Page 2 - Zaccone_al_2001

200 R. ZACCONE, R. LA FERLA, M. AZZARO, G. CARUSO AND E. CRISAFI

MATERIALS AND METHODS
Enzymatic microbial activity (EEA) on the labile component of particulate and
dissolved organic matter was determined by the hydrolysis of the fluorogenic
substrate Leucina-7amino-4methylcoumarin and spectrofluorometric measurements.
The utilisation of this substrate was proposed as a valid indicator of the protease
activity in aquatic environments (Hoppe et al., 1988, Zaccone and Caruso, 1996).

Respiratory rates ( R ) and the consequent metabolic production of CO2 were
evaluated by the ETS assay (Electron Transport System) which exploits the reduction
of tetrazolium salts in formazan (Packard and Williams, 1981). The conversion
factors of ETS to CO2 for the euphotic and aphotic zones are reported in La Ferla et
al. (1996) and Azzaro et al. (in press), respectively.

RESULTS AND DISCUSSION
Spatial variations
In the Mediterranean the average levels of protease activity ranged between fairly
reduced levels in sites characterised by moderate trophism as in the Egadi Islands, to
higher levels as in the Straits of Messina, reaching their maximum in the eutrophic
waters in the Northern Adriatic (Fig.1).

Fig. 1 Distribution of ectoenzymatic (in the circled letters) and respiratory activities (both expressed
as µg C h-1 dm-3) in the superficial waters of the Mediterranean Sea. (a: Martinez et al., 1990; b: Agustì
and Cruzado, 1992; c: Karner and Rassoulzadegan, 1995; d: Caruso et al., 1988; e: Data Report,1997; f:
Caruso, unpublished data; g: La Ferla et al., 1996; h: La Ferla et al., in press; i: La Ferla et al., 1996; l and
m: Prisma-2, unpublished data; n: Azzaro, 1997).