| The influence of the ENSO cycle on marine fauna and flora has only recently
been given the attention it deserves. The very strong 1997–1998 El Niño
and its obvious effects on marine biota was a key point in ENSO research,
but unfortunately few quantitative data about the 1997–1998 El Niño
itself are available.
To gather information about the effect of ENSO on the macrobenthos, we
performed a bi-weekly transect monitoring on an Ecuadorian sandy beach in
2000–2001, during the strong La Niña following the 1997–1998 El
Niño, and in the normal period of 2002–2004.
In this paper, intertidal macrofaunal densities at higher taxonomic level
are used to compare a La Niña phase with the 'normal' situation. The few
existing documents about El Niño and sandy beach macrobenthos, and
scattered data from previous and current research, were used to complete the
picture.
Total macrobenthos densities were 300% lower during the La Niña phase
compared with equal months in the normal phase. Especially Crustacea and
Mollusca showed a marked increase in densities towards the normal situation
(94% and 341% respectively). Polychaeta and Echinodermata, however,
showed higher densities during the La Niña phase (22% and 73%
respectively).
Two possible explanations are proposed. (1) Low densities during the La
Niña could be due to the very strong preceding El Niño, suggesting
the populations were still recovering. This hypothesis is supported by
previous work done in the south of Peru. This is, however, a cold water
system, compared to the Ecuadorian warm water system. (2) The second
hypothesis states that a La Niña will have a very severe impact on the
intertidal macrofauna of a warm water system like the Ecuadorian coast. |