Artificial reefs made of steel slag have been used to create sea forests off the coast of South Korea, providing a new habitat and breeding ground for fish populations.

The sea floor environment around South Korea’s coastline has been degrading steadily due to desertification, a process which destroys ocean life and has been linked to climate change and pollution.

The situation had led to the destruction of over 60% of marine plants along a 220km stretch of the country’s eastern coast. The desertification of sea forest algae, including seaweed and kelp, is devastating to ecosystems and impacts heavily on fish populations.

With reducing catches for South Korea’s fishing industry, in 2009 the country’s Ministry of Oceans and Fisheries began a process of planting, with a target of creating 54,000 hectares of sea forest by 2030.


POSCO Triton blocks on a ship
POSCO Triton blocks are planted with marine algae ahead of being installed on the sea bed


A co-product of necessity

In the year 2000, the research unit of POSCO, South Korea’s largest steel company, was working with the Research Institute of Industrial Science & Technology on an artificial reef based on steel slag, a co-product of the steel manufacturing process.

Produced during the separation of molten steel from impurities, slag is a dense, rock-like material that has traditionally been used as ballast, or as a construction aggregate or addition to agricultural soil.

POSCO’s research team realised that steel slag’s high mineral content, including calcium and iron, made it highly supportive for the growth of marine plant life. This led to the creation of the Triton®, an artificial reef that has since been installed in 30 different sea forests across South Korea.

Made up of 85% slag aggregates, 15% slag cement and water, more than 29,000 Triton® blocks have been installed in over 7,500 reefs since 2007. The blocks, which are heavy enough to resist being moved by typhoon or tsunami activity, are planted with marine algae before they are installed on the sea floor, helping regenerate previously barren stretches of coastline.

POSCO is committed to sustainability so local reef manufacturers are provided with steel slag entirely free of charge so that costs can be kept low. The steel company can process 13,500 tonnes of slag every year, ensuring a steady supply of new reefs for coastal areas in need.



A range of benefits

In addition to being a sustainable reuse of a steel-making co-product and providing an environment for marine algae to thrive, Triton® sea forests also sequestrate and store carbon from the ocean and atmosphere.

A single hectare of Triton® sea forest captures around 16 tonnes of CO2 annually. With the 29,000 blocks covering nearly 38 hectares, this totals more than 600 tonnes of CO2 uptake per year.

The sea forests’ increased seaweed and kelp also helps boost fish populations, with increased fish catches seen in areas with Triton reefs. It is estimated that the total economic value of existing sea forests to local communities is over $1m.

The steel industry is continuing to improve the sustainability of its processes. Its research teams are reducing emissions and discovering innovative new ways to use steel manufacturing co-products.

The Triton® Sea Forestation Project is just one of these and the benefits are already being felt.


Images: POSCO