Seasonal Studies of a Pelagic Ecosystem (Meridian 110° E)
509
is correlated with several others in the tropics and none at all in the subtropics. This
suggests that the former is a subtropical and the latter a tropical species. Other species are
more uniformly distributed throughout both zones.
Of the remaining correlations (110), more than half (61) are positive, providing
further evidence of the general response to what must surely be a common determining
influence. The block with the highest proportion (100%) of significant correlations
occurred in the tropical zone (H: H) as did the block with the lowest proportion (10%)
of significant correlations (C: C). The remaining blocks were ranked as follows:
H: H, Subtropics (approx. 66%)
C : C, Subtropics (approx. 66 %)
H: C, Subtropics (approx. 40%)
H: C, Tropics (approx. 40%)
Two of the negative correlations were in the block C: C (Tropics) and one each in H: C
(Tropics) and H: C (Subtropics).
The results show that, in the tropics, the seasonal cycles of copepod herbivores are
more generally in phase, and the seasonal cycles of copepod carnivores less generally in
phase, than in the subtropics. The phase relationship between herbivores and carnivores
is generally much the same from one zone to the other.
5. Zooplankton and Benthos
Along the coasts of western Australia and southern Indonesia are benthic populations
whose larvae drift into the open ocean where, for the duration of their larval life, they
coexist with the epipelagic plankton community. Prominent among these are the larvae
of stomatopods (mantis shrimps) and panulirid lobsters. These were taken along the
110° E. section during the study period, particularly by the midwater trawl.
The distribution and abundance of stomatopod larvae from the midwater trawl
collections formed the subject of a special study by MICHEL (1968). His material was
made up of two main groups, concentrated to the north and to the south of the tropicalsubtropical boundary. MICHEL believes that these 2 stocks came from the shores of
southern Indonesia and the shores of western Australia respectively. The populations
of west Australian origin begin their life cycle in the southern summer (JanuaryFebruary), as indicated by the frequency of early larval stages, and leave the plankton
in the spring and early summer of the following year. Indonesian populations have a
continuous breeding season.
The west Australian species of rock lobster are separated into tropical and subtropical components, the southern species (Panulirus longipes cygnus) forming the basis
of a lucrative fishery (BOWEN and CHITILEBOROUGH, 1966) from which about 11 million
individuals are taken each year. The larvae (phyllosoma) of P. longipes are concentrated
south of 18 ° S., while those of tropical species, for example P. penicillatus, are concentrated to the north of this boundary (CHITILEBOROUGH and THOMAS, 1969).
The life cycle of P. longipes is similar to that of the stomatopods studied by MICHEL.
The early phyllosoma leave the coast during the summer months and return as late-stage
phyllosoma in the spring and early summer of the following year, making an approximate
larval life of 10 -12 months.
These long-lived meroplankton organisms are important in two main respects. They
are an integral part of the pelagic ecosystem; and they are an indicator of seasonal
509
is correlated with several others in the tropics and none at all in the subtropics. This
suggests that the former is a subtropical and the latter a tropical species. Other species are
more uniformly distributed throughout both zones.
Of the remaining correlations (110), more than half (61) are positive, providing
further evidence of the general response to what must surely be a common determining
influence. The block with the highest proportion (100%) of significant correlations
occurred in the tropical zone (H: H) as did the block with the lowest proportion (10%)
of significant correlations (C: C). The remaining blocks were ranked as follows:
H: H, Subtropics (approx. 66%)
C : C, Subtropics (approx. 66 %)
H: C, Subtropics (approx. 40%)
H: C, Tropics (approx. 40%)
Two of the negative correlations were in the block C: C (Tropics) and one each in H: C
(Tropics) and H: C (Subtropics).
The results show that, in the tropics, the seasonal cycles of copepod herbivores are
more generally in phase, and the seasonal cycles of copepod carnivores less generally in
phase, than in the subtropics. The phase relationship between herbivores and carnivores
is generally much the same from one zone to the other.
5. Zooplankton and Benthos
Along the coasts of western Australia and southern Indonesia are benthic populations
whose larvae drift into the open ocean where, for the duration of their larval life, they
coexist with the epipelagic plankton community. Prominent among these are the larvae
of stomatopods (mantis shrimps) and panulirid lobsters. These were taken along the
110° E. section during the study period, particularly by the midwater trawl.
The distribution and abundance of stomatopod larvae from the midwater trawl
collections formed the subject of a special study by MICHEL (1968). His material was
made up of two main groups, concentrated to the north and to the south of the tropicalsubtropical boundary. MICHEL believes that these 2 stocks came from the shores of
southern Indonesia and the shores of western Australia respectively. The populations
of west Australian origin begin their life cycle in the southern summer (JanuaryFebruary), as indicated by the frequency of early larval stages, and leave the plankton
in the spring and early summer of the following year. Indonesian populations have a
continuous breeding season.
The west Australian species of rock lobster are separated into tropical and subtropical components, the southern species (Panulirus longipes cygnus) forming the basis
of a lucrative fishery (BOWEN and CHITILEBOROUGH, 1966) from which about 11 million
individuals are taken each year. The larvae (phyllosoma) of P. longipes are concentrated
south of 18 ° S., while those of tropical species, for example P. penicillatus, are concentrated to the north of this boundary (CHITILEBOROUGH and THOMAS, 1969).
The life cycle of P. longipes is similar to that of the stomatopods studied by MICHEL.
The early phyllosoma leave the coast during the summer months and return as late-stage
phyllosoma in the spring and early summer of the following year, making an approximate
larval life of 10 -12 months.
These long-lived meroplankton organisms are important in two main respects. They
are an integral part of the pelagic ecosystem; and they are an indicator of seasonal