variation, which can enhance a plant's ability to adapt to a changing environment, but asexual reproduction requires less effort and is what ''Z. muelleri'' typically uses to maintain its population.
When reproducing sexually, the plant's flowers form an inflorescence that is enclosed in a spathe (a large sheathing bract that encloses flower clusters in certain plant species).
Each shoot can have up to 6 spathes, which contain 4-12 pairs of male and female flowers.
Larger plants will have more flowers. Male flowers typically mature before female flowers.
Once a flowering shoot matures, it darkens and breaks off the plant, and floats away. The enclosed seeds then become deposited in sediment someplace else.
''Zostera muelleri'' can reproduce asexually via rhizome encroachment,
which is a form clonal reproduction. The plant can use this form of regeneration to recover from high intensity disturbances.
Threats and losses
Threats to this species include coastal development,
eutrophication
Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...
,
boat mooring,
dredging,
agricultural/
urban runoff
Urban runoff is surface runoff of rainwater, landscape irrigation, and car washing created by urbanization. Impervious surfaces (roads, parking lots and sidewalks) are constructed during land development. During rain , storms and other precip ...
,
and sedimentation.
Meadows of ''Z. muelleri'' have been lost in areas of
Port Phillip Bay
Port Phillip ( Kulin: ''Narm-Narm'') or Port Phillip Bay is a horsehead-shaped enclosed bay on the central coast of southern Victoria, Australia. The bay opens into the Bass Strait via a short, narrow channel known as The Rip, and is compl ...
and
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
due to habitat disturbance, sedimentation, and turbidity.
During the 1960s, meadows of ''Z. muelleri'' in New Zealand were affected by a wasting disease.
Because it is less tolerant of heat than other tropical species, climate change may be a threat to meadows of this species in tropical regions.
Conservation
There are currently no conservation measures for this species.
References
{{Taxonbar, from=Q15612717
muelleri
Flora of Tasmania
Flora of Victoria (Australia)
Flora of South Australia
Plants described in 1867
Salt marsh plants
Taxa named by Paul Friedrich August Ascherson