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marins renovables

The pattern of microgrowth bands in shell sections of the Mediterranean clam Chamelea gallina shows a seasonal variation in width. Widely spaced growth bands are formed in winter and late spring between January and June, whilst narrow growth increments are deposited in summer and early autumn between August and October, following the maximum summer seawater temperature. The warm summer seawater temperature of 33 "C in the western Mediterranean may be responsible for the suppression of shell growth, as evidenced both by the narrowing of the growth increments and by the later appearance of clefts in shell sections. There is no correlation between spawning and the formation of clefts in the shell of C. gallina. The annual pattern of narrow and wide growth increments has been used to estimate the age of C. gallina and to construct growth curves for this species from the eastern coast of Spain. Growth curves for the clams, determined from the internal microgrowth bands and from the spacing between the clefts in shell sections, differed from curve calculated using surface growth rings

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.

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.