| Abstract | The macrobenthic community was compared at four sites characterized by varying degrees of freshwater
input, organic enrichment and confinement in the Cabras lagoon (Sardinia, Italy). Three sites, riverine
(C1), confined (C2) and seaward (C3), were studied on two dates of summer 2010 and on two dates of
winter 2011. A fourth site (C12), representative of the central sector of the Cabras lagoon, was included in
this study using the extensive historical datasets at our disposal from previously published work. We
aimed to test the hypothesis that (1) the benthos is distributed according to the recently proposed
concept of habitat saprobity for coastal lagoons that unifies the PearsoneRosenberg (sensu organic
enrichment) and GuélorgetePerthuisot (sensu confinement) models, and (2) indicator species of
different saprobic levels can be identified among dominant species occurring along the saprobity
gradient. Salinity was also considered as an additional agent of selection in brackish environments.
Irrespective of significant seasonal changes within each site, our results highlighted major environmental
and biotic differences between sites. At the northward riverine site (C1), most affected by freshwater
input and with limited organic matter (OM) enrichment, Corophium orientale was the single dominant
species. The most confined site (C2) was characterized by the highest levels of sedimentary OM and
benthic Chlorophyll-a and by mesohaline conditions; the site was inhabited mainly by the halolimnobic
Hediste diversicolor and Hydrobia spp. Site C12, characterized by a high OM load and high residence time,
was dominated by the opportunistic detritivorous Alitta succinea and Polydora ciliata. At the southernmost
seaward site (C3) the considerable seawater renewal, resulting in high salinity (only in summer)
and limited OM load, favored a much more diverse macrobenthic assemblage, essentially composed of
both marine species, such as Corophium insidiosum, Gammarus aequicauda, and brackish-water species,
such as Lekanesphaera hookeri and Idotea chelipes. We conclude that the biotic and abiotic characteristics
of the Cabras lagoon can be represented by a succession of spatial zones along two main gradients
determined by salinity and saprobity. The salinity gradient proved to be the main structural feature in the
oligohaline pole, while in the range of variable salinity, saprobity appeared to be the main selection
factor. To illustrate our findings, we provide a graphical representation summarizing the changes in
environmental parameters and indicator species along the salinity and saprobity gradients. |
| Text | 349264 2014 Macrobenthos Brackish waters Organic enrichment Saprobity Salinity Mediterranean lagoons Testing the saprobity hypothesis in a Mediterranean lagoon Effects of confinement and organic enrichment on benthic communities A. Foti , G.A. Fenzi , F. Di Pippo , M.F. Gravina , P. Magni Department of Biology, University of Rome Tor Vergata , Via della Ricerca Scientifica, 00133 Rome, Italy CNR IAMC, National Research Council, Institute for Coastal Marine Environment, Localita Sa Mardini, Torregrande, 09170 Oristano, Italy CNR IRSA, National Research Council, Water Research Institute, Area della Ricerca di Roma 1, Via Salaria km 29, Monterotondo stazione, 00015 Rome, Italy CNReISMAR, National Research Council, Institute of Marine Science, Arsenale Tesa 104, Castello 2737/F, 30122 Venice, Italy The macrobenthic community was compared at four sites characterized by varying degrees of freshwater input, organic enrichment and confinement in the Cabras lagoon Sardinia, Italy . Three sites, riverine C1 , confined C2 and seaward C3 , were studied on two dates of summer 2010 and on two dates of winter 2011. A fourth site C12 , representative of the central sector of the Cabras lagoon, was included in this study using the extensive historical datasets at our disposal from previously published work. We aimed to test the hypothesis that 1 the benthos is distributed according to the recently proposed concept of habitat saprobity for coastal lagoons that unifies the PearsoneRosenberg sensu organic enrichment and GuelorgetePerthuisot sensu confinement models, and 2 indicator species of different saprobic levels can be identified among dominant species occurring along the saprobity gradient. Salinity was also considered as an additional agent of selection in brackish environments. Irrespective of significant seasonal changes within each site, our results highlighted major environmental and biotic differences between sites. At the northward riverine site C1 , most affected by freshwater input and with limited organic matter OM enrichment, Corophium orientale was the single dominant species. The most confined site C2 was characterized by the highest levels of sedimentary OM and benthic Chlorophyll a and by mesohaline conditions; the site was inhabited mainly by the halolimnobic Hediste diversicolor and Hydrobia spp. Site C12, characterized by a high OM load and high residence time, was dominated by the opportunistic detritivorous Alitta succinea and Polydora ciliata. At the southernmost seaward site C3 the considerable seawater renewal, resulting in high salinity only in summer and limited OM load, favored a much more diverse macrobenthic assemblage, essentially composed of both marine species, such as Corophium insidiosum, Gammarus aequicauda, and brackish water species, such as Lekanesphaera hookeri and Idotea chelipes. We conclude that the biotic and abiotic characteristics of the Cabras lagoon can be represented by a succession of spatial zones along two main gradients determined by salinity and saprobity. The salinity gradient proved to be the main structural feature in the oligohaline pole, while in the range of variable salinity, saprobity appeared to be the main selection factor. To illustrate our findings, we provide a graphical representation summarizing the changes in environmental parameters and indicator species along the salinity and saprobity gradients. 99 Published version Articolo in rivista Applied Science Publishers, 0141 1136 Marine environmental research Marine environmental research Mar. environ. res. Marine environmental research. Journal of marine environmental research paolo.magni MAGNI PAOLO francesca.dipippo DI PIPPO FRANCESCA |
