Zostera muelleri

Zostera muelleri
Scientific classification
Kingdom:Plantae
Clade:Angiosperms
Clade:Monocots
Order:Alismatales
Family:Zosteraceae
Genus:Zostera
Species: Z. muelleri
Binomial name
Zostera muelleri
Synonyms[1]
  • Nanozostera capricorni (Asch.) Toml. & Posl.

Zostera muelleri is a southern hemisphere temperate species[2] of seagrass native to the seacoasts of South Australia, Victoria and Tasmania.[3][4] and New Zealand. Today, Zostera muelleri can be found in regions of Australia, New Zealand, and Papua New Guinea,[5] as well as areas of the eastern Indian Ocean, and the southwest and western central Pacific Ocean.[5] Zostera muelleri is a marine angiosperm, and is commonly referred to as eelgrass or garweed.[6] It is a fast growing and readily colonizing species that serves as a feeding ground for wading birds[7] and aquatic animals,[8] and a breeding ground for juvenile fish[8] and shrimp species.[7]

Seagrasses are a flowering plant species, not to be confused with seaweed,[6] 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.[2] Secondly, meadows of seagrass are important carbon reservoirs or sinks,[2] sequestering 10-18% of the ocean's carbon accumulation for long-term storage.[9] Seagrasses also enhance sediment accretion,[9] and protect coastlines from destructive wave energy.[7]

Taxonomy

Zostera muelleri belongs to the order Alismatales. There are approximately 72 species of seagrasses.[2] There are three families of seagrasses, Zosteraceae, Hydrocharitaceae, and Cymodoceaceae.[2] There is some taxonomic uncertainty with this species.[5] Zostera muelleri is synonymous with Z. mucronata, Z. capricorni, and Z. novazelandica,[5] which were once separate species, but since then molecular and morphological studies have confirmed that they are members of the same species.[7] In 2006, Jacobs et al. (2006) suggested the final name of the species be Z. muelleri.[5] Zostera muelleri has three subspecies, Z. muelleri subsp. capricorni, Z. muelleri subsp. mucronata, and Z. muelleri subsp. muelleri.[6]

Habitat and geographic range

Zostera muelleri is a perennial species, meaning populations of it endure year round.[10] They are mostly found in places such as littoral or sublittoral sand flats,[10] sheltered coastal embayments,[10] soft, muddy, sandy areas near a reef,[6] estuaries,[7] shallow bays,[7] and in intertidal shoals.[7] They aren’t common on reefs because there is little space and nutrients for them to grow there.[6] Zostera muelleri is a marine species, but it can tolerate some freshwater inputs.[7] It mostly occurs in mono-specific meadows, but it can grow alongside Ruppia, Halophila, and Lepilena.[7] Zostera muelleri is widespread in Southern Australia, and its also found in New Zealand and Papua New Guinea.[5]

Morphology

This species has long strap-shaped leaves,[2] rounded leaf tips[7] and thin rhizomes that are <3 mm in diameter.[7] There are visible cross-veins in the leaf.[7] The rhizomes are either dark brown or yellow.[7] Young rhizomes are typically yellow, but the leaves of this plant can turn red if they're under high sunlight.[7] Because of its phenotype, Z. muelleri can be confused with Z. tasmanica and Z. capensis.[7] The leaf width morphology is variable, so Z. muelleri with thin leaves can sometimes also be confused with H. uninervus.[5]

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 period.[2] 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.[2] Some of the genes that were lost include genes associated with ethylene synthesis and signaling pathways, as well as genes involved in pectin catabolism.[2] Additionally, genes for stomatal differentiation, terpenoid synthesis, and ultraviolet resistance were lost.[2] The genes responsible for salinity tolerance and stress-resistance remain in the genome.[2]

Reproduction

Seagrasses are flowering species,[6] but they can reproduce both sexually and asexually.[10] 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.[10] 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).[7] Each shoot can have up to 6 spathes, which contain 4-12 pairs of male and female flowers.[7] Larger plants will have more flowers. Male flowers typically mature before female flowers.[7] 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.[7] Zostera muelleri can reproduce asexually via rhizome encroachment,[11] which is a form clonal reproduction. The plant can use this form of regeneration to recover from high intensity disturbances.[11]

