FAUNA AND FLORA OF MANGROVE SWAMPS
165
V. DISTRIBUTION OF MARINE ANIMALS WITHIN THE MANGAL
The fauna of marine animals living within the mangal has two
components: an infauna of burrowing forms; an epifauna of errant or
wandering forms. The burrowing forms are mainly crustacean but
there are also a few bivalves and one genus of fish. The errant forms
include several gastropod molluscs and some crabs.
Gerlach (1958) has shown that nematodes and other small worms
are an important constituent of the burrowing fauna in Brazil but little
is known about the Indo-west-Pacific forms.
Only a few highly specialized polychaetes occur in the strongly
deoxygenated soils of the mangal ; these include several species of
Dendronereis and of Marphysa, M . mossambica Day being the commonest and most widespread (Day, in litt.).
While most species of crab live in the shade of the mangrove trees
and bushes a few have become adapted to living in the bare areas
which develop within and at the upper edges of the mangal.
The animals of marine origin show, as Berry (1964) has pointed
out, two distinct modes of zonation in the mangal. I n Malaya there is,
particularly in the trees and bushes of the seaward fringes, a zonation
affecting those molluscs, mainly snails, which live amongst the leaves
and on the twigs. Secondly there is a zonation of the fauna that is tied
to the surface of the mud, and to burrowing within it.
A. Vertical zonation affecting tree dwelling animals
This mode of zonation is, due to paucity of fauna, not shown over
most of the Indo-west-Pacific zoogeographic region. Only in Malaya
and adjacent areas is it clearly defined.
In eastern Africa and in Queensland only Littorina (Melarapha)
scabra (L.) is found on the leaves of the mangrove trees, and it tends t o
be common only in the seaward fringes.
I n South East Asia several species occur among the leaves, on the
twigs and on the trunks. When disturbed all will drop and suspend
themselves on a cord of thick mucus. Littorina melanostoma (Gray)
climbs to levels well above that reached by even the highest tides. L.
scabra climbs almost but not quite so high. L. carinifera (Menke) and
L. undulata (Gray) occur a t a slightly lower level, at a little below
ordinary high water mark. L. undulata may be found, too, on debris
lying on the surface of the mud. The bivalve Enigmonia rosea (Gray)
is the only other animal normally to be found on the leaves. It occurs
at low levels only on the most seaward trees.
This group of climbing snails all penetrate the mangal, clinging to
the leaves, etc., of the trees forming the lower storeys and reaching
165
V. DISTRIBUTION OF MARINE ANIMALS WITHIN THE MANGAL
The fauna of marine animals living within the mangal has two
components: an infauna of burrowing forms; an epifauna of errant or
wandering forms. The burrowing forms are mainly crustacean but
there are also a few bivalves and one genus of fish. The errant forms
include several gastropod molluscs and some crabs.
Gerlach (1958) has shown that nematodes and other small worms
are an important constituent of the burrowing fauna in Brazil but little
is known about the Indo-west-Pacific forms.
Only a few highly specialized polychaetes occur in the strongly
deoxygenated soils of the mangal ; these include several species of
Dendronereis and of Marphysa, M . mossambica Day being the commonest and most widespread (Day, in litt.).
While most species of crab live in the shade of the mangrove trees
and bushes a few have become adapted to living in the bare areas
which develop within and at the upper edges of the mangal.
The animals of marine origin show, as Berry (1964) has pointed
out, two distinct modes of zonation in the mangal. I n Malaya there is,
particularly in the trees and bushes of the seaward fringes, a zonation
affecting those molluscs, mainly snails, which live amongst the leaves
and on the twigs. Secondly there is a zonation of the fauna that is tied
to the surface of the mud, and to burrowing within it.
A. Vertical zonation affecting tree dwelling animals
This mode of zonation is, due to paucity of fauna, not shown over
most of the Indo-west-Pacific zoogeographic region. Only in Malaya
and adjacent areas is it clearly defined.
In eastern Africa and in Queensland only Littorina (Melarapha)
scabra (L.) is found on the leaves of the mangrove trees, and it tends t o
be common only in the seaward fringes.
I n South East Asia several species occur among the leaves, on the
twigs and on the trunks. When disturbed all will drop and suspend
themselves on a cord of thick mucus. Littorina melanostoma (Gray)
climbs to levels well above that reached by even the highest tides. L.
scabra climbs almost but not quite so high. L. carinifera (Menke) and
L. undulata (Gray) occur a t a slightly lower level, at a little below
ordinary high water mark. L. undulata may be found, too, on debris
lying on the surface of the mud. The bivalve Enigmonia rosea (Gray)
is the only other animal normally to be found on the leaves. It occurs
at low levels only on the most seaward trees.
This group of climbing snails all penetrate the mangal, clinging to
the leaves, etc., of the trees forming the lower storeys and reaching