Protecting Seagrass When Anchoring

Posidonia oceanica, sometimes called Neptune grass, is a flowering plant that grows only in the Mediterranean. It looks like a dense meadow of long, ribbon-like green leaves rising from the seabed, usually on sandy bottoms from the shallows down to depths of several tens of metres in clear water.

It grows extremely slowly, with its creeping stems spreading by only a few centimetres a year. Over centuries, a meadow builds up a thick mat of roots, stems and trapped sediment. Some meadows are thought to be thousands of years old.

In autumn and winter the old leaves fall and wash up on beaches in brown banks. These banks are part of the plant's natural cycle and are harmless.

This guide is part of our safety information for sailing weeks.

• Habitat. Meadows are nursery grounds and shelter for fish, octopus, sea urchins, starfish and many smaller animals. The noble pen shell, a large and now rare Mediterranean mollusc, lives among them.
• Clear water. The leaves slow currents and trap fine sediment, which is one reason Adriatic bays are so clear.
• Beaches. Meadows reduce wave energy near the shore, and the banks of dead leaves help protect beaches from erosion in winter storms.
• Carbon and oxygen. Posidonia produces oxygen and stores carbon in its mat for very long periods, which makes it an important natural carbon store.

When an anchor is dropped onto a meadow, it digs into the mat and tears out plants. As the yacht swings with the wind, the chain sweeps across the seabed and scours a wider area. Pulling the anchor up can rip out more.

One anchoring leaves a scar. Hundreds of yachts anchoring in the same popular bays every summer leave bare patches that grow larger each year. Because the plant grows so slowly, those patches can take decades to fill in again, if they recover at all.

In clear water you can usually see the difference from the yacht:

• Sand looks pale and bright, giving the water a light turquoise colour
• Seagrass looks dark green to almost black, in patches or wide meadows
• Rock looks uneven and brown or grey, often with weed

Polarised sunglasses help cut the glare. Many skippers also look over the bow as they approach, or ask a guest with a mask to snorkel and check the spot. Charts and some anchoring apps show seagrass areas, though they are not always complete.

Responsible anchoring in the Adriatic comes down to a few habits:

1. Pick a patch of clear sand, large enough for the yacht to swing without the chain reaching seagrass.
2. Lower the anchor slowly rather than letting it drop and drag.
3. Use a mooring buoy where one is provided, even if there is a fee.
4. When leaving, motor gently up to the anchor so it lifts vertically.

In many bays, local concessions lay mooring buoys for visiting yachts, and some national and nature parks use eco-moorings designed to touch the seabed as little as possible. See anchoring and mooring buoys for how overnight stops work and national and nature park fees for what parks usually charge.

Posidonia meadows are a priority habitat under the EU Habitats Directive, and the species is protected under Croatian nature protection law. Many meadows lie within Natura 2000 sites, national parks and nature parks, where anchoring may be limited to designated areas or banned in places.

Rules differ from one area to another and can change. Your skipper follows the local rules for each stop, and signs or park rangers may also give instructions.

• Snorkel and look, but do not stand on, pull up or collect seagrass or the animals living in it
• Never touch or disturb a noble pen shell if you see one
• Use less sun cream by covering up, and choose products with care
• Keep all rubbish on board until you can dispose of it ashore
• Ask your skipper about the seabed at each stop; most enjoy explaining it

Read more about safety and care for the coast on our safety page.