Restoration of Seagrass Meadows in the Mediterranean Sea: A Critical Review of Effectiveness and Ethical Issues

Abstract

Some species of seagrasses (e.g., Zostera marina and Posidonia oceanica) have declined in the Mediterranean, at least locally. Others are progressing, helped by sea warming, such as Cymodocea nodosa and the non-native Halophila stipulacea. The decline of one seagrass can favor another seagrass. All in all, the decline of seagrasses could be less extensive and less general than claimed by some authors. Natural recolonization (cuttings and seedlings) has been more rapid and more widespread than was thought in the 20th century; however, it is sometimes insufficient, which justifies transplanting operations. Many techniques have been proposed to restore Mediterranean seagrass meadows. However, setting aside the short-term failure or half-success of experimental operations, long-term monitoring has usually been lacking, suggesting that possible failures were considered not worthy of a scientific paper. Many transplanting operations (e.g., P. oceanica) have been carried out at sites where the species had never previously been present. Replacing the natural ecosystem (e.g., sandy bottoms, sublittoral reefs) with P. oceanica is obviously inappropriate in most cases. This presupposes ignorance of the fact that the diversity of ecosystems is one of the bases of the biodiversity concept. In order to prevent the possibility of seagrass transplanting from being misused as a pretext for further destruction, a guide for the proper conduct of transplanting is proposed.

Green Nourishment: An Innovative Nature-Based Solution for Coastal Erosion

“…Seagrass has historically been found in temperate and subtropical oceans around the world, but its distribution has been significantly impacted by direct and indirect human activity (e.g., dredging, pollution). Seagrass beds are ecologically important marine habitats (Boudouresque et al, 2021;da Ros et al, 2021) that stabilize sandy substrates through the binding effects of their roots and rhizomes and, through the hydrodynamic buffering capabilities of their leaves, dissipate wave energy, tidal currents and storm surges (Fonseca, 1994;Reidenbach and Thomas, 2018;Montgomery et al, 2019). A dense seagrass meadow is able to reduce wave height by 40% during storm events (Ondiviela et al, 2014).…”

The World of Edges in Submerged Vegetated Marine Canopies: From Patch to Canopy Scale

“…The coastal marine seascape is characterized by, among others, the presence of saltmarshes, seaweeds, and macrophyte canopies that form both submerged and partially emerged habitats which occupy a narrow fringe-from the upper intertidal zone to about 90 m depth, with the shallow limit considered as the landward continuous front settled on the soft bottom [6][7][8]. Despite their small number, approximately 60 species [9], seagrass communities provide significant and crucial ecosystem services that contribute to human welfare and shoreline protection [8,10,11]. Canopies, for instance, seagrass meadows, also provide ecological services such as attenuating waves, currents, and storms [12][13][14], mitigating storm surges and marine heat waves, preventing the erosion of coastal beds [12,15,16], promoting sediment accumulation [14,17], contributing to nutrient cycling and carbon sequestration [9], shaping estuarine geomorphology [18], and providing refuge and nursery grounds for the local biota [12,19].…”

“…At the deepest edge, light affects the chlorophyll content and morphological characteristics of leaves such as the changes in leaf thickness [46]. However, as a consequence of modern pollution and water turbidity, in many areas an extensive belt of dead matter limits the deep positions of meadows, [10], as is the case of the Posidonia oceanica meadows in the Gulf of Marseille where the limit is found to be between 22 and 30 m deep [10]. Likewise, shoot density and coverage decreases in the regressive deep limits of Posidonia oceanica meadows have been found along the coastlines of Corsica [47].…”

Stakeholders’ Attitudes about the Transplantations of the Mediterranean Seagrass Posidonia oceanica as a Habitat Restoration Measure after Anthropogenic Impacts: A Q Methodology Approach

“…In the European Union, such works are subject to environmental impact assessment (EIA) or strategic environmental assessment (SEA) according to the Impact Assessment Directive (2014/52/EU), and to national laws that provide for compensation when maritime works are expected to damage the meadows. In particular, transplantations of P. oceanica shoots have been prescribed often in Italy as a suitable compensation measure [14], although their effectiveness is still debated [15].…”