Seasonal Trends in the Adriatic Seagrass Communities of Posidonia oceanica (L.) Delile, Cymodocea nodosa (Ucria) Ascherson, Zostera marina L.: Plant Phenology, Biomass Partitioning, Elemental Composition and Faunal Features
Three seagrass systems, represented by Posidonia oceania (L.) Delile, Cymodocea nodosa(Ucria) Ascherson and Zostera marina L. were studied on a yearly cycle in their seasonal evolution in different sites of the Adriatic Sea.The aim of this study, conducted in the frame of the programme PRISMA 2 (Programmma di Ricerca e Sperimentazione per la Salvaguardia del mare Adriatico) was to follow the temporal patterns of these seagrass ecosystems in the Adriatic Sea, in order to investigate their functional mechanisms. Structural attributes of the meadows (i.e. shoot density and phenological parameters) were measured and biomass contributions of the different plant compartments and associated communities (epiphytes and vagile fauna) were estimated Analyses of macronutrients (carbon and nitrogen) of plant compartments and associated communities were aimed at identifying their relative proportion within the living part of the ecosystem. Shoot density showed a marked seasonality in C nodosa and in Z. Marina, while it was constant, as well known, in P. oceanica. Some phenological and structural parameters (i.e. shoot density, leaf length, LAI) varied seasonally, in the different seagrasses, following patterns in accordance with plant eco-physiology. Total biomass was highest in P. oceanica. Different plant compartments (above- vs below-ground) contributed differently to the total biomass in the investigated seagrass species. In P. oceanica and C. nodosa, below-ground parts accounted for the highest biomass through the year, while in Z. marina above- and below-ground contributions were more balanced.The study of carbon and nitrogen composition of different seagrass organs showed a comparative stability of carbon content over time, whereas nitrogen levels followed welldefined seasonal trends in each of the three species, with maxima generally occurring in winter, except for C. nodosa. The patterns observed point to the occurrence of different strategies among the three species at more than one level.
KeywordsSeasonal Trend Shoot Density Zostera Marina Seagrass Species Biomass Partitioning
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