The Importance of Plants to Western Port

The energy system that supports life in Western Port is based on photosynthetic plants. Without these plants, there would be no food chain and Western Port could not sustain its diverse ecosystems and biodiversity. These plants also play a vital role in stabilizing coast lines and mud flats and hence influence the water quality within the bay.

Similarly, the quality of the terrestrial ecosystems and the stability of the landscape and hence the quality of water flowing into Western Port is dependent on healthy and sustainable terrestrial plant communities.

The WPSP gives its priority attention to the preservation and restoration of marine and coastal plant communites, and in particular the seagrasses, mangroves and saltmarshes.

In the catchment, the WPSP fully supports the actions of the Landcare movement on private land and the efforts of Friends Groups and Authorities on public lands, to achieve sustainable landscapes by protecting and restoring native plant communities and practicing sustainable farming land management practices.

Seagrasses

Seagrasses are marine angiosperms (flowering plants) that have physiology adapted to aquatic environments allowing for pollination, seed formation and germination in water. During the day seagrasses absorb carbon dioxide and release oxygen to the water through a thin outer leaf membrane. A slower reverse process (respiration) occurs at night.

Right: Seagrass leaves covered with algal epiphytes. Photo: WPSP.

Air is transported to the roots via air canals, assisting survival in anaerobic muds. Being dependent on light for photosynthesis, seagrasses usually occur at depths from 2 - 12 metres. Most species are sub-tidal but some inter-tidal species have adapted to exposure to the air at low tide. Water quality is a major limiting factor, with turbid waters restricting light availability.

High levels of dissolved nutrients in the water can cause excessive algal growth on the surface of leaves that also interfere with photosynthesis. Sediment deposits and sand movements can also physically smother seagrasses.

Left: Mud banks stabilized by seagrass meadows. Photo: EPA Victoria.
Right: Unstable mudflats arising from seagrass loss. Photo: EPA Victoria.

Hence factors like catchment run-off into embayments and in-bay dredging can determine the sustainability of seagrass communities. Seagrasses can form large mats or banks of plants (meadows) that effectively stabilize marine substrates and can influence local water quality and chemistry. Where seagrass losses occur, as in Western Port, muddy sediments are mobilized causing deteriorating water quality, flattened profiles and loss of channel profiles.

Left: Weedy seadragon feeding on mysid shrimp in seagrass Heterozostera nigricaulis Flinders. Photo: Courtesy of www.marine-ecology.com.au.
Right: Swans grazing upon Zostera muelleri at Coronet bay. Photo: T. Ealey WPSP.

Seagrasses act as a nursery and refuge for many small marine organisms, including seahorses and juvenile whiting.
The leaves are home for algae and many small organisms called epiphytes. These epiphytes are a major food source for shellfish, crustaceans and fish. A few animals like garfish, leatherjackets and black swans are adapted to eating and digesting the tough seagrass leaves.

Seagrass detritus on beach at Coronet Bay. Photo: T. Ealey WPSP.

Seagrasses generate considerable standing biomass and represent sizable nutrient pools.  Storms and autumn leaf drop results in large accumulations of detritus along shorelines. This detritus eventually breaks down and provides food and a steady release of nutrients into the water column and sediments.

Seagrass Reproduction

The three methods by which seagrass reproduce are seeds, propagules (plantlets) and spreading rhizomes. As with terrestrial flowering plants, the seeds are produced as a result of pollination between male and female parts of the flower.  Some species like Halophila and Amphibolis have male and female plants and flowers.

Left: *Source:  From Aquatic Plants of Australia, H.I. Aston (Melbourne University Press: 1973) with kind permission. Copy Helen I Aston
Right: Germinating seeds with roots and leaves, ready to lodge into suitable substrate. Photo: S. Seddon, SARDI

Zostera and Herozostera have male and female flowers alternating in a swollen stem structure called a spandex. Pollination occurs in the spandex and the fruits mature prior to release. The seeds ripen to an advanced state within the spandex prior to their release.

