Today the variety of artificial reef designs and materials is increasing as more and more individuals and communities step up to manage their coastal zones. But not all artificial reefs designs are successful, and some may even be harmful. At the NHRCP we have been carefully and slowly experimenting with many different techniques, styles, and designs over the last 7 years and are now getting a very clear picture of what works, and what unfortunately does not. We are working on developing a comprehensive overview of all of our findings, and the first installment of this series is about one of our favorite artificial reefs, our Bottle Reef Modules.
What are the Bottle Reef Modules?
These are a very simple yet effective method of creating artificial reef structure on which to transplant either broken corals or corals from a nursery. The units are constructed using a plastic tub about 35 cm in diameter, into which concrete is poured and then 5-6 recycled glass bottles are arranged inside. The surface of the concrete can be further modified to include shells, bits of tile, rocks, or other features to add texture for larval settlement and micro-habitats for marine invertebrates.
After drying, the molds are turned over and the units are allowed to sit for a few days to cure and for the pH to begin balancing. Each unit weighs about 15-20 kgs, so they can be moved by 1-2 persons quite easily. Although caution should be taken on land and on the boat to ensure that none of the glass bottles are broken. Once put into the sea, the units are sunk into the sand about 10-15cm so that they do not move around, and then immediately transplanted with corals, often added by the use of underwater epoxies. As the units shape and size mimics a natural branching coral, fish and other marine life will very quickly start to inhabit the new structure.
- Simple, Cheap, and easy to make: The units can be made in almost any location around the world, with just about any budget. There are no special skills or tools needed to make or deploy to units.
- Safe and non-toxic: Unlike some other reef types, these units contain no potentially hazardous materials (plastics, PVCs, Rubber, etc). As the corals are actually growing on chemically inert glass, we have witnessed incredible growth of the corals over the units compared with all other materials we have tried.
- Rapid Deployment: As the units can be quickly made and deployed they are ideal when restoring damage due to anchors, dynamite fishing, or other physical disturbances. In many cases, larger broken corals can be immediately transplanted to the unit without a need for the nursery stage.
In what cases do they work best?
From the basic design and shape of the units you have probably guessed that they work best in areas where we are restoring fields of branching corals (Acropora, Pocilliopora, etc). But in fact many different types of corals can be transplanted onto the units. We have had varying degrees of success depending on where the units have been placed, but the list below outlines some of the more effective uses of the units:
- Anchor Damage: in Chalok Ban Kao a shallow reef consisting mostly of branching, bushy, and table corals has been greatly damaged by storms and anchors. Where anchors have reduced the reef to small bits of rubble and sand, the units have been placed into the drag marks and then propagated with corals from a nursery. Immediately many types of fish moved in, and today the most visitors do not even notice that they are looking at an artificial reef.
- Adding new reef structure/extending the reef: In areas such as Ao Leuk and Hin Ngam we have used the structure to add to artificial reefs and alternative dive sites. In these sites, consisting mostly of sand, fish and other marine animals will be very abundant around the structures, but as it is not a natural coral reef, more maintenance will be needed to get corals to thrive on the structures.
- Navigation Aids: At the Suan Olan Diver Training site we have used the modules to facilitate easier navigation by divers between the larger artificial reef structures (see video link below). The modules make an effective system of marking sites in the sand without having to rely on unnatural looking alternatives.
- Erosion control: Currently we are experimenting with using the blocks as a sort of underwater retaining wall in an area with a steep reef slope consisting primarily of unconsolidated coral rubble. Many corals become dislodged during storms and roll down the reef slope, eventually dying. We believe that by creating small walls with the modules we can prevent some of the coral mortality and begin to add some solid structure to the slope.
Are they patented, or can anybody make them?
Unlike Biorock and some other reef restoration groups, we feel that everybody should benefit from any effective coral restoration technologies and techniques that protect our marine resources. The design is quite simple, and we hope that others will also use it. We have however been using the technique since we built the first modules with two of our very enthusiastic interns, James & Ames, in 2010. So anybody wishing to begin using the techniques is invited to contact us first for pointers and tips.
How many units has the NHRCP Deployed?
2010: Chalok Ban Kao, 14 modules
2011: Ao Leuk, 7 modules
2012: Suan Olan, 135 modules
2013: Chalok Ban Kao: 32 Modules
2014 (planned): 40 modules in Chalok Ban Kao, 50 modules in Ao Tien Og with Haad Tien Resort