Unit 7   Learning about Mangroves            

Authors：Wen-Shiung Lu(呂文雄)Jen-He Chen(陳仁和)    Translator:Gloria Fung

1. Green Red Trees

At the beginning of June, our school organized a field trip.  The bus stopped in front of Jhenwu Temple (真武殿) in Cingluo Village (青螺村) in Husi Township (湖西鄉).  Our teacher said, “The little hill on the east side is called Dingji Mountain (鼎臍山); the piece of wetland you see to the west of the hill is the largest wetland in Penghu – Cingluo Wetlands (青螺溼地).  Today we are here to learn about mangroves.”
    We looked to our left and right but we could not see any red trees.  Our teacher explained that the word “mangrove” (or “red trees” in Chinese) originally came from the plant “crimson flowered mangrove (紅茄苳).” The wood from the tree is red in color and its bark can be used to make red dye.  The Malays call it “Red Bark Tree.”  In Chinese, it is called “Red Tree.”  The red mangrove grows in the mudflats in the intertidal areas near mouths of rivers or marine shorelines.  This is why plants which grow in similar conditions are all referred to as “mangroves.”

2. Swamps along the Seashore

We walked towards the Bird-Watching Pavilion (賞鳥亭).  In the swamp on the southeast side of the breakwater was a large green mangrove bush. In the low tide, the mangroves stood on the dry muddy ground.  During high tide, the lower halves of the trees would be immersed in the brackish water of the seashore, making them look like a forest in water.  For this reason, mangroves are also known as tidal forests.
    Our teacher said, “Mangroves grow in unique environments.  First, they grow in seawater with high salinity.  Secondly, not much air can go into the mud of the mudflats in which they grow. Where mangroves live, there are high and low tides two times a day; this means in the intertidal areas there are great changes in temperature and humidity.  In order to survive, mangroves have developed some rather special features.  Let us observe these carefully.”

3. Studying the Grey Mangrove (海茄苳)

We noticed that all over the mudflat were things which looked like short sticks.  According to our teacher, that was one of the characteristics of the Grey Mangrove – breathing tubes.  The roots of the Grey Mangrove grow sideways so that the plant is spread over a larger site. Then, growing up from the roots are many vertical breathing tubes.  The breathing tubes not only provide support for the plant, but also ensure that there is adequate exchange of oxygen.
    The leaf of the Grey Mangrove is shiny.  This prevents evaporation.  The back of the leaf is grayish green.  Its function is to secrete salt.  When we observed carefully, we noticed salt crystals, which tasted salty when we licked them with our tongues.  The extra salt in the plant is concentrated in the aging leaves.  When the leaves fall, the plant disposes of the salt at the same time.
    The flower of the Grey Mangrove is an orangey yellow, with four petals.  It is roughly 0.5 cm in size and is fragrant.  The fruit, which is shaped like a flattened sphere similar to the broad bean, contains buoyant materials.  This allows the fruit to drift in the water to seashores farther away where it puts downs roots and germinates.  The fruit matures in October. During this time (June) of the year, it was almost impossible to see the fruit.

4. Studying the Black Mangrove (欖李）

From the Bird-Watching Pavilion, we walked eastward.  We saw a whole cluster of plants that were emerald green in color.  Those were Black Mangroves.  The leaf of the Black Mangrove is shaped like an upended egg with a slight indentation in front.  It looks a bit like the roe of the sea mullet.  The leaf feels a lot thicker than the leaf of the Grey Mangrove – that, surely, would help the plant to keep its moisture.  It is also efficient at secreting salt.  There were a lot of little white flowers with five petals among the bushes of Black Mangroves.  It is a well-known nectariferous plant.  Its fruit is longish oval, with a diameter of about 1 cm.  The inner layer of the seed wall is hard, while the outer layer is spongy.  This enables the fruit to disperse by water.
    Under the clumps of Black Mangroves, we saw a lot of little caves.  These turned out to be the homes of the large and ferocious blue land crab (圓軸蟹). The crabs have brown bodies; the two claws are of different sizes; but they look really sturdy and strong, nevertheless.

5. Studying the Red Mangrove I (Stilt Mangrove紅海欖)

Following the ridges, we walked down to the mudflats on the east side.  There we saw the Red Mangrove (stilt mangrove紅海欖). It has well-developed breathing tubes which have grown out of the trunk of the plant and have turned downwards to become prop roots.  To our surprise, we found a lot of seedlings (propagule) attached to the plants.  These are covered all over with air holes that help the plant to breathe.  The leaf is particularly large, with soft bristles.  Quite a lot of periwinkles were playing on the leaves.  Most of the flowers had withered; we saw only one or two.  Both the white flower and yellow calyx have four petals.

6. Studying the Red Mangrove II (Kandelia Obovata水筆仔)

Near the stilt mangrove, we found another species of Red Mangrove known as Kandelia Obovata (水筆仔). There were a lot of white flowers with five petals; they looked a little like starfish.  The leaves are longish oval, smaller than that of the stilt mangrove, but bigger than the leaves of the Grey Mangrove and Black Mangrove.  Prop roots grow out of the base of the trunk to anchor the plant.
    There are four types of mangroves at Qing Luo Wetlands.  Of these, the Grey Mangrove and Black Mangrove do not have viviparous seedlings, which are found in both types of Red Mangroves. However, we were unable to see any of the seedlings of the Kandelia Obovata (水筆仔) even though we spent a lot of time looking.  It turned out that May to July is when the flowers of Kandelia Obovata (水筆仔) bloom.  The fruit becomes mature in August and September; the viviparous seedlings start to grow round about October and November.  The seedlings become mature in March and April of the following year.  These will fall to the ground and grow into saplings.

7. Ecology Classroom

On the mudflat we found many creeper shells (海蜷), as well as fiddler crabs (粗腿綠眼招潮).  The male crabs have one large and one small claw, but the females have two very small claws.  We also saw some grapsid crabs (台灣厚蟹), whose claws are of the same size.  Numerous young sea mullets were swimming in the little creek, and, on the far side of the mudflats some Little Egret、Marsh Sandpiper were busy looking for food.
    Around the mudflat, we also saw a lot of plants which can grow well in dry, saline environments. The herbaceous seepweed or seablite (鹽定) grows prostrate on the ground -- its leaves often have a red tint.  The bluegreen saltbush (台灣濱藜) has shiny, silvery, scaly hairs; among the leaves of the shoreline seapurslane (濱水菜) are lovely purplish red flowers; the seashore dropseed (鹽地鼠尾粟) has needlelike panicle.

Qing Luo Wetlands is a rich resource for ecological education.  Every season comes with its own unique features which we will do well to observe carefully.