Fish farming is one of themost rapidly developing food sectors in the world recently surpassing beef production on land (FAO, 2013, 2014). In Southeast Asia, the yearly growth rates have reached a staggering increase of 29.5%
Fig. 1. Map of cage farming clusters (blue filled circles) in investigated areas, Number of farms within each cluster are represented by size of the circles (continuous size representation). To avoid overlaps of circles, thin lines are used to indicate the actual location of clusters. Yellow areas show coral reef distribution. East side of Luzon (shaded area) not mapped because no good images available.
Other studies reported that nutrient enrichment from marine farms reduced coral reproductive capacity at 150 m (Loya et al., 2004) and at a distance of 600 m larval metamorphosis was still affected and coral mortality clearly noticeable (Villanueva et al., 2005, 2006). In Taiwan increased nutrient loads, turbidity and sedimentation generated by cage farms affected interspecific competition and alterations in coral species composition and algal cover at 600 m distance from the farming sites (Huang et al., 2011, 2012b) Garren et al. (2008) showed that the abundance of bacteria and viruslike particles, as well as microbial communities, changed along a eutrophication gradient from cage farms with significant effects still evident at 2600 m and 5000 m, respectively
Known effects of eutrophication on coral reefs – such as a decreased calcification rates increased bleaching and heightened disease susceptibility (Hoegh-Guldberg et al., 1997; Tomascik, 1990; Vega Thurber et al., 2014) (Garren et al., 2008) The effect from cage farms less than 1 km from the reef may result in permanent destruction while reefs within distances 1–5 km will be impacted depending on type and magnitude of farming and local hydrographic conditions.