Threats and losses

Threats to this species include coastal development,[5] eutrophication,[9] boat mooring,[9] dredging,[9] agricultural/urban runoff,[9] and sedimentation.[5] Meadows of Z. muelleri have been lost in areas of Port Phillip Bay and New Zealand due to habitat disturbance, sedimentation, and turbidity.[7] During the 1960s, meadows of Z. muelleri in New Zealand were affected by a wasting disease.[5] 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.[5]

Conservation

There are currently no conservation measures for this species.[5]

References

  1. ↑ The Plant List
  2. 1 2 3 4 5 6 7 8 9 10 11 HueyTyng Lee; Agnieszka A. Golicz; Philipp E. Bayer; Yuannian Jiao; Haibao Tang; Andrew H. Paterson; Gaurav Sablok; Rahul R. Krishnaraj; Chon-Kit Kenneth Chan; Jacqueline Batley; Gary A. Kendrick; Anthony W.D. Larkum; Peter J. Ralph & David Edwards (3 July 2016). "The Genome of a Southern Hemisphere Seagrass Species (Zostera muelleri)". Plant Physiology. 172 (1): 272–283. doi:10.1104/pp.16.00868. PMC 5074622. PMID 27373688. Retrieved 16 April 2017.
  3. ↑ Paul Friedrich August Ascherson. 1867. Linnaea 35: 168 Zostera muelleri
  4. ↑ Paul Friedrich August Ascherson. 1867. Sitzungsberichte der Gesellschaft Naturforschender Freunde zu Berlin : 15. Zostera muelleri
  5. 1 2 3 4 5 6 7 8 9 10 11 12 Short, F.T.; Williams, S.L.; Carruthers, T.J.R.; Waycott, M.; Kendrick, G.A.; Fourqurean, J.W.; Callabine, A.; Kenworthy, W.J. & Dennison, W.C. "Zostera muelleri". The IUCN Red List of Threatened Species. IUCN. Retrieved 16 April 2017.
  6. 1 2 3 4 5 6 "Zostera muelleri subsp. capricorni (Asch.) S.W.L.Jacobs". Atlas of Living Australia. Atlas of Living Australia. Retrieved 16 April 2017.
  7. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Michelle Waycott; Kathryn McMahon; Paul Lavery (2014). A Guide to Southern Temperate Seagrasses. Csiro Publishing. pp. 90–91. ISBN 1486300162. Retrieved 16 April 2017.
  8. 1 2 "Seagrass database launched". UTS. UTS. 28 May 2015. Retrieved 16 April 2017.
  9. 1 2 3 4 5 6 Mathieu Pernice; Sutinee Sinutok; Gaurav Sablok; Audrey S. Commault; Martin Schliep; Peter I. Macreadie; Michael A. Rasheed; Peter J. Ralph (21 October 2016). "Molecular physiology reveals ammonium uptake and related gene expression in the seagrass Zostera muelleri". Marine Environmental Research. 122: 126–134. doi:10.1016/j.marenvres.2016.10.003. PMID 28327303.
  10. 1 2 3 4 5 Virginie M. Dos Santos; Fleur E. Matheson (16 December 2016). "Higher seagrass cover and biomass increases sexual reproductive effort: A rare case study of Zostera muelleri in New Zealand". Aquatic Botany. 138: 29–36. doi:10.1016/j.aquabot.2016.12.003. Retrieved 16 April 2017.
  11. 1 2 Peter I. Macreadie; Paul H. York; Craig D.H. Sherman (21 January 2014). "Resilience of Zostera muelleri seagrass to small-scale disturbances: the relative importance of asexual versus sexual recovery". Ecology and Evolution. 4 (4): 450–461. doi:10.1002/ece3.933. PMC 3936391. PMID 24634729. Retrieved 16 April 2017.
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