Biology Reference
In-Depth Information
projections, and impacts on diversity. Australia, similar to trends else-
where on Earth, has warmed by about 0.8 8C over the last century.
Projections are that, by 2030 and 2070, annual average temperatures
will increase (relative to 1990) by 0.4-2.0 8C, and 1.0-6.0 8C, respect-
ively. Predictions for changes in rainfall are even more difficult, although
increases in potential evaporation and reductions in the extent and duration
of snowfall over much of the continent are likely. Hughes discusses the
effects of climate change on various ecosystems. We select one example,
i.e., coral reefs, which are of particular concern to Australia because the
Great Barrier Reef is the largest system of coral reefs on Earth. In 1998
alone, approximately 16% of the living corals on Earth died, and in the
Indian Ocean mortality was more than 40%. The main culprit was coral
bleaching, i.e., the loss of symbiotic zooxanthellae essential for the survival
of corals, due to increased temperatures. Modelling showed that bleaching
comparable in strength to that in 1998 will become common within 20
years. It is impossible to predict how many species will disappear when
reefs are radically reduced in size. One reason for this is that the vast
majority of species are very small invertebrates.
Lower invertebrates are not included in the estimates given by
Freeman and Herron (
2004
), which is not surprising because estimates
for such small organisms are practically impossible; not to mention the fact
that most species have not even yet been described, and this refers also
and particularly to parasites, which probably represent the majority of
species on Earth. On pp. 43-46 I have given some estimates for species
numbers based on surveys of marine fish. The approximately 14 000
species of marine fish probably have at least 150 000 species of parasites,
and the parasite fauna of many other groups of vertebrates is at least as rich.
Rohde (
2001c
) gives data for various groups. The Platyhelminthes (flat-
worms) alone comprise at least 80 000 species, of which a minimum of
65 000 are parasitic. The number of described species is only a small fraction
of these (several thousand), and estimates of extinction rates are impossible
because species are small and lack substantial hard skeletons, i.e., they do
not fossilize. Estimates of the number of nematode species vary greatly, not
only because they are small and many of them are parasitic, but also because
a vast number (possibly millions) are thought to live in habitats which have
hardly been examined, such as the deep sea and the sand fauna of beaches.
The interstitial sand fauna (meiofauna) of coasts, which consists of very
small animals, has been examined more or less thoroughly only at one
locality, the island of Sylt in the North Sea; 652 species have been recorded
to date, and another 200 are thought to exist (Armonies and Reise
2000
).
