After Charlie Frew emailed Keen, with some reservations about tyres for artificial reefs, Keen obtained this info from an engineer friend:
“16th November 2004
RE: MERITS OF TYRE ARTIFICIAL REEFS (ARS)
I shall address each of the five issues raised concerning the tyre artificial reefs as follows:
1. Would toxins leach out from tyres?
Many scientific studies have been carried out in the past ten years to determine whether tyre AR will contaminate the seawater.
The following is a list of references we have at hand confirming that tyres are safe to use for ARs:-
(a) The US National Artificial Reef Plan (Stone, 1995) includes tyres as a reef construction material, noting that no toxic effects attributable to leaching or decomposition have been demonstrated.
(b) National Artificial Reef Plan. NOAA Tech. Memorandum NFMS OF-6, US Dept. of Comm., Wash, D.C, Nov. 70; Stone, R.B., 1995.
(c) A review of waste tyre utilization in the marine environment; Chemistry and Ecology 10: 205-216; Collins, K.J, A.C. Jensen and S. Albert, 1995. …. No adverse impacts demonstrated.
(d) Bio-accumulation studies of tyre artificial reef biota. Paper presented to the Third International Ocean Pollution Symposium, Harbor Branch Oceanographic Institution, Florida April 1997. Chemistry and Ecology; Collins, K.J, W. Figley, and E. Spanier, (in press).
(e) Acceptable use of waste materials. In European Artificial Reef Research, Proceedings of the 1st EARRN conference, Ancona, Italy, Southampton Oceanography Centre, 1996, pp 377-390; Collins, K.J., and Jensen, A.C., 1997.
(f) Scrap tyres for marine construction: environmental impact. In Recycling and Reuse of Used Tyres; p-p. 149-162. ed. By R.K. Dhir, M.C. Limbachiyya, and K.A. Paine. Thomas Telford London; Collins, K.J., Jensen, A.C., Mallinson, J.J., Mudge, S.M., Russel, A., and Smith, I.P. 2001.
(g) Epifauna of tyre reefs in Israel have been studied in detail. No significant excess levels of contaminants (for a range of heavy metals) were found (Collins et al in press.)
For, Hong Kong, in AFCD’s first tyre AR contract for Hoi Ha Wan and Yan Chau Tong Marine Parks in 1997, laboratory tests were carried out to detect possible toxins leaching from the waste tyre samples. None were detected. Since then, AFCD has deployed tyre ARs extensively in Marine Parks at Yan Chau Tong, Ho Ha Wan and Sa Chau- Long Ku Chau, and at the Airport Marine exclusion Zone, Kit-O Marine Research Center, the Long Harbour PFA and the Outer Port Shelter PFA.
2. Would tyres break loose from ARs
The tyre reef project in Florida is a well-documented failure which highlights the importance of using special design to cater for the corrosive environment in the sea. Even today, many countries still use steel fasteners to bond tyres together to form Tyre ARs. These steel fasteners corrode quickly in seawater and the tyres eventually break loose spilling tyres along the coasts.
In Hong Kong, the tyre reef designs were selected after an international tender and uses non-metallic fasteners in a patented construction. In the past 7 years, these tyre ARs have withstood many typhoons, impacts of huge trawler booms and fish dynamites without disintegration. These reefs are regularly checked and some of them have been dragged along the sea floor, far from original positions, and still retain their structural integrity.
3. Can tyre ARs act as anti-trawling devices?
In the last two years, AFCD has successfully deployed anti-trawling ARs specially designed to withstand Hong Kong’s most powerful trawlers. Moreover, these special anti-trawling ARs are able to rest on the silty seabed without sinking.
In short, with careful design and construction, mechanical strength and anti-trawling properties can be built into tyres ARs, or ARs of other selected materials.
4. Are tyre ARs productive?
Through extensive studies since 1997, AFCD has tried out many different types of artificial reefs using concrete, rocks, boats, tyres and special synthetic materials with various AR designs.
AFCD found that rock pile ARs and concrete ARs are both too heavy and prone to sink into Hong Kong’s muddy seabed.
AFCD also found that, the ship hulls are relatively empty and not very productive for its huge mass. Fish tend to aggregate in the small pilot cabins where the structures are more complex. However, when tyre ARs are deployed in these hulls as those in Long Harbour PFA and Outer Shelter PFA, the productivity of the boat ARs increases by several order of magnitude. The most obvious observations were that there were more fish in the tyre AR than the pilot cabin of the same boat.
AFCD also found that elevated tyre ARs of sufficiently large sizes are comparable to their most prolific ARs with bio-filters.
5. Do ARs pull fish away from rocky shores without adding to the total biomass?
HK’s shorelines have been damaged by extensive land reclamations over the last four decades and this trend shows no sign of stopping. Some recent examples include the reclamations in Victoria harbour, the west Kowloon reclamation, the reclamation for the Disney Theme Park at Yam O and the Lamma Island Power Station reclamation. Clearly an extensive portion of HK’s natural marine habitats is continuously been destroyed. The deployment of ARs even at the proposed rate of 200 ARs per year for the whole of Hong Kong, can only partially replace these lost habitats. To put it in anyway, where would those fish go now that their natural habitats at Victoria Harbour (or west Kowloon) are destroyed?
Similarly, away from shore line, most of the hard bottom substrates in HK’s inshore seabed are destroyed by the intensive use of bottom-scrapping trawler nets in the past three decades. Again ARs must be deployed to replace the lost habitats for the marine lives.
Therefore the question of ARs pulling fish away without adding to the total biomass is really not applicable to HK’s badly damaged marine landscape.