CHAPTERS6
Environmental Constraints on Pathways of Organic Detritus
in a Semi-enclosed Marine System (W-Mediterranean)
M. Fabiano l , G. Saril 1 , A. Mazzola 1 , and A. Pusceddu 3
ABSTRACT
In order to assess seasonal and spatial changes in water-sediment interaction processes in a
semi-enclosed marine system of Western Sicily (Marsala lagoon; W-Mediterranean), the biochemical composition of suspended and sediment organic matter was studied, during a one-year
sampling period. The observed dynamic balance of resuspension vs. sedimentation processes
and the macroalgal and vascular plant coverage appear major factors in affecting both amounts
and biochemical composition of suspended and sedimentary organic matter and allowed us to
identify two different sub-systems. The northern area, characterised by frequent wind-induced
sediment resuspension events and by a scant vegetation, displayed higher amounts of high
quality (i.e. protein) sedimentary organic matter and higher amounts of particulate organic matter. By contrast, the southern area, characterised by less wind exposure and a deeper water
column, displayed lower particulate organic matter concentrations and increasing sedimentary
organic matter concentrations. The oligotrophy of the system (phytoplankton biomass < 0.1 }lg
Chl-a 1-') and the relatively low concentrations of photosynthetic pigments in the sediments (on
annual average 3.1 }lg g-1) suggest that this system is largely dominated by organic material of
detrital and/or heterotrophic origin. The overall picture of the study area suggests that the
Marsala lagoon is a lipulsing" environment characterised by no clear seasonal change of the primary production processes and by the accumulation of large amounts of organic detritus in the
sediments. Such uncoupling between amounts and nutritional value of suspended and sediment organic detritus suggests that this particular environment behaves probably as a detrital
Utrap~
Introduction
Coastal lagoons are controlled by the dynamic
balance between external water inputs (marine
and fresh waters) and wind and wave auxiliary
energy inputs. Lagoons of semi-arid regions. as
those facing the Tyrrhenian Sea, show little tidal
ranges and scant or absent continental inflows.
Thus, in these environments, wind become the
main physical factor in conditioning biological
functions both in the water column and sediments (Millet and Cecchi 1992; Pusceddu 1999).
A large number of studies dealing with ecological features of shallow coastal areas are available in the literature. Most deal with the role of
unpredictable fluctuations of physical variables
(Painchaud et a1. 1990; Navarro et a1. 1993;
Navarro and Thompson 1995; Chassany de
Casabianca et al. 1995; Clavier et a1. 1995;
Savenkoff et al.1995; Pusceddu et al.1996). Other
papers also showed that spatial and temporal
changes in quality and quantity of organic detritus, rather than changes in physical variables
could affect both benthic and plankton
(Pusceddu et al. 1997a; Sdlipoti et al. 1997).
In lagoon environments, primary production
from phytoplankton, macrophytes and salt
marsh plants generally exceeds consumption by
herbivores (Newell 1982). Thus. a large amount
of primary organic matter might be directly avai1 Dipartimento per 10 Studio del Territorio e delle Sue RUorse, UniversitA di Genova, Viale Benedetto XV, 16100 Genova, Italy
2 Dipartimento di Biologia Animale, Universita di Palermo, Via Archirafi HI, 90123 Palermo. Italy
3 Istituto di Scienze Marine, Universita di Ancona, Via Breece Bianche, 60 131 Ancona, Italy
EM. Faranda, L. Guglielmo, G. Spezie (eds)
Mediterranean Ecosystems: Sttuctures and Processes
© Springer-Verlag !talia 2001
Environmental Constraints on Pathways of Organic Detritus
in a Semi-enclosed Marine System (W-Mediterranean)
M. Fabiano l , G. Saril 1 , A. Mazzola 1 , and A. Pusceddu 3
ABSTRACT
In order to assess seasonal and spatial changes in water-sediment interaction processes in a
semi-enclosed marine system of Western Sicily (Marsala lagoon; W-Mediterranean), the biochemical composition of suspended and sediment organic matter was studied, during a one-year
sampling period. The observed dynamic balance of resuspension vs. sedimentation processes
and the macroalgal and vascular plant coverage appear major factors in affecting both amounts
and biochemical composition of suspended and sedimentary organic matter and allowed us to
identify two different sub-systems. The northern area, characterised by frequent wind-induced
sediment resuspension events and by a scant vegetation, displayed higher amounts of high
quality (i.e. protein) sedimentary organic matter and higher amounts of particulate organic matter. By contrast, the southern area, characterised by less wind exposure and a deeper water
column, displayed lower particulate organic matter concentrations and increasing sedimentary
organic matter concentrations. The oligotrophy of the system (phytoplankton biomass < 0.1 }lg
Chl-a 1-') and the relatively low concentrations of photosynthetic pigments in the sediments (on
annual average 3.1 }lg g-1) suggest that this system is largely dominated by organic material of
detrital and/or heterotrophic origin. The overall picture of the study area suggests that the
Marsala lagoon is a lipulsing" environment characterised by no clear seasonal change of the primary production processes and by the accumulation of large amounts of organic detritus in the
sediments. Such uncoupling between amounts and nutritional value of suspended and sediment organic detritus suggests that this particular environment behaves probably as a detrital
Utrap~
Introduction
Coastal lagoons are controlled by the dynamic
balance between external water inputs (marine
and fresh waters) and wind and wave auxiliary
energy inputs. Lagoons of semi-arid regions. as
those facing the Tyrrhenian Sea, show little tidal
ranges and scant or absent continental inflows.
Thus, in these environments, wind become the
main physical factor in conditioning biological
functions both in the water column and sediments (Millet and Cecchi 1992; Pusceddu 1999).
A large number of studies dealing with ecological features of shallow coastal areas are available in the literature. Most deal with the role of
unpredictable fluctuations of physical variables
(Painchaud et a1. 1990; Navarro et a1. 1993;
Navarro and Thompson 1995; Chassany de
Casabianca et al. 1995; Clavier et a1. 1995;
Savenkoff et al.1995; Pusceddu et al.1996). Other
papers also showed that spatial and temporal
changes in quality and quantity of organic detritus, rather than changes in physical variables
could affect both benthic and plankton
(Pusceddu et al. 1997a; Sdlipoti et al. 1997).
In lagoon environments, primary production
from phytoplankton, macrophytes and salt
marsh plants generally exceeds consumption by
herbivores (Newell 1982). Thus. a large amount
of primary organic matter might be directly avai1 Dipartimento per 10 Studio del Territorio e delle Sue RUorse, UniversitA di Genova, Viale Benedetto XV, 16100 Genova, Italy
2 Dipartimento di Biologia Animale, Universita di Palermo, Via Archirafi HI, 90123 Palermo. Italy
3 Istituto di Scienze Marine, Universita di Ancona, Via Breece Bianche, 60 131 Ancona, Italy
EM. Faranda, L. Guglielmo, G. Spezie (eds)
Mediterranean Ecosystems: Sttuctures and Processes
© Springer-Verlag !talia 2001