When ripe, the seeds are released to the water and dispersed by tides and currents to form new plants at locations suitable for their establishment.

Left: Plantlets with fully formed leaves, rhizomes and roots. Photo: WPSP.
Right: A sprig floating on the tide after breaking free from parent plant. Photo: WPSP.

Reproduction can also occur via sprigs or propagules (small plantlets) that grow on the stems of mature pants. They eventually break free from the adult plants and float to new locations. Sprigs can survive for quite long periods enabling them to be transported considerable distances.

As the rhizome expands, it sends down anchor roots and sprouts new stems. Photo: WPSP.

The final means of reproduction is vegetative expansion via lateral rhizomes that anchor the plants to sandy or muddy substrates.

Seagrass Species of Western Port

There are at least four recorded species of seagrass occurring in Western Port, and maybe five, taking into account more recent taxanomic debate around Zostera and Heterozostera species. (Refer: A Revision of the genus Heterozostera – John Kuo)

These being:

• Amphibolis antarctica
• Halophila australis
• Zostera muelleri
• Heterozostera nigricaulis
• Heterozostera tasmanica

Most people will find it difficult to see the difference between Zostera muelleri, Heterozostera tasmanica and Heterozostera nigricaulis. There are physiological differences between leaf and stem sections when examined under a microscope, but to assist with field identification the following simple guide can be used:

Zostera muelleri is more commonly found in the intertidal zones closer to shore, but can be interspersed amongst Heterozostera species. The easiest way to identify this species is to look for its truncate or flattened leaf tip and green stem in mature plants. Heterozostera nigricaulis, true to its name has a distinctive black main stem, long leaves with flattened and slightly notched tip. It is mainly found in subtidal zones and along channel banks.

Heterozostera tasmanica is almost identical to H. nigricaulis, but does not have a black stem and has a rounded leaf tip.  It is thought to prefer deeper water, closer to oceanic influences, but this is to be confirmed for Western Port.

Zostera muelleri

This intertidal species often forms patchy colonies in shallow water, and is quite resilient to low tide exposure.

Zostera muelleri at Coronet Bay. Photo: T. Ealey WPSP.

Heterozostera tasmanica

Heterozostera tasmanica has also previously been described as Zostera tasmanica. It was once thought to be the predominant species in Western Port but recent reclassifications have confirmed Heterozostera nigricaulis as the dominant species. Although Heterozostera tasmanica occurs in Victoria and Tasmania there have been no confirmed samples from Western Port. This species is believed to prefer deeper water and if it did exist in Western Port it would be found closer to oceanic entrances.

Heterozostera tasmanica grows in subtidal meadows like the one shown. (EPA Victoria)

Heterozostera nigricaulis

Still the most common species in Western Port, it formed extensive and lush seagrass meadows in the northern sector of Western Port, especially along channel banks. This species however has also experienced the brunt of the huge seagrass losses in the 1970s and 1980s and only a small recovery has been noted since this time. Scientists who have worked with the species in Western Port claim that flowers and seeds are rarely noted, in contrast to Heterozostera tasmanica. It would seem then that vegetative reproduction is the prime means of regeneration for this species.

Heterozostera nigricaulis: Photo: A. Stephens (EPA Victoria)

Halophila australis

Halophila australis has very small oval leaves and grows in sparse patches, mostly on sheltered sandy substrate and at the southern end of Western Port, where the water is clear and subject to oceanic influences.

Left: Halophila australis Photo: EPA Queensland.

Amphibolis antarctica

Amphibolis antarctica has a preference for sandy substrate and can be found mostly around the western entrance and lower section of Western Port where the water is cleaner and subject to oceanic influences. The stems can grow over a metre in length and have clusters of leaves that are about 5 cm in length. Significant quantities of these plants are deposited along the western beaches during the late autumn period when they shed their leaves.

