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Symbiosis
Living together on Chek Jawa
Eating and being eaten is not the only way living things interact
on Chek Jawa. Many live in close association with one another to increase
the chances of survival of one or both of them. This inlcues animals
which are quite different and even plants living inside animals. Such
a relationship is called symbiosis.
 Mutualism:
In mutualism, both partners benefit.
The Carpet anemones at Chek Jawa harbour in their
tentacles, microscopic algae (called zooxanthellae) which make food
through photosynthesis. The algae share the food produced in exchange
for shelter and nutrients from the anemone.
Tiny transparent shrimps (about 1cm) are sometimes seen among the
Carpet anemone's tentacles. It is not certain how they avoid being
stung by the tentacles. The shrimps find refuge and in turn, they
may help keep the Carpet anemone clean.
 Commensalism:
In commensalism, one living thing benefits at no expense
or gain to the other.
When a tiny brittle star shelters inside a sponge, it enjoys a continuous
flow of food and oxygen. But it makes no difference to the sponge.
More about sponges and the animals that live
with them.
 The
Slipper snail (Crepidula sp.) is white and looks like a clam.
It often settles on the inside of a shell occupied by a hermit crab.
The snail enjoys the food and oxygen brought in with the flow of water
generated by the hermit crab. The snail's presence, however, probably
makes no difference to the hermit crab.
Other examples of commensalism include:
The little sea anemone that hitches a ride
on a whelk's shell
 Parasitism:
In parasitism, one living thing gains considerably at
the expense of the other.
 For
example, the parasitic barnacle Thompsonia littoralis grows
through the host crab like a root system, eventually breaking through
the joints to produce egg sacs as shown in the photo at right. The
parasite does not kill the crab but affects its reproductive system
so it becomes infertile. For more about barnacles
in general.
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Links
The
Secret Life of Barnacles by Phil Rainbow on the Fathom website: more
detailed by still easy introduction with lots of photos; including a grissly
account of the effects of Sacculina on a crab.
Other references
- Tan, Leo W. H.
& Ng, Peter K. L., 1988. A Guide to Seashore Life. The Singapore
Science Centre, Singapore. 160 pp. online
version
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