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Advisor(s)
Abstract(s)
Patterns of interannual variation are described for an inshore fish assemblage off the
Arrábida rocky coast (Portugal). During an 11 yr period, the fish assemblage showed pronounced
changes especially within its tropical, warm-temperate and cold-temperate elements. These changes
followed a fluctuating pattern connected with the North Atlantic Oscillation (NAO) with a series of
years where the modifications were slight, interspersed with years where faunal changes were very
rapid, affecting up to 35% of the total number of species recorded in those years. After a transition
year from a cold to a warm period or vice versa, the majority of the newcomers from the preceding
phase were eliminated. Winter conditions, but not summer conditions, were good predictors of the
observed patterns. Increases in sea surface temperature (SST) were associated with increases in the
proportions of tropical and warm-temperate fish and with decreases in the proportion of cold-temperate
elements, the reverse being true for decreases in SST. Interannual variation in faunal composition
was not simply a consequence of changes in SST. Changes in other factors such as current flow direction
and transport mechanisms, capable of bringing fishes from different biogeographical sources,
may also play a role in the observed patterns. The influence of the NAO is therefore not only mediated
by its effects on SST but also by the changes it induces in wind and current patterns along the
Portuguese shore. Long-term trends caused by persistent changes, like those involving global warming,
may be masked by the fact that at an intermediate time scale, faunal changes are characterised
by a succession of oscillations rather than by a steady modification in a single direction. This outlines
the importance of long-term monitoring data, since short-term studies may only capture single
phases of a complex oscillation, giving a false picture of the overall pattern of change.
Description
Keywords
Faunal changes Portugal North Atlantic Oscillation NAO Sea surface temperature SST Wind stress Temperate fish assemblage
Citation
Marine Ecology Progress Series, 340, 259-270
Publisher
Inter-Research