A well-developed deep chlorophyll maximum (DCM) is a prominent feature of the Northwestern Mediterranean during a large part of the year. Data from 7 oceanographic surveys carried out across the Catalano-Balearic Sea, between 1982 and 1987, have been used to analyze shortterm (within cruises) and seasonal+interannual (between cruises) variation of several parameters (such as surface and DCM chlorophyll concentration, integrated chlorophyll, DCM, nitracline and nitrite maximum depths). S~gnificant positlve correlations (p < 0.01) were found between the depths of the DCM, of the nitracline and of the nitrite maximum. Surface chlorophyll concentrations and average chlorophyll values for the upper 110 m of the water column were signicantly correlated for only 2 of the 7 cruises. The relationship between integrated primary production and surface or integrated chlorophyll concentrations presented considerable scatter due, in part, to physiological variability of the sampled communities. After exclusion of 1 statistically outlying point, apparently corresponding to a sedlmenting bloom, a multiple linear regression model of integrated primary production (mg C m-' h-') on integrated chlorophyll, euphotic zone depth and a stability parameter explained 74 D/o of the data variance. However, the presence of such 'outliers' limits the usefulness of these models and stresses the need of physiological informat~on for a rellable prediction of primary product~vity.

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Abstract. Biotic zonation and severe impoverishment of benthic macrofauna are two of the most conspicuous features of submarine caves. The prevailing explanation assumes trophic depletion caused by reduction of water flow. However, no isolation of water was found in the studied Catalan submarine cave, even in the wall microlayer. Fluorescein diffusion was so fast that it was detectable everywhere in the cave already only a few minutes after the injection. The rate of dissolution of plaster spheres was even greater in the cave than in a nearby tunnel – without benthic macrofauna impoverishment – showing a considerable water flow. The oxygen concentration of water in dialysis bags placed at varying distances from the cave walls showed that no wall microlayer gradients were present. Biochemical gradients did not indicate any decrease in food supply. Although photosynthetic pigment concentration generally decreased inside the cave, and although the gradients were not linear but formed different patterns throughout the cave, the BOD5, the POM, the C:N ratio, the [3H]‐thymidine incorporation rate, and the ETS activity were higher in the inner part of the cave. There was an accumulation of detritic material and bacteria in the inner parts that constitute a plausible food supply for benthic macrofauna. If neither water motion nor food supply can be invoked, research into the causes of zonation and disappearence of benthic macrofauna is proposed to be carried out on biotic interactions and behavioural processes.

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