510
D. J. TRANTER:
oceanic drift. It is this drift that distributes the products of the food web throughout the
pelagic biotope.
6. Zooplankton and Micronekton
One would, perhaps, expect that the time lag between the zooplankton and micronekton cycles would be much greater than between the zooplankton and phytoplankton
cycles, since life span generally increases progressively along the food chain. However
on our study section, concurrent micronekton and zooplankton values were frequently
well correlated (Table 7). This is a matter of considerable interest. Four patterns of
interaction can be distinguished, corresponding to each zone and season.
a) Tropical Zone, August- February
Here there is a progressive trend towards closer correlations between zooplankton
and micronekton with greater (positive) phase shift. The serial correlation (ZN: MN+ 1) is
closest with a time displacement of 6 -12 weeks corresponding to the interval between
consecutive cruises. Such a correlation could be based, in this case, on a direct lifehistory response (spawning and larval development) by micronekton populations to
fluctuations in the supply of zooplankton food; in any event the aggregation is a transient
phenomenon (Fig. 10).
b) Tropical Zone, March- August
The time lag here is shorter than in the opposing season. Values separated in time
by only 1-2 weeks (Zn: Mn+ 1), corresponding to the interval between consecutive
legs of the same cruise, are serially correlated. The correlation is very close (0.87); even
concurrent values are well correlated (0.42), Such a swift response by the micronekton
population in terms of spawning and larval development is most unlikely. This is
probably a translation effect-that is, the result of micronekton populations drifting
through the area of observation. This thesis is later discussed in more detail in relation
to micronekton life histories.
c) Subtropical Zone, March - August
During this period, the only correlation that approached significance was that
between micronekton on the first leg of a cruise and zooplankton on the return leg
(Mn: Zn + 1), the (negative) time displacement being 3-4 weeks. This is probably fortuitous. On the other hand, such a situation could arise as a result of a spawning migration
timed to anticipate a regular, cyclical zooplankton maximum.
7. Micronekton and Nekton
LEGAND has made a detailed study of the distribution, abundance, and life histories
of 23 species of mesopelagic fish taken by the midwater trawl (LEGAND,1967; LEGAND
and RIVATON, 1967, 1969; LEGAND et al., 1971). These species are polarized into tropical
and subtropical components, some species having separate populations in each zone.
The boundary between the 2 zones lies between 15 and 18
0
S. The subtropical component
is concentrated between 24 and 26 0 S.
D. J. TRANTER:
oceanic drift. It is this drift that distributes the products of the food web throughout the
pelagic biotope.
6. Zooplankton and Micronekton
One would, perhaps, expect that the time lag between the zooplankton and micronekton cycles would be much greater than between the zooplankton and phytoplankton
cycles, since life span generally increases progressively along the food chain. However
on our study section, concurrent micronekton and zooplankton values were frequently
well correlated (Table 7). This is a matter of considerable interest. Four patterns of
interaction can be distinguished, corresponding to each zone and season.
a) Tropical Zone, August- February
Here there is a progressive trend towards closer correlations between zooplankton
and micronekton with greater (positive) phase shift. The serial correlation (ZN: MN+ 1) is
closest with a time displacement of 6 -12 weeks corresponding to the interval between
consecutive cruises. Such a correlation could be based, in this case, on a direct lifehistory response (spawning and larval development) by micronekton populations to
fluctuations in the supply of zooplankton food; in any event the aggregation is a transient
phenomenon (Fig. 10).
b) Tropical Zone, March- August
The time lag here is shorter than in the opposing season. Values separated in time
by only 1-2 weeks (Zn: Mn+ 1), corresponding to the interval between consecutive
legs of the same cruise, are serially correlated. The correlation is very close (0.87); even
concurrent values are well correlated (0.42), Such a swift response by the micronekton
population in terms of spawning and larval development is most unlikely. This is
probably a translation effect-that is, the result of micronekton populations drifting
through the area of observation. This thesis is later discussed in more detail in relation
to micronekton life histories.
c) Subtropical Zone, March - August
During this period, the only correlation that approached significance was that
between micronekton on the first leg of a cruise and zooplankton on the return leg
(Mn: Zn + 1), the (negative) time displacement being 3-4 weeks. This is probably fortuitous. On the other hand, such a situation could arise as a result of a spawning migration
timed to anticipate a regular, cyclical zooplankton maximum.
7. Micronekton and Nekton
LEGAND has made a detailed study of the distribution, abundance, and life histories
of 23 species of mesopelagic fish taken by the midwater trawl (LEGAND,1967; LEGAND
and RIVATON, 1967, 1969; LEGAND et al., 1971). These species are polarized into tropical
and subtropical components, some species having separate populations in each zone.
The boundary between the 2 zones lies between 15 and 18
0
S. The subtropical component
is concentrated between 24 and 26 0 S.