Distribution and dynamics of Posidonia oceanica beds along the Albères coastline

Spatial patterns of Posidonia oceanica structural and functional features in the Eastern Mediterranean (Aegean and E. Ionian Seas) in relation to large-scale environmental factors

In the context of general ecosystem monitoring of the Greek coastal marine environment, a total of 22 descriptors of Posidonia oceanica meadows were studied in 69 study sites. Spatial variation of P. oceanica meadows' features in relation to specific environmental factors (i.e., light, physical exposure, temperature, and nutrients) controlling their dynamics was assessed in three sub-ecoregions of the Hellenic seas (Eastern Ionian, North Aegean, and South Aegean). The studied meadows differentiated by exhibiting varying growth patterns at both the local and sub-ecoregional scale. Significant differences in morphological and demographic descriptors were observed for meadows of the N. Aegean Sea as compared to those of the S. Aegean and the Eastern Ionian Seas. Light limitation was determined as the main driver differentiating the P. oceanica meadows' distribution (i.e., lower limit depth), demography (i.e., shoot density, meadow cover) and shoots' biometry (i.e., shoot length, shoot leaf surface and leaf biomass) along the mainland coastal zone of the N. Aegean Sea. Considering the projected decline of P. oceanica in the face of increasing natural and human impacts, this study offers a crucial ecological baseline that can enhance our understanding of P. oceanica meadows' trends, against which the efficiency of conservation plans and management actions may be monitored.

Self-organisation in striped seagrass meadows affects the distributional pattern of the sessile bivalve Pinna nobilis

Striped seagrass meadows are formed by narrow ribbons which are elevated over the seabed and separated by channels. Limited information on the genesis and development of this morphological pattern, including the adaptive responses of associated biota, is preventing holistic insight into the functioning of such protected ecosystems. This paper assessed the structural dynamics of a Posidonia oceanica striped meadow and the distribution and 3D orientation of the associated bivalve Pinna nobilis. Our analysis of the interaction between bedforms, bottom currents, and the distribution of P. nobilis revealed that the striped seascape is the result of a self-organisation process driven by feedback interactions among seagrass growth, sediment deposition, and hydrodynamics. The results suggest that the ribbon wall is the most suitable sub-habitat for this species, because it supports the highest density of P. nobilis, compared to the meadow top and bottom. Here, specimens can take advantage of the resuspension induced by hydrodynamics and open their shells towards the current, thus enhancing food intake. Therefore, our results show that self-organisation in striped seagrass meadow affects the distributional pattern of P. nobilis, providing new insights into the autoecology of this species beyond the conservation implications for its habitat.

Seagrass (Posidonia oceanica) monitoring in western Mediterranean: implications for management and conservation

The seagrass Posidonia oceanica is extensively monitored in Mediterranean coastal waters and is an ideal candidate for an eco-regional assessment of the coastal ecosystem. The aim of this study is to evaluate the potential of P. oceanica as eco-regional indicator for its assessment at the scale of Mediterranean basin. For this purpose, regional and national P. oceanica monitoring programmes are identified, and their data and metadata are collected and compared in terms of objectives, strategies, sampling designs and sampling methods. The analysis identifies a number of issues concerning data quality, reliability and comparability. In particular, the adoption of different sampling designs and methods may introduce relevant errors when comparing data. The results of this study stress the necessity of carefully planning monitoring programmes. Moreover, it highlights that the adoption of a number of common tools would facilitate all Mediterranean monitoring activities and allows an optimisation of management efforts at an eco-regional scale.

Does coverage matter at mesoscale within a Posidonia oceanica seagrass meadow?

Despite the fact that coverage is one of the most widely used descriptors for seagrass meadows, the spatial structure of coverage at mesoscale has not often been taken into account. The present work investigates the structure of P. oceanica coverage at mesoscale and its possible relationship with several factors (depth, type of substrate, relative level within the meadow, type of shoot density and level of anthropic pressure). Five classes of coverage structure are delineated within P. oceanica meadows and statistical analysis of the data did not provide evidence of a link with the factors taken into consideration. This result could be explained by the prevailing role of endogenic processes in the structuring of the P. oceanica meadow.

Underwater acoustic positioning systems as tool for Posidonia oceanica beds survey

The study of the dynamics of Posidonia oceanica beds, and more particularly, the position of their lower limit, are usually carried out by the installation and monitoring of markers set on the sea bottom. Acoustic telemetry could constitute an interesting alternative solution to the marking of the lower limit seagrass beds. In order to test the potentialities of this system, an experiment was conducted in the Natural Marine Reserve of Cerbère-Banyuls (eastern Pyrenees, France). The possibility of very precise mapping offers many potentialities with regards to the work of monitoring networks in the marine environment (species and assemblages of importance), but also in the monitoring of competition dynamics between the species.