Page 2 - Caruso_Zaccone_2000

952 G. CARUSO AND R. ZACCONE

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ÿ1
tial' microbial enzyme activity. Fluorescence units were 634 ng C l ÿ1 h , with a peak at 13054 ng C l ÿ1 h .
calibrated with a 05 mmol l ÿ1 stock solution of the stan- Their distribution was closely in¯uenced by the peculiar
dard MCA (Sigma) and the results are expressed in terms hydrological structure of water masses; here, Atlantic
ÿ1
of maximum velocity of hydrolysis (Vmax, mg C l ÿ1 h ) waters are strongly strati®ed over the surface layers and
(Hoppe et al. 1988). carry trophic resources towards the southern part where a
Since 1995, seawater samples have been collected from higher aminopeptidase activity was observed in the upper
different marine and brackish areas; at the same time, the zone. Moving from the south to the north (Fig. 2), the
main environmental parameters were recorded in situ by highest proteolytic activity levels shifted to the deeper
automatic probes (temperature, salinity), or determined in layers (on average, 128 ng C h ÿ1 ÿ1 in the photic zone and
l
l
the laboratory by standard analytical methods (Chlorophyll 55 ng C h ÿ1 ÿ1 in the bottom layer), with a trend similar
a and POC contents, viable plate counts of heterotrophic to that observed for particulate organic nitrogen content
bacteria on Marine agar). (PON), in relation to the sinking, from a depth of 100±150
Statistical elaborations were performed using the m to 200 m, of the picnocline originated by the saline gra-
ANOVA test and Pearson correlation coef®cient r, in order dient (Leonardi et al. 1998a).
to assess the signi®cance of enzyme data and measure their Enzyme activity was related neither to temperature and
degree of association with environmental variables, respec- salinity nor to bacterial densities, but it was signi®cantly
tively. Values which differed from the normal distribution and positively related to particulate organic carbon (POC)
were log-transformed. content at two southern stations (10C, r ˆ 086; 10F, r ˆ
082, P < 005) (Caruso et al. 1998).
RESULTS
Marine environments Northern Adriatic Sea. The Northern Adriatic Sea is a
semi-enclosed basin with peculiar hydrological conditions
The areas studied were characterized by conditions of
which determine the occurrence of periodic distrophic
moderate trophism, as in Egadi Islands or in the Straits of
crises and mucilage phenomena. The main features of this
Messina, or by eutrophy, as in the Northern Adriatic Sea
(Fig. 1). ecosystem include the shallow depth, the strong organic
matter input of both autochthonous (primary production)
and allochthonous (¯uvial and continental inputs) origin,
Egadi Archipelago. In April 1996, seawater samples were the presence of frontal systems between saltier and more
collected from Egadi Islands at 13 stations located between diluted waters, and the water circulation determining varia-
Favignana and Marettimo Islands. The levels of leucine tions on a seasonal scale, i.e., intensive mixing in winter
aminopeptidase found in the euphotic layer (0±100 m) and strati®cation of waters in the other seasons (Artegiani
were, in general, very low, ranging on average from 128 to et al. 1997).

45° N
Adriatic
Sea

40° Oliveri
Tindari
Egadi
Islands Messina
Straits
and Faro lake
35°
Mediterranean
Sea
30°
5° W 0° 5° 10° 15° 20° 25° 30° 35° E

Fig. 1 Areas sampled

= 2000 The Society for Applied Microbiology, Journal of Applied Microbiology, 89, 951ÿ959