222
WILLIAM NACNAE
Australian gulfs, in New Zealand and at Bunbury are all representative
of the fauna of the local mud flats, an@ though they may contain
tropical genera they contain no tropical species (Womersley and
Edmunds, 1958 ; Macnae, 1966).
This difference between South African and Australian shores may
no doubt be explained by the vagaries of circulation of the warm water
currents off shore.
The strongly flowing Agulhas current impinges on the Natal coast
near Cape St. Lucia and runs south along the edge of the continental
shelf a t a distance of about 5 miles. When approaching East London
where the coast trends more strongly westward, the current gets farther
off shore until near Port Elizabeth it runs some 30 miles out to sea. I n
theory eddies sent off from the current will transgress over the colder
waters of the counter current and bring warm water organisms and
flotsam of tropical origin in shore.
This may occur far to the south. Dr John Muir, a country physician
of Riversdale between Knysna and the Cape, collected seeds of several
tropical plants on local beaches and recorded (1937) finding viable seeds
of Thespesia populnea and of Heritiera littoralis. The former occurs
commonly in northern Natal, the latter is not found south of Inhambane
close to the Tropic of Capricorn. Hence these seeds at least can retain
their viability while floating considerable distances in sea water.
The comparable current off the Australian east coast runs strongly
only off south Queensland and northern New South Wales-southward
it tends to veer away. Clearly it is not so efficient a transporter of drift
material along Australian coasts, but it may well have carried seeds of
Avicennia marina t o New Zealand’s North Island.
Northwards the Kuro Shio transports drift seeds along the Rye-Kyfi
archipelago and is no doubt responsible for the occurrence of mangroves
and the associated fauna in these islands.
B. Biogeographical comment
It is abundantly clear that the littoral fauna and flora of the
Indo-west-Pacific region constitute a unit (Ekman, 1935, 1953), yet
within this region there are quite distinct and definite divisions.
As Hall (1962) has noted, Ekman recognized that the faunistic
centre of thc region is the Malayan archipelago, centred on the southern
tip of the Malayan peninsula, Sumatra, western Java and southwestern Borneo. The farther one moves away from this centre in any
direction the more the fauna becomes progressively impoverished, and
the addition of endemic elements only to a minor extent makes good
the loss of Malayan forms. Such a statement is in general true also of
WILLIAM NACNAE
Australian gulfs, in New Zealand and at Bunbury are all representative
of the fauna of the local mud flats, an@ though they may contain
tropical genera they contain no tropical species (Womersley and
Edmunds, 1958 ; Macnae, 1966).
This difference between South African and Australian shores may
no doubt be explained by the vagaries of circulation of the warm water
currents off shore.
The strongly flowing Agulhas current impinges on the Natal coast
near Cape St. Lucia and runs south along the edge of the continental
shelf a t a distance of about 5 miles. When approaching East London
where the coast trends more strongly westward, the current gets farther
off shore until near Port Elizabeth it runs some 30 miles out to sea. I n
theory eddies sent off from the current will transgress over the colder
waters of the counter current and bring warm water organisms and
flotsam of tropical origin in shore.
This may occur far to the south. Dr John Muir, a country physician
of Riversdale between Knysna and the Cape, collected seeds of several
tropical plants on local beaches and recorded (1937) finding viable seeds
of Thespesia populnea and of Heritiera littoralis. The former occurs
commonly in northern Natal, the latter is not found south of Inhambane
close to the Tropic of Capricorn. Hence these seeds at least can retain
their viability while floating considerable distances in sea water.
The comparable current off the Australian east coast runs strongly
only off south Queensland and northern New South Wales-southward
it tends to veer away. Clearly it is not so efficient a transporter of drift
material along Australian coasts, but it may well have carried seeds of
Avicennia marina t o New Zealand’s North Island.
Northwards the Kuro Shio transports drift seeds along the Rye-Kyfi
archipelago and is no doubt responsible for the occurrence of mangroves
and the associated fauna in these islands.
B. Biogeographical comment
It is abundantly clear that the littoral fauna and flora of the
Indo-west-Pacific region constitute a unit (Ekman, 1935, 1953), yet
within this region there are quite distinct and definite divisions.
As Hall (1962) has noted, Ekman recognized that the faunistic
centre of thc region is the Malayan archipelago, centred on the southern
tip of the Malayan peninsula, Sumatra, western Java and southwestern Borneo. The farther one moves away from this centre in any
direction the more the fauna becomes progressively impoverished, and
the addition of endemic elements only to a minor extent makes good
the loss of Malayan forms. Such a statement is in general true also of