506
D. J. TRANTER:
that translation (water mass movement) may be involved. This question is discussed in
detail at a later stage.
For the remainder of the year (August-February), correlations in the subtropical
zone were not very well developed.
b) Tropical Zone, August- February
Here, the phytoplankton and zooplankton cycles were more in phase. The response
by zooplankton (Zn+l) to changes in the standing stock of phytoplankton (Pn) was
much swifter than in the subtropical zone. The time lag coincided fairly closely with the
interval between consecutive legs of the same cruise, which in this part of the section
was less than 2 weeks. Zooplankton and phytoplankton were not negatively correlated as
in the subtropical zone during the alternate season. This indicated that the food supply
(primary production) was keeping pace with the grazing rate.
c) Tropical Zone, March - August
There is no clear pattern here as in the cases described above. The only correlation
that approached significance was that between the zooplankton of one cruise (ZN) and
the phytoplankton of the next (PN + 1). Such a situation could arise if the zooplankton
were recycling nutrients later used in phytoplankton production. This possibility arises
again in connection with other results and is there discussed at greater length.
3. Zooplankton and Nutrients
a) Tropical Zone
We have already seen that concurrent phytoplankton and zooplankton values are
not well correlated in the tropical zone; there is a time lag of 1- 2 weeks between
phytoplankton fluctuations and the consequent zooplankton response. The high correlations between zooplankton on the one hand, and phosphate, nitrate, and productivity
on the other are therefore most intriguing. These correlations were compared with
corresponding serial correlations (Table 8). This table shows that correlations between
zooplankton and productivity, phytoplankton and productivity, and phytoplankton and
nitrate are reduced by time intervals (either positive or negative) as short as 1- 2 weeks;
the introduction of a time lag does not materially increase the value of the correlation.
These results indicate that the relationship between zooplankton and nutrients is a
direct and fairly immediate one. They suggest that, in the tropical zone at least, zooplankton plays a mayor role in the recycling and regeneration of nutrients. The fact that
the NIP ratio declines towards the surface (Fig. 3) suggests that the recycling of phosphate
may be faster than that of nitrate. The fact that phytoplankton is well correlated with
nitrate (0.46), but not with phosphate (0.23), (Table 6 a), is probably connected with this
NIP differential; it seems likely that both phytoplankton and NIP fluctuate in unison
under heavy grazing pressure, the one as a direct result of grazing, the other as a result
of the more rapid rate of phosphate recycling associated with zooplankton excretion.
b) Subtropical Zone
Apart from the correlation between phosphate and nitrate which is a general feature
of most oceanic systems, the only variables that are well correlated by day are phyto-
D. J. TRANTER:
that translation (water mass movement) may be involved. This question is discussed in
detail at a later stage.
For the remainder of the year (August-February), correlations in the subtropical
zone were not very well developed.
b) Tropical Zone, August- February
Here, the phytoplankton and zooplankton cycles were more in phase. The response
by zooplankton (Zn+l) to changes in the standing stock of phytoplankton (Pn) was
much swifter than in the subtropical zone. The time lag coincided fairly closely with the
interval between consecutive legs of the same cruise, which in this part of the section
was less than 2 weeks. Zooplankton and phytoplankton were not negatively correlated as
in the subtropical zone during the alternate season. This indicated that the food supply
(primary production) was keeping pace with the grazing rate.
c) Tropical Zone, March - August
There is no clear pattern here as in the cases described above. The only correlation
that approached significance was that between the zooplankton of one cruise (ZN) and
the phytoplankton of the next (PN + 1). Such a situation could arise if the zooplankton
were recycling nutrients later used in phytoplankton production. This possibility arises
again in connection with other results and is there discussed at greater length.
3. Zooplankton and Nutrients
a) Tropical Zone
We have already seen that concurrent phytoplankton and zooplankton values are
not well correlated in the tropical zone; there is a time lag of 1- 2 weeks between
phytoplankton fluctuations and the consequent zooplankton response. The high correlations between zooplankton on the one hand, and phosphate, nitrate, and productivity
on the other are therefore most intriguing. These correlations were compared with
corresponding serial correlations (Table 8). This table shows that correlations between
zooplankton and productivity, phytoplankton and productivity, and phytoplankton and
nitrate are reduced by time intervals (either positive or negative) as short as 1- 2 weeks;
the introduction of a time lag does not materially increase the value of the correlation.
These results indicate that the relationship between zooplankton and nutrients is a
direct and fairly immediate one. They suggest that, in the tropical zone at least, zooplankton plays a mayor role in the recycling and regeneration of nutrients. The fact that
the NIP ratio declines towards the surface (Fig. 3) suggests that the recycling of phosphate
may be faster than that of nitrate. The fact that phytoplankton is well correlated with
nitrate (0.46), but not with phosphate (0.23), (Table 6 a), is probably connected with this
NIP differential; it seems likely that both phytoplankton and NIP fluctuate in unison
under heavy grazing pressure, the one as a direct result of grazing, the other as a result
of the more rapid rate of phosphate recycling associated with zooplankton excretion.
b) Subtropical Zone
Apart from the correlation between phosphate and nitrate which is a general feature
of most oceanic systems, the only variables that are well correlated by day are phyto-