ANTARUTIU BENTHOS
39
mostly on the shelf. The two genera Haliclona (with 20 species) and
Adocia (with seven species) are the best represented genera.
The Poecillosclerida as might be expected, is as well represented in
the Antarctic as it is elsewhere, with 124 Antarctic species grouped in
47 genera. Most of these are widely distributed genera, with strong
Antarctic representation. Many are circumpolar in distribution and
seem to be related to the faunas of the Falkland Islands and southern
South America.
Burton (1932, p. 369) brought together the available information
on the breeding seasons of Antarctic sponges. Information was available for 46 species, and although the records were too incomplete to
enable definite conclusions to be reached, the indications given lead to
some tentative deductions. There does not seem to be any major common breeding season. Some species seem to be breeding in any particular month. It also appears that most species of Calcarea breed
throughout the year.
Burton believed that the Antarctic sponges showed to a marked
degree a free-living habit, extremely rare amongst adult sponges
elsewhere. Most of the evidence seems circumstantial but the arguments seem strong that some of the species considered by Burton are
not normally attached to a substrate.
Koltun (1968) has shown the degree to which the free siliceous
spicules of sponges occur in bottom sediments. From a study of the
upper horizons of sediment cores in the Indian Ocean sector of the
Southern Ocean he was able to demonstrate that siliceous spicules were
extremely common. On the continental shelf and slope of Antarctica
and in the adjacent ocean bottoms Koltun found areas containing from
100 to 300 spicules/cm2. On the shelf itself some areas produced more
than 300 spicules/cm2. In these areas silica was found to make up from
50 to 70% of the actual sediment and in places the surface " looks like
spicular felt 65 cm thick ". Koltun records such sediments off the
Banzare Coast, in the Davis Sea, off Lars Christensen Coast, MacRobertson Land and Kronprins Olav Kyst. The main contributing
sponge genera are Rosella, Tetilla and Cinachyra. A very similar type
of formation occurs in parts of McMurdo Sound (Bullivant, 1967).
Farther north from the Antarctic Continent Koltun found a steady fall
off in the number of spicules, ranging between 10 to 100 spicules/cm2.
In the southern part of the Indian Ocean the general figure is less than
10/cm2, although this figure rises considerably around the Subantarctic
Islands and around shallow water banks.
Sponges are only extremely abundant in the Antarctic down to
between 600 and 600 m, the limit being usually fairly abrupt. Around
39
mostly on the shelf. The two genera Haliclona (with 20 species) and
Adocia (with seven species) are the best represented genera.
The Poecillosclerida as might be expected, is as well represented in
the Antarctic as it is elsewhere, with 124 Antarctic species grouped in
47 genera. Most of these are widely distributed genera, with strong
Antarctic representation. Many are circumpolar in distribution and
seem to be related to the faunas of the Falkland Islands and southern
South America.
Burton (1932, p. 369) brought together the available information
on the breeding seasons of Antarctic sponges. Information was available for 46 species, and although the records were too incomplete to
enable definite conclusions to be reached, the indications given lead to
some tentative deductions. There does not seem to be any major common breeding season. Some species seem to be breeding in any particular month. It also appears that most species of Calcarea breed
throughout the year.
Burton believed that the Antarctic sponges showed to a marked
degree a free-living habit, extremely rare amongst adult sponges
elsewhere. Most of the evidence seems circumstantial but the arguments seem strong that some of the species considered by Burton are
not normally attached to a substrate.
Koltun (1968) has shown the degree to which the free siliceous
spicules of sponges occur in bottom sediments. From a study of the
upper horizons of sediment cores in the Indian Ocean sector of the
Southern Ocean he was able to demonstrate that siliceous spicules were
extremely common. On the continental shelf and slope of Antarctica
and in the adjacent ocean bottoms Koltun found areas containing from
100 to 300 spicules/cm2. On the shelf itself some areas produced more
than 300 spicules/cm2. In these areas silica was found to make up from
50 to 70% of the actual sediment and in places the surface " looks like
spicular felt 65 cm thick ". Koltun records such sediments off the
Banzare Coast, in the Davis Sea, off Lars Christensen Coast, MacRobertson Land and Kronprins Olav Kyst. The main contributing
sponge genera are Rosella, Tetilla and Cinachyra. A very similar type
of formation occurs in parts of McMurdo Sound (Bullivant, 1967).
Farther north from the Antarctic Continent Koltun found a steady fall
off in the number of spicules, ranging between 10 to 100 spicules/cm2.
In the southern part of the Indian Ocean the general figure is less than
10/cm2, although this figure rises considerably around the Subantarctic
Islands and around shallow water banks.
Sponges are only extremely abundant in the Antarctic down to
between 600 and 600 m, the limit being usually fairly abrupt. Around