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Growth performance of rhizomes has become among the most used descriptors for monitoring Posidonia oceanica seagrass dynamics and population status. However, ability to detect any change of growth in space or in time is often confounded by natural age-induced decline. To overcome this problem, we have produced reference growth charts, which in other areas are universally recognized as a very powerful tool for comparing growth of living beings during their ontogeny. Reference growth charts involving different P. oceanica growth performance measures (speed of growth and primary production of rhizomes) have been built using proper statistical frameworks (GLMM, Segmented and Quantile Regressions), based on more than 13 × 10 3 annual growth data recorded by lepidochronology on about 1600 shoots collected at 4–32 m depth range. Growth patterns exhibited distinct trends as regards the relationships with depth: neither speed of growth nor primary production of rhizomes depended on depth until 14 m, while at deeper stands significant linear decrease by 3.5–2.0% for 1 m increase in depth was observed. According to these results, the depth of 14 m was used as breakpoint for building two distinct sets of reference growth charts. The considerable size of the dataset allowed to estimate the accurate shapes of the percentile curves (5th, 10th, 25th, 50th, 75th, 90th, and 95th), revealing non monotonic relationships of growth performance with respect to shoot age with an initial increase followed by an overall decrease of about 40% during the following years of the explored lifespan. The accompanying model-based classification procedures described in this paper, allow to obtain comparable results also when age of shoots is largely different (up to 20 years). While this approach is flexible enough to produce satisfactory results using any growth measure (speed of growth and primary production of rhizomes, annual or cumulative), it maintains low complexity with trivial computations performed straightforwardly. The growth charts may represent a noteworthy tool for researchers involved in studying of different aspects of seagrass monitoring. It is hoped that the proposed framework will facilitate assessment of growth performance status and comparative analysis of growth data from different populations around the Mediterranean Sea. [ABSTRACT FROM AUTHOR]

Mediterranean Sea is among the world's leading tourist destinations; however, the sharp increase in tourists during the high season may affect coastal seawater. The main aim of this study was to evaluate the occurrence and temporal variation of anthropogenic nutrients in coastal seawater in relation to tourist flows in three Mediterranean islands (Cyprus, Sicily and Rhodes), through short-term macroalgae deployments, coupled with δ15N analysis and GIS mapping. In all islands, an overall increase in macroalgae δ15N occurred over the deployment carried out in August in the tourist sites, suggesting the presence of anthropogenic nutrients. Decreasing δ15N values occurred at increasing distance from the coastline in two out of the three islands (Cyprus and Sicily). This study revealed the usefulness of the approach used in the assessment of tourism impact in terms of trophic enrichment and its potential to support competent authorities for the development of sustainable coastal management plans. Unlabelled Image • Deployed Cystoseira was a good bioindicator of anthropogenic nutrient enrichment. • Macroalgae Δδ15N peaked in August compared to June and October in all tourist sites. • Macroalgae 15N-enrichment decreased from landward to seaward in most tourist sites. • Δδ15N range was −1.4–+1.4‰ denoting low/moderate inputs of anthropogenic nutrients. • GIS maps were a powerful tool to represent tourism impact in coastal water. [ABSTRACT FROM AUTHOR]

Alagna et al. (2019) suggest new transplantation methods for Posidonia oceanica (Linnaeus) Delile, inspired by its natural recovery process after disturbance due to dredging operations for gas-pipelines. They observe that P. oceanica vegetative fragments naturally settled only on loose calcareous stones deployed to fill the trenches of the gas-pipeline. No recovery was noted on dead matte , sand and large calcarenitic boulders. Following a new pilot restoration project currently ongoing in the same area, we demonstrate that natural recovery also occurs on dead matte. After examining other alternative transplantation methods for P. oceanica , the Authors suggest using their " habitat enhancement units " method for the restoration of seagrasses, not only on rocky bottom but also on sand and other bare substrate requiring general environmental restoration. Here we express disagreement on certain issues reported in the paper. [ABSTRACT FROM AUTHOR]

Understanding the response of species to disturbance and the ability to recover is crucial for preventing their potential collapse and ecosystem phase shifts. Explosive submarine activity, occurring in shallow volcanic vents, can be considered as a natural pulse disturbance, due to its suddenness and high intensity, potentially affecting nearby species and ecosystems. Here, we present the response of Posidonia oceanica, a long-lived seagrass, to an exceptional submarine volcanic explosion, which occurred in the Aeolian Archipelago (Italy, Mediterranean Sea) in 2002, and evaluate its resilience in terms of time required to recover after such a pulse event. The study was carried out in 2011 in the sea area off Panarea Island, in the vicinity of Bottaro Island by adopting a back-dating methodological approach, which allowed a retrospective analysis of the growth performance and stable carbon isotopes (δ13C) in sheaths and rhizomes of P. oceanica , during a 10-year period (2001–2010). After the 2002 explosion, a trajectory shift towards decreasing values for both growth performance and δ13C in sheaths and rhizomes was observed. The decreasing trend reversed in 2004 when recovery took place progressively for all the analysed variables. Full recovery of P. oceanica occurred 8 years after the explosive event with complete restoration of all the variables (rhizome growth performance and δ13C) by 2010. Given the ecological importance of this seagrass in marine coastal ecosystems and its documented large-scale decline, the understanding of its potential recovery in response to environmental changes is imperative. • We studied resilience of Posidonia oceanica after a natural pulse disturbance. • We carried out a 10-year retrospective analysis of growth, and sheath and rhizome δ13C. • Growth performance and δ13C decreased soon after disturbance. • The decreasing trend reversed 2 years after disturbance. • Full recovery occurred 8 years after disturbance. [ABSTRACT FROM AUTHOR]