The Mangroves

Most of the mangroves are concentrated either along the bay edge or on the drainage canals. Others occur in the ditches left after the construction of the causeway or scattered sparsely across the salt marsh flat. Those on the salt marsh are sometimes associated with a depression holding water.

Salt Marsh with scattered Mangroves

Flood

cattered small mangrove shrubs grow on the salt marsh. often in areas where tidal cover is deeper. This view shows a spring tide covering areas occupied by Sarcocornia.

The fringing mangrove stand, which includes the largest specimens, occupies the area between neap high water mark and a little below the mid-tide level. The root systems of all of these mangroves are covered by water twice each day.

There are two species of mangroves present on Towra Point

Aegiceras corniculatum

Aegiceras corniculatum - the River Mangrove is a shrub or small tree with dark coloured bark and no pneumatophores. The stem base is covered with prominent pink-brown lenticels. The root system is shallow with occasional knob-like, lenticel covered protrusions above the soil surface. The interior of the root system has a pinkish tinge. The leaves are alternate, ovate, glossy green above and paler below. Salt is secreted from glands on the upper surface of the leaf and salt crystals can often be seen there.

 

 

 

 

Avicennia

Avicennia marina -the Grey Mangrove is a shrub to medium sized tree with a well defined trunk. The bark is grey and lightly fissured. The root system is extensive and has many pneumatophores which are covered with many grey to white lenticels. The interior of the root system is creamy white. The leaves are opposite, ovate with an acute apex, glossy green above and the lower surface of the leaf is covered with a grey tomentum (felty layer). Salt is secreted from the lower surface of the leaf (and can be tasted by licking).

 

 

 

 

Avicennia marina


Avicennia marina,
TS leaf.
(stained)
showing hairs on lower surface.

Small mangroves growing in a pond beside the causeway

Avi root

The extent of their root system can be seen by the rows of pneumatophores in the water. The root systems of Avicennia marina are very extensive and we have found pneumatophores up to 30 metres away from the base of the nearest tree. In these pools, concentrations of many thousands of seedlings can often be found near the strand line. All of these seedlings cannot survive, however this prodigal production of seedlings is part of the mangrove's strategy for distribution. Growth to adult size occurs rarely and probably depends on the availability of light and nutrients. More details are provided if you want to find out about Mangroves.

 

 

 

 

 

Hormosira banksii
Towards the bay edge it is possible to find the Brown alga Hormosira banksii (Neptune's Necklace) and a variety of other algal species, especially clinging to the pneumatophores. (Bostrychia sp.,Caloglossa sp., Catenella sp.)

 

Mangroves - Looking towards Weeny Bay
The soil surface is largely bare except for a vast number of pneumatophores. Up to 50% of the soil volume is occupied by mangrove roots. Just beyond the mangrove fringe occur beds of the narrow leafed sea grass Zostera capricorni , which grows in the area which is uncovered by the lowest tides. The broad leafed sea grass Posidonia australis occurs further into the bay where it is never uncovered by the tide. The leaves of these two angiosperms are often found washed up on the salt flat after heavy weather.