294
P. Guidetti et aL
Carbon and Nitrogen Content of Epiphytes
and Vagile Fauna
In percentage of dry weight, carbon average content of leaf epiphytes was 22.8±3.6 in P. oceanica,
21.9±7.0 in C. nodosa and 19.8±0.67 in Z. marina, while N content was 3.05±0.89, 2.32±1.42 and
1.85±0.38, respectively.
As for vagile fauna, yearly average content in
carbon was 28.9±4.5 for P. oceanica, 32.4±3.9 for
C. nodosa and 3S.24±4.1 for Z. marina. Nitrogen
content averaged 6.01±1.14 in P. oceanica fauna.
7.2S±0.93 in C. nodosa and 7.99±0.93 in Z. marina one.
In both epiphytic and vagile fauna compartments, no obvious variations in C and N composition with season were detected.
Discussion
Differences among the three seagrass systems
studied occur at more than one level. At plant
level, a trend can be recognised in which P.
oceanica shows the more complex structural
architecture (as indicated e.g. by values of both
leaf biomass and LAI), followed by Z. marina
and, in turn, by C. nodosa. Partitioning of total
biomass is also quite different among the three
species, as well as patterns of nutrient allocation
between the above- and the below-ground compartments. Seasonality in all considered structural parameters (shoot density, LAI and total
biomass) is remarkable in C. nodosa andZ. marina, while in P. oceanica variations are not obvious. On the other hand, a clear seasonality is
shown by N relative content in all three species;
fluctuations in carbon content would be
obscured, as is common in seagrasses, by the
high contribution by structural compounds
(Duarte 1990).
All the above observations point to marked
differences among the three species in both
strategies of resource allocation and structuring
capacity with respect to the system. Posidonia
oceanica appears fundamentally as a biomassstorer in which a key role is played by storage
compartments mainly located in the belowground parts. By contrast, Z. marina seems to
maximise allocation of resources to the aboveground compartment. In C. nodosa, while belowground biomass dominates in all seasons, a more
even partitioning of nutrients occurs between
the two compartments. Such strategy patterns
compare well with those exhibited by other
Mediterranean populations of the same species
(Sfriso and Ghetti 1998; Pire and Wollenweber
1988), while absolute values assumed by a number of parameters would indicate that the three
Adriatic populations studied grow under nonlimiting conditions (Sfriso and Ghetti 1998;
Duarte 1990).
Both absolute values and seasonal variations
of the epiphytic community seemed to be not
strictly related to the available plant surface
(LAI). The environmental stress (i.e. salinity and
temperature variations) is thus invoked as a disturbance factor. In the same way, the biomass of
vagile invertebrates, often related to the level of
habitat complexity, was higher on the average in
Z. marina. The above issues involve the existence
of other superimposed factors which could
explain our results> such as the influence of environmental disturbance (i.e. current tide, amplitude of salinity and temperature variations.
nutrient availability) acting at different temporal
scales as well as the amount and quality of detritus. As far as the nutrient composition of associated communities is concerned, one has to keep
in mind that, dealing with mixed populations in
which a seemingly varying taxonomic composition overlaps with seasonal effects, the values
herein obtained are average figures which
encompass differences within the two compartments across seasons.
Acknowledgements. This study, promoted by the regretted Dr.
Lucia Mazzella, has been carried out in the framework of the
national research programme PRISMA 2 (subproject 3:
"Alterations of Communities"). Dr. P. Guidetti benefited from
a grant founded by CNR. The authors are grateful to A.
Rismondo and D. Curiel for their help during sampling at
Grado, and to S. Caressa and P. Scaffidi for their field assistance.
References
Benacchio N (1938) Osservazioni sistematiche e biologic.:he sulle
Zosteracee dell'Alto Adriatico. Thalassia 3 (3): 2-41
Buia MC, Marzocchl M (1995) Dinamica dei sistemi a Cymodocea
nodasa, Zostera marina e Zostera noltii nel Mediterraneo. G
Bot Ital129 (1): 319-336
Caressa S, Ceschia C, Ore! G, Tre!eani R (1995) Popolamenti
attuali e pregressi nel Golfo di Trieste da Punta Salvore a
Punta Tagliamento (Alto Adriatico). In: Cinelli, Fresi et al
(eds). In: Posidonia oceanica. A Contribution to the preservation of a major mediterranean marine ecosystem. Rivista
Marina 12: 160-187 (suppl)
Damiani V, Bianchi CN, Ferretti 0, Bedu1li D, Morri C, Vie! M.
