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C. Morri and C.N. Bianchi
behaviour}; (2) effects mediated by biotic interactions (conferral of competitive advantage to
one of a pair of overlapping species); (3) indirectly through ocean currents (changes in climate may alter the emphasis of water flow and
the pattern of water circulation). Note that this
meaning of "direct" and "indirect" effects is different from that commonly used in community
ecology (Strauss 1991). The data from the
Ligurian Sea apparently provided examples for
all these mechanisms.
Population dynamics of Pentapora jascialis,
growth of Cladocora caespitosa. and change in
shoot density of Posidonia oceanica seem to
stand for a direct effect of climate on the organisms, whereas the alternate dominance between
Spisula subtruncata and Chamelea gallina in
sandy bottom communities might correspond
with an effect mediated by conferral of advantage
to one of them in turn. Both species are ftlterfeeding bivalves, sharing the same habitat, and a
competition between them can be suspected.
The same hypothesis is not tenable in the
case of the alternation between Auxis rochei and
Sarpa salpa. The adults of two species occupy
very different niches in the marine ecosystems
and, although we probably do not know enough
about the ecology of their larval phases, a competition is unlikely. Rather, we can think of the
influence of an altered pattern of water flow.
Changes in subtidal rock communities might
also be due to such collateral effects, whereas the
influence of current variability upon the occurrence of southern species in the Ligurian Sea
seems sufficiently proved (Astraldi et al. 1995;
Aliani and Meloni 1999).
Supply side ecology (Roughgarden et al.
1987) emphasises the role of physical transport
processes in structuring marine communities,
and Barry and Dayton (1991) coined the expression "hydrodynamic biological oceanography" to
underline that the variations in the distribution
and abundance of marine organisms are strictly
linked to the movement of water masses. Veron
(1995) introduced the concepts of "surface circulation vicariance" to indicate that the fluctuations in surface currents have a major impact on
shallow marine life.
The alternation observed within bivalves
and fish is consistent with the idea that climatic
fluctuations favour the coexistence of species
potentially redundant (Blandin 1987), thus acting as a biodiversity pump on both evolutionary
and ecological scales (Sara 1985; Astraldi et al.
1995).
An aspect that turned out to be obvious in
our analysis of these Ligurian Sea examples is
that for most of them the observed change can be
equally driven either by climate or by anthropogenic causes. Distinguishing between the two
is often difficult (Bianchi 1997) and can also
cause animated debates, as in the case of the
alleged eutrophication of Skagerrak (BuhlMortensen 1996; Gray 1996). It is true that
anthropogenic and climatic actions can combine
their effects on the marine biota (Bourcier 1996).
All this encourages caution when examining
changes in marine ecosystems and emphasises
the need of planning studies in the context of the
physical setting and the relevant space and time
scales (Levin 1992).
Finding an appropriate space and time scale
was the main problem we met when designing
the layout of this paper. After consulting both
published data and our own archives, we dearly
realised that most of the wealth of scientific
research on the Ligurian Sea (Bianchi et al. 1987;
Cattaneo-Vietti et al. 1988) concerns studies of
local relevance andior carried out for short periods. In part, this reflects the common
Mediterranean research attitude, traditionally
directed toward the identification and description of biocoenosis-types rather than the
dynamic aspects (Bianchi 1997; Bianchi et al.
1998b). We are now getting fully aware that. contrary to the demand of most funding agencies,
any small-scale and short-term approach to ecological monitoring and research will not enable
us to understand ecosystem change, both climate
or man-induced, but will likely result an unproductive investment of time and resources.
Acknowledgements. Change of marine ecosystems is the core
topic of the national research project SINAPSI (Seasonal,
INterannual and decAdal variability of the atmosPhere,
oceanS and related marIne ecosystems). Research on
Cladocora caespitosa was started within the project "Gil
Cnidari del benthos marino: ecologia e biogeografia" of the
University of Genoa (60% MURST). Studies on seagrass beds,
epibenthic communities on rocky reefs and southern species
occurrence in the Ligurian Sea fall within the scope of the
activities on marine biodiversity at the Marine Environment
Research Centre of La Spezia (5% MURST). We wish to thank:
S. Tucci and F. Guercio-Skara (University of Genoa) for kindly providing air temperature data from the Meteorological
Observatory of Genoa.
