Sand is a key element of marine-coastal environments, thanks to its innate modesty and beauty. It also provides the ideal substrate for a whole range of useful and valuable plant and animal species.
We are talking about the dune ecosystems lining the Italian coast and the meadows of Mediterranean tapeweed.

Adriatic instances of such ecosystems would be the dunes in the protected marine area of Torre del Cerrano in the Province of Teramo and the Dune di San Giuseppe in the Po Delta.

Generally speaking, dunes are hills of sand shaped by the wind, therefore continuously shifting place and shape with wind changes.
Coastal dunes act as a buffer zone between different environments, marking the transition between sea and inland areas, featuring thickets of typically Mediterranean shrubs and evergreen trees.

Dunes can be stationary and fossilised or mobile where wind speeds exceed around 4 m/s, causing the sand grains to shift.
Their shape depends on the available amounts of sand and on wind direction and speed. In terms of their size, dunes can be up to 15 metres high, with a length of up to 500 metres.

Coastal dunes are divided into primary and secondary dunes and are a typical feature of the ‘beach-dune system’.

Primary dunes, or foredunes, occupy the ‘deposition area’. These are small actively accumulating piles that gradually combine and can be stabilised only partially by the presence of vegetation.
Secondary dunes, on the other hand, lie beyond the limit of the primary dunes and represent old foredune belts that have become more stable.

Illustration of the dune profile of the beach-dune system: the dune belt is divided into two dune habitats, the primary dune or forward dune, more exposed to the action of the wind, and the secondary dune or back dune immediately after the first one going inland.

The sand on the windward side of dunes is compact, with closely packed, well-compressed grains of a consistency that ideally allows walking.
On the leeward side, however, grains tend to accumulate randomly by wind action, with spaces often left between them. Here, the pressure exerted by walking inevitably leads to footsteps sinking into the sand.
Wind action and the characteristics of the sediments can create regular accumulations of granules in the form of ripples. These flatten out and disappear as the surface wind speed increases.

Plants and the sand play a team game. Dune vegetation needs the sand as a substrate, and the sand in turn needs the presence of plants to be able accumulate and stabilise, creating a dune.

Specifically, dune formation is linked to the presence of pioneer species, including plants of the Ammophila arenaria species. These help the initial sand deposits to accumulate, even very close to the shoreline.
Ammophila is a genus of plants of the Graminaceous family typically found on sandy shorelines, especially in the Mediterranean basin and on the Atlantic coasts of France and Spain.
Ammophila arenaria, an emblematic dune species, is only found to a limited extent in the Po Delta in the Province of Ferrara due to degradation of its dune ecosystems.

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Ammophila arenaria

European searocket (Cakile maritima), sand couch-grass (Thinopyrum junceum) and sea bindweed (Convolvulus soldanella) are all commonly found on the sandy strands and dunes of the Ferrara Po Delta, together with rare examples of the sea daffodil (Pancratium maritimum).

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European searocket (Cakile maritima) and Sea daffodil (Pancratium maritimum)

Coastal dune ecosystems have, however, been substantially reduced even compared to the recent past due to human activities and progressive erosion of the shoreline, and their existence is under threat.
Among the reasons for the disruption and removal of dune ecosystems is the increase in built-up areas and tourist facilities along the coast, as well as the severe impact of mechanical cleaning of strands aimed at rendering beaches more pleasant and attractive to tourists.

According to ISPRA (the Italian Institute for Environmental Protection and Research), human action during the last two decades has led to an overall loss of 5 km of natural coastline per year, with 13% of the Italian coastline currently built-over.
Apart from their great ecological value, dunes are also of considerable economic importance to coastal areas. This is because they protect the coast from the action of the sea and act as a source of sand to replenish beaches suffering erosion.

Sustainable management and enhancement of dune ecosystems is both necessary and feasible. 
An example of this can be seen in the wooden walkways built in Scotland to avoid walking on the dunes and to allow the large numbers of tourists arriving access to the beaches, thus ensuring survival and protection of bird species.

