Unusual larval fish distribution pattern in coastal zone of the western Mediterranean

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The coast of Catalonia was divided into three zones on the basis of heterogeneity in their physical features and in the structure of the larval fish populations. Both physical and biological processes are normally more stable overall in the middle zone. However, in May 1983 an anomalous hydrodynamic event took place over the continental shelf in this zone and resulted in a major alteration in the structure of the larval fish population. An intense inverted density front changed the direction of coastal flow. The resulting density gradient confined larvae inshore in a zone in which the main larval concentrations are normally located over the shelf break during the rest of the year. This anomalous distribution of the larval fish population at that time was a consequence of the unpredictable hydrographic event and contrasted with the structure of the larval population over the rest of the year, produced by a more constant hydrodynamic pattern.