Amphibolis antarctica seagrass, Flinders, Western Port, www.marine-ecology.com.au

Seagrass Information

Links - More information about seagrasses
Research Papers & Reports - PDF

Mangroves

Left: Mangroves at low tide. Photo: I. Morgans, PP&WCMA.
Right: Mangroves at high tide. Photo: I. Morgans PP&WCMA.

Western Port has one species of mangrove, the white mangrove, Avicennia marina.

Mangroves are unique in being the only trees capable of living in the tidal zone along coastal or estuarine shorelines. They are advantaged by having no competitors for the niche they occupy but seem unable to compete outside this unique range. These flowering trees have many special features that enable them to survive and take advantage of these extremely harsh conditions.

Mangrove Habitat & Distribution

The mangroves of Western Port are at their most southern limit of distribution. In the cold winters of this southern climate the seedlings are subject to frost damage and death, whilst adult trees have reduced annual growth and fruiting frequency. Ideally mangroves prefer sheltered gently sloping muddy coastlines where seeds can germinate and establish without being undercut by strong wave action. For this reason mangroves are not found along Western Port’s oceanic beaches, but are prolific along the sheltered northern parts of Phillip Island, around French Island and most of the northern segment of the bay.

Left: Mangroves in Rhyll Inlet – ideal sheltered habitat. Photo: G. Rooney Melbourne Water.
Right: Saltmarsh behind protective mangrove fringe Tooradin. Photo: T. Ealey WPSP.

Whilst preferring fully sheltered environs, with defined tidal zone preferences, established mangroves are capable of withstanding significant storm and tidal events. Mangroves are very beneficial in providing natural coastal erosion barriers and are renowned as coastal colonisers due to their ability to trap sediments and extend shorelines. The regions of Western Port with established mangroves exhibit very stable coastlines, typically with mature saltmarsh communities behind them. Areas devoid of mangroves, particularly those subject to historic clearing, are highly unstable and eroding with consequent loss or deterioration on adjacent saltmarsh habitat. Once destroyed, natural mangrove recovery can be very slow especially if conditions are hostile to seed establishment.

Saltmarsh being eroded away along northern coastline of Western Port due to absence of mangroves. Photo: T. Ealey WPSP.

The mangrove stands of Western Port also represent a major store and supply of biomass and nutrients. The leaves that drop into the bay are a valuable source of food and slow release nutrients. Like seagrasses, mangroves are the energy power houses for the Bay’s ecosystem – supplying the raw material at the base of the food chain, which is then utilized by the bacteria, algae, mollusks, crustaceans, fish, birds and mammals.

Mangrove Root System

Left: Young mangroves showing cable roots radiating from base. Photo: T. Ealey WPSP.
Right: Pneumataphores at low tide. Photo: T. Ealey, WPSP

The extensive cable root system of mangroves anchors them into the thick muddy substrates that they prefer and enables them to withstand severe winds and tidal impacts.

The cable roots have holding roots that penetrate vertically downwards into the mud and finer root networks expanding outwards. Cable roots also have root extensions called pneumataphores, which protrude vertically upward out of the mud and into the water and air. These structures enable the roots to obtain oxygen which is not available in the anaerobic mud in which they grow. Mangroves often die when their pneumataphores are destroyed or covered in oil.

Mangrove Salt Control

Right: Mangrove leaves with crystals of excreted salt. Photo: T. Ealey WPSP.

To survive in salt water, mangroves have developed three methods of regulating their internal salt levels. The first method is exclusion, whereby special membranes in the roots effectively block salt uptake and only allow water to enter into the plant. The second method is to secrete salt via special glands in the leaves. Finally salt can be concentrated in bark and leaves which the plant later drops. Avicennia leaves turn yellow and drop off when loaded with salt.

Mangrove Leaves 

Avicennia leaves. Photo: T. Ealey WPSP.

