Mineral Accretion Coral Nursery Kimbe Bay

Global Reef Alliance in collaboration with local communities, Walindi Plantation, the Papua New Guinea Dive Association, and Mahonia na Dari installed a trial mineral accretion coral and oyster nursery in Kimbe Bay, New Britain, Papua New Guinea intended to restore coral, shellfish and finfish diversity in the fringing reefs of Kimbe bay. These reefs were found to be suffering several specific stress factors caused by human change to the surrounding environment, and climate change-related impacts like increased water temperatures. Stress factors included bleaching, coral diseases, sedimentation and other human impacts causing declines in reef health (Goreau, 2000).

The unique advantage of mineral accretion technology is its action directly at the surface of the growing limestone structure, and that it can be used to make structures of any size or shape (Goreau, 2000). In Kimbe Bay, three ungalvanized steel construction mats (each 2.3m by 2.4m and constructed of 6mm steel, in a 20cm grid) were placed between existing corals on the seaward edge of the reef flat. Salvaged solar panels were used, attached to a nearby dock and connected via cable to the structure. The solar panels provided a low electrical current (6 volts and 16 amperes), safe for humans and marine life but enough to promote the process of mineral accretion on the structures (Goreau, 2000).

“Electrical currents generated by the solar panels flow through seawater between the construction mats and the smaller meshes located beneath them. Due to their electrolytic activity, the red rust on the construction mat will quickly turn from red to black and grey as the rust is converted back into metallic iron. Within a few days white limestone crystals will begin to grow on top of them” Goreau, (2000).

The growth of limestone itself connects and permanently adheres to the mats to the reef structure beneath them. Corals beneath the mats will grow upwards at an accelerated rate because of increased calcium precipitation, filling and overgrowing the mesh structures. The structures will also over time act as new sheltered hiding spaces for fish. An additional aim of this pilot project was to increase the growth rates of local species of oysters eaten by local communities (Goreau, 2000). The project was seeded with coral transplanted from similar habitats in nearby reef areas. Ideally these come from naturally broken reef fragments to avoid damaging healthy intact coral.

The project team recommends that mineral accretion as a reef restoration is only viable if it improves outcomes for local communities, especially food in the form of harvestable oysters, and an increased abundance of corals and fish (Goreau, 2000). While the pilot was developed, the project team requested a temporary tambu (restriction, no-take zone) to prevent harvesting and allow experimental measurements to occur (see customary resource management). Despite some negative impacts, the damage to coral in Kimbe Bay is minimal. Having a unique sheltered position and highly diverse natural coral species diversity make it a potential location for a larger coral reef nursery project (Goreau, 2000; Silcock, 2015).