Grand Designs: The Reef Builders of our Seas

For most of us, an architectural achievement means assembling a bookcase from IKEA. But some marine species build structures that support entire ecosystems!

As green roofs, bird bricks, and bug hotels become more common, people across the UK are pondering how to share their homes with wildlife. Down in the deep, many species are ahead of the curve by creating, modifying, and maintaining valuable habitats - they're called ecosystem engineers.

By making their environment more varied, ecosystem engineers play an important role in encouraging biodiversity. Our local coasts and seas offer many great examples, such as seagrasses forming underwater meadows and plankton changing water clarity. Some of this marine engineering takes the form of architectural marvels known as biogenic reefs.

Only a few species are reef builders, and as they must gather or produce their materials the construction process is slow. The results are worth the wait though: biogenic reefs can reduce coastal erosion by dissipating wave energy and even improve water quality by increasing the number of filter feeders.

These impressive structures are full of nooks and crannies, making them an ideal home for animals like crabs, shrimp, and periwinkles. Being solid and static, they also offer a great anchor for barnacles, sea mats, and seaweeds. A study of one biogenic reef in the Wash (a bay in East Anglia) found a whopping 88 species living there! Let's take a look at some reef-building superstars here in our local waters.

Native oyster © Paul Naylor

Native oyster © Paul Naylor

Extraordinary oysters

Native oysters are comfortable in a crowd, and anchor themselves in their surroundings with a natural adhesive. They can form reefs spanning tens of hectares, and were still doing so in UK waters during the 19th century. Records of the time detail 40 ships each landing 20,000 oysters a day in the English Channel, and one 1883 map shows them covering an area of seabed the size of Wales.

Sadly, a combination of disease, pollution, invasive species, physical disturbance, and over-fishing has seen the world's oyster reefs reduced by 85%. The Solent Oyster Restoration Project is tackling this by breeding native oysters and seeding them at protected sites. Amazingly, the cages in which the oysters are grown have formed a sort of artificial reef, with 97 different species found living inside!

Blue or common mussels © Becky Hitchin

Blue or common mussels © Becky Hitchin

Magnificent mussels

The common mussel and the horse mussel both hang out with others of their species. They attach themselves to surfaces, and each other, using sticky fibres called byssus threads. Both flexible and incredibly strong, these fibres allow the mussels to withstand the movement of the waves. If you've ever seen a mussel with a 'beard', you've seen byssus threads!

As a group of mussels grows it binds together mud, silt, sand, and empty shells, forming a reef that can be six individuals high. Some of these reefs are exposed at low tide, prompting enthusiastic visits from hungry ducks and wading birds. They're also popular with another species: many local populations are harvested to be eaten by people both at home and abroad.

Honeycomb worm reef © Julie Hatcher

Honeycomb worm reef © Julie Hatcher

Wonderful worms

Honeycomb worms (Sabellaria alveolata) form protective tubes around themselves from shell fragments and sand. This species is a fan of communal living, so individuals build their compartments in a honeycomb-like reef that can be a metre high and several metres long. Look out for these distinctive shapes on rocks and coastal defences near the low water mark.

A relative of the honeycomb worm known as the ross worm (Sabellaria spinulosa) is also partial to a bit of reef-building, but only in very specific circumstances. When it does take the plunge its reefs are smaller - several metres across, but at most 60cm high - and more likely to be hidden under the waves.

Do your bit for wildlife

Our local waters are full of fascinating species, but many are under threat from human activity. You can help to secure their future by becoming a marine volunteer or making easy lifestyle changes that support our seas.