Use electrical current to stimulate coral growth

Supporting evidence from individual studies

1. A replicated study (year not given) in the Gulf of Aqaba, Jordan (van Treeck & Schuhmacher 1997), reported that using and electrical current to stimulate mineral formation resulted in all transplanted stony coral nubbins (small fragments) attaching to the substrate, but survival rates were species, but not depth-dependent. Eight weeks after transplanting, all coral nubbins were fully attached to the steel mesh cathodes. After three months, survival rate for all nubbins was over 80%, except Pocillopora damicornis at 6 m deep (16%) and Acropora squarrosa (reported on graph as Pocillopora damicornis) at 12 m (72%). Survival after seven months ranged from 0% (Polillopora damicornis at 6 m) to 96% (Acropora variabilis at 6 m and 18 m deep), and after 12 months (12 m depth only) survival ranged from 36% (Acropora squarrosa) to 72% (Acropora variabilis). Results were not statistically tested. A total of 400 nubbins from six stony coral species (Acropora variabilis, Acropora squarrosa, Stylophora pistillata, Pocillopora damicornis, Montipora danae, and Pavona varians) were collected from colonies near the experimental site. Four cathodes comprising 1 × 3 m non-galvanized 10 mm steel mesh squares were fixed horizontally to the natural coral rock at each of 1, 6, 12 and 18 m deep using steel wire. The anode (titanium mesh square) was suspended 20 cm above the cathode. Nubbins were attached to each square (25 from each of four of the six species/square; see paper for configuration). The cathode and anode were attached to a power supply and an electrical current was put through the squares for 18h/day for two months, then switched off. Attachment was recorded after two and eight weeks. Survival was recorded after three and seven months, and after 12 months just for 12 m depth.

   Study and other actions tested

   Referenced paper

   Treeck P.V. & Schuhmacher H. (1997) Initial survival of coral nubbins transplanted by a new coral transplantation technology-options for reef rehabilitation. Marine Ecology Progress Series, 150, 287-292.

2. A replicated, randomized, controlled study in 1999–2000 at a coral reef at Quezon Island, northern Philippines (Sabater & Yap 2002) found that using electrical current to stimulate mineral accretion on stony coral Porites cylindrica nubbins (small fragments) resulted in a higher survival rate and greater girth growth than unstimulated nubbins but no difference in % linear growth. However, survival and linear growth of electrically stimulated nubbins were both lower than naturally growing coral. Six months after electrical stimulation started, survival of stimulated nubbins (86%) was higher than unstimulated (70%) but lower than adjacent natural colonies (95%). Average girth growth after six months was higher for stimulated (1.4–1.7 mm) than unstimulated (0.8–1.1 mm) nubbins. There was no difference in % linear growth between stimulated (38%) and unstimulated (36%) nubbins but both were lower than natural colonies (45%). Results for corallite development are presented in the original paper. In December 1999, two-hundred-and-sixty ‘thumb-sized’ nubbins were randomly collected from three patches of wild-growing stony coral colonies within the experiment site. An additional 40 branches on colonies on each patch were randomly tagged and left to grow naturally. Two 1 × 1 m galvanized steel mesh sheets were attached to the seabed at each of three locations 4 – 8 m deep. At each site, a PVC frame was constructed above each sheet with electricity supplied to the stimulated nubbins (see paper for methods). Survival, linear, and girth growth were measured every two months for six months.

   Study and other actions tested

   Referenced paper

   Sabater M.G. & Yap H.T. (2002) Growth and survival of coral transplants with and without electrochemical deposition of CaCO3. Journal of Experimental Marine Biology and Ecology, 272, 131-146.

3. A randomized, replicated, controlled study in 1999–2001 at a coral reef at Quezon Island, northern Philippines (Sabater & Yap 2004) found that six months after an electrical current to stimulate mineral accretion was switched off, survival of stony coral Porites cylindrica nubbins (small fragments) was higher for stimulated nubbins than unstimulated, but there was no difference in linear or girth growth. After six months, the number of surviving nubbins was higher for previously stimulated (63/66, 95%) than unstimulated (55/64, 86%) nubbins. There was no difference in linear growth between stimulated (2.4–4.0 mm/2 months) and unstimulated (2.5–4.4 mm/2 months) nubbins. Girth growth did not differ after six months between stimulated (2.2 mm) and unstimulated (2.0 mm) nubbins. In December 1999, two-hundred-and-sixty ‘thumb-sized’ nubbins were randomly collected from three patches of wild-growing Porites cylindrica colonies within the experiment site. Two 1 × 1 m galvanized steel mesh sheets were attached to the seabed at each of three locations 4–8 m deep. At each site, a PVC frame was constructed above each sheet with electricity supplied to the stimulated nubbins (see study 2 for experimental set-up). After six months, the electrical current was switched off and 66 stimulated, and 64 unstimulated nubbins were left in-situ for a further six months. Survival and linear growth were measured every two months for six months, girth growth was measured after six months.

   Study and other actions tested

   Referenced paper

   Sabater M.G. & Yap H.T. (2004) Long-term effects of induced mineral accretion on growth, survival and corallite properties of Porites cylindrica Dana. Journal of Experimental Marine Biology and Ecology, 311, 355-374.

4. A replicated, controlled study in 2006 at an artificial nursery on coral rubble in North Sulawesi, Indonesia (Borell et al. 2010) found that cultivating stony coral Acropora youngei and Acropora pulchra fragments inside an electric field with a cathode led to lower survival for Acropora youngei and lower linear growth for both species than fragments cultivated inside an electric field without a cathode, or fragments cultivated outside the electric field. After four months, Acropora yongei fragments cultivated with a cathode had a lower survival rate (68%) than fragments without a cathode (99%) or outside the electric field (99%). However, there was no difference in survival for Acropora pulchra (with cathode: 83%, without cathode: 91%, outside electric field: 87%). Linear growth was lower for both species with cathode (A. yongeii: 10 mm, A. pulchra: 8 mm) compared to without cathode (A. yongeii: 22 mm, A. pulchra: 11 mm) and for A. yongeii outside the electric field (15 mm) but higher than A. pulchra outside the electric field (5 mm). There were mixed effects for chlorophyll fluorescence, chlorophyll a, and zooxanthellae density and concentrations (see original paper for results). In March 2006, three hundred and fifty fragments (6–8 cm) each from A. yongei and A. pulchra were collected from near the experiment site. Fourteen frames were placed on coral rubble substrate (five electric field with cathode, five electric field insulated from the cathode, four outside the electric field) (see original paper for methods). Twenty-five fragments from both species were glued to each frame. Monitoring took place every four weeks for four months. Final mortality rate and growth (linear skeletal extension) was measured after four months.  

   Study and other actions tested

   Referenced paper

   Borell E.M., Romatzki S.B.C. & Ferse S.C.A. (2010) Differential physiological responses of two congeneric scleractinian corals to mineral accretion and an electric field. Coral Reefs, 29, 191-200.