FAUNA AND FLORA OF MANGROVE SWAMPS
221
killing frosts. I n South Africa they grow well at the Bashee estuary
where the average daily minimum in July is 12°C and the minimum
recorded in thirty-seven years is 4.4"C, but not at East London where
the average daily minimum in July is 10°C and the minimum recordcd
in sixty-eight years is 2.8"C. This suggests that an absolute minimum
of around 4°C is the extreme that can be tolerated. The yearly mean at
Bashce is 19"C, at East London 17*7"C, and these too are almost
certainly significant-but howl
As a contrast A . marina at Western Port Bay is growing in a region
where the average daily minimum for July is 4°C and the lowest
temperature recorded is 0°C (figures for Melbourne, Australia, some
45 miles away).
I n the Northern Hemisphere the local populations would appear to
bc less tolerant. Oyama (1950) reports that the lowest temperature
recorded in the Yaeyama Islands is 15°C and the average winter
temperature 17-22°C. No doubt the Ryii-Kyii Islands show a comparable range. This is very similar to the temperature regimen at
Inhaca and the Bay of Lourenpo Marques a t a similar latitude in the
Sout hern Hemisphere.
Clearly the Victorian and New Zealand demes of A . marina are
much more low-temperature-tolerant than either the eastern African or
east Asiatic demes.
In South Africa, Day et al. (1952) and other workers have shown that
tropical animals extend farther south in estuaries than others characteristic of open coasts. Macnae (1963) has traced the southward
extension of the animals associated with the mangroves at Inhaca and
has shown that many of them occur in the well-developed and wellzoned mangals at the estuary of the Umngazana river some 18 km south
of Port St John's. A few only go farther, and several of these reach
south coast localities. Two elements have to be distinguished at
Inhaca: a tropical element with species of Sesarma and Uca, with
Cerithidea decollata, Peronia peroni and Terebralia palustris ; and a
southern element with Upogebia africana and Sesarma catenata. The
latter, naturally, extend farther to the south. The former group have
mostly dropped out before or reach their limit a t Knysna.
This process clearly operates too in Japan where tropical genera and
species are common in the Inland Sea and extend northwards in
estuaries along Honshu Island.
In Australia the fauna associated with the mangroves in Sydney
Harbour is a depauperate tropical one-all the species recorded (see
Dakin et al., 1953) being from Queensland (Macnae, 1966). On the other
hand, the fauna of the mangals in Western Port Bay, in the South
221
killing frosts. I n South Africa they grow well at the Bashee estuary
where the average daily minimum in July is 12°C and the minimum
recorded in thirty-seven years is 4.4"C, but not at East London where
the average daily minimum in July is 10°C and the minimum recordcd
in sixty-eight years is 2.8"C. This suggests that an absolute minimum
of around 4°C is the extreme that can be tolerated. The yearly mean at
Bashce is 19"C, at East London 17*7"C, and these too are almost
certainly significant-but howl
As a contrast A . marina at Western Port Bay is growing in a region
where the average daily minimum for July is 4°C and the lowest
temperature recorded is 0°C (figures for Melbourne, Australia, some
45 miles away).
I n the Northern Hemisphere the local populations would appear to
bc less tolerant. Oyama (1950) reports that the lowest temperature
recorded in the Yaeyama Islands is 15°C and the average winter
temperature 17-22°C. No doubt the Ryii-Kyii Islands show a comparable range. This is very similar to the temperature regimen at
Inhaca and the Bay of Lourenpo Marques a t a similar latitude in the
Sout hern Hemisphere.
Clearly the Victorian and New Zealand demes of A . marina are
much more low-temperature-tolerant than either the eastern African or
east Asiatic demes.
In South Africa, Day et al. (1952) and other workers have shown that
tropical animals extend farther south in estuaries than others characteristic of open coasts. Macnae (1963) has traced the southward
extension of the animals associated with the mangroves at Inhaca and
has shown that many of them occur in the well-developed and wellzoned mangals at the estuary of the Umngazana river some 18 km south
of Port St John's. A few only go farther, and several of these reach
south coast localities. Two elements have to be distinguished at
Inhaca: a tropical element with species of Sesarma and Uca, with
Cerithidea decollata, Peronia peroni and Terebralia palustris ; and a
southern element with Upogebia africana and Sesarma catenata. The
latter, naturally, extend farther to the south. The former group have
mostly dropped out before or reach their limit a t Knysna.
This process clearly operates too in Japan where tropical genera and
species are common in the Inland Sea and extend northwards in
estuaries along Honshu Island.
In Australia the fauna associated with the mangroves in Sydney
Harbour is a depauperate tropical one-all the species recorded (see
Dakin et al., 1953) being from Queensland (Macnae, 1966). On the other
hand, the fauna of the mangals in Western Port Bay, in the South