Vol
8 No 3
Dec 2001
chek jawa's
wet wonderland
aqua-tion for life roles of
water in life
where water
meets the lands
fishes of the Park
dispersal by h2o
seeds dispersed by water
some interesting notes on the pacific golden
plover
10th international coastal cleanup 2001 and
5th mangrove cleanup
young ecologists@
sungei buloh nature park
an ode to a turtle
|
|
dispersal
by H2O |
ali
ibrahim
conservation officer
|
| Walking
along the beach especially after high tide can be a learning experience
if you were to ponder upon what the eye can spot—fruits, seeds
and even seedlings adrift amongst the flotsam and jetsam. Have you
ever wondered: "Has this been going on for millions of years?"
"Where did this living assortment come from?" and "How
did they arrive?" |
It
was Sir Isaac Newton who once said: "I don't know what I may seem
to the world, but, as to myself, I seem to have been only like a boy
playing on the sea shore, and diverting myself in new and then finding
a smoother pebble or a prettier shell than ordinary..." (continued
below) |
Yes, this regenerative cycle through dispersal has been going on since the
dawn of time. These botanical gems on the beach originated not only from
our own shores but from the neighbouring archipelago and even ocean-drifted
ones. Let's take a look at the amazing mechanism involved.
Besides mangroves, water-dispersed vegetation is confined to the fringes
of beaches and inland watercourses. With sufficient buoyancy and a long
period of impermeability to water, their propagules can drift as far and
no farther than is necessary to stay viable. The classic example is the
coconut (Cocos nucifera) which can keep it afloat because its thick
fibrous husk contains air. The fruit will travel a long distance, eventually
ending up as a sprouted palm on some coast months later.
Api-api bulu
Avicennia rumphiana
Api-api ludat
Avicennia officinalis
Api-api putih
Avicennia alba
Bakau putih
Bruguiera cylindrica
Bakau minyak
Rhizophora apiculata
Bakau kurap
Rhizophora mucronata
Pong-pong
Cerbera odollam
|
The buoyant propagules of all mangroves are adapted to dispersal by
water currents. This period of floating may be as brief as four days,
but much longer periods are more usual. The mangrove species belonging
to the family of Rhizophoraceae have spongy hypocotyls with air-filled
walls to make it light-weight. Seedlings contained in the fruits of
Api-api (Avicennia) have dense, fibrous air-filled rootlets
that keep themselves water-borne for a period of time. Leathery fruits
of Perepat, Berembang and Gedabu (Sonneratia) with persistent
calyces are enclosed by water impermeable walls. In addition, within
the fleshy pulp their floatable seeds are protected by resistant seed
coats.
For any dispersed seedlings to get established, they have to find
suitable substrates to grow in and be able to withstand wave action.
With other seedlings, they simply develop right on the spot where
they drop, within the ambit of their parent trees.
The term 'viviparous' is used to indicate the precocious germination
and growth of the embryo while it is still enclosed by the fruit wall
and while the fruit is still attached to the mother tree. This is
an adaptation to ensure the seedling's higher chances of survival
prior to its dispersal and precarious establishment in soft mud and
tidal inundation. It is not surprising that in some instances, even
wind-dispersed fruits and seeds can be aided by water agent through
the principle of flotation.
Amongst the colourful tapestry of living archive on the beach mentioned
earlier were the curious but almost similar looking fibrous drupes
of the Nipah (Nypa fruticans) and the Sea Screw-pine (Pandanus
tectorius). Fruits of Pong-pong (Cerbera odollam) having
lost their red peel appeared like worn-out tennis balls. The almond-shaped
fruits with lateral ridges belonging to the Ketapang (Terminalia
catappa) are green to maroon when fresh but turning brown and
woody when aged. The chocolate-brown and smooth Dungun (Heritiera
littoralis) fruit actually looked like the hull of a boat with
a small keel. The squarish turnip-looking fruit of Putat laut (Barringtonia
asiatica) seemed most bizarre when compared to the rest of the
scattered fruits. Finally, the community of angular and corky seeds
of Nyireh (Xylocarpus granatum) were another odd puzzle when
seen with several pieces of thern side by side.
Needless to say, the list goes further! But for the purpose of this
article, only plants belonging to either the mangrove or beach habitats
were mentioned. |
Nyreh
Xylocarpus granatum
Ketapang
Terminalia catappa
Dungun
Heritiera
littoralis
Perepat
Sonneratia alba
Berembang
Sonneratia caseolaris
Putat laut
Barringtonia asiatica
Nipah
Nypa fruticans
Screw-pine
Pandanus
tectorius |
(continued
from above) ".... whilst the great ocean of truth lay all undiscovered
before me." (Newton) |
wetlands