Mangroves

One of the less photogenic aspects of Coochie is the mangroves which make up about a third of the Coochiemudlan coastline. The mangroves are nothing unusual for the islands in Moreton Bay and as a result, this area tends to be ignored by most visitors who are more interested in the beach-related, more hedonistic aspects of Coochie’s charms. Furthermore, mangroves tend to be seen by the majority as swamps, which are ridden with mosquitoes and sand flies, and which are inhospitable, unhealthy and dangerous.

However, mangroves are a highly productive ecosystem with various important economic and environmental functions. The uses of mangroves fall into two major categories: Firstly the indirect use of the mangrove ecosystem are in the form of vital ecological functions such as control of coastal erosion and protection of coastal land, stabilization of sediment, natural purification of coastal water from pollution. Secondly, the economic benefits which are many and varied. Apart from prawn fisheries, many other species of economic importance are associated with mangroves; these include crabs, shrimp, oysters, lobsters and fish. An estimated 75 percent of fish caught commercially spend some time in the mangroves or are dependent on food chains which can be traced back to these coastal forests. While providing a buffer for the land on one side, mangroves also interact with the sea on the other. Sediments trapped by roots prevent silting of adjacent marine habitats where cloudy water might cause corals to die. In addition, mangrove plants and sediments have been shown to absorb pollution, including heavy metals.

Worldwide, vast tracts of mangroves have been destroyed so we are lucky to have relatively large areas of Australia’s tallest and best-developed mangroves still existing on our doorstep.

The mangroves form an integral part of the Coochiemudlan eco-system. The term mangrove refers not only to the individual plant, but also to the habitat in which it lives. This habitat is characterised by large fluctuations in water salinity. Depending upon high or low tide, or whether heavy rains have swelled the rivers, the salinity level varies enormously. Added to this is the effect of silt brought by the rivers which produces a particularly soft and muddy soil ; a soil which contains very little oxygen. The mangrove plant is unique in it’s ability to survive this harsh, constantly changing environment.

Since the soil is not particularly nutritious, mangroves have adapted by modifying their roots. Most mangroves share root modifications that keep salt out and help bring in water, carbon dioxide, oxygen, and other nutrients essential to the photosynthetic process. Several species of mangroves have developed prop roots, which are more or less a root system that splits off from the trunk above ground rather than below ground. Prop root systems allow mangroves to take up gasses directly from the atmosphere and various other nutrients, like iron, from the otherwise inhospitable soil. They quite often store gasses directly inside the roots so that they can be processed even when the roots are submerged during high tide. The gasses that mangrove plants absorb can also be passed down to roots that grow in the permanently anoxic parts of the soil.

Mangroves support unique ecosystems, especially on their intricate root systems. In areas where roots are permanently submerged, mangroves may be host to a wide variety of organisms, including algae, barnacles, oysters, sponges, and bryozoans, which all require a hard substrata for anchoring while they filter feed. Some of these communities can become so dense that they block off the lenticles of the mangrove and suffocate it, though this is not a common occurrence, since it would benefit neither the mangrove nor its guests. Sponges can actually help the mangroves by supplying them with soluble nitrogen compounds, though some of them grow so massive that they simply fall off their supports. This diverse community also attracts mobile browsers and predators, such as crabs, snails, and fish, all of which feed not only on the root-fouling community, but sometimes on the mangrove leaves as well.

The mangrove ecosystem thrives along coastal mudflats in tropical areas. However, in recent years, many mangrove communities have been uprooted and destroyed by human activity. More recently, some effort has been put into preserving and reintroducing these communities in the areas where they once flourished. Mangroves are excellent buffers between the violent ocean and the fragile coast, especially during hurricanes, which can bring powerful storm surges onto shores. The only two yachts undamaged by Cyclone Tracey in Darwin in 1974 had sheltered in a mangrove creek. The massive mangrove root system is quite efficient at dissipating wave energy. This same root system also helps prevent coastal erosion. As tidal water flows through the root system, it is slowed substantially enough so that it deposits its sediment as the tide comes in, and the return flow is kept slow as the tide goes out to prevent resuspension of some of the finer particles. As a result, mangroves can build their own environment.

The Regional Coastal Plan prepared by Queensland’s Environmental Protection Agency is reproduced in part on the following webpage: Regional Coastal Plan A CD containing in-depth research can be purchased from the EPA.

We have included this research into the much-maligned mangroves on this website in the hope that those who want to destroy them, for whatever reason, can be made to think twice.

We are immeasurably indebted to Suzana Barber for

    1) bringing the ecological importance of the mangroves to our attention, and
      2) for providing us with

ALL

     of the information, research and pictures. We were unfortunately only able to include a fraction of the wealth of knowledge she provided us with on these pages.

If you have any comments on the above, or would generally like to air your views on Coochie-related topics, please send a mail to the authors/editors and we will publish them on this website. Please indicate if you would prefer to remain anonymous.