FATJNA AND FLORA O F MANGROVE SWAMPS
79
Inhaca Island off Lourenyo Marques, and of 279 m on Moreton Island
a t the same latitude in Queensland. Rivers entering the sea in these
dune regions are deflected northwards and large bays develop behind
the growing tips of the dune systems. The sheltered parts of Durban
Bay, of the Bay of Lourenpo Marques and of Moreton Bay are, or until
recently were, occupied by well-developed and well-zoned mangals.
Off Africa, reefs,
mostly fringing reefs, are more or less continuous from Pebane in north
central Mopmbique to Somalia. Off Australia, the Great Barrier Reef
is much better known.
I n many areas the sea is shallow and the short but quite high waves
disturb the bottom close to the beach making the sea turbid so that
corals are rare. The shores do not develop high dunes ; instead, one
finds systems of cheniers, low dunes rarely reaching elevations of 20 m
and running approximately parallel to one another and to the present
shore line. These may occur in several sequences (see Fig. l l ) , especially
where the deltas of large rivers bring down, or have in the past brought
down, quantities of alluvium which is sorted by wave action and the
sand deposited on the cheniers and the finer material elsewhere. Such
a succession of cheniers seen .from the air resembles a series of giant
ripple marks.
The most seaward chenier is typically colonized just above high
water mark by a narrow zone, often only one to four trees in width, of
Casuarina equisetifolia L. These trees also occur in a similar single series
on relatively stable sandy coastlines along oceanic or other shores
exposed to wave action. The most famous example of this occurs
along almost the entire east coast of the Malay Peninsula (Watson,
1928). Shorter examples are common on all suitable tropical shores of
the Indo-west-Pacific. These narrow zones of Casuarinq equisettfolia
give the impression of having been planted by man. Why else would
they be so regular? Although provision of wind breaks and dune
binding has been achieved by planting these trees on coastal dunes on
Mauritius between 1945 and 1950 (Sauer, 1962), these long, continental,
very narrow belts of Casuarina are not there by human design.
Small rivers are deflected northwards in the southern hemisphere
and southwards in the northern by the growing tips of cheniers or
beach ridges and they may be closed off. Between the successive
cheniers the lows are sometimes under freshwater influence, becoming
extensive swamps of reeds, sedges or papyrus ; or open l 1 ponds ” with
water lilies, floating ferns mainly species of Azolla, and nowadays the
alien water hyacinth (Eichhornia crassipes (Mart.) Solms.), imported
from America. Sometimes the lows are brackish, under marine influence
Farther north reefs of coral develop off shore.
79
Inhaca Island off Lourenyo Marques, and of 279 m on Moreton Island
a t the same latitude in Queensland. Rivers entering the sea in these
dune regions are deflected northwards and large bays develop behind
the growing tips of the dune systems. The sheltered parts of Durban
Bay, of the Bay of Lourenpo Marques and of Moreton Bay are, or until
recently were, occupied by well-developed and well-zoned mangals.
Off Africa, reefs,
mostly fringing reefs, are more or less continuous from Pebane in north
central Mopmbique to Somalia. Off Australia, the Great Barrier Reef
is much better known.
I n many areas the sea is shallow and the short but quite high waves
disturb the bottom close to the beach making the sea turbid so that
corals are rare. The shores do not develop high dunes ; instead, one
finds systems of cheniers, low dunes rarely reaching elevations of 20 m
and running approximately parallel to one another and to the present
shore line. These may occur in several sequences (see Fig. l l ) , especially
where the deltas of large rivers bring down, or have in the past brought
down, quantities of alluvium which is sorted by wave action and the
sand deposited on the cheniers and the finer material elsewhere. Such
a succession of cheniers seen .from the air resembles a series of giant
ripple marks.
The most seaward chenier is typically colonized just above high
water mark by a narrow zone, often only one to four trees in width, of
Casuarina equisetifolia L. These trees also occur in a similar single series
on relatively stable sandy coastlines along oceanic or other shores
exposed to wave action. The most famous example of this occurs
along almost the entire east coast of the Malay Peninsula (Watson,
1928). Shorter examples are common on all suitable tropical shores of
the Indo-west-Pacific. These narrow zones of Casuarinq equisettfolia
give the impression of having been planted by man. Why else would
they be so regular? Although provision of wind breaks and dune
binding has been achieved by planting these trees on coastal dunes on
Mauritius between 1945 and 1950 (Sauer, 1962), these long, continental,
very narrow belts of Casuarina are not there by human design.
Small rivers are deflected northwards in the southern hemisphere
and southwards in the northern by the growing tips of cheniers or
beach ridges and they may be closed off. Between the successive
cheniers the lows are sometimes under freshwater influence, becoming
extensive swamps of reeds, sedges or papyrus ; or open l 1 ponds ” with
water lilies, floating ferns mainly species of Azolla, and nowadays the
alien water hyacinth (Eichhornia crassipes (Mart.) Solms.), imported
from America. Sometimes the lows are brackish, under marine influence
Farther north reefs of coral develop off shore.