Mangrove leaves are strong and leathery, ideal to withstand winds, sea-spray and saltwater inundation. Water loss through evaporation and wind is minimized by their thick waxy cuticle and sunken stomata (pores). These slightly succulent leaves also store water.

Mangrove Reproduction

Left: Avicennia flowers Photo: T. Ealey WPSP.
Right: Mature mangrove fruits. Photo T. Ealey WPSP.

Avicennia marina has small, pale orange flowers that are pollinated by bees and other insects. The fruits are almond sized, green and slightly furry. The fruit ripens in summer and takes two months to mature. Inside the fruit, a single seed develops to an advanced state. When ripe the fruit drops into the sea or onto the mud. The seeds float until their coat is shed, the timing of which is linked to bay salinity levels.

Left: Mangrove seeds showing rapid germination and root development after losing their protective coats. Photo: T. Ealey, WPSP.
Right: Young seedlings growing at edge of the saltmarsh.  Photo: T. Ealey, WPSP.

Seeds can stay alive in water for three to four days. Only a small number of seeds succeed in anchoring themselves in the mud, with others stranded at high tide mark or eaten by crabs. Those that establish under existing mangroves will eventually be shaded out and die.

Link - More information about mangroves

Saltmarshes

Coastal Saltmarshes

Left: Saltmarsh behind mangroves Tooradin Photo: T. Ealey, WPSP.
Right: Saltmarsh establishing behind maturing mangroves. Photo: T. Ealey, WPSP.

Saltmarshes are comprised of plant species adapted to coastal wetlands that undergo regular or periodic saltwater inundation or sea spray. Saltmarshes are found in the sheltered intertidal or estuarine zones, especially between mangroves (seaward side) and Melaleuca scrub (landward side). They require protection from strong currents, wave action, significant freshwater inputs and human and stock disturbance. Saltmarsh range is either extended or diminished according to whether mangroves are colonizing new shoreline or in retreat due to coastal erosion.

Left: Mangrove stumps mark the original coast line and show the extensive coastal erosion and loss of saltmarsh that followed. Photo: T. Ealey ,WPSP.
Right: Seawalls collapsing – coastal destabilization due to mangrove removal and consequent loss of saltmarshes. Photo: T. Ealey, WPSP.

Where mangroves have been removed, saltmarshes will be eroded away quickly, followed by aggressive coastal erosion. Saltmarshes behind retreating mangroves or where mangroves have been removed can face obliteration if landward movement is blocked by man made coastal barriers. Salmarshes are also important sheltering and feeding areas for birds, especially migratory waders covered by the Ramsar convention.

Saltmarsh species include low succulents, herbs, shrubs, rushes and sedges, with each species having a different salt tolerance.

Ecosystem types include

Coastal Saltmarsh Species

Brackish Wetland & Sedgeland Species

Salty Grasslands and Rush Species

Estuarine Grassland & Swamp Scrub Species

Marine Flora of Western Port

Angiospermae

Coastal Flora of Western Port

Angiospermae

Terrestrial / Catchment Flora of Western Port

Angiosperme

Flora Categories and Identification Resources

To assist with the identification of plant species growing in Western Port we have provided some typical categories (classes) of plants and the families of plants found within these categories.  Where possible we have provided both the scientific names and the common names to make it easier for your to narrow down your identification choices.

In addition to this we have provided an extract of the key regional species listed in the Biosphere application which should provide good guidance to the species likely to be found in the region.

Fauna Species List

We have also provided some links to a number of web sites that provide helpful guides and indexes of plant species, many of which contain species names, descriptions and photographs. These should prove helpful in identifying the species you have discovered and photographed in the region.

Finally we have provided a few hints on how to go about identifying species in the field and checking on your determinations.

Flora Categories and Identification Resources

Once you have photographed and identified what you believe the species to be, you are ready to submit it to us for inclusion on this web site.

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