Building Coral Viewing Platforms on Tourist Pontoons

Harvesting and growing corals to enhance underwater observatories on floating tourist pontoons is technically simple and environmentally sustainable according to a recent CRC Reef Research Centre Ltd project at James Cook University.

The study of coral transplantation techniques, conducted by masters student Jamie White in 1994-95, also found that corals on small, artificial platforms near the surface attracted fish and invertebrates, and spawned at the same time as naturally growing corals.

Coral viewing platforms at underwater observatories provide visitors who don't snorkel with an opportunity to see corals and fish close up.

The CRC project, originally proposed by Sunlover Cruises in Cairns, was designed to answer concerns over the potential mortality of corals transported to a floating pontoon environment and the effect of removing coral fragments from their host colonies.

"The results indicate that coral viewing platforms are technically feasible and clearly sustainable," said Mr White. "The general principles developed in this study can also be applied to raising scleractinian corals for the aquarium trade. These hard skeleton corals were first successfully transplanted in public aquaria in the late seventies, but were regarded as being impossible to keep by hobbyists. The situation has changed over the past decade, due to improvements in aquarium technology and coral management information."

To assess how transplanted corals adapted to their new environment, three experimental coral viewing platforms were attached to Sunlover Cruises tourist pontoon at Moore Reef for 12 months. Fragments of Acropora formosa and Pocillopora damicornis were transplanted to the platforms and to experimental racks at adjacent control sites. Mortality, growth and condition of the transplants were measured at both locations after 12 months.

Fragments of coral transplanted to platforms close to the sea surface had low mortality rates of between 2-5 % and showed good growth, indicating the pontoon environment did not adversely affect either species. In fact, growth of P. damicornis was greater on the platforms than at the control sites.

While the number of fish observed at the natural patches of reef and the experimental reef racks were similar, species diversity was higher in the natural reef sites. Invertebrate fauna, however, was similar at all locations.

The project also tested different methods to harvest, handle and attach corals to the viewing platform. The methods included using cement, plastic cable ties and marine epoxy putty to fix fragments to the racks. Of the five methods trialed, cement proved the best, resulting in the greatest growth of coral skeleton and tissue. It also prevented abrasion of the coral by underwater movement.

Mr White said that removal of up to 50% of a colony's biomass to stimulate different harvesting regimes had no detectable effect on growth, condition or mortality of either species. "The experiment did find that fragments of arborescent species such as A. formosa should be harvested from actively growing branches in order to reduce damage to the donor colony and the harvested fragment," he said

Based on the project's results, Mr White report makes the following recommendations for artificial coral viewing platforms that have been approved by relevant natural resource or marine park agencies:

1. Always develop a clear set of goals in the planning stage to help measure performance.

2. Regularly monitor the project and plan for corrective action if necessary.

3. Firmly fasten each fragment to prevent tissue abrasion. Use cement or certain types of epoxy compounds to fix fragment to a base or in small pots.

4. Cover lesions formed during harvesting with cement to prevent any invasion by algae or boring organisms to the damaged coral tissue.

5. Transplant fragments to new sites with similar physical characteristics to the donor site to help reduce environmental stress.

6. Undertake coral transplantation in cooler, winter periods (for example during April to September in Australia) when sunlight and sea temperatures are lower.

7. Try to replicate a diverse reef-scape by using different hard coral species, shapes and overhangs, and use `live' calcarous rock with invertebrates. The presence of other fauna and algae is important to the survival and recruitment of corals and fish onto the platform.

8. Harvest fragments from actively growing coral branches to minimise damage to the donor colonies.

9. Design viewing platforms to allow easy access by divers and for building suitable `natural' coral structures. Consider factors such as exposure to sunlight, viewing access by visitors and shading from the pontoon.

Mr White says the results of the feasibility study have applications for the emerging coral aquarium trade and in rehabilitating damaged coral reefs.

"But the approach in this study demonstrates the need to clearly define the goals for any restoration project. A collaborative approach between stakeholders is always needed to develop these goals," he said.

By Don Alcock