swimming pool along a direct route between Panama City and Tahiti. Serial
abundance estimates for the copepods Clausocalanus species and Euchaeta rimana
from the equator to 2°N and for Calanus minor from the equator to 2°S (Fig. 11.36)
showed both strong (and somewhat different) seasonality and dramatic reduction
during the 1982–1983 El Niño. A long list of other species also nearly vanished in that
event. At least the stocks of herbivorous species rebounded immediately in 1984; E.
rimana, a predator, had another reduced seasonal peak in that year. Dessier and
Donguy propose that the seasonality is driven by variations in equatorial upwelling
strength and production. They note that peaks of herbivorous species (Clausocalanus
spp., C. minor) alternate with peaks of carnivores (E. rimana), implying a lag along
the food-chain in response to the seasonal variation. Seasonal advective shifts of the
strong, trans-equatorial abundance gradients are also a possible explanation.
Fig. 11.36 Time-series of abundance estimates for three copepod species sampled
along the equator from a passenger liner on a regular schedule.
(^) (After Dessier & Donguy 1987.)