No abstract

Posidonia oceanica (L.) Delile meadows are recognized to be one of the most productive ecosystems of the Mediterranean basin. Due to the impacts of human activities in coastal areas, seagrasses are experiencing a critical decline. In this context, the understanding of the dynamics of production and photosynthesis in response to the environmental factors is essential to address efficient conservation strategies that limit this trend and to assess the ecological status of marine ecosystems. Pulse Amplitude Modulated (PAM) fluorometry has been widely implemented to assess seagrass health and productivity. Here we analyzed the photosynthetic dynamics of P. oceanica according to its bathymetric distribution and daily light availability along a depth gradient to be used as baseline for monitoring purposes on the health status of the seagrass meadows in the Northern Tyrrhenian Sea. Moreover, to investigate the effects of the environmental factors on the health status of P. oceanica within the study area through a multidisciplinary approach, the models contained in the Civitavecchia Coastal Environmental Monitoring System were used. In this study, significant photo-physiological changes have been observed among the investigated meadows. Moreover, the integration of physiological and hydrodynamic information allowed the description of how P. oceanica modulates its photosynthetic capacity at different environmental conditions.

<p>Today, biological invasions represent a threat to endemic animal and plant communities and a major cause of biodiversity loss worldwide. In the Mediterranean Sea, there are about 100 species of macrophytes, introduced intentionally or accidentally, most of which are highly invasive. Among these, the macroalga <em>Caulerpa cylindracea</em> Sonder, 1845, entered in the Mediterranean basin since 1990 through the Suez Canal and now it is widespread along the Italian coasts. This species is able to colonize a high number of coastal substrates and it can affect the density of some seagrasses, such as <em>Cymodocea nodosa</em> (Ucria) Ascherson, 1870 and <em>Posidonia oceanica</em> (L.) Delile, 1813. Its colonization ability is enhanced in environments with a high concentration of nutrients and its growth can modify the redox potential of the substrate making it unsuitable for the establishment of other seagrasses and algae. This work aimed to analyse and describe the potential interaction between the <em>C. racemosa</em> and <em>P. oceanica</em> in the coastal area of Civitavecchia. The potential effects of this interaction were studied inside of two different <em>P. oceanica</em> patches, located at a depth of 3-5 m and characterized by the presence/absence of the invasive alga, through the morphostructural analysis of the two species. In particular, the seagrass growth and primary production were analysed using some direct and indirect techniques (phenology and lepidochronology), while for the alga were analysed the phenological characteristics and the percentage of coverage of the substrate. The sampling campaigns were carried out in two different months of the same year, June and October 2019, in order to observe both the growth phase and the maximum bloom phase of the <em>C. racemosa.</em></p>

Industrial and commercial, together with touristic and ecological, are two of the main uses of the Civitavecchia coastal area that bring wealth and of course influence this marine ecosystem. The port, one of the most important in the Mediterranean Sea, recorded in the last three decades a major increment of its commercial traffic, becoming also strategic for important Mediterranean cruise routes and for passenger flow. New passenger facilities and enhanced and enlarged wharfs allowed to increment the hosted cruise liners from 50 ships in 1996 to 500 in 2003. The creation of new quays and the extension of the anti-mural dame caused on the ecosystems a direct and indirect impact due to the modification of the currents and the dispersion of the dredged materials. The characterisation and assessment of the coastal marine environment of Civitavecchia and its surroundings constitutes, since its creation in 2001, is one of the main activities of the Laboratory of Experimental Oceanology and Marine Ecology (LOSEM) of Tuscia University, who studied the impact of anthropic activities and the influence of climatic events, investigating the chemical and physical parameters of both water column and sediments. Benthic biocenoses and Posidonia oceanica were used to evaluate benthos geochemical and ecological characteristics and a specific effort was devoted to hypothesize the possible incidence of dredging works on the benthic ecosystem. The results of the research activities are synthetically reviewed in this paper.