FAUNA AND FLORA O F MANGROVE SWAMPS
117
together. But what determines which will occur is difficult to say. In
bays protected from the prevailing winds, but not necessarily from
other winds, pure stands of Sonneratia develop. Often these show no
regeneration at all, nor any conspicuous fauna (Figs. 27 and 28).
Along river banks and in other areas where the salinity is reduced
by abundant fresh water, S. caseolaris is dominant. This species also
occurs alongside creeks a t the back of the mangal.
De Haan recognizes a t Tjilatjap an avicennia-sonneratia alba
association which develops in zone Al, on soils which are mostly level,
soft and deep. These are young unconsolidated soils. The tree layer
comprises Avicenniu marina and Sonneratia alba with an undergrowth
of Acanthus ilicifolius and of saplings of Aegiceras corniculatum.
This association is compounded of my sonneratia zone and seaward
avicennia zone.
Muller and Hou-Liu (1966) have described suspected hybrids
between 8. alba and 8. caseolaris and between X. alba and X. ovata.
These were found in the mangals of Brunei.
Sonneratia would appear to prefer warmer conditions than do most
of the others-it does not come south of Inhambane on the Moqambique coast nor south of Innisfail in Queensland.
This zone corresponds to Watson’s class (i).
1. Bostrychietum
The pneumatophores of Avicennia, and of Sonneratia, the prop roots
of Rhizophora and the knee roots of Bruguiera gymnorhiza may locally
be densely covered with a bostrychietum which is an association of
algae comprising several species of the genera Rostrychia, Caloglossa,
Catenella and of Murrayella. For the identity of these see Post (1963,
1964a,b, 1966), where one will find detailed descriptions and distributions of the various species. Many of these appear to be widespread in
the Indo-west-Pacific, not only from Africa to Australia and Japan, but
also from the cool waters of southern Africa and Victoria to the tropics.
A problem associated with this association is its relatively localized
distribution within the seaward fringe of a mangal. The roots of one
group of trees will be thickly clothed with algae and neighbouring trees
will be bare of them. Does their presence interfere with the proper
functioning of the roots, and do the roots, in due course, cast off the
bark invested by the algae?
The presence of this association on the roots of the mangroves
allows comparisons with rocky shores, for this association occurs too
on the shaded side of, and under, overhanging portions of the rocks,
just a t or just above or just below the level colonized by rock oysters.
117
together. But what determines which will occur is difficult to say. In
bays protected from the prevailing winds, but not necessarily from
other winds, pure stands of Sonneratia develop. Often these show no
regeneration at all, nor any conspicuous fauna (Figs. 27 and 28).
Along river banks and in other areas where the salinity is reduced
by abundant fresh water, S. caseolaris is dominant. This species also
occurs alongside creeks a t the back of the mangal.
De Haan recognizes a t Tjilatjap an avicennia-sonneratia alba
association which develops in zone Al, on soils which are mostly level,
soft and deep. These are young unconsolidated soils. The tree layer
comprises Avicenniu marina and Sonneratia alba with an undergrowth
of Acanthus ilicifolius and of saplings of Aegiceras corniculatum.
This association is compounded of my sonneratia zone and seaward
avicennia zone.
Muller and Hou-Liu (1966) have described suspected hybrids
between 8. alba and 8. caseolaris and between X. alba and X. ovata.
These were found in the mangals of Brunei.
Sonneratia would appear to prefer warmer conditions than do most
of the others-it does not come south of Inhambane on the Moqambique coast nor south of Innisfail in Queensland.
This zone corresponds to Watson’s class (i).
1. Bostrychietum
The pneumatophores of Avicennia, and of Sonneratia, the prop roots
of Rhizophora and the knee roots of Bruguiera gymnorhiza may locally
be densely covered with a bostrychietum which is an association of
algae comprising several species of the genera Rostrychia, Caloglossa,
Catenella and of Murrayella. For the identity of these see Post (1963,
1964a,b, 1966), where one will find detailed descriptions and distributions of the various species. Many of these appear to be widespread in
the Indo-west-Pacific, not only from Africa to Australia and Japan, but
also from the cool waters of southern Africa and Victoria to the tropics.
A problem associated with this association is its relatively localized
distribution within the seaward fringe of a mangal. The roots of one
group of trees will be thickly clothed with algae and neighbouring trees
will be bare of them. Does their presence interfere with the proper
functioning of the roots, and do the roots, in due course, cast off the
bark invested by the algae?
The presence of this association on the roots of the mangroves
allows comparisons with rocky shores, for this association occurs too
on the shaded side of, and under, overhanging portions of the rocks,
just a t or just above or just below the level colonized by rock oysters.