EXTRACELLULAR ENZYME-ACTIVITY - INDICATIONS FOR HIGH SHORT-TERM VARIABILITY IN A COASTAL MARINE ECOSYSTEM

Extracellular alpha-glucosidase, beta-glucosidase, and aminopeptidase activity variations (measured by use of fluorogenic substrate analogs) at a coastal station in the Mediterranean Sea were investigated over a 1-year period. A 27-h cycle and daily measurements were made in a su mmer situation. We observed strong relative diurnal variations, compar ed to seasonal variations, in alpha- and beta-glucosidase. Within 24 h , 0-100% of both alpha- and beta-golucosidase were found in the dissol ved phase. The aminopeptidase activities did not show a strong diurnal variation, but day to day variations were similar in magnitude to sea sonal changes. Consistently, high proportions of all three enzymes wer e found in the dissolved phase on a seasonal scale. Seasonal measureme nts at 50- and 100-m depths showed a weak negative dependency on depth for extracellular enzyme activity. The potential importance of both h ourly and daily changes in extracellular enzyme activity and of free e nzymes is considered.