P. Guidetti et aL
Carbon and Nitrogen Content of Epiphytes
and Vagile Fauna
In percentage of dry weight, carbon average content of leaf epiphytes was 22.8±3.6 in P. oceanica,
21.9±7.0 in C. nodosa and 19.8±0.67 in Z. marina, while N content was 3.05±0.89, 2.32±1.42 and
1.85±0.38, respectively.
As for vagile fauna, yearly average content in
carbon was 28.9±4.5 for P. oceanica, 32.4±3.9 for
C. nodosa and 3S.24±4.1 for Z. marina. Nitrogen
content averaged 6.01±1.14 in P. oceanica fauna.
7.2S±0.93 in C. nodosa and 7.99±0.93 in Z. marina one.
In both epiphytic and vagile fauna compartments, no obvious variations in C and N composition with season were detected.
Discussion
Differences among the three seagrass systems
studied occur at more than one level. At plant
level, a trend can be recognised in which P.
oceanica shows the more complex structural
architecture (as indicated e.g. by values of both
leaf biomass and LAI), followed by Z. marina
and, in turn, by C. nodosa. Partitioning of total
biomass is also quite different among the three
species, as well as patterns of nutrient allocation
between the above- and the below-ground compartments. Seasonality in all considered structural parameters (shoot density, LAI and total
biomass) is remarkable in C. nodosa andZ. marina, while in P. oceanica variations are not obvious. On the other hand, a clear seasonality is
shown by N relative content in all three species;
fluctuations in carbon content would be
obscured, as is common in seagrasses, by the
high contribution by structural compounds
(Duarte 1990).
All the above observations point to marked
differences among the three species in both
strategies of resource allocation and structuring
capacity with respect to the system. Posidonia
oceanica appears fundamentally as a biomassstorer in which a key role is played by storage
compartments mainly located in the belowground parts. By contrast, Z. marina seems to
maximise allocation of resources to the aboveground compartment. In C. nodosa, while belowground biomass dominates in all seasons, a more
even partitioning of nutrients occurs between
the two compartments. Such strategy patterns
compare well with those exhibited by other
Mediterranean populations of the same species
(Sfriso and Ghetti 1998; Pire and Wollenweber
1988), while absolute values assumed by a number of parameters would indicate that the three
Adriatic populations studied grow under nonlimiting conditions (Sfriso and Ghetti 1998;
Duarte 1990).
Both absolute values and seasonal variations
of the epiphytic community seemed to be not
strictly related to the available plant surface
(LAI). The environmental stress (i.e. salinity and
temperature variations) is thus invoked as a disturbance factor. In the same way, the biomass of
vagile invertebrates, often related to the level of
habitat complexity, was higher on the average in
Z. marina. The above issues involve the existence
of other superimposed factors which could
explain our results> such as the influence of environmental disturbance (i.e. current tide, amplitude of salinity and temperature variations.
nutrient availability) acting at different temporal
scales as well as the amount and quality of detritus. As far as the nutrient composition of associated communities is concerned, one has to keep
in mind that, dealing with mixed populations in
which a seemingly varying taxonomic composition overlaps with seasonal effects, the values
herein obtained are average figures which
encompass differences within the two compartments across seasons.
Acknowledgements. This study, promoted by the regretted Dr.
Lucia Mazzella, has been carried out in the framework of the
national research programme PRISMA 2 (subproject 3:
"Alterations of Communities"). Dr. P. Guidetti benefited from
a grant founded by CNR. The authors are grateful to A.
Rismondo and D. Curiel for their help during sampling at
Grado, and to S. Caressa and P. Scaffidi for their field assistance.
References
Benacchio N (1938) Osservazioni sistematiche e biologic.:he sulle
Zosteracee dell'Alto Adriatico. Thalassia 3 (3): 2-41
Buia MC, Marzocchl M (1995) Dinamica dei sistemi a Cymodocea
nodasa, Zostera marina e Zostera noltii nel Mediterraneo. G
Bot Ital129 (1): 319-336
Caressa S, Ceschia C, Ore! G, Tre!eani R (1995) Popolamenti
attuali e pregressi nel Golfo di Trieste da Punta Salvore a
Punta Tagliamento (Alto Adriatico). In: Cinelli, Fresi et al
(eds). In: Posidonia oceanica. A Contribution to the preservation of a major mediterranean marine ecosystem. Rivista
Marina 12: 160-187 (suppl)
Damiani V, Bianchi CN, Ferretti 0, Bedu1li D, Morri C, Vie! M.