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]