12
B. H. MILLAR
Amongst the ascidians of Asamushi, Japan, Hirai (1963) recorded some
species as breeding in summer, and others only in autumn or winter and
these restricted seasons may also relate to the position occupied by the
species within their total distribution.
In tropical waters a much longer reproductive season is possible.
Goodbody (1 9 6 1 4 found that Ascidia nigra, Diplosoma macdonaldi
Herdman and Symplegmu viride Herdman settled throughout the year
in Kingston Harbour, Jamaica, although not at a uniform rate. Two
of the species showed marked peaks, which did not, however, correlate
obviously with variations in any environmental factor. As Goodbody
noted, the peaks were of settlement and could have indicated greater
larval survival rather than greater spawning activity. Prolonged
breeding with an interruption in winter was found in a species-probably a Pyura-at Madras, India (Raja, 1963). Since the sea temperature
in Madras harbour varies only between about 26°C and 29°C (Sebastian,
1953) other environmental factors may have imposed the seasonal cycle
on reproduction, Elsewhere in warm waters Weiss (1948) observed a
similar pattern of long but interrupted breeding in Botryllus planus
(Van Name) and Botry1loh-h nigmm Herdman at Florida, U.S.A., and
Didemnum candidum lutarium Van Name settled continuously but not
uniformly.
In warm seas with a marked seasonal temperature cycle ascidians
may also breed throughout the year, with periods of greater and lesser
intensity. Skerman (1959), in a study of fouling at Auckland, New
Zealand, found at least four species which probably settle in every
month. Here the mean annual range of sea temperature is about
11*7OC, but the temperature rarely falls below 11°C. It appears that in
regions with a relatively high winter temperature, breeding is possible
throughout the year, even when there is a large seasonal fluctuation in
temperatures.
Relatively little is known of the reproductive patterns of ascidians
in polar seas, because of the difficulty of collecting in these regions
throughout the year. Millar (1960) produced some evidence that subantarctic and antarctic species do not breed during the southern winter,
and although larvae were present in specimens of Sycozoa sigillinoides
Lesson collected in eight months of the year, it is not known how long
they had been retained in the colonies or when they were released.
Other compound species were found to have larvae during three or four
summer months. In solitary species the evidence from the state of gonad
development suggests a breeding period confined to the least cold
months.
Brewin (1946) studied ascidians from Portobello, New Zealand, and
B. H. MILLAR
Amongst the ascidians of Asamushi, Japan, Hirai (1963) recorded some
species as breeding in summer, and others only in autumn or winter and
these restricted seasons may also relate to the position occupied by the
species within their total distribution.
In tropical waters a much longer reproductive season is possible.
Goodbody (1 9 6 1 4 found that Ascidia nigra, Diplosoma macdonaldi
Herdman and Symplegmu viride Herdman settled throughout the year
in Kingston Harbour, Jamaica, although not at a uniform rate. Two
of the species showed marked peaks, which did not, however, correlate
obviously with variations in any environmental factor. As Goodbody
noted, the peaks were of settlement and could have indicated greater
larval survival rather than greater spawning activity. Prolonged
breeding with an interruption in winter was found in a species-probably a Pyura-at Madras, India (Raja, 1963). Since the sea temperature
in Madras harbour varies only between about 26°C and 29°C (Sebastian,
1953) other environmental factors may have imposed the seasonal cycle
on reproduction, Elsewhere in warm waters Weiss (1948) observed a
similar pattern of long but interrupted breeding in Botryllus planus
(Van Name) and Botry1loh-h nigmm Herdman at Florida, U.S.A., and
Didemnum candidum lutarium Van Name settled continuously but not
uniformly.
In warm seas with a marked seasonal temperature cycle ascidians
may also breed throughout the year, with periods of greater and lesser
intensity. Skerman (1959), in a study of fouling at Auckland, New
Zealand, found at least four species which probably settle in every
month. Here the mean annual range of sea temperature is about
11*7OC, but the temperature rarely falls below 11°C. It appears that in
regions with a relatively high winter temperature, breeding is possible
throughout the year, even when there is a large seasonal fluctuation in
temperatures.
Relatively little is known of the reproductive patterns of ascidians
in polar seas, because of the difficulty of collecting in these regions
throughout the year. Millar (1960) produced some evidence that subantarctic and antarctic species do not breed during the southern winter,
and although larvae were present in specimens of Sycozoa sigillinoides
Lesson collected in eight months of the year, it is not known how long
they had been retained in the colonies or when they were released.
Other compound species were found to have larvae during three or four
summer months. In solitary species the evidence from the state of gonad
development suggests a breeding period confined to the least cold
months.
Brewin (1946) studied ascidians from Portobello, New Zealand, and