Inputs of biogenic carbonate sediment from Posidonia oceanica seagrass meadows to four beaches of the Sinis peninsula (Sardinia, western Mediterranean) were evaluated.Beach and continental shelf sediment samples were analysed for grain size distribution and composition, biogenic vs. siliciclastic,
in order to identify the provenance of beach sediments and sediment transport pathways. Seabed mapping was carried out in order to identify the distribution of meadows and sediment deposits offshore. Shelf sediments were collected in unvegetated sites and in P. oceanica meadows. Sediments from unvegetated sites were coarse
sands and gravel, mainly siliciclastic (biogenic carbonate content is 3–7%). Sediments from P. oceanica meadows were coarse sand, mainly biogenic (carbonate contents varying between 60 and 90%). Beach sediments showed bimodal grain size distribution (59% of samples) resulting from mixing of coarser siliciclastic with finer
biogenic materials in variable proportions. Biogenic carbonate contents in beach sediments range from 0 to 90%, reaching the highest values in offshore samples. Analysis of grain size and compositional trends from shelf to beach sediments highlighted that the latter originate from two
different sources: erosion of granitic outcrops, providing the siliciclastic component, and export of sediments from P. oceanica meadows, providing biogenic material. P. oceanica meadows also influence shore by contributing towards maintaining the beach
sediment budget.
Lo studio dei popolamenti ittici mediante censimenti visivi subacquei (Underwater Visual Census) sta assumendo un ruolo importante come strumento per la valutazione degli effetti delle Aree Marine Protette (AMP) e delle relative misure di regolamentazione sugli ecosistemi costieri. Nell’ambito del progetto EMPAFISH (European Marine Protected Areas as tools for Fisheries managment and conservation) è stato effettuato lo studio della fauna ittica nell’AMP “Penisola del Sinis-Isola di Mal di Ventre” utilizzando la tecnica del Video Visual Census. L’indagine è stata svolta mediante una telecamera subacquea, lungo transetti all’interno dell’AMP e in due aree di riferimento, alla profondità di 5 m e su tre diversi substrati: roccia, Posidonia oceanica e sabbia. I dati raccolti forniscono i primi risultati sulla struttura e la distribuzione dei popolamenti ittici dell’AMP Sinis-Maldiventre. In totale sono state censite 42 specie e 17 famiglie; sono state evidenziate differenze, nella struttura dei popolamenti, tra i tre substrati considerati, con un numero maggiore di specie su roccia (36) e nelle praterie di P. oceanica (22); sono state infine rilevate le specie più rappresentative e quelle legate in modo esclusivo al tipo di substrato. Le analisi preliminari condotte per valutare eventuali differenze tra località interne ed esterne alla riserva mostrano variazioni significative dell’indice di ricchezza specifica con valori più elevati in AMP rispetto alle aree di riferimento
The contribution of biogenic sediments produced by the Posidonia oceanica seagrass ecosystem to shore sediment composition was studied in four beaches along the Sinis Peninsula, west Sardinia. The beach sediments showed a variable amount of biogenic carbonate derived from sediments of P.oceanica meadows.
Marine reserves are assumed to protect a wide range of species from deleterious effects stemming from exploitation. However, some species, due to their ecologicalcharacteristics, may not respond positively to protection. Very little is known about the effects of life history and ecological traits (e.g., mobility, growth, and habitat) on responses of fish species to marine reserves. Using 40 data sets from 12 European marine reserves, we show that there is significant variation in the response of different species of fish to protection and that this heterogeneity can be explained, in part, by differences in their traits. Densities of targeted size classes of commercial species were greater in protected than unprotected areas. This effect of protection increased as the maximum body size of the targeted species increased, and it was greater for species that were not obligate schoolers. However, contrary to previous theoretical findings, even mobile species with wide home ranges benefited from protection: the effect ofprotection was at least as strong for mobile species as it was for sedentary ones. Noncommercial bycatch and unexploited species rarely responded to protection, and when they did (in the case of unexploited bentho-pelagic species), they exhibited the opposite response: their densities were lower inside reserves. The use of marine reserves for marine conservation and fisheries management implies that they should ensure protection for a wide range of species with different life-history and ecological traits. Our results suggest this is not the case, and instead that effects vary with economic value, body size, habitat, depth range, and schooling behavior.
Marine reserves are widely used throughout the world to prevent overfishing and conserve biodiversity, but uncertainties remain about their optimal design. The effects ofmarine reserves are heterogeneous. Despite theoretical findings, empirical studies have previously found no effect of size on the effectiveness of marine reserves in protecting commercial fish stocks. Using 58 datasets from 19 European marine reserves, we show that reserve size and age do matter: Increasing the size of the no-take zone increases the density of commercial fishes within the reserve compared with outside; whereas the size of the buffer zone has the opposite effect. Moreover, positive effects of marine reserve on commercial fish species and species richness are linked to the time elapsed since the establishment of the protection scheme. The reserve size-dependency of the response to protection has strong implications for the spatial management of coastal areas because marine reserves are used for spatial zoning.
