Effects of Concrete-Bamboo Cages on Coral Fragments: Evaluation of a Low-Tech Method Used in Artisanal Ocean-Based Coral Farming

Abstract

To evaluate the effect of inexpensive cages made from concrete and bamboo on the skeletal extension rates of the scleractinian corals Acropora gomezi and Pavona cactus, fragments were cultured without cages, inside partial cages, and inside full cages with bamboo covers of two mesh sizes at different depths around Sambangan Island, Indonesia. An additional experiment was designed to assess the impact of shading by cages on skeletal extension. Linear extension rates of all fragments were measured over a period of four months. Culture inside cages led to significantly reduced extension rates of A. gomezi at both depths, while P. cactus only showed significantly reduced extension rates when cultured in full cages at greater depth. Caging lead to a significant increase in skeletal damage at both depths in A. gomezi, and at shallow depth in P. cactus. Shaded fragments of A. gomezi had much smaller extension rates (5 ± 1 mm/132 days, mean ± SE) than unshaded fragments (24 ± 1 mm/132 days) and sustained significantly more damage, while shaded fragments of P. cactus grew significantly better (15 ± 0 mm/132 days) than unshaded fragments (12 ± 0 mm/132 days) and sustained less damage, although the difference was not significant. The culture of coral fragments without cages may yield the best results. However, the choice of the optimal culture method will depend on the species to be cultured and the conditions encountered in the reef.

KEYWORDS:

• Indonesia
• coral farming
• low tech
• coral fragments
• aquarium trade
• rural development project

The authors would like to thank Jacobus Busono of Pt. PURA and Hans Schwinn for giving permission and assistance for the work on Sambangan Island. Daniel Knop gave invaluable comments and helped to improve the study design. Dwi Murtono, Arif Wibowo, and the staff of Sambangan Island are thanked for their help in the field. Carden Wallace kindly helped in the identification of A. gomezi. S. Ferse was financially supported by a grant from the German National Academic Foundation. Comments by an anonymous reviewer helped to improve an earlier version of this paper.