C. Morri and C.N. Bianchi
behaviour}; (2) effects mediated by biotic interactions (conferral of competitive advantage to
one of a pair of overlapping species); (3) indirectly through ocean currents (changes in climate may alter the emphasis of water flow and
the pattern of water circulation). Note that this
meaning of "direct" and "indirect" effects is different from that commonly used in community
ecology (Strauss 1991). The data from the
Ligurian Sea apparently provided examples for
all these mechanisms.
Population dynamics of Pentapora jascialis,
growth of Cladocora caespitosa. and change in
shoot density of Posidonia oceanica seem to
stand for a direct effect of climate on the organisms, whereas the alternate dominance between
Spisula subtruncata and Chamelea gallina in
sandy bottom communities might correspond
with an effect mediated by conferral of advantage
to one of them in turn. Both species are ftlterfeeding bivalves, sharing the same habitat, and a
competition between them can be suspected.
The same hypothesis is not tenable in the
case of the alternation between Auxis rochei and
Sarpa salpa. The adults of two species occupy
very different niches in the marine ecosystems
and, although we probably do not know enough
about the ecology of their larval phases, a competition is unlikely. Rather, we can think of the
influence of an altered pattern of water flow.
Changes in subtidal rock communities might
also be due to such collateral effects, whereas the
influence of current variability upon the occurrence of southern species in the Ligurian Sea
seems sufficiently proved (Astraldi et al. 1995;
Aliani and Meloni 1999).
Supply side ecology (Roughgarden et al.
1987) emphasises the role of physical transport
processes in structuring marine communities,
and Barry and Dayton (1991) coined the expression "hydrodynamic biological oceanography" to
underline that the variations in the distribution
and abundance of marine organisms are strictly
linked to the movement of water masses. Veron
(1995) introduced the concepts of "surface circulation vicariance" to indicate that the fluctuations in surface currents have a major impact on
shallow marine life.
The alternation observed within bivalves
and fish is consistent with the idea that climatic
fluctuations favour the coexistence of species
potentially redundant (Blandin 1987), thus acting as a biodiversity pump on both evolutionary
and ecological scales (Sara 1985; Astraldi et al.
1995).
An aspect that turned out to be obvious in
our analysis of these Ligurian Sea examples is
that for most of them the observed change can be
equally driven either by climate or by anthropogenic causes. Distinguishing between the two
is often difficult (Bianchi 1997) and can also
cause animated debates, as in the case of the
alleged eutrophication of Skagerrak (BuhlMortensen 1996; Gray 1996). It is true that
anthropogenic and climatic actions can combine
their effects on the marine biota (Bourcier 1996).
All this encourages caution when examining
changes in marine ecosystems and emphasises
the need of planning studies in the context of the
physical setting and the relevant space and time
scales (Levin 1992).
Finding an appropriate space and time scale
was the main problem we met when designing
the layout of this paper. After consulting both
published data and our own archives, we dearly
realised that most of the wealth of scientific
research on the Ligurian Sea (Bianchi et al. 1987;
Cattaneo-Vietti et al. 1988) concerns studies of
local relevance andior carried out for short periods. In part, this reflects the common
Mediterranean research attitude, traditionally
directed toward the identification and description of biocoenosis-types rather than the
dynamic aspects (Bianchi 1997; Bianchi et al.
1998b). We are now getting fully aware that. contrary to the demand of most funding agencies,
any small-scale and short-term approach to ecological monitoring and research will not enable
us to understand ecosystem change, both climate
or man-induced, but will likely result an unproductive investment of time and resources.
Acknowledgements. Change of marine ecosystems is the core
topic of the national research project SINAPSI (Seasonal,
INterannual and decAdal variability of the atmosPhere,
oceanS and related marIne ecosystems). Research on
Cladocora caespitosa was started within the project "Gil
Cnidari del benthos marino: ecologia e biogeografia" of the
University of Genoa (60% MURST). Studies on seagrass beds,
epibenthic communities on rocky reefs and southern species
occurrence in the Ligurian Sea fall within the scope of the
activities on marine biodiversity at the Marine Environment
Research Centre of La Spezia (5% MURST). We wish to thank:
S. Tucci and F. Guercio-Skara (University of Genoa) for kindly providing air temperature data from the Meteorological
Observatory of Genoa.