CHAPTER 43
Role of Macrodetritivores - Detritus Trophic Relationships in
Phosphorus Dynamics at the Marine Water-sediment Interface:
Laboratory Experiments Using 32p
L. Rossi and G. Mancinelli
ABSTRACT
We investigated the combined effects on sediment 32p uptake of bioturbation and particulate
detritus processing by macrodetritivores in laboratory microcosms. Sediment and sediment +
detritus microcosms were set using sediment and vascular plant detritus sampled in northwestern Adriatic Sea. The effects of macrodetritivores at the water-sediment interface were tested by adding to microcosms individuals of the amphipod Gammarus insensibilis in different densities (541 and 1624 individuals m- 2 , respectively). In defaunated controls, plant detritus caused
a significant positive variation in sediment 32p adsorption rates (ca. 40% increase). Under "sediment only" conditions, the presence of macrodetritivores stimulated both uptake and diffusion
of the radiotracer in sediments. Furthermore, the analysis of water-amphipod concentration factors highlighted an effective inability of macrodetritivores to feed upon the finest organic particles constituting the bulk of sediment organic matter. Excluding any significant trophic interaction with the clayish matrix, amphipod bioturbation activity at the water-sediment interface
resulted decisively in affecting 32p dynamics. On the other hand, under "sediment + detritus"
conditions, amphipod processing of plant detritus determined a significant, animal densityrelated increase of dissolved 32p originally immobilised by detritus and/or sequestered by the
microbial component.
Our experimental investigation highlighted a clear "short-circuiting" effect of the detritivores-detritus trophic interaction on benthic phosphorus dynamics, potentially significant also
in natural environments. In this perspective, phosphorus regeneration in coastal systems, conventionally related to abiotic factors and microbial mineralization, might result strongly influenced also by macrodetritivores trophic exploitation of allochthonous detritus.
Introduction
Sediments can immobllise or release nutrients in
aquatic systems, influencing the concentration of
dissolved elements in overlying waters, and indirectly affecting both benthic and pelagic primary production. Even though only scattered information is available from comparative studies
between freshwater and marine environments
{e.g. Enell1989}, phosphorus uptake by sediment
seems to represent in freshwater systems the primary process, whereas in salt marsh and estuarine environments regeneration from sediments
prevails over immobilisation; P may thus behave
as a conservative tracer of benthic decomposition (Caraco et al. 1990). In this perspective, in
coastal benthic systems biotic factors directly
taking part in decomposition processes (e.g.
micro- and macrofauna) may playa crucial role
in P dynamics.
Nutrient exchange at the sediment-water
interface is deeply influenced by benthic organisms (Andersson et al. 1988; Clavero et al. 1994).
Faunal trophic activity can accelerate the rate of
organic matter decomposition, increasing phosphorus release from the sedimentary compartment (Holdren and Armstrong 1980; Gardner et
al. 1981). On the other hand, burrowing and ventilation activity by macro invertebrates may
speed up oxygen diffusion into sediments and
increase the thickness of the oxidised surface
layer, enhancing sediment P binding capacity
(Kamp-Nielsen et a1. 1982).
Scarce efforts have been made to analyse the
Sezione Ecoiogia, Dip. di Genetica e Biologia Molecolare, Universita di Roma I "La Sapienza", Via Lancisi 29, 00161 Roma, Italy
F.M. Faranda, 1. Guglielmo, G. Spezie (eds)
Mediterranean Ecosystems: Structures and Processes
@ Springer-Verlag Italia 200 1
Role of Macrodetritivores - Detritus Trophic Relationships in
Phosphorus Dynamics at the Marine Water-sediment Interface:
Laboratory Experiments Using 32p
L. Rossi and G. Mancinelli
ABSTRACT
We investigated the combined effects on sediment 32p uptake of bioturbation and particulate
detritus processing by macrodetritivores in laboratory microcosms. Sediment and sediment +
detritus microcosms were set using sediment and vascular plant detritus sampled in northwestern Adriatic Sea. The effects of macrodetritivores at the water-sediment interface were tested by adding to microcosms individuals of the amphipod Gammarus insensibilis in different densities (541 and 1624 individuals m- 2 , respectively). In defaunated controls, plant detritus caused
a significant positive variation in sediment 32p adsorption rates (ca. 40% increase). Under "sediment only" conditions, the presence of macrodetritivores stimulated both uptake and diffusion
of the radiotracer in sediments. Furthermore, the analysis of water-amphipod concentration factors highlighted an effective inability of macrodetritivores to feed upon the finest organic particles constituting the bulk of sediment organic matter. Excluding any significant trophic interaction with the clayish matrix, amphipod bioturbation activity at the water-sediment interface
resulted decisively in affecting 32p dynamics. On the other hand, under "sediment + detritus"
conditions, amphipod processing of plant detritus determined a significant, animal densityrelated increase of dissolved 32p originally immobilised by detritus and/or sequestered by the
microbial component.
Our experimental investigation highlighted a clear "short-circuiting" effect of the detritivores-detritus trophic interaction on benthic phosphorus dynamics, potentially significant also
in natural environments. In this perspective, phosphorus regeneration in coastal systems, conventionally related to abiotic factors and microbial mineralization, might result strongly influenced also by macrodetritivores trophic exploitation of allochthonous detritus.
Introduction
Sediments can immobllise or release nutrients in
aquatic systems, influencing the concentration of
dissolved elements in overlying waters, and indirectly affecting both benthic and pelagic primary production. Even though only scattered information is available from comparative studies
between freshwater and marine environments
{e.g. Enell1989}, phosphorus uptake by sediment
seems to represent in freshwater systems the primary process, whereas in salt marsh and estuarine environments regeneration from sediments
prevails over immobilisation; P may thus behave
as a conservative tracer of benthic decomposition (Caraco et al. 1990). In this perspective, in
coastal benthic systems biotic factors directly
taking part in decomposition processes (e.g.
micro- and macrofauna) may playa crucial role
in P dynamics.
Nutrient exchange at the sediment-water
interface is deeply influenced by benthic organisms (Andersson et al. 1988; Clavero et al. 1994).
Faunal trophic activity can accelerate the rate of
organic matter decomposition, increasing phosphorus release from the sedimentary compartment (Holdren and Armstrong 1980; Gardner et
al. 1981). On the other hand, burrowing and ventilation activity by macro invertebrates may
speed up oxygen diffusion into sediments and
increase the thickness of the oxidised surface
layer, enhancing sediment P binding capacity
(Kamp-Nielsen et a1. 1982).
Scarce efforts have been made to analyse the
Sezione Ecoiogia, Dip. di Genetica e Biologia Molecolare, Universita di Roma I "La Sapienza", Via Lancisi 29, 00161 Roma, Italy
F.M. Faranda, 1. Guglielmo, G. Spezie (eds)
Mediterranean Ecosystems: Structures and Processes
@ Springer-Verlag Italia 200 1