Can dynamite-blasted reefs recover? A novel, low-tech approach to stimulating natural recovery in fish and coral populations
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Published source details
Raymundo L.J., Maypa A.P., Gomez E.D. & Cadiz P.L. (2007) Can dynamite-blasted reefs recover? A novel, low-tech approach to stimulating natural recovery in fish and coral populations. Marine Pollution Bulletin, 54, 1009-1019.
Published source details Raymundo L.J., Maypa A.P., Gomez E.D. & Cadiz P.L. (2007) Can dynamite-blasted reefs recover? A novel, low-tech approach to stimulating natural recovery in fish and coral populations. Marine Pollution Bulletin, 54, 1009-1019.
Summary
Dynamite fishing is a major cause of reef degradation in the Indo-Pacific. The resulting fragmented coral dies and creates unstable underwater rubble fields. The goal of this pilot study was to develop and test a low-cost, low-technology method of stabilizing rubble to create substrates suitable for coral re-establishment. A marine protected area (MPA) on Negros Island (The Philippines) was used as the restoration site to ensure that the study plots were protected from anchor damage and to allow an assessment of rehabilitation efforts on fish recovery in the absence of fishing.
Study area: The experiment was undertaken at Calagcalag MPA (10.4 ha) which encompasses a 3.3 ha reef. The reef includes a 0.24 ha rubble field (created by repeated dynamite fishing which this ceased in the mid-1980s) representing about 8% of the reef area.
Rubble stabilization and enhancement: The reef was surveyed prior to rehabilitation efforts to provide baseline data. Five 17.5 m² plots were established: three in June 2003 (coral spawning season) and two in October 2003 (prior to the storm season). The rehabilitated area (including spaces between plots), covered about 20% of the rubble field. Locally-available plastic mesh screen (2 cm diameter mesh), was laid on the rubble and anchored with stakes. Holes, cut in the mesh accommodated existing coral heads, acted as additional anchorage. Hollow, pyramid-shaped rock piles (0.5 m², 1 m in height) were constructed (onshore) using reef rock and cement, and positioned on the mesh. Studies suggest that coral recruit survival is higher on surfaces elevated from the substrate; the artificial piles performed this function as well as increasing recruitment surface area and microhabitat availability to encourage a more diverse fish assemblage.
Monitoring: The plots were censused for fish and coral recruitment 3-4 times per year for four years (i.e. until July 2006).
After 3 years, the fish community within the rehabilitated area had shifted from that characteristic of rubble fields to one similar to the adjacent healthy reef. Coral recruitment and cover increased, with 64% recruit survivorship within plots, compared with 6% on unconsolidated rubble. This low-cost approach (materials and labour averaged $75/17.5 m² plot) created a stable substrate favouring natural recovery.
The rehabilitation plots have remained intact over three storm seasons. There was concern that mesh sheets would become detached but all remained in place. One particularly severe storm in October 2004 resulted in partial coverage by shifting rubble (1/3 of each) of two plots resulting in higher coral mortality. These plots were located on a slight slope, which was considered a major factor in rubble movement. This storm represented the most severe weather this area generally receives.
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Output references
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