Reef cubes – the building blocks for saving the ocean

ARC Marine Reef Cubes Vobster Quay Crayfish ARK sites Concrete Society

Above: Reef Cubes – 500mm version

ARC Marine crayfish-UK-sustainable-ARK Sites-Concrete-Society-Vobster-Quay

Above: Crayfish discovered nine months after deployment, still using the reef as their home

ARC Marine crayfish-UK-sustainable-ARK Sites-Concrete-Society-Vobster-Quay

Above: Crayfish had individual numbers written on them for identification and had electronic tags implanted to monitor their movements accurately around the reef














Tom Birbeck and James Doddrell of ARC Marine discuss the importance of marine conservation and how artificial reef construction using concrete could repair and restore marine habitats.

In the modern world we now know the importance of conserving our marine environment and the benefits that it brings. Currently, only 1.2% of our oceans are protected; they are by far the largest carbon ‘sink’ in the world. Some 93% of CO² is stored in algae, vegetation and coral under the sea, according to the US-based Worldwatch Institute. Commercial fishing is extremely vulnerable where 53% of the world’s fisheries are fully exploited and 32% are overexploited, depleted, or recovering from depletion:

• over 80% of worldwide reefs are overfished
• over 93 countries have serious reef degradation
• around 58% of reefs are threatened by human activity
• at least 25% of known marine fish are in coral reefs.

Unless the current situation improves, stocks of all species currently fished for food are predicted to collapse by 2048. Founded in 2015, ARC Marine is the first ecological engineering company of its type in the UK. Its main objective is to repair and regenerate damaged marine habitats by producing ecologically friendly reef cubes from precast concrete. The company aims to combine academic institutes with commercial subsea infrastructure and development to build vast, sustainable and complex marine habitats for the benefit of both the environment and the future of mankind’s development. After research into procuring and sinking ex-naval ships made from steel, the authors decided to experiment with different-shaped concrete structures. Steel ships will only last approximately 100–150 years as an artificial reef, whereas some concretes boast an estimated 500 years. The long-term goal is to create the largest, most comprehensive artificial reef network throughout the world by combining marine habitat reserves with large offshore construction projects. Reef Cubes are a worldwide patented invention. Their robust and simple interlocking design makes them perfect for restoring complex marine habitats. The
benefits include:

• habitat complexity for multiple species
• food and shelter for marine flora and fauna
• nursing/spawning grounds for aquatic species
• increased biodiversity
• species preservation
• improved water quality
• surface texture – advanced casting techniques that create surface textures that replicate natural reef features and enhance biological recruitment.

Concrete Matrices

The reef cubes use a new group of low carbon cements based on a geopolymeric binder system. They have been specifically developed to manufacture products that are resistant to chemical and saltwater attack or may be used as a low-carbon replacement for Portland cement (CEM I). As such, the cubes have:

• reduced carbon emissions of 75–80% compared to the processes necessary with CEM I
• integrated recycled materials
• a minimum 60% less impact on the environment as a result of the extraction of raw materials.

The processes used to form geopolymers (or alkali-activated cements) also expend less energy. Approximately 30% of embodied energy for geopolymers (990MJ/tonne) in comparison with CEM I (3430MJ/tonne). Reef cubes are currently being trialed at three sites across the south-west: Lyme Bay, Vobster Quay and Plymouth Sound. A variety of bespoke concretes are being trialed in both freshwater and saltwater environments to see which material best suits marine life.

Habitat Regeneration and Creation

In April 2017, ARC Marine broke the record for raising the highest amount of funds on a crowdfunding platform for a marine conservation project. The project was to cast and deploy 250 Reef Cubes into Vobster Quay Inland Diving Centre and registered 36-acre (14.5-hectare) ARK site. ARK sites were developed in order to conserve the white-clawed crayfish and to establish isolated new refuge sites – known as ‘Ark sites’ – where new populations can be established, safe from threats and the invasive American signal crayfish, which carries a deadly plague. There is an urgent need to establish Ark sites to safeguard the long-term survival of white-clawed crayfish across its UK range.

ARC Marine, Habitat inserts, Reef Cubes, Vobster Quay , Eco-engineering

Above: A mixture of shapes, hole sizes and numbers were used in this experiment to ascertain what the crayfish prefered.

The 250mm reef cubes were primarily used for the Vobster Quay site with specifically engineered inserts to cater for juvenile crayfish of all sizes. The hard substrate will also form a shelter for fish and provide a landing platform for sponges to settle. Achieving the right level of pH is key for surface recruitment and, depending on the location and water properties, can vary. Local sand and aggregate were used to manufacture the reef structures, which were important to help them blend into the natural surroundings. Thanks to the supporters of the project, in September 2017 the reef was deployed into 12m of water from an aluminium work boat. In October 2017, 36 crayfish were electronically tagged and released by divers onto the reef to track how they use the new
habitat. Even though the reef was deployed in an exceptionally cold winter, recruitment rate was surprisingly quick and in the first few weeks zebra mussels, perch, radix balthica and gastropods were all seen on and inside the reef. Since the crayfish have come out of hibernation they have been seen regularly on the reef using the structures for shelter. The plan is to see which part of the reef they use the most and what shaped insert was the preferred choice for the crayfish to take refuge in.

Off-shore Renewable Energy

There is also a growing opportunity for Reef Cubes in the offshore renewable energy sector, whereby artificial reefs could be used as habitat mitigation. The reefs not only provide suitable habitat for the local marine life but they can also be used for scour prevention and to protect the turbines and cabling from strong subsea currents.


Above: Offshore cable protection also acting as a marine habitat. The trenches also make ROV and AUV inspections easier.

Future Plans

Currently, ARC Marine is part of a tender bid to expand on the existing artificial reef site off Virgin Gorda (British Virgin Islands). The firm is also developing concept designs for eco-friendly breakwater and coastal defence formations for clients in the Middle East. This is to help mitigate any displacement of marine life or loss of habitat during the construction of artificial islands. Meanwhile, a Reef Cubes exhibition is going into the National Marine Aquarium in Plymouth to display the history of the artificial reef and the bright future reef cubes can bring by repopulating the oceans with vulnerable corals and other marine flora and fauna.


Above: A conceptual design for a wind turbine farm client. This would offer protection to the foundation and boost biodiversity around wind farms.

This article was published in The Concrete Societies Concrete Magazine: Volume 52 Issue 06 July 2018