Search

In this paper the results of a manipulative experiment aimed to evaluate the interactive short- and long-term effect of three different stressors, herbivory, nutrient and mucilage, on a macroalgal assemblage are presented. The experiment was conducted in Tavolara Punta Coda Cavallo Marine Protected Area during a bloom of the benthic mucilage-producing microalga Chrysophaeum taylorii Lewis and Bryan (Pelagophyceae), recently spreading in the Mediterranean Sea. On a rocky substratum, 18 plots 20x20 cm in size were prepared and, according to different treatments, nutrients were added in some of them to simulate eutrophication, macroalgae were removed to simulate clearings produced by grazers and mucilage was manually removed to simulate mucilage-free conditions. Differences in the composition of macroalgal assemblages were found when considering the short term effect of the considered stressors, and also the response of the most abundant taxa (DFA, ECA, Dictyotales, Laurencia spp. and Padina pavonica) varied among treatments, proving that a combined effect of such stressors on the recovery of macroalgae was present. On the contrary, the effect of treatments was neither highlighted on the most abundant algae nor on the whole structure of the macroalgal assemblage.

C. mediterranea tissue nutrient content (mean + SE, n=15) in fertilized (F) and non-fertilized (NF) conditions. Significant differences indicate fertilizer effectiveness (ANOVA, p < 0.01).

Predicting where state-changing thresholds lie can be inherently complex in ecosystems characterized by nonlinear dynamics. Unpacking the mechanisms underlying these transitions can help considerably reducing this unpredictability. We used empirical observations, field and laboratory experiments and mathematical models to examine how differences in nutrient regimes mediate the capacity of macrophyte communities to sustain sea urchin grazing. In relatively nutrient-rich conditions, macrophyte systems were more resilient to grazing, shifting to barrens beyond 1800 g m−2 (urchin biomass), more than twice the threshold of nutrient-poor conditions. The mechanisms driving these differences are linked to how nutrients mediate urchin foraging and algal growth: controlled experiments showed that low-nutrient regimes trigger compensatory feeding and reduce plant growth, mechanisms supported by our consumer–resource model. These mechanisms act together to halve macrophyte community resilience. Our study demonstrates that by mediating the underlying drivers, inherent conditions can strongly influence the buffer capacity of nonlinear systems.

Maps of the Mediterranean basin presenting mean values for 2013 for A) Chlorophyll A concentration, B) sea surface temperature and C) Photosynthetically available radiation. Yellow and blue dots illustrate the position of the studied locations in the high and low nutrient regions respectively. Note the strong differences in Chlorophyll A concentrations and the similarities in the other environmental parameters between the two regions. These maps were obtained from the NASA's Earth Observing System Data and Information System (EOSDIS) http://oceancolor.gsfc.nasa.gov/cms/.

Mean percentage macroalgal cover + SE in plots of four different treatments in the low nutrient region (nutrient-enriched, without urchins: N+U0, nutrient-enriched, with urchins: N+U+, not enriched, with urchins N0U+, and not enriched, without urchins: N0U0). The percentage difference between N0U0 and N+U0 plots shows the effect of nutrient mediated growth (35.5% blue shadowed area). Additionally, the percentage difference between the N+U0 and the N+U+ shows the effect of both compensatory feeding and nutrient mediated growth together (71% green shadowed area).

P. oceanica tissues nutrient content (mean + SE) was analysed in each region as an indicator of nutrient availability to confirm differences in nutrient regimes [37]. Significant differences (ANOVA, p < 0.01) confirmed that the Catalan coast is more eutrophic than Sardinia [30].

Map of the Western Mediterranean basin presenting productivity data from Bosc 2004. Note the big differences in productivity between regions. Yellow and blue dots represent the position of the studied locations within both high and low nutrient regions respectively.

A manipulative experiment was carried out in a small bay of Tavolara Punta Coda Cavallo Marine Protected Area in order to investigate the triggers for formation and storage of the macroscopic mucilaginous aggregates of the benthic microalga Chrisophaeum taylorii Lewis & Bryan (Pelagophyceae) and to test the efficacy of mucillage removal.

In the summer months of 2010 the cell density of the alien benthic microalga Chrysophaeum taylorii Lewis & Bryan (Pelagophyceae) was assessed on hard benthic substrates in sixteen study sites along the north-eastern coast of Sardinia in order to obtain useful information on spatial and temporal variations of the species in the area during summer.

The introduced alga Caulerpa racemosa (Forsskal) J. Agardh (Caulerpales, Chlorophyta) has become an important component of rocky assemblages in the subtidal of the Mediterranean. Understanding the faetors that regulate the establishment and spread of this species is, therefore, crucial to predicting future pathways of invasion and susceptible locales. Further, the aim of this study was to investigate on the factors responsible for Ihe successful invasion of C. racemosa in the Asinara Gulf (NW-Sardinia).

