Mangroves 6: Activities

MANGROVES 6: Activities

Activity 1. Zonation

In small teams, construct a diagram that shows the different zones described above and the species to be found in each zone. Use different symbols for the different species of mangroves. Having constructed a cross-section of a mangrove community and shoreline to your satisfaction (discuss the diagram's clarity, use of symbols, key etc.) make two photocopies of it. Show the following data on the copies.

Copy one (heights are elevation above datum)

Sonneratia/Avicennia zone       3.0 - 3.6 m

Rhizophora zone                        3.6 - 6.5 m

Ceriops zone                              6.5 - 8.0 m

Bruguiera zone                           8.0 - 9.0 m

Copy two (Elevation above datum):

HAT                            8.0 m

MHWS                        6.9 m

MHWN                       5.0 m

MSL                             4.1 m

MLWN                        3.2 m

MLWS                        1.4 m

Compare the two diagrams. Discuss the distribution of the various species and the degree of adaptation shown by individual species and of the mangroves as a whole. What groupings or distribution patterns can you see? How do the two sets of levels match?

Be assured that this activity is an important one. It supplies you with a reference base upon which further information about the mangroves can be built. The influence of the tides upon the plants and animals of the mangroves is a beautiful example of nature working in a logical mode. The tides affect the life processes of all organisms in the intertidal zone: their food gathering, their respiration, their life cycles and their growth. The tides in turn are driven by the movements of the Moon around the Earth and these movements are sequential, predictable, and measurable.

Activity 2. Know your mangroves

To help you to become familiar with some of the more common mangrove species, small teams of 2 or 3 students can prepare fact sheets for different species and present their sheets to the whole class for discussion and display. Your team will in effect become the experts on one particular type of mangrove so that the rest of the class can become familiar with that species through your team's efforts.

The species which the teams can research are as follows

Sonneratia alba                                       Aegialitis annulata (club mangrove)

Avicennia marina(white mangrove)         Rhizophora stylosa (stilt-rooted mangrove)

Ceriops tagal var. australis                      Bruguiera exaristata (red mangrove)

Xylocarpus mekongensis                          Lumnitzera racemosa

Lumnitzera littorea                                  Bruguiera gynmnorrhiza

Osbornia octodonta                                 Aegiceras corniculatum (river mangrove)

Not all mangroves have a common name and often these names (and their use) vary from place to place. All of the species named above are described and illustrated in Brock (1988). The first edition of Brock’s Top End Native Plants describes a tree which he calls Xylocarpus australasicus. This name has been changed and is now called Xylocarpus mekongensis.

Students researching the two Bruguiera species may find it difficult to distinguish one from the other. Consult the book by Wightman (1989) to find minor differences in the shapes of the fruit, flowers and leaves.

In preparing the fact sheets, teams should include

  • identifying features - leaves, flowers, fruit, bark, habit (shape and size)

  • habitat

  • distribution, status (common or not common)

  • Aboriginal and overseas use of tree

  • special features (e.g. Aegialitis annulata excretes salt from salt glands on its leaves).

Illustrations and photographs will aid in identification, and you may need to produce more than one sheet. Consider producing a uniform page layout for the class.

The sheets produced by the class can be photocopied and, with an appropriate cover, bound to produce a field guide for an excursion to a mangrove area.

Activity 3. Conservation -Team Research and Evaluation

By now your team will have gathered as much information as you need for the completion of this activity. Your final tasks are to produce a report on the three aspects of conservation that you were asked to investigate i.e. potential environmental threats to the estuarine environment, preventative measures in place to minimise the threats and steps being taken to ensure future conservation of foreshore ecosystems e.g. mangroves.

Having written part one (the report on the three conservation issues) your team can now discuss the effectiveness of the overall management plans for Darwin Harbour. Your discussions should be analytical and balanced. When examining the information you have gathered, distinguish between statements of intention (often using the word 'action' without any indication of what real 'action' is to be taken) and actual measures in place. Look for legislation, acts of parliament and subsequent departmental regulations that are in operation rather than 'policies' and 'plans'. Once enacted, how are the laws enforced? At the same time, beware of making emotionally loaded statements without evidence to back up your statements.

Prepare a summary of your discussions and make an evaluation of the conservation measures and management strategies that exist for the protection of the marine environment of Darwin Harbour.

Your evaluation should be an analysis of the effectiveness of the various aspects of environmental protection and conservation that you have researched. Make comments and suggestions about any improvements your team think are necessary. Conclude with a general statement about how your team feels regarding the future integrity of  Darwin Harbour wetlands as heritage sites.

Discuss with your teacher the culmination of this activity e.g. sending some of your reports to the local Member of Parliament.

Activity 4. Animal Roles in Ecosystems

Read through the above description of the way in which different animals are affected by tidal movements in the mangrove. Pay particular attention to how the organisms interact with each other and their environment. What plants, animals or other organic materials does each use as a food resource? What are their predators? How do the organisms affect the mangrove ecosystem by their presence? In what ways do animals adapt to the conditions of the mangrove habitat?

Write a magazine article about one particular animal of the mangroves using the above questions as a guide to the life processes that you will describe. In your article include a diagram of a food web which is built around the animal of your choice. You may need to consult other reference sources to gather more data about your subject and to discover more about the nature of ecology. Illustrate the article if possible.

Activity 5. Adaptation

Describe the ways in which different species of mudskippers are adapted to life in the mangroves. Consider body structure, behaviour, choice of habitat, and food gathering techniques in relation to the physical conditions of their surroundings.

Activity 6. Conservation Poster

In teams design and paint a poster that has the conservation of mangroves as its message. Think of an eye-catching slogan that presents mangroves as valuable economic resources and include it in the design.  

 

Other activities

Another source for activities in the mangroves is Claridge, D., & Burnett, J. (1993). Mangroves in focus. Ashmore, Qld.: Wet Paper.

 

1. Mangrove as Forest 2. Mangrove as Plant 3. Mangrove as Habitat 4. Mangrove as Resource 5. Use by Northern Aboriginal Clans  

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