Anchovy
SST
Figure 13 Relationship
between the annual
anomaly of Sea Surface
Temperature (SST) and the
annual catch of anchovy
off Peru. The anomaly
scale is inverted:
downwards indicates
warmer (El Nin o) phases
whole terrestrial ecosystems from South America to Africa (see review in ref. 86).
In the equatorial Pacific El Nin o affects primary productivity through the
reduction of the coastal upwelling, and through a depression of the nutricline,
which reduces the amount of nutrients that are transported to surface waters.
This reduction in overall productivity cascades through to higher trophic levels.
El Nin o is also responsible for major concomitant shifts in the distribution of
some species, re-structuring the community away from its equilibrium points.
For example, the 1982/83 El Nin o caused massive latitudinal shifts in the
distributions of hake, Merluccius gayi, and sardine, Sardinops sagax, to avoid
unfavourable environmental conditions. Other species were simply removed
from the system by the dominant near-shore southwards flow that characterizes
El Nin o, such as the shrimps Xiphopenaeus riueti and Penaeus occidentalis. A
combination of habitat reduction and increased predation by species favoured by
El Nin o conditions (like bonito, Sarda chiliensis, dorado, Coryphaena hippurus,
and yelowfin, Thunnus albacores) are thought to have affected the abundance of
other major species, like jack mackerel, Trachurus symmetricus. But the most
affected marine species was probably the anchovy, Engraulis ringens, the world’s
largest fishery (Figure 13). The 20-fold reduction in primary production severely
limited anchovy growth and survival. Other components of the ecosystem
showed positive responses, such as the scallop, Argopecten purpuratus, possibly
because of the metabolic advantages of warmer conditions.
The ENSO signature can be found in oceanographic processes beyond the
tropical Pacific as well. For example the path and intensity of the Gulf Stream is
generally forecastable from the intensity of the North Atlantic Oscillation Index
(NAO), which accounts for half of its variance. Much of the remaining variance
is accounted for by the Southern Oscillation in the Pacific. The Gulf Stream
appears to be displaced northwards following ENSO events, and the total
freshwater export from the Atlantic is about 0.1 Sverdrups (Sv) larger during El
Nin o events. Therefore changes in the South Pacific can, through global
teleconnections, influence oceanographic conditions in the North Atlantic,
M. Holmgren, M. Scheffer, E. Ezcurra, J. R. Gutierrez and G. M. J. Mohren, Tree, 2001, 16, 89—94.
R. T. Barber and F. P. Chavez, Nature, 1986, 319, 279—285.
A. H. Taylor and J. H. Stephens, Tellus, 1998, 50A, 134—142.
A. H. Taylor, M. B. Jordan, J. A. Stephens, Nature, 1998, 393, 638.
A. Schmittner, C. Appenzeller and T. F. Stocker, 2000, Geophys. Lett., 27, 1163—1166.
M. Barange
72
SST
Figure 13 Relationship
between the annual
anomaly of Sea Surface
Temperature (SST) and the
annual catch of anchovy
off Peru. The anomaly
scale is inverted:
downwards indicates
warmer (El Nin o) phases
whole terrestrial ecosystems from South America to Africa (see review in ref. 86).
In the equatorial Pacific El Nin o affects primary productivity through the
reduction of the coastal upwelling, and through a depression of the nutricline,
which reduces the amount of nutrients that are transported to surface waters.
This reduction in overall productivity cascades through to higher trophic levels.
El Nin o is also responsible for major concomitant shifts in the distribution of
some species, re-structuring the community away from its equilibrium points.
For example, the 1982/83 El Nin o caused massive latitudinal shifts in the
distributions of hake, Merluccius gayi, and sardine, Sardinops sagax, to avoid
unfavourable environmental conditions. Other species were simply removed
from the system by the dominant near-shore southwards flow that characterizes
El Nin o, such as the shrimps Xiphopenaeus riueti and Penaeus occidentalis. A
combination of habitat reduction and increased predation by species favoured by
El Nin o conditions (like bonito, Sarda chiliensis, dorado, Coryphaena hippurus,
and yelowfin, Thunnus albacores) are thought to have affected the abundance of
other major species, like jack mackerel, Trachurus symmetricus. But the most
affected marine species was probably the anchovy, Engraulis ringens, the world’s
largest fishery (Figure 13). The 20-fold reduction in primary production severely
limited anchovy growth and survival. Other components of the ecosystem
showed positive responses, such as the scallop, Argopecten purpuratus, possibly
because of the metabolic advantages of warmer conditions.
The ENSO signature can be found in oceanographic processes beyond the
tropical Pacific as well. For example the path and intensity of the Gulf Stream is
generally forecastable from the intensity of the North Atlantic Oscillation Index
(NAO), which accounts for half of its variance. Much of the remaining variance
is accounted for by the Southern Oscillation in the Pacific. The Gulf Stream
appears to be displaced northwards following ENSO events, and the total
freshwater export from the Atlantic is about 0.1 Sverdrups (Sv) larger during El
Nin o events. Therefore changes in the South Pacific can, through global
teleconnections, influence oceanographic conditions in the North Atlantic,
M. Holmgren, M. Scheffer, E. Ezcurra, J. R. Gutierrez and G. M. J. Mohren, Tree, 2001, 16, 89—94.
R. T. Barber and F. P. Chavez, Nature, 1986, 319, 279—285.
A. H. Taylor and J. H. Stephens, Tellus, 1998, 50A, 134—142.
A. H. Taylor, M. B. Jordan, J. A. Stephens, Nature, 1998, 393, 638.
A. Schmittner, C. Appenzeller and T. F. Stocker, 2000, Geophys. Lett., 27, 1163—1166.
M. Barange
72