CHAPTER 44
Structural and Trophic Variations in a Bathyal Community
in the ligurian Sea
S. Schiaparelli, M. Chiantore, R. Cattaneo-Vietti, F. Novelli, N. Drago, and G. Albertelli
ABSTRACT
The structure of a Mediterranean bathyal community living between 400 and 700 m depth in
front of Portofino Promontory (Ligurian Sea) has been investigated, using sets of data collected
in 1981 and 1996 respectively. Percent community composition, total density and biomass don't
show any significant change, at least on the whole. Although total species numberfound in the
two considered years is comparable, as well as diversity and evenness values, the specific composition shows an almost complete substitution. In particular, the disappearance of epifaunal
species, mainly of large size, is outstanding. A real biocoenotical change did not occur, as evidenced by the qualitative (species dominance) and quantitative (numerical dominance) analyses of biocoenotical stocks, which show only a light increase in abundance of Iimicolous species
and species linked to deep muds (VP) versus coastal terrigenous muds (VTC). Conversely, multivariate analysis evidences a clear clustering of 1996 and 1981 data due to presence/absence or
different abundance of some key species: Amphilepis norvegica, Spiophanes kroyeri rejssi and
Amphiura filiformis are present only in 1981, Aricidea quadrilobata and Paradoneis lyra appear
in 1996. The analysis of community trophic structure highlights a significant increase of carnivorous species (mainly scavengers), mostly in terms of numerical dominance, opposed to a
strong decrease of deposit-feeders.
The traditional use of descriptive tools, such as species number, total density and biomass
lead to the classic hypothesis of general stability of bathyal communities. Conversely, changes in
faunal composition of the bathyal benthic community of the Portofino Promontory were
stressed only through the coupling of uni- and multi-variate approaches, suggesting that deepsea benthic assemblages are not so stable as usually considered, probably partly because of
small-scale changes in sedimentary regime (natural and anthropogenic) and heavy fishing
trawling activities, both affecting the surface sediments, determining unfavourable conditions
for the epifauna and favouring, instead, omnivorous and scavenger species.
Introduction
Deep-sea communities are considered to be
characterised by a high degree of stability, due to
the widespread uniformity of environmental
parameters and food availability: increasing stability is correlated with increasing depth. as
changes in the environment are decreased
(Hessler and Sanders 1967; Rex 1981).
The stability-time hypothesis (Margalef,
1968; Sanders 1969; Slobodkin and Sanders,
1969) relates low diversity (= low degree of
organisation) with severe andlor unpredictable
hydrochemical environmental conditions. On
the contrary. low variations of environmental
parameters allow the stabilisation of biotic interactions which lead to high degree of specialisation. While there have been a great number of
studies dealing with deep-sea benthic community structure from a static point of view, data on
its persistence are still scarce (Bernstein and
Meador 1979; Josefson 1981).
Lack of variation in the water column and in
benthic environment below the thermocline
have been a basic tenet of physico-chemical and
ecological studies in the deep-sea. Whilst the
Dipartimento per 10 Studio del Territorio e delle Sue Risorse, Universita di Genova. 16132 Genova, Italy
F.M. Faranda, 1. Guglielmo, G. Spezre (eds)
Mediterranean Ecosystems: Structures and Processes
@ Springel'-Verlag ltalia 2001
Structural and Trophic Variations in a Bathyal Community
in the ligurian Sea
S. Schiaparelli, M. Chiantore, R. Cattaneo-Vietti, F. Novelli, N. Drago, and G. Albertelli
ABSTRACT
The structure of a Mediterranean bathyal community living between 400 and 700 m depth in
front of Portofino Promontory (Ligurian Sea) has been investigated, using sets of data collected
in 1981 and 1996 respectively. Percent community composition, total density and biomass don't
show any significant change, at least on the whole. Although total species numberfound in the
two considered years is comparable, as well as diversity and evenness values, the specific composition shows an almost complete substitution. In particular, the disappearance of epifaunal
species, mainly of large size, is outstanding. A real biocoenotical change did not occur, as evidenced by the qualitative (species dominance) and quantitative (numerical dominance) analyses of biocoenotical stocks, which show only a light increase in abundance of Iimicolous species
and species linked to deep muds (VP) versus coastal terrigenous muds (VTC). Conversely, multivariate analysis evidences a clear clustering of 1996 and 1981 data due to presence/absence or
different abundance of some key species: Amphilepis norvegica, Spiophanes kroyeri rejssi and
Amphiura filiformis are present only in 1981, Aricidea quadrilobata and Paradoneis lyra appear
in 1996. The analysis of community trophic structure highlights a significant increase of carnivorous species (mainly scavengers), mostly in terms of numerical dominance, opposed to a
strong decrease of deposit-feeders.
The traditional use of descriptive tools, such as species number, total density and biomass
lead to the classic hypothesis of general stability of bathyal communities. Conversely, changes in
faunal composition of the bathyal benthic community of the Portofino Promontory were
stressed only through the coupling of uni- and multi-variate approaches, suggesting that deepsea benthic assemblages are not so stable as usually considered, probably partly because of
small-scale changes in sedimentary regime (natural and anthropogenic) and heavy fishing
trawling activities, both affecting the surface sediments, determining unfavourable conditions
for the epifauna and favouring, instead, omnivorous and scavenger species.
Introduction
Deep-sea communities are considered to be
characterised by a high degree of stability, due to
the widespread uniformity of environmental
parameters and food availability: increasing stability is correlated with increasing depth. as
changes in the environment are decreased
(Hessler and Sanders 1967; Rex 1981).
The stability-time hypothesis (Margalef,
1968; Sanders 1969; Slobodkin and Sanders,
1969) relates low diversity (= low degree of
organisation) with severe andlor unpredictable
hydrochemical environmental conditions. On
the contrary. low variations of environmental
parameters allow the stabilisation of biotic interactions which lead to high degree of specialisation. While there have been a great number of
studies dealing with deep-sea benthic community structure from a static point of view, data on
its persistence are still scarce (Bernstein and
Meador 1979; Josefson 1981).
Lack of variation in the water column and in
benthic environment below the thermocline
have been a basic tenet of physico-chemical and
ecological studies in the deep-sea. Whilst the
Dipartimento per 10 Studio del Territorio e delle Sue Risorse, Universita di Genova. 16132 Genova, Italy
F.M. Faranda, 1. Guglielmo, G. Spezre (eds)
Mediterranean Ecosystems: Structures and Processes
@ Springel'-Verlag ltalia 2001