In August 2009 the distribution and density of the alien microalga Chrysophaeum taylorii Lewis & Bryan (Pelagophyceae) were investigated on hard benthic substrates in seventeen sites from northern to central-eastern Sardinia, in order to estimate the distribution and abundance of this species in the area.

The sandy shore comprised between Alghero and Fertilia (Alghero Gulf, NW-Sardinia) has been monitored through satellite and aerial images from 1977 to 2009 and uploaded in ARCGIS system. Results indicate that the area is suffering a severe erosion mainly due to the building of marina docks and breakwaters.

A pilot study was performed in order to evaluate the ecological status of the clam Ruditapes decussatus and its occurrence in specific harvested areas within the Gulf of Olbia. Indeed, since 1998, stocks of this clam seems to be decreased, due to intense human harvesting.

Canopy algae of the genus Cystoseira are considered important habitat formers providing shade and shelter for a diversified assemblage of animals and plants. Some evidence suggested that these algae are highly sensitive to anthropogenic disturbances and their presence could be used as an `ecological quality' indicator. In this paper we tested the hypothesis that structure of assemblages understoried by these algae is dependent on Cystoseira species. To achieve this aim the composition of benthic assemblages under the canopy of three Cystoseira species was estimated at Sinis-Mal di Ventre MPA (western Mediterranean), where at some sites these algae occur on the same upper-infralittoral platforms. At one site 2 areas have been sampled and in each area 5 replicates were taken per Cystoseira species. The percent coverage of benthic species was estimating in the field using a 20X20 cm multiple-scale quadrats. A multivariate analysis was performed to highlight differences in taxa composition. Results have evidenced significant variations in assemblages depending on Cystoseira species (ANOSIM R=0.585 p=0.1%). These results suggest that the three Cystoseira species co-occurring on the same platforms do structure different habitats supporting diversified species assemblages. Hence, given the high variability on small spatial scale of habitats it is necessary to perform well designed experiments to correctly interpret results collected during monitoring program.

The sea urchin Paracentrotus lividus (Lamarck) is the most common grazer in the Mediterranean infralittoral that at high densities overgrazes complex algal assemblages turning them into barren areas. This study has the aim to investigate whether abundance and population structure of P. lividus is consistent between rocky boulders and Posidonia oceanica habitat. At this aim, we have sampled P. lividus at six sites in the Gulf of Alghero (North West Sardinia), 3 fished (sea urchin are harvested) and 3 controls (no harvest is allowed) and at each site the two habitats, 6-10 m deep, were considered. For each combination site x habitat 10 replicates were taken. Density of P. lividus was assessed using quadrats of 1 x 1 m. The size of 20 individual (test diameter without spines) per site was measured by means of a calliper (1#1 0.1mm). Sea urchins, finally were grouped into size classes to examine frequency distributions. Sampling was performed at the end of a harvesting period (April-May 2006). Analyses of data have highlighted a significant variability for both response variables among sites while in Posidonia oceanica habitat a lower density and a higher size were found rather than in rocky habitat. Further data collected at three types of Posidonia oceanica (patches close to rocky habitat, far from rocky habitat and patches bordered by sediment) suggest that the abundance of adults in the seagrass is probably sustained by immigration from the rocky habitat.

Rocky intertidal platforms at Asinara Island Marine Protected Area (Italy, Mediterranean Sea) were experimentally trampled to assess the impact of human visitation on polychaetes. Trampling at two different experimental intensities (60,120 steps/20x20 cm quadrat) and controls were applied at two locations (“no-entry, no-take” zones) of the MPA. One day after the experimental trampling, benthic samples were collected and the polychaetes counted and identified. Overall 1146 individuals were collected; Salvatoria clavata, Polyophthalmus pictus, Syllis prolifera, Amphiglena mediterranea, Fabricia stellaris, Platynereis dumerilii and Sphaerosyllis taylori were the most abundant species. Analyses of variance on all polychaetes and on each of the important polychaete species showed a significant higher abundance in controls than in trampled plots. Given the short-term decline in abundance, these results suggest that polychaetes are vulnerable even to the lowest experimental level of trampling., Las plataformas rocosas intermareales del Área Marina Protegida (AMP) de la Isla de la Asinara (Cerdeña, Italia), fueron experimentalmente pisoteadas para evaluar el impacto de la presencia humana sobre las comunidades de poliquetos. Se aplicaron dos diferentes intensidades experimentales (60,120, pasos sobre una superficie de 20x20cm) y control en dos zonas (zonas definidas como “no-entry, no-take”) de la AMP. Un día después de la perturbación experimental, se recogían muestras bentónicas identificando y cuantificando los poliquetos. Un total de 1.146 poliquetos fueron recogidos; Salvatoria clavata, Polyophthalmus pictus, Syllis prolifera, Amphiglena mediterranea, Fabricia stellaris, Platynereis dumerilii y Sphaerosyllis taylori fueron las especies más abundantes. El análisis de la variación global de los poliquetos y de sus especies permitieron observar una abundancia significativamente superior en las áreas de control que en las parcelas pisoteadas. Considerando en el corto plazo la disminuciòn de la abundancia, estos resultados sugieren que los poliquetos son vulnerables, includo en el nivel experimental más bajo probado.

