CHAPTER 61
Enzymatic Activities and Carbon Flux through the Microbial
Compartment in the Adriatic Sea
R. La FerIa, R. Zaccone, G. Caruso, and M. Azzaro
ABSTRACT
(arbon flux through the microbial community by the determination of biomass, heterotrophic
bacteria, aminopeptidase and respiratory activities has been studied in two areas of the Adriatic
sea with different trophic characteristics during four oceanographic surveys, carried out in June
96,97 and February 97,98. In front of the Po delta (area A), the average rates of the carbon
released by aminopeptidase activity ranged from 4.9 to 9.9 ]lg ( 1- 1 h- 1 and near the Ancona
coast (area B) from 3.1 to 7.6]lg C 1- 1 h- 1 , whereas the microbial respiration as metabolic carbon
production ((0) ranged from 0.19 to 2.29 and from 0.24 to 1.40]lg ( 1- 1 h- 1 in the two areas,
respectively.
In area A, both the microbial activities showed a seasonal trend with higher values in summer than in winter. In area B, respiration increased during years whilst aminopeptidase activity
decreased; bacterioplankton abundance increased on average in the second year of the
research (June 97 and February 98). However, all these differences were not statistically significant. The biovolume resulted always significantly higher during summer.
Relationships between bacterial carbon production and organic carbon content were discussed. Bacterial growth efficiency ranged from 17 to 38% and from 13 to 44% in areas A and Bt
respectively. The relationship between hydrolysis of peptides and bacterial carbon production
indicated a good coupling of processes during June 97. Various ratios between bacterial activities were reckoned with the aim to define the role of bacteria in the biogeochemical flux of ( in
the Northern Adriatic Sea. The ( transfer from the biotic versus the abiotic compartment seems
to flow better in summer, particularly in area A.
Introduction
The Northern Adriatic Sea represents a semienclosed basin in which strong river runoff
occurs causing important organic matter load
and nutrient enrichment. Moreover, the peculiar
hydrological characteristics of the environment
consist of shallow depths, occurrence of frontal
systems, strong wind mediated winter mixing
and summer stratification (Artegiani et al.1997a.
b). As a consequence, this peculiar environment
often suffers distrophic crisis and occurrence of
mucilagenous phenomena, particularly in summer, with dramatic implications on the ecology
of the whole Adriatic Sea.
In aquatic ecosystems, the role of bacterial
community in the biogeochemical fluxes is very
important. In fact, the C flux is mainly ruled by
bacterial activity that, by means of extracellular
hydrolytic enzymes, transforms organic macromolecules into soluble products so that the
resulting monomers can be widely available for
incorporation into bacterial biomass. If hydrolysis and uptake are coupled, monomers liberated
by hydrolysis will be taken up. So enzymatic
hydrolysis plays a key role in the initial step of
the carbon flux in aquatic ecosystems (Azam et
al. 1993). The fate of such biomass could be the
export to higher trophic levels or the sinking
through the water column towards the bottom.
The following metabolic oxidation of biomass by
respiration liberates carbon dioxide newlyavailable for autotrophic production (Heip et al. 1995;
Del Giorgio et al. 1997).
Istituto Sperimentale Talassografico, CNR, Spianata S. Raineri,98122 Messina, Italy
P.M. Faranda, L. Guglielmo, G. Spezie (eds)
Mediterranean Ecosystems: Structures and Processes
Ie Springer-Verlag ltalia 2001
Enzymatic Activities and Carbon Flux through the Microbial
Compartment in the Adriatic Sea
R. La FerIa, R. Zaccone, G. Caruso, and M. Azzaro
ABSTRACT
(arbon flux through the microbial community by the determination of biomass, heterotrophic
bacteria, aminopeptidase and respiratory activities has been studied in two areas of the Adriatic
sea with different trophic characteristics during four oceanographic surveys, carried out in June
96,97 and February 97,98. In front of the Po delta (area A), the average rates of the carbon
released by aminopeptidase activity ranged from 4.9 to 9.9 ]lg ( 1- 1 h- 1 and near the Ancona
coast (area B) from 3.1 to 7.6]lg C 1- 1 h- 1 , whereas the microbial respiration as metabolic carbon
production ((0) ranged from 0.19 to 2.29 and from 0.24 to 1.40]lg ( 1- 1 h- 1 in the two areas,
respectively.
In area A, both the microbial activities showed a seasonal trend with higher values in summer than in winter. In area B, respiration increased during years whilst aminopeptidase activity
decreased; bacterioplankton abundance increased on average in the second year of the
research (June 97 and February 98). However, all these differences were not statistically significant. The biovolume resulted always significantly higher during summer.
Relationships between bacterial carbon production and organic carbon content were discussed. Bacterial growth efficiency ranged from 17 to 38% and from 13 to 44% in areas A and Bt
respectively. The relationship between hydrolysis of peptides and bacterial carbon production
indicated a good coupling of processes during June 97. Various ratios between bacterial activities were reckoned with the aim to define the role of bacteria in the biogeochemical flux of ( in
the Northern Adriatic Sea. The ( transfer from the biotic versus the abiotic compartment seems
to flow better in summer, particularly in area A.
Introduction
The Northern Adriatic Sea represents a semienclosed basin in which strong river runoff
occurs causing important organic matter load
and nutrient enrichment. Moreover, the peculiar
hydrological characteristics of the environment
consist of shallow depths, occurrence of frontal
systems, strong wind mediated winter mixing
and summer stratification (Artegiani et al.1997a.
b). As a consequence, this peculiar environment
often suffers distrophic crisis and occurrence of
mucilagenous phenomena, particularly in summer, with dramatic implications on the ecology
of the whole Adriatic Sea.
In aquatic ecosystems, the role of bacterial
community in the biogeochemical fluxes is very
important. In fact, the C flux is mainly ruled by
bacterial activity that, by means of extracellular
hydrolytic enzymes, transforms organic macromolecules into soluble products so that the
resulting monomers can be widely available for
incorporation into bacterial biomass. If hydrolysis and uptake are coupled, monomers liberated
by hydrolysis will be taken up. So enzymatic
hydrolysis plays a key role in the initial step of
the carbon flux in aquatic ecosystems (Azam et
al. 1993). The fate of such biomass could be the
export to higher trophic levels or the sinking
through the water column towards the bottom.
The following metabolic oxidation of biomass by
respiration liberates carbon dioxide newlyavailable for autotrophic production (Heip et al. 1995;
Del Giorgio et al. 1997).
Istituto Sperimentale Talassografico, CNR, Spianata S. Raineri,98122 Messina, Italy
P.M. Faranda, L. Guglielmo, G. Spezie (eds)
Mediterranean Ecosystems: Structures and Processes
Ie Springer-Verlag ltalia 2001