520
D. J. TRANTER: Seasonal Studies of a Pelagic Ecosystem (Meridian 110 0 E)
During this season, species reach the southern limit of their meridional drift, the
distance of their journey being determined by the duration of their life. The longer-lived
micronekton become concentrated in the subtropics where the southerly drift comes to
rest. Here they are exploited by pelagic schools of sperm whales and southern bluefin tuna
which, in turn, are harvested by Man. Those late-stage larvae of rock lobsters and mantis
shrimps that lie on the coastal fringes of this return drift are repatriated and recruited to
the adult stocks.
The next part of the annual cycle may be considered to begin at this point. With the
changing of the seasons, high-salinity subtropical water from the main South Indian
Ocean gyre begins to drift north and east across the study area carrying with it, perhaps,
the early larvae of stomatopod and rock lobster populations which habitually spawn in
the summer months (MICHEL, 1968; CHIITLEBOROUGH and THOMAS, 1969).
As a result of the previous heavy grazing and excretion, primary production continues
well into November (Fig. 5). The resultant detritus decomposes and remineralizes and, as
grazing pressures weakens (Figs. 8, 9), there is further algal production. This is rapidly
grazed down in the subtropics by the surviving zooplankton herbivores, which now face
starvation as stratification reduces primary production to the seasonal minimum (Fig. 6),
and as predators drift northward through the area taking heavy toll. Those predators with
the longest life cycle penetrate deep into the tropical area (LEGAND et aI., 1971) where
they find surviving populations of certain plankton carnivores (e.g. Euchaeta russel/i) on
which to feed. The continuity of plankton production associated with the South Equatorial
Current throughout the winter provides forage for those macroplankton and micro nekton
which develop fast enough to exploit such food reserves (Table 2; Fig. 10).
Appendix *
Species of copepods used in calculating indices of diversity, species with .' have been used
in Table 9.
Eucalanidae
* Eucalanus subtenuis
* E. attenuatus
E. crassus
E. dentatus
E. elongatus
E. hyalinus
* E. mucronatus
* E. pileatus
* E. subcrassus
* Rhincalanus cornutus
* R. nasutus
Euchaetidae
Euchaeta acuta
* E. concinna
* E. longicornis
* E. marina
* E. media
E. russelli
E. spinosa
E. tenuis
* E. wolfendeni
Copiliidae
Copilia mirabilis
C. hendorfii
C. lata
C. longistylus
C. mediterranea
C. quadrata
C. vitrea
Sapphirinidae
Sapphirina gemma
S. angusta
S. auronitens
S. darwinii
S. gastrica
S. nigromaculata
S. intestinata
S.lactens
S. maculosa
S. metallina
S. stellata
S. opalina
S. ovatolanceolata
S. sali
S. scarlata
S. bicuspidata
S. sinuicauda
S. salpae
S. vorax
D. J. TRANTER: Seasonal Studies of a Pelagic Ecosystem (Meridian 110 0 E)
During this season, species reach the southern limit of their meridional drift, the
distance of their journey being determined by the duration of their life. The longer-lived
micronekton become concentrated in the subtropics where the southerly drift comes to
rest. Here they are exploited by pelagic schools of sperm whales and southern bluefin tuna
which, in turn, are harvested by Man. Those late-stage larvae of rock lobsters and mantis
shrimps that lie on the coastal fringes of this return drift are repatriated and recruited to
the adult stocks.
The next part of the annual cycle may be considered to begin at this point. With the
changing of the seasons, high-salinity subtropical water from the main South Indian
Ocean gyre begins to drift north and east across the study area carrying with it, perhaps,
the early larvae of stomatopod and rock lobster populations which habitually spawn in
the summer months (MICHEL, 1968; CHIITLEBOROUGH and THOMAS, 1969).
As a result of the previous heavy grazing and excretion, primary production continues
well into November (Fig. 5). The resultant detritus decomposes and remineralizes and, as
grazing pressures weakens (Figs. 8, 9), there is further algal production. This is rapidly
grazed down in the subtropics by the surviving zooplankton herbivores, which now face
starvation as stratification reduces primary production to the seasonal minimum (Fig. 6),
and as predators drift northward through the area taking heavy toll. Those predators with
the longest life cycle penetrate deep into the tropical area (LEGAND et aI., 1971) where
they find surviving populations of certain plankton carnivores (e.g. Euchaeta russel/i) on
which to feed. The continuity of plankton production associated with the South Equatorial
Current throughout the winter provides forage for those macroplankton and micro nekton
which develop fast enough to exploit such food reserves (Table 2; Fig. 10).
Appendix *
Species of copepods used in calculating indices of diversity, species with .' have been used
in Table 9.
Eucalanidae
* Eucalanus subtenuis
* E. attenuatus
E. crassus
E. dentatus
E. elongatus
E. hyalinus
* E. mucronatus
* E. pileatus
* E. subcrassus
* Rhincalanus cornutus
* R. nasutus
Euchaetidae
Euchaeta acuta
* E. concinna
* E. longicornis
* E. marina
* E. media
E. russelli
E. spinosa
E. tenuis
* E. wolfendeni
Copiliidae
Copilia mirabilis
C. hendorfii
C. lata
C. longistylus
C. mediterranea
C. quadrata
C. vitrea
Sapphirinidae
Sapphirina gemma
S. angusta
S. auronitens
S. darwinii
S. gastrica
S. nigromaculata
S. intestinata
S.lactens
S. maculosa
S. metallina
S. stellata
S. opalina
S. ovatolanceolata
S. sali
S. scarlata
S. bicuspidata
S. sinuicauda
S. salpae
S. vorax