Caulerpa racemosa (Forsskål) J. Agardh è una specie lessepsiana altamente invasiva e le conoscenze sull'effetto della sua diffusione sui popolamenti zoobentonici in Mediterraneo sono molto scarse. Lo scopo di questo studio è quello di valutare l'effetto immediato della rimozione di C. racemosa sui popolamenti zoobentonici dell'infralitorale superficiale roccioso. E' stato condotto un esperimento manipolativo in un sito prospiciente un'area urbanizzata del nord Sardegna (Porto Torres). Durante l'estate 2004 sono state scelte delle aree random di 20x20 cm, nelle quali C. racemosa è stata rimossa, e delle aree di controllo. Successivamente (ad un giorno e ad un mese di distanza dopo la prima rimozione), sono stati raccolti campioni attraverso l'uso di cilindri di plastica (diametro 40 mm) e di un raschietto metallico. Il materiale è stato fissato in formalina e gli animali raccolti sono stati identificati e contati. Dall'analisi multivariata risulta che non vi è differenza significativa (ANOSIM p=39,4% R=0,004) tra l'abbondanza dei taxa raccolti nelle aree di rimozione e le aree di controllo in entrambi i tempi di campionamento. I risultati ottenuti, del tutto preliminari, sottolineano la necessità di approfondire le conoscenze sul risultato delle interazioni di C. racemosa con gli altri taxa presenti nell'area su una scala temporale più lunga.

Generally, through the LOICZ model application to the lagoon, it is observed that there is prevalence of nutrient storing processes rather than that of nutrient mobilisation. Nitrogen fixation always prevailed over denitrification. The productive processes in the lagoon thus seem to be prevalent over most of the year. These results confirm that S’Ena Arrubia Lagoon is to be considered an autotrophic system as far as the net total metabolism is concerned.

La ricerca qui descritta si è svolta nell'AMP dell'Isola dell'Asinara e ha cercato di valutare l'effetto del calpestio sulla comunità zoobentonica associata ad alghe del medio- ed infralitorale superiore di fondo roccioso. È stato condotto un esperimento multifattoriale di simulazione del calpestio: in due cale `no entry, no take' sono state scelte 6 aree e, 3 intensità di calpestio sperimentale (0, 60 e 120 calpestii per quadrato di 20x20 cm), sono state attribuite a random nelle aree. I prelievi sono stati compiuti con cilindri di plastica (diametro 40 mm) e un raschietto metallico; sono stati raccolti 2 campioni per quadrato. Il materiale è stato fissato in formalina. In laboratorio sono state separate le due componenti mediante adeguati setacci; gli animali raccolti sono stati identificati e contati. Dall'analisi multivariata risulta che, per entrambe le componenti, vi è differenza significativa tra i controlli e le aree dove è stato effettuato il calpestio (ANOSIM macrofauna p=0,4% R=0,45, meiofauna p=0,5% R=0,50). Inoltre dai confronti a coppie tra i livelli di calpestio risulta una differenza significativa tra i controlli e le due intensità di trampling (60 e 120), mentre non vi è differenza significativa tra le due intensità di calpestio. Sebbene non si possa fare nessuna previsione sul recupero della comunità, questi risultati suggeriscono che sia la macrofauna sia la meiofauna siano estremamente vulnerabili a questo tipo di disturbo.

The spatio-temporal variability of phytoplankton and some environmental parameters in the gulf of Asinara are examined (05/97-04/98). Along the whole coastal area, stations at 500 and 3000 mfrom coast across 6 transects are considered. Results point out some variations in phytoplankton composition and dynamics. Multidimensional Scaling ordinations and Bray-Curtis cluster analuses identified two major zones at 500 m from coast, one for the site of Lu Bagnu and one for the other five sites; at each stations, a great similarity was found in its respactive share. On the contrary, at 3000 m from coast, no cluster was identified.

Water samples and environmental data were examined at four stations at biweekly or monthly intervals, depending on the period, from February 1990 to December 1999. Phytop/ankton composition was estimated in these samples. The abiotic parameters revealed a difference in environmental conditions between the outer area of the lagoon and those closer to the coast. Phytoplankton structure was quite consistent among different areas of the lagoon. Absolute abundance was very different among classes, with Chlorophyceae much more abundant than Bacillariophyceae. Haptophyceae and Chrysophyceae were the least represented classes. Density of classes reached peaks in different periods of the year, suggesting a recurrent pattern in taxa succession.