Zostera muelleri

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]

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]

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]

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]

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 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]

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