Zostera muelleri
StatusLC
Status systemIUCN3.1
GenusZostera
Speciesmuelleri
AuthorityIrmisch ex Asch.[1][2]
Synonyms
  • Nanozostera capricorni (Asch.) Toml. & Posl.

Zostera muelleri is a southern hemisphere temperate species[3] of seagrass native to the seacoasts of South Australia, Victoria and Tasmania[4][5] and New Zealand. Today, Zostera muelleri can be found in regions of Australia, New Zealand, and Papua New Guinea,[6] as well as areas of the eastern Indian Ocean, and the southwest and western central Pacific Ocean.[6] Zostera muelleri is a marine angiosperm, and is commonly referred to as eelgrass or garweed.[7] It is a fast growing and readily colonizing species that serves as a feeding ground for wading birds[8] and aquatic animals,[9] and a breeding ground for juvenile fish[9] and shrimp species.[8]

Seagrasses are a flowering plant species, not to be confused with seaweed,[7] 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.[3] Secondly, meadows of seagrass are important carbon reservoirs or sinks,[3] sequestering 10-18% of the ocean's carbon accumulation for long-term storage.[10] Seagrasses also enhance sediment accretion,[10] and protect coastlines from destructive wave energy.[8]

Taxonomy

Zostera muelleri belongs to the order Alismatales. There are approximately 72 species of seagrasses.[3] There are three families of seagrasses, Zosteraceae, Hydrocharitaceae, and Cymodoceaceae.[3] There is some taxonomic uncertainty with this species.[6] Zostera muelleri is synonymous with Z. mucronata, Z. capricorni, and Z. novazelandica,[6] which were once separate species, but since then molecular and morphological studies have confirmed that they are members of the same species.[8] In 2006, Jacobs et al. (2006) suggested the final name of the species be Z. muelleri.[6] Zostera muelleri has three subspecies, Z. muelleri subsp. capricorni, Z. muelleri subsp. mucronata, and Z. muelleri subsp. muelleri.[7]

Habitat and geographic range

Zostera muelleri is a perennial species, meaning populations of it endure year round.[11] They are mostly found in places such as littoral or sublittoral sand flats,[11] sheltered coastal embayments,[11] soft, muddy, sandy areas near a reef,[7] estuaries,[8] shallow bays,[8] and in intertidal shoals.[8] They aren't common on reefs because there is little space and nutrients for them to grow there.[7] Zostera muelleri is a marine species, but it can tolerate some freshwater inputs.[8] It mostly occurs in mono-specific meadows, but it can grow alongside Ruppia, Halophila, and Lepilena.[8] Zostera muelleri is widespread in Southern Australia, and its also found in New Zealand and Papua New Guinea.[6]

Morphology

This species has long strap-shaped leaves,[3] rounded leaf tips[8] and thin rhizomes that are <3 mm in diameter.[8] There are visible cross-veins in the leaf.[8] The rhizomes are either dark brown or yellow.[8] Young rhizomes are typically yellow, but the leaves of this plant can turn red if they're under high sunlight.[8] Because of its phenotype, Z. muelleri can be confused with Z. tasmanica and Z. capensis.[8] The leaf width morphology is variable, so Z. muelleri with thin leaves can sometimes also be confused with H. uninervus.[6]

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.[3] 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.[3] Some of the genes that were lost include genes associated with ethylene synthesis and signaling pathways, as well as genes involved in pectin catabolism.[3] Additionally, genes for stomatal differentiation, terpenoid synthesis, and ultraviolet resistance were lost.[3] The genes responsible for salinity tolerance and stress-resistance remain in the genome.[3]

Reproduction

Seagrasses are flowering species,[7] but they can reproduce both sexually and asexually.[11] 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.[11] 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).[8] Each shoot can have up to 6 spathes, which contain 4-12 pairs of male and female flowers.[8] Larger plants will have more flowers. Male flowers typically mature before female flowers.[8] 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.[8] Zostera muelleri can reproduce asexually via rhizome encroachment,[12] which is a form clonal reproduction. The plant can use this form of regeneration to recover from high intensity disturbances.[12]

Threats and losses

Threats to this species include coastal development,[6] eutrophication,[10] boat mooring,[10] dredging,[10] agricultural/urban runoff,[10] and sedimentation.[6] Meadows of Z. muelleri have been lost in areas of Port Phillip Bay and New Zealand due to habitat disturbance, sedimentation, and turbidity.[8] During the 1960s, meadows of Z. muelleri in New Zealand were affected by a wasting disease.[6] 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.[6]

Conservation

There are currently no conservation measures for this species.[6]

References

  1. ^ "Zostera muelleri Irmisch ex Asch.". Plants of the World Online. The Trustees of the Royal Botanic Gardens, Kew. n.d. Retrieved September 27, 2020.
  2. ^ "Zostera muelleri Irmisch ex Asch.". World Flora Online. The World Flora Online Consortium. n.d. Retrieved September 27, 2020.
  3. ^ 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
  4. ^ Paul Friedrich August Ascherson. 1867. Linnaea 35: 168 Zostera muelleri
  5. ^ Paul Friedrich August Ascherson. 1867. Sitzungsberichte der Gesellschaft Naturforschender Freunde zu Berlin : 15. Zostera muelleri
  6. ^ 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". Vol. 2010. doi:10.2305/IUCN.UK.2010-3.RLTS.T173384A7004901.en. Retrieved 20 November 2021.
  7. ^ "Zostera muelleri subsp. capricorni (Asch.) S.W.L.Jacobs". Atlas of Living Australia. Retrieved 16 April 2017.
  8. ^ Michelle Waycott; Kathryn McMahon; Paul Lavery (2014). A Guide to Southern Temperate Seagrasses. Csiro Publishing. pp. 90–91. ISBN 978-1-4863-0016-7. Retrieved 16 April 2017.
  9. ^ "Seagrass database launched". UTS. 28 May 2015. Retrieved 16 April 2017.
  10. ^ 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. Bibcode:2016MarER.122..126P. doi:10.1016/j.marenvres.2016.10.003. hdl:10453/58802. PMID 28327303
  11. ^ 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
  12. ^ 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. Bibcode:2014EcoEv...4..450M. doi:10.1002/ece3.933. PMC 3936391. PMID 24634729