488
D. J. TRANTER:
far enough north to cross the South Equatorial Current (WYRTKI, 1962; HAMON, 1965),
and far enough south to enter the northern fringe of the West Wind Drift. The concept of
a parallel section farther west was rejected in favour of greater frequency of observations
on a single section line.
Fig. 1 shows the study area and the sampling strategy. Stations were at regular intervals
in space (90 miles) and time (12 hours). Each of the 16 stations was worked twice per
cruise-on the way north and on the way south, once by night and once by day. The
interval between consecutive observations at the same station varied from 1 - 2 weeks
in the northern part, to 3 - 4 weeks in the southern part. This interval was regular from
cruise to cruise. The interval between cruises varied from 6 -12 weeks. Six cruises were
made in all.
The first results were introduced by ROCHFORD in Volume 20 of the Australian Journal
of Marine and Freshwater Research (ROCHFORD, 1969; NEWELL, 1969; HUMPHREY
and KERR, 1969; JITTS, 1969; TRANTER and KERR, 1969; LEGAND, 1969). A brief note
on the phytoplankton from 2 of the 6 cruises was published by DESROSIERES (1965).
Various components of the midwater trawl collections were the subject of special studies
(ROGER, 1966; LEGAND, 1967; LEGAND and RIVATON, 1967, 1969; MICHEL, 1968;
CASTLE, 1969; REPELIN, 1970; GUEREDRAT, 1971) and these results have recently been
brought together in a review (LEGAND et aI., 1971).
The present paper deals with the ecosystem as a whole, with particular emphasis on
the cycles of change at each trophic level-their seasonal amplitudes and phase relationships. An attempt is made to distinguish changes due to ecological succession from
changes due to horizontal translation.
I. Material and Methods
The study is based principally on data and results already published. The data, together
with the field and laboratory methods used, appear in a series of Oceanographic Cruise
Reports (CSIRO Aust., 1965 a-d; 1966 a, b) and are available also from World Data
Centres. The information on zooplankton taxa and cope pod species is not yet published;
it is available in the data store of the CSIRO Division of Fisheries and Oceanography,
Cronulla, Australia. Other data from the literature were used to calculate seasonal
amplitudes for various waters.
In investigating the various interactions in this ecosystem, extensive use was made of
correlation and regression analysis, the strengths and weaknesses of which (CASSIE,
1961; MARGALEF, 1968) are recognized. In interpreting the biological significance of
correlations that are significant statistically, frequent reference was made to the distribution patterns of each variable as a function of latitude and time (Fig. 4-10, 15).
II. Physical Environment
The epipelagic habitat in the eastern Indian Ocean is a lens of warm water bounded
below by a permanent thermal discontinuity (ROCHFORD, 1962, 1969). This lens, like
that in the Sargasso Sea (MENZEL and RYTHER, 1960), is deepest in the subtropics
(200-300 m). Towards lower latitudes the layer shallows (50-100 m). As a result of
this convexity, a rich supply of nutrients lies immediately beneath the tropical euphotic
layer, and far beneath the euphotic layer of the subtropics (Fig. 2 and WYRTKI, 1973,
D. J. TRANTER:
far enough north to cross the South Equatorial Current (WYRTKI, 1962; HAMON, 1965),
and far enough south to enter the northern fringe of the West Wind Drift. The concept of
a parallel section farther west was rejected in favour of greater frequency of observations
on a single section line.
Fig. 1 shows the study area and the sampling strategy. Stations were at regular intervals
in space (90 miles) and time (12 hours). Each of the 16 stations was worked twice per
cruise-on the way north and on the way south, once by night and once by day. The
interval between consecutive observations at the same station varied from 1 - 2 weeks
in the northern part, to 3 - 4 weeks in the southern part. This interval was regular from
cruise to cruise. The interval between cruises varied from 6 -12 weeks. Six cruises were
made in all.
The first results were introduced by ROCHFORD in Volume 20 of the Australian Journal
of Marine and Freshwater Research (ROCHFORD, 1969; NEWELL, 1969; HUMPHREY
and KERR, 1969; JITTS, 1969; TRANTER and KERR, 1969; LEGAND, 1969). A brief note
on the phytoplankton from 2 of the 6 cruises was published by DESROSIERES (1965).
Various components of the midwater trawl collections were the subject of special studies
(ROGER, 1966; LEGAND, 1967; LEGAND and RIVATON, 1967, 1969; MICHEL, 1968;
CASTLE, 1969; REPELIN, 1970; GUEREDRAT, 1971) and these results have recently been
brought together in a review (LEGAND et aI., 1971).
The present paper deals with the ecosystem as a whole, with particular emphasis on
the cycles of change at each trophic level-their seasonal amplitudes and phase relationships. An attempt is made to distinguish changes due to ecological succession from
changes due to horizontal translation.
I. Material and Methods
The study is based principally on data and results already published. The data, together
with the field and laboratory methods used, appear in a series of Oceanographic Cruise
Reports (CSIRO Aust., 1965 a-d; 1966 a, b) and are available also from World Data
Centres. The information on zooplankton taxa and cope pod species is not yet published;
it is available in the data store of the CSIRO Division of Fisheries and Oceanography,
Cronulla, Australia. Other data from the literature were used to calculate seasonal
amplitudes for various waters.
In investigating the various interactions in this ecosystem, extensive use was made of
correlation and regression analysis, the strengths and weaknesses of which (CASSIE,
1961; MARGALEF, 1968) are recognized. In interpreting the biological significance of
correlations that are significant statistically, frequent reference was made to the distribution patterns of each variable as a function of latitude and time (Fig. 4-10, 15).
II. Physical Environment
The epipelagic habitat in the eastern Indian Ocean is a lens of warm water bounded
below by a permanent thermal discontinuity (ROCHFORD, 1962, 1969). This lens, like
that in the Sargasso Sea (MENZEL and RYTHER, 1960), is deepest in the subtropics
(200-300 m). Towards lower latitudes the layer shallows (50-100 m). As a result of
this convexity, a rich supply of nutrients lies immediately beneath the tropical euphotic
layer, and far beneath the euphotic layer of the subtropics (Fig. 2 and WYRTKI, 1973,