FAUNA AND FLORA OF MANGROVE SWAMPS
123
and Tilapia mossambica Peters) in fish ponds developed in mangrove
areas. The blue-green and green algae seem to show substratum
preferences and the former may convert a soil into a suitable habitat
for the latter. The blue-greens prefer a soft, hydrophilic, biologically
active mud with much organic matter, whereas green algae prefer a
more or less solid soil with an adequate supply of nitrate and phosphate.
These inorganic radicles may have been released by the oxidative
action of blue-green algae and bacteria on humus in the soil, converting
ammonia to nitrate, and releasing bound phosphate. The faeces of the
animals living in the mangal are an important constituent of the
surface layers of the soil and must constitute a source of nitrate, phosphate and other substances for the photosynthetic micro-organisms of
the soil.
Sulphatereducing bacteria flourish in anoxic conditions and are completely
anaerobic. They obtain the sulphate from the soil water or from
organic sulphur-containing debris. The presence of hydrogen sulphide
reduces the ferric compounds in the soil to various hydrated ferrous
sulphides which give mangrove soils their characteristic black colour.
Only the surface layers to a depth of a few centimetres are oxygenated
and show amounts decreasing with depth. Tube dwelling thalassinidean prawns, such as species of Upogebia and Thnlassina, by their
activities of fanning a current of water through their burrow systems
oxygenate the soils immediately surrounding the burrow. Alplieid
prawns create mazes of shallow burrows in water-logged soil and help in
keeping the upper layers oxygenated and so assist the bacteria, and
other organisms, in making available the ions required by higher plants.
It would seem, too, that the presence of shell or other calcareous
debris in the soil is essential for the proper development of mangroves,
particularly in areas of higher salinity. It is noteworthy that in
citrus orchards on the Sundays River Valley (near Port Elizabeth,
South Africa) where, perforce, the orchards are often irrigated with
brackish water derived from Cretaceous marine shales, a generous
dressing of lime prevents the scorching of the leaves on the trees. The
presence of calcium ions seems to reduce or prevent any damage
which may be done by excess of sodium ions, because calcium reduces
the level of internal sodium.
When the mangal has been cleared by cutting out the timber, what
happens to the mangrove soils? Why do recently cleared areas often
become a desert, useful only for salt production? Such areas may be
seen along the shores of the Gulf of Thailand both west and east of
Bangkok. When cleared areas have been used for prawn and fish
Only in the upper layers is the soil well oxygenated.
123
and Tilapia mossambica Peters) in fish ponds developed in mangrove
areas. The blue-green and green algae seem to show substratum
preferences and the former may convert a soil into a suitable habitat
for the latter. The blue-greens prefer a soft, hydrophilic, biologically
active mud with much organic matter, whereas green algae prefer a
more or less solid soil with an adequate supply of nitrate and phosphate.
These inorganic radicles may have been released by the oxidative
action of blue-green algae and bacteria on humus in the soil, converting
ammonia to nitrate, and releasing bound phosphate. The faeces of the
animals living in the mangal are an important constituent of the
surface layers of the soil and must constitute a source of nitrate, phosphate and other substances for the photosynthetic micro-organisms of
the soil.
Sulphatereducing bacteria flourish in anoxic conditions and are completely
anaerobic. They obtain the sulphate from the soil water or from
organic sulphur-containing debris. The presence of hydrogen sulphide
reduces the ferric compounds in the soil to various hydrated ferrous
sulphides which give mangrove soils their characteristic black colour.
Only the surface layers to a depth of a few centimetres are oxygenated
and show amounts decreasing with depth. Tube dwelling thalassinidean prawns, such as species of Upogebia and Thnlassina, by their
activities of fanning a current of water through their burrow systems
oxygenate the soils immediately surrounding the burrow. Alplieid
prawns create mazes of shallow burrows in water-logged soil and help in
keeping the upper layers oxygenated and so assist the bacteria, and
other organisms, in making available the ions required by higher plants.
It would seem, too, that the presence of shell or other calcareous
debris in the soil is essential for the proper development of mangroves,
particularly in areas of higher salinity. It is noteworthy that in
citrus orchards on the Sundays River Valley (near Port Elizabeth,
South Africa) where, perforce, the orchards are often irrigated with
brackish water derived from Cretaceous marine shales, a generous
dressing of lime prevents the scorching of the leaves on the trees. The
presence of calcium ions seems to reduce or prevent any damage
which may be done by excess of sodium ions, because calcium reduces
the level of internal sodium.
When the mangal has been cleared by cutting out the timber, what
happens to the mangrove soils? Why do recently cleared areas often
become a desert, useful only for salt production? Such areas may be
seen along the shores of the Gulf of Thailand both west and east of
Bangkok. When cleared areas have been used for prawn and fish
Only in the upper layers is the soil well oxygenated.