#5 of 6-Part Blog Series dedicated to the protection of Posidonia and seagrass meadows from the detrimental effects of dragging anchors.

As a company committed to marine conservation, we believe that raising awareness and educating the yachting community about responsible anchoring practices is vital. By starting this series on World Ocean Day, we aim to highlight the importance of protecting our oceans and the delicate ecosystems within them. Throughout this series, we will explore various aspects of Posidonia protection, including regulations, communication strategies, international efforts, and technological innovations.

Join us on this journey as we delve into the measures needed to safeguard these underwater treasures and ensure the sustainability of our marine environments.

The Mediterranean Continental Shelf: Biodiversity and the Impact of Anchoring on Shallow Sea Habitats

The Mediterranean continental shelf makes up almost 20% of the Mediterranean Sea’s total area, which is estimated to be 2.5 million square kilometres. With an estimated 17,000 marine species, the Mediterranean harbours around 7% of the world’s marine biodiversity, despite its comparatively small size when compared to other oceans. 

An extensive variety of marine species can be identified on the Mediterranean continental shelf, especially in zones that are shallower than 50 metres.  It does, however, face many threats, including anchoring.

This blog addresses the biodiversity, dynamics, and ecological effects of anchoring in the shallow waters of the Mediterranean Continental Shelf.

The Mediterranean Continental Shelf: A Biodiversity Hotspot

The Mediterranean Sea’s unique geologic, biogeographic, physical, and ecological features, give rise to a variety of habitats, from sandy seabeds to seagrass meadows and stony reefs, and an amazing biodiversity.

Key Habitats & Species

Rocky Reefs: A broad range of species can be found in these places, including the Mediterranean monk seal, which is endangered, as well as several grouper and octopus species.

Coralligenous Assemblages: A vast variety of species, including sponges, bryozoans, and different fish species, find homes in these intricate formations, which are created by the aggregation of calcareous creatures. They are especially vulnerable to changes in their bodily state.

Seagrass Meadows: Because seaweeds and seagrasses are photosynthetic organisms, their development is limited to shallow areas where there is enough light for growth. Posidonia oceanica is an endemic Mediterranean plant species that supports many different kinds of organisms, absorbs carbon dioxide and creates oxygen daily, and produces a substantial amount of biomass yearly.

The biodiversity of the Mediterranean Sea is not evenly distributed throughout its depth zones. The distinct adaptations needed for survival at various depths are reflected in the disparities in species composition throughout depth zones. Coastal areas and the shallow parts of the continental shelf show the highest biodiversity in the Mediterranean Sea. There is a general trend of decreasing species richness from west to east along the northern Mediterranean shelf. As depth increases, there is a general trend of decreasing biodiversity. (source: Ifremer). While deep-sea organisms have adapted to high pressure, darkness, and restricted food availability, shallow-water species are more likely to rely on photosynthesis and are subject to wave action and human impact.

The Mediterranean basin is renowned for having a high endemism content, which includes the biodiversity hotspots of Corsica and the French Mediterranean coast. About 20–30% of the animal and plant species in these waters are native to the Mediterranean, and some, like the Mediterranean monk seal, are endangered. (Source 1, pg 7-8). Prior to 2020, under France’s Investments for the Future Programme (PIA), there were not many ocean-related research projects.  They have since been introduced as part of the France 2030 plan, including the multiple Priority Research Programmes and Equipment (PEPRs).  Despite the magnitude of the issues associated with the ocean, the UN SDG 14 (Sustainable Development Goal on the Ocean) has the least funding from public and private sectors alike with a recent study estimating the missing funding required at over €120 billion a year. (Source: 2)

After the United States and China, France is a global leader in oceanographic research. Over 7000 researchers, scientists, PhD students, technicians and engineers from the Institut Méditerranéen de Biodiversité et d’Ecologie marine et continentale (IMBE), the National Centre for Scientific Research (CNRS), the Ifremer, the IRD, the French National History Museum and French university groups such as the Mediterranean Institue of Oceanology (MIO) and L’Institut Pythéas are just a few of the French research organisations and university groups that work on ocean issues.

The Ifremer and the CNRS have a strong working relationship, as seen by the numerous large-scale projects like the Ocean and Climate PPR that also include the IRD.  Marine research is additionally pushed and cooperative networks are fostered by European framework programmes such as Horizon Europe, the 9th multi-annual research and innovation financing programme, which will run from 2021 to 2027. (Source: 3). For the interest of the national scientific community, the Ifremer also manages the French Oceangraphic Fleet, one of the biggest oceanographic fleets in Europe

The Impact of Anchoring on Shallow Sea Habitats

The fragile marine ecosystems of the Mediterranean are continuously threatened by anchoring, especially in regions that are less than 30 metres deep. Wide-ranging physical damage or destruction from chains and anchors can result in habitat destruction and biodiversity loss.

Seagrass meadows can be uprooted, coralligenous formations can be broken apart, and the sediment layers on sandy bottoms can be disturbed by anchors. On the seafloor, a single anchor drag can cause huge damage which takes decades to repair, and the cumulative effect of anchoring may cause the seagrass cover to decrease in highly touristed areas.

The extent of Posidonia has shrunk between 13% and 38% since 1960, and since the 1990s, the density of Posidonia bundles has dropped by 50% in some locations, per the findings of a study done by researchers in the Balearic Islands. (Source:  4)

The Posidonia meadows at Juan les Pins in southern France were stable from 2016 to 2019, but since then, there has been a tendency to locally regress. This can be explained by the site’s placement in an anchorage zone that is required for vessels with an overall length of at least 80 metres (Arrête 131/2022).(Arrête 131/2022).