Ocean Ranching of Abalone – Biofouling Critical Problem

The reef is constructed of 10,000 modules, with dimensions of approximately 2m wide by 1m height. The individual modules are termed ABITATS. They are constructed from concrete, 35MPa hardness, 14mm aggregate with 20mm poly fibres added for strength. There is 10m surface area per ABITAT.

The reef is serviced by OGA’s team of 14 commercial divers. The divers have a variety of tasks including:

  • Seeding the reef with juvenile abalone;
  • Harvesting abalone;
  • Lifting ABITATS after storms cause some sinking into the sandy seabed;
  • Removing biofouling to keep the ABITAT surfaces clean for growth of the abalone.

The removal of biofouling from the reef by divers is the activity that consumes approximately 60% of all dive time on the ranch.

 The Critical Problem – Removal of Biofouling.

The reef is constantly attracting numerous biofouling organisms to settle and grow on the reef. Soft corals, macro algae, ascidians, flat oysters, tube worms, coralline algae, diatoms are just some of the many organisms that find the reef an attractive place to live. If the biofouling was left to grow unabated then the ABITATS will be smothered by these organisms and the surface area available for abalone to grow on is substantially reduced.

We have found that cleaning the ABITATS of biofouling organisms once annually maintains clear surfaces on the reef for the abalone to grow on. The company has found that the most effective method of cleaning the ABITATs is for divers to manually scrape the reefs clean using paint scrapers. The divers are able to target the areas that the abalone grow on, without removing abalone.

The company has trialled methods to mechanise the process without success.

  • A high-pressure cleaner (https://www.caviblaster.com/) was purchased to blast the

reef clean. It was an effective cleaner but would not discriminate between biofouling

and abalone and caused the loss of too many abalone.

  • An air powered mechanical chipper. The chipper was powered by a piston, the noise

of which would reverberate through the water and effect the divers hearing. The piston would also require daily stripping and cleaning to prevent the piston seizing.

If there were a solution to mechanise the process of biofouling removal that sped up the process and made it easier on the divers’ bodies (wrist injuries are a potential issue) it would lead to massive productivity gains for the business.