ANTARCTIC BENTHOS
111
Odontaster validus in the McMurdo Sound area occurs mainly down
to about 60 m. From the shore down to about 20 m the bottom consists of basaltic gravel and boulders and life is relatively sparse, largely
no doubt due to the unstable conditions. The area is subject to large
amounts of fresh water from melting snow and ice during the summer
while during the winter the bottom is scoured by ice-floes. Anchor ice
also forms on the bottom and floats to the undersurface of the floating
sea ice in the early summer. Odontaster has been shown to be able to
survive in much diluted sea water. In general it has obviously been able
to adapt to these d s c u l t conditions and often occurs in large numbers.
It appears to be largely omnivorous, feeding normally on bottom
detritus. Specimens are attracted to seal, beef or fish meat in traps and
they have been observed feeding on sea urchins, amphipods and euphausiids and even seal faeces. The stomachs examined normally contain
detritus and small invertebrates.
The main digestive and nutrient storage organs of seastars such as
Odontaster are the pyloric caeca. Pearse showed that measured by dry
weight, pyloric caecal lipid ranged from about 15 to 25%, and carbohydrate from about 2 to 12%. Pearse observed that in areas of high
plant production the pyloric caeca nearly doubled their weight in the
summer and the carbohydrate content mainly in the form of poly.
saccharides increased by nearly 500%. A marked decrease took place
after diatom production ceased. In areas where the summer benthic
diatom production was low animals tended to be pale coloured, whereas
they were deep red or orange in areas where diatom concentrations were
high. Since Odontaeter has never been collected from beneath the permanent ice cover of the Ross Ice Shelf, Pearse supposes that some plant
food may be necessary for this species.
A large part of Pearse’s work on Odontaster was concerned with
reproduction and development. Sexes in this species are separate.
Spawning occurs only during the winter months (in McMurdo Sound
between late May and mid-September). The gonads gradually reduce
in size so that it would appear that eggs or sperm are released gradually
over a period. The development of gametes is slow, developing eggs or
sperm remaining in the adult for up to two years, although release is
annual. In adult females up to three separate size classes of eggs
are present, representing eggs to be released in three separate years.
The actual number of gametes produced is related to the food supply,
but the stage of gamete production and the spawning time seems to
be essentially the same in all the localities examined in the Ross Sea
and even beyond. Since there are marked differences between the
amount of light and temperatures between these localities it seems that
111
Odontaster validus in the McMurdo Sound area occurs mainly down
to about 60 m. From the shore down to about 20 m the bottom consists of basaltic gravel and boulders and life is relatively sparse, largely
no doubt due to the unstable conditions. The area is subject to large
amounts of fresh water from melting snow and ice during the summer
while during the winter the bottom is scoured by ice-floes. Anchor ice
also forms on the bottom and floats to the undersurface of the floating
sea ice in the early summer. Odontaster has been shown to be able to
survive in much diluted sea water. In general it has obviously been able
to adapt to these d s c u l t conditions and often occurs in large numbers.
It appears to be largely omnivorous, feeding normally on bottom
detritus. Specimens are attracted to seal, beef or fish meat in traps and
they have been observed feeding on sea urchins, amphipods and euphausiids and even seal faeces. The stomachs examined normally contain
detritus and small invertebrates.
The main digestive and nutrient storage organs of seastars such as
Odontaster are the pyloric caeca. Pearse showed that measured by dry
weight, pyloric caecal lipid ranged from about 15 to 25%, and carbohydrate from about 2 to 12%. Pearse observed that in areas of high
plant production the pyloric caeca nearly doubled their weight in the
summer and the carbohydrate content mainly in the form of poly.
saccharides increased by nearly 500%. A marked decrease took place
after diatom production ceased. In areas where the summer benthic
diatom production was low animals tended to be pale coloured, whereas
they were deep red or orange in areas where diatom concentrations were
high. Since Odontaeter has never been collected from beneath the permanent ice cover of the Ross Ice Shelf, Pearse supposes that some plant
food may be necessary for this species.
A large part of Pearse’s work on Odontaster was concerned with
reproduction and development. Sexes in this species are separate.
Spawning occurs only during the winter months (in McMurdo Sound
between late May and mid-September). The gonads gradually reduce
in size so that it would appear that eggs or sperm are released gradually
over a period. The development of gametes is slow, developing eggs or
sperm remaining in the adult for up to two years, although release is
annual. In adult females up to three separate size classes of eggs
are present, representing eggs to be released in three separate years.
The actual number of gametes produced is related to the food supply,
but the stage of gamete production and the spawning time seems to
be essentially the same in all the localities examined in the Ross Sea
and even beyond. Since there are marked differences between the
amount of light and temperatures between these localities it seems that