Abstract
significantly related to water temperature regimes, were observed. The number of new leaves per year (16 leaves y-1), the leaf Plastochrone Interval (23 days) and the life span of the single leaves (from 2 to 6 months) were also calculated. Relevant yearly fluctuations of the leaf canopy, representing about 20% of the total meadow biomass, testify the strong seasonal variability of leaf phenological parameters and shoot density (the latter, between 925 ± 323 and 1925 ± 267 shoots · m -2 ). On the other hand, a constant and well developed layer of rhizomes and roots is present throughout the year (80% of total biomass), with an annual rhizome elongation of about 30 cm. In spite of the temporal variability of the above-ground compartment (CV=55%), the below-ground portion represents the conservative compartment of the meadow (CV=7%). Nevertheless, the remarkable number of seeds present in this meadow (up to 2112 m-2), does not seem to effect the stability of the system through the sexual reproduction. Although similar growth trends have been reported for C. nodosa meadows from different geographical areas and habitats (eutrophic zones, confined shallow waters, estuaries), remarkable differences may be found in the highest and lowest values of growth rate. This comparison highlights the ability of this species to grow in different habitats and that growth process seems to be amplified by a high influence of environmental constraints. Moreover, differences from P. oceanica, both in the growth rate and reproductive patterns, are identified in order to explain the dynamics of these vegetated systems and their role in the Mediterranean basin.
Highlights
IntroductionIn the Mediterranean basin, seagrass meadows play a crucial role in coastal areas because of their high primary production and their support to the increasing biodiversity (Mazzella et al, 1993) and food web complexity (Mazzella et al, 1992; Buia et al,(2000).Cymodocea nodosa (Ucria) Aschers. is a common seagrass species throughout the Mediterranean and partly in the Mauritania region and the Algarve coasts, colonising coastal areas of the CanaryIslands (Den Hartog, 1970; Reyes et al, 1995).Studies on C. nodosa growth in various Mediterranean areas (Terrados and Ros, 1992; Perez and Romero, 1992; Pérez et al, 1994; Reyes et al, 1995; Marbà et al, 1996) have shown that this plant can colonise different types of environment, such as open coastal waters, coastal lagoons and estuaries, and form both monospecific and mixed stands, in association with other seagrasses such as Posidonia oceanica (L.) Delile and Zostera noltii Hornemann (Buia and Marzocchi, 1995).Several papers have highlighted relevant differences between C. nodosa and P. oceanica in their growth strategies, such as the regular, year by year flowering and faster colonisation patterns in C.nodosa, vs. the irregular, stochastic flowering and slower growth rates in P. oceanica (Buia and Mazzella, 1991; Mazzella et al, 1993; Pergent-Martini and Pergent, 1995; Marbà et al, 1996)
SUMMARY: The seasonal changes in the structure and growth dynamics of a Cymodocea nodosa meadow off the island of Ischia (Tyrrhenian Sea) were studied from July 1988 to August 1989 using leaf and rhizome marking methods
In spite of the temporal variability of the above-ground compartment (CV=55%), the below-ground portion represents the conservative compartment of the meadow (CV=7%)
Summary
In the Mediterranean basin, seagrass meadows play a crucial role in coastal areas because of their high primary production and their support to the increasing biodiversity (Mazzella et al, 1993) and food web complexity (Mazzella et al, 1992; Buia et al,(2000).Cymodocea nodosa (Ucria) Aschers. is a common seagrass species throughout the Mediterranean and partly in the Mauritania region and the Algarve coasts, colonising coastal areas of the CanaryIslands (Den Hartog, 1970; Reyes et al, 1995).Studies on C. nodosa growth in various Mediterranean areas (Terrados and Ros, 1992; Perez and Romero, 1992; Pérez et al, 1994; Reyes et al, 1995; Marbà et al, 1996) have shown that this plant can colonise different types of environment, such as open coastal waters, coastal lagoons and estuaries, and form both monospecific and mixed stands, in association with other seagrasses such as Posidonia oceanica (L.) Delile and Zostera noltii Hornemann (Buia and Marzocchi, 1995).Several papers have highlighted relevant differences between C. nodosa and P. oceanica in their growth strategies, such as the regular, year by year flowering and faster colonisation patterns in C.nodosa, vs. the irregular, stochastic flowering and slower growth rates in P. oceanica (Buia and Mazzella, 1991; Mazzella et al, 1993; Pergent-Martini and Pergent, 1995; Marbà et al, 1996). Nodosa, vs the irregular, stochastic flowering and slower growth rates in P. oceanica (Buia and Mazzella, 1991; Mazzella et al, 1993; Pergent-Martini and Pergent, 1995; Marbà et al, 1996) All these studies ascribed to C. nodosa a higher fitness to environmental variability and, in particular, a more direct response to variations in light, seasonal temperature fluctuations and nutrient load (Caye and Meinesz, 1986; Marbà et al, 1996), providing further support to the classical ecological theory of C. nodosa as a coloniser species and P. oceanica as a climax species (Molinier and Picard, 1952; Den Hartog, 1970).
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