CHAPTER 40
Influence of Allochthonous Plant Detritus on Gammarus insensibilis
Stock (Amphipoda) Occurrence in the Soft-bottom Epifauna of the
Northern Adriatic Sea
G. Mancinelli and L. Rossi
ABSTRACT
Sediments and benthic epifauna were examined at a coastal station (ca. 26 m water depth) located in the northwestern Adriatic Sea. Sediment cores were taken every 90 days from April 1995
to January 1996. Epifauna was further investigated by means of trophic traps deployed on the
sea bottom. Sediments were characterized by the occurrence of coarse plant detritus derived
from aquatic angiosperms (Zostera sp., Cymodocea nodosa) commonly distributed in lagoons
and salt marshes of the Po delta area. The epifauna was dominated by the brackish amphipod
Gammarus insensibilis Stock, whereas other taxa occurred in negligible densities (< 2% quantitative dominance). A positive relationship was found between coarse organic matter in sediments and G. insensibilis spatial abundance. Analyses of population parameters from core samples and of size-frequency distributions from trophic traps permitted to exclude passive dispersal as the causative factor for the constant, even though seasonally variable, presence of the
amphipod in the benthic system. Our results provide clear evidence of an "outwelling" flux of
particulate plant detritus linking brackish coastal areas to adjacent marine environments in the
northwestern Adriatic Sea. Moreover, they give support to the hypothesis that advection of allochthonous particulate detritus in marine environments may determine an "estuarine" characterization of epifaunal soft-bottom assemblages.
Introduction
Plant detritus export from salt marshes, estuaries and coastal lagoons plays a significant role
in nutrients and energy dynamics of marine
ecosystems (Nixon 1980 and literature cited therein; Dame et al. 1991; Taylor and Allanson
1995). On a global scale, macrophytal net primary production exceeds by ca. 40% total
energy requirements of estuaries and salt marshes (Duarte and Cebrian 1996). In this perspective, angiosperms act as major sources of the
organic carbon stored and subsequently buried
in sediments of adjacent marine environments
(ca. 30% of total ocean carbon storage).
Furthermore, allochthonous macrophytal detritus may represent a relevant structuring factor
at different levels of marine benthic systems, e.g.
enhancing rates of microbial activity (Peduzzi
and Herndl 1991), or affecting macrobenthic
communities structure and secondary production (Vetter 1995).
In the northwestern Adriatic Sea, the distribution and productivity of macrophytes in coastal lagoons have been widely investigated (e.g.
the Venice Lagoon: Scarton et al. 1995; den
Hartog et al.1996; Sfriso and Ghetti 1998). On the
other hand, scarce information is available on the
fate of macrodetritus, in terms of particulate
matter fluxes from brackish to adjacent marine
environments, and on effects of detritus advection on benthic assemblages.
Our study examines sediment characteristics
and the epibenthic macrofauna at a coastal site
located in northwestern Adriatic Sea, focusing on
relationships between organic matter richness of
sediment coarsest dimensional fractions and
dominant epifaunal taxa.
Materials and Methods
A sampling station (45°08.96' N, 12°23.21' E;
water depth: 26 m; Fig. 1) was located in the
Dipartimento di Genetica e Biologia Molecolare, Universita di Roma I "La Sapienza", Sezione Ecologia, Via Lancisi 29, 00161
Roma,Italy
EM. Faranda, 1.. Guglielmo, G. Sperle (eds)
Mediterranean Ecosystems: Structures and Processes
@ Sprlnger-Verlag [talla 200 1
Influence of Allochthonous Plant Detritus on Gammarus insensibilis
Stock (Amphipoda) Occurrence in the Soft-bottom Epifauna of the
Northern Adriatic Sea
G. Mancinelli and L. Rossi
ABSTRACT
Sediments and benthic epifauna were examined at a coastal station (ca. 26 m water depth) located in the northwestern Adriatic Sea. Sediment cores were taken every 90 days from April 1995
to January 1996. Epifauna was further investigated by means of trophic traps deployed on the
sea bottom. Sediments were characterized by the occurrence of coarse plant detritus derived
from aquatic angiosperms (Zostera sp., Cymodocea nodosa) commonly distributed in lagoons
and salt marshes of the Po delta area. The epifauna was dominated by the brackish amphipod
Gammarus insensibilis Stock, whereas other taxa occurred in negligible densities (< 2% quantitative dominance). A positive relationship was found between coarse organic matter in sediments and G. insensibilis spatial abundance. Analyses of population parameters from core samples and of size-frequency distributions from trophic traps permitted to exclude passive dispersal as the causative factor for the constant, even though seasonally variable, presence of the
amphipod in the benthic system. Our results provide clear evidence of an "outwelling" flux of
particulate plant detritus linking brackish coastal areas to adjacent marine environments in the
northwestern Adriatic Sea. Moreover, they give support to the hypothesis that advection of allochthonous particulate detritus in marine environments may determine an "estuarine" characterization of epifaunal soft-bottom assemblages.
Introduction
Plant detritus export from salt marshes, estuaries and coastal lagoons plays a significant role
in nutrients and energy dynamics of marine
ecosystems (Nixon 1980 and literature cited therein; Dame et al. 1991; Taylor and Allanson
1995). On a global scale, macrophytal net primary production exceeds by ca. 40% total
energy requirements of estuaries and salt marshes (Duarte and Cebrian 1996). In this perspective, angiosperms act as major sources of the
organic carbon stored and subsequently buried
in sediments of adjacent marine environments
(ca. 30% of total ocean carbon storage).
Furthermore, allochthonous macrophytal detritus may represent a relevant structuring factor
at different levels of marine benthic systems, e.g.
enhancing rates of microbial activity (Peduzzi
and Herndl 1991), or affecting macrobenthic
communities structure and secondary production (Vetter 1995).
In the northwestern Adriatic Sea, the distribution and productivity of macrophytes in coastal lagoons have been widely investigated (e.g.
the Venice Lagoon: Scarton et al. 1995; den
Hartog et al.1996; Sfriso and Ghetti 1998). On the
other hand, scarce information is available on the
fate of macrodetritus, in terms of particulate
matter fluxes from brackish to adjacent marine
environments, and on effects of detritus advection on benthic assemblages.
Our study examines sediment characteristics
and the epibenthic macrofauna at a coastal site
located in northwestern Adriatic Sea, focusing on
relationships between organic matter richness of
sediment coarsest dimensional fractions and
dominant epifaunal taxa.
Materials and Methods
A sampling station (45°08.96' N, 12°23.21' E;
water depth: 26 m; Fig. 1) was located in the
Dipartimento di Genetica e Biologia Molecolare, Universita di Roma I "La Sapienza", Sezione Ecologia, Via Lancisi 29, 00161
Roma,Italy
EM. Faranda, 1.. Guglielmo, G. Sperle (eds)
Mediterranean Ecosystems: Structures and Processes
@ Sprlnger-Verlag [talla 200 1