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West Sands beach, St Andrews, Scotland

Often confused with an alga, Posidonia oceanica is in fact a vascular plant. Unlike algae, which have no vascular system, Neptune grass is equipped with roots, rhizomes and leaves and can produce flowers and fruit with seeds.
Endemic in the Mediterranean, this species plays a key role in conserving coastal biodiversity and stability. It is protected as a priority habitat under the EU’s Habitats Directive. 

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Posidonia oceanica

Although it also grows on rocky or detritic beds, Neptune grass prefers mobile substrates, such as more or less fine-grained sand, sometimes mixed with mud.
It is also a plant that needs a lot of light, and so water transparency and depth are limiting factors for its development and growth.

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When it finds suitable conditions, Posidonia oceanica colonises vast areas of the seabed, forming wide expanses known as meadows, which tend to become sparser with depth. Meadows extend from the surface down to a depth of 30-35 metres, even reaching 40 metres in particularly clear waters.

The important role played by Posidonia oceanica meadows in removing CO₂ from the sea and acting as a ‘refuge’ for several animal species far outweighs the actual surface area occupied by the plant, which plays a key role in the overall economy of coastal areas.

A typical feature of Neptune grass is the development of a dense network of rhizomes that develop both horizontally and vertically.
The horizontally growing ‘plagiotropic’ rhizomes are used to anchor the plant to the substrate, thanks to the presence of roots at the bottom of the plant, thus allowing colonisation of new areas. The ‘orthotropic’ rhizomes, on the other hand, grow vertically and prevent the silting that would otherwise occur from continuous sand sedimentation.

Illustration of Posidonia showing the vertical and horizontal arrangement of its rhizomes in sandy soil to form mats, and the leaves standing upright above them.

This vertical growth gradually raises areas of the seabed, leading to the appearance of distinctive bioconstructions known as ‘mattes’, over which green leaf bundles develop.

Expansion of Posidonia oceanica meadows is ensured in particular by the plant’s asexual reproduction strategy, which disperses rhizome fragments that grow horizontally by developing branches.

Neptune grass also uses sexual reproduction through its flowers and fruits.

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Posidonia oceanica flowers

Its fruit, also known as ‘sea olives’, separate from the plant once mature and float, thus ensuring seed dispersion while also fostering increased genetic variability and colonisation of new areas.

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Posidonia oceanica fruit

As the living parts of the plant grow and renew, Neptune grass meadows release organic material that is washed onto the shoreline by the tide, where it accumulates. This material forms ‘sea balls’ (Aegagropiles) and heaps known as ‘banquettes’.

Banquettes are layered deposits of dead leaves washed up on the beaches by storm surges, where they can form large mounds sometimes several metres high.

Aegagropiles, or ‘sea balls’, on the other hand, are aggregations of rhizome fibres shaped by the action of the waves.

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Aegagropila

The main dangers to Posidonia oceanica are chemical pollution and turbidity of the water. Since light intensity is a significant limiting factor for the species, it is particularly sensitive to both of these threats.

Increased turbidity is chiefly caused by use of coastal areas for human activities. Major threats include the construction of tourism-related port infrastructure, laying of cables and building of breakwaters, anchorage, discharge of sewage and the introduction of invasive species.

Further damage is caused by creation of artificial beaches and the removal of dead leaves from the beach.
In tourist and bathing areas, swimmers tend to dislike the presence of banquettes, often seeing them as a form of waste rather than a natural part of the shore environment.

A joint ISPRA and ARPA (Regional Environmental Protection Agency) survey conducted in 2007-2010 on management of Italian beaches found that the method most often adopted by coastal municipalities to render beaches more attractive and practical for the bathing season was removal of Neptune grass accumulations and their disposal in landfills.

This practice in effect causes the removal of large quantities of sand trapped in the banquettes, requiring subsequent sand replenishment and protection against coastal erosion.
The ecological role played by banquettes and their protection of beaches from erosion is therefore now recognised under Italian law, which recommends that accumulations should be left in place wherever possible.

Vertical growth of mattes is very slow, estimated to be no more than 1 cm per year, making its recovery after stress events extremely difficult.

Neptune grass plays an essential role on sandy shorelines due to its protective action against erosion and because it serves as a habitat for many species of organisms.
Protecting this species is therefore vital for safeguarding coastal ecosystems and for the wellbeing and safety of local areas.