Zostera muelleri

Zostera muelleri is a southern hemisphere temperate species[5] of seagrass native to the seacoasts of South Australia, Victoria and Tasmania.[6][7] and New Zealand. Today, Zostera muelleri can be found in regions of Australia, New Zealand, and Papua New Guinea,[1] as well as areas of the eastern Indian Ocean, and the southwest and western central Pacific Ocean.[1] Zostera muelleri is a marine angiosperm, and is commonly referred to as eelgrass or garweed.[8] It is a fast growing and readily colonizing species that serves as a feeding ground for wading birds[9] and aquatic animals,[10] and a breeding ground for juvenile fish[10] and shrimp species.[9]

Zostera muelleri
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Order: Alismatales
Family: Zosteraceae
Genus: Zostera
Species:
Z. muelleri
Binomial name
Zostera muelleri
Irmisch ex Asch.[2][3]
Synonyms[4]
  • Nanozostera capricorni (Asch.) Toml. & Posl.

Seagrasses are a flowering plant species, not to be confused with seaweed,[8] 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.[5] Secondly, meadows of seagrass are important carbon reservoirs or sinks,[5] sequestering 10-18% of the ocean's carbon accumulation for long-term storage.[11] Seagrasses also enhance sediment accretion,[11] and protect coastlines from destructive wave energy.[9]

Taxonomy

Zostera muelleri belongs to the order Alismatales. There are approximately 72 species of seagrasses.[5] There are three families of seagrasses, Zosteraceae, Hydrocharitaceae, and Cymodoceaceae.[5] There is some taxonomic uncertainty with this species.[1] Zostera muelleri is synonymous with Z. mucronata, Z. capricorni, and Z. novazelandica,[1] which were once separate species, but since then molecular and morphological studies have confirmed that they are members of the same species.[9] In 2006, Jacobs et al. (2006) suggested the final name of the species be Z. muelleri.[1] Zostera muelleri has three subspecies, Z. muelleri subsp. capricorni, Z. muelleri subsp. mucronata, and Z. muelleri subsp. muelleri.[8]

Habitat and geographic range

Zostera muelleri is a perennial species, meaning populations of it endure year round.[12] They are mostly found in places such as littoral or sublittoral sand flats,[12] sheltered coastal embayments,[12] soft, muddy, sandy areas near a reef,[8] estuaries,[9] shallow bays,[9] and in intertidal shoals.[9] They aren’t common on reefs because there is little space and nutrients for them to grow there.[8] Zostera muelleri is a marine species, but it can tolerate some freshwater inputs.[9] It mostly occurs in mono-specific meadows, but it can grow alongside Ruppia, Halophila, and Lepilena.[9] Zostera muelleri is widespread in Southern Australia, and its also found in New Zealand and Papua New Guinea.[1]

Morphology

This species has long strap-shaped leaves,[5] rounded leaf tips[9] and thin rhizomes that are <3 mm in diameter.[9] There are visible cross-veins in the leaf.[9] The rhizomes are either dark brown or yellow.[9] Young rhizomes are typically yellow, but the leaves of this plant can turn red if they're under high sunlight.[9] Because of its phenotype, Z. muelleri can be confused with Z. tasmanica and Z. capensis.[9] The leaf width morphology is variable, so Z. muelleri with thin leaves can sometimes also be confused with H. uninervus.[1]

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.[5] 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.[5] Some of the genes that were lost include genes associated with ethylene synthesis and signaling pathways, as well as genes involved in pectin catabolism.[5] Additionally, genes for stomatal differentiation, terpenoid synthesis, and ultraviolet resistance were lost.[5] The genes responsible for salinity tolerance and stress-resistance remain in the genome.[5]

Reproduction

Seagrasses are flowering species,[8] but they can reproduce both sexually and asexually.[12] 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.[12] 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).[9] Each shoot can have up to 6 spathes, which contain 4-12 pairs of male and female flowers.[9] Larger plants will have more flowers. Male flowers typically mature before female flowers.[9] 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.[9] Zostera muelleri can reproduce asexually via rhizome encroachment,[13] which is a form clonal reproduction. The plant can use this form of regeneration to recover from high intensity disturbances.[13]

Threats and losses

Threats to this species include coastal development,[1] eutrophication,[11] boat mooring,[11] dredging,[11] agricultural/urban runoff,[11] and sedimentation.[1] Meadows of Z. muelleri have been lost in areas of Port Phillip Bay and New Zealand due to habitat disturbance, sedimentation, and turbidity.[9] During the 1960s, meadows of Z. muelleri in New Zealand were affected by a wasting disease.[1] 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.[1]

Conservation

There are currently no conservation measures for this species.[1]

References
  1. 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. (2010). "Zostera muelleri". IUCN Red List of Threatened Species. 2010: e.T173384A7004901. doi:10.2305/IUCN.UK.2010-3.RLTS.T173384A7004901.en. Retrieved September 27, 2020.CS1 maint: multiple names: authors list (link)
  2. "Zostera muelleri Irmisch ex Asch". Plants of the World Online. The Trustees of the Royal Botanic Gardens, Kew. n.d. Retrieved September 27, 2020.
  3. "Zostera muelleri Irmisch ex Asch". World Flora Online. The World Flora Online Consortium. n.d. Retrieved September 27, 2020.
  4. The Plant List
  5. 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.
  6. Paul Friedrich August Ascherson. 1867. Linnaea 35: 168 Zostera muelleri
  7. Paul Friedrich August Ascherson. 1867. Sitzungsberichte der Gesellschaft Naturforschender Freunde zu Berlin : 15. Zostera muelleri
  8. "Zostera muelleri subsp. capricorni (Asch.) S.W.L.Jacobs". Atlas of Living Australia. Atlas of Living Australia. Retrieved 16 April 2017.
  9. Michelle Waycott; Kathryn McMahon; Paul Lavery (2014). A Guide to Southern Temperate Seagrasses. Csiro Publishing. pp. 90–91. ISBN 978-1486300167. Retrieved 16 April 2017.
  10. "Seagrass database launched". UTS. UTS. 28 May 2015. Retrieved 16 April 2017.
  11. 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. hdl:10453/58802. PMID 28327303.
  12. 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.
  13. 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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