Individual study: Experimental rehabilitation of coral reefs damaged by blast fishing using rock piles, Komodo National Park, Nusa Tenggara archipelago, Indonesia
Fox H., Mous P.J., Pet J.S., Muljadi A.H. & Caldwell R.L. (2005) Experimental assessment of coral reef rehabilitation following blast fishing. Conservation Biology, 19, 98-107
Throughout South-east Asia there has been extensive damage to coral reefs due to illegal fishing with explosives, termed blast or dynamite fishing. An explosive device is thrown into the water above a reef. The explosion kills or stuns fish, which float to the waters surface, but it also shatters coral skeletons on the reef below. As a further problem, areas of broken coral shift in the water currents abrading or covering new coral colonies, which slows or prevents reef recovery. In this study, the effect of reef rehabilitation by creating rock piles on coral colonisation was investigated.
Study site: The study was undertaken in the Komodo National Park around several larger and smaller islands in the Nusa Tenggara archipelago of Indonesia. Nine blast sites were selected, and three to four replicate rock piles were installed within each 10 x 10 m site in April and May 2000. Rocks were of limestone and lithic sandstone quarried from the island of Flores.
At each site, rocks were thrown overboard from a small boat, and scuba divers positioned and consolidated them to form 3-4 rock piles (0.5-2.0 m³ volume, 70-90 cm high, spaced 2-4 m apart). Control coral rubble quadrats (using remnant coral from the surroundings) were also created at this time.
Coral monitoring: Sites were measured every six months after installation until May 2002 and again in March 2003. The number, size, life-form and taxon of all hard (scleractinian) corals were recorded in six 1 x 1 m quadrats per site (1-3 quadrats per rock pile). Additionally, cover of soft coral and other dominant benthos was estimated.
Rock pile monitoring: To measure the persistence of rock piles, the size of each pile (length, width, height and circumference) was measured every six months after installation until autumn 2001, and again in March 2003.
Hard coral colonisation: The rock piles rapidly developed a ‘biofilm’ of coralline algae and other encrusting organisms. Hard coral recruits were recorded in the first survey. Within one year there were many recruits of 2-4 cm diameter in size. Hard coral recruits continued to increase at most sites until 18 months after installation of the rock piles, after which the number stopped increasing and in some cases, started to decrease. The hard coral recruits were mainly branching corals, dominated by the family Pocilloporidae and the genus Acropora, with fewer velvet corals Montipora, stony coral Poritidae, and other large corals.
Hard coral area: Despite the decrease in coral numbers towards the end of the study, the total area of coral continued to increase, reaching its highest in spring 2003. Area increased by 464% from spring 2001 until autumn 2001, by 77% from autumn 2001 to spring 2002, and by 216% from spring 2002 to spring 2003. In contrast, there was no increase in coral cover in rubble control plots over this time period.
Soft coral and other recruits: Soft coral (primarily Xenia spp.) colonised and grew very quickly at some sites, although there was relationship between the amount of soft and hard corals. Other sessile organisms also colonised the rock piles, including: algae; sponges; jellyfish (tunicates); echinoderms - sea lilies; (crinoids), sea urchins (echinoids), and sea cucumbers (holothurians); Trochus snails; day octopus Octopus cyanea, and various fish species.
High current sites: At the highest current sites, there was a decrease in hard coral area in the 2002 and 2003 surveys.
Rock piles: Volume of rock piles did not decrease significantly with time. However, there was a decrease in rock pile volume at the highest current sites.
Conclusions: Rock piles were successful in aiding hard coral growth and therefore reef rehabilitation at most sites, except those where there were strong currents.
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