In the South China and Java Seas, cage farming is a recent regional activity, which since the year 2000 has experienced
an annual growth of 29%. The region holds the highest diversity of marine life, which is partly or
completely dependent on coral reefs. The increasingly growing coastal human population in the area relies on
ecosystem goods and services provided by the reefs that are threatened by anthropogenic activities. Sea cage
farming is one of the stressors negatively impacting coral reefs by being point sources of nutrients and other effluents.
To date no systematic information is available on the physical location of marine farms in relation to the
coral reefs. Little is known about the distancewhere impact fromthe farms can be detected on nearby coral reefs.
The present survey aimed to fill this gap by assessing to what extent marine cage farms in South East Asia are
placed in the vicinity of the reefs and at which distance stress indicators from the farms are observed. We used
Google Earth satellite images to investigate the extension and spatial distribution of sea cage aquaculture in relation
to the presence of coral reefs. The stress indicators were locally assessed in Central Vietnam by recording
turf algal overgrowth, coral mortality, live coral and branching coral cover at increasing distances from the farms.
Wefound that 90% of sea cage farms throughout the region clustered closer than 5 kmfromcoral reefs and 50% of
them closer than 1 km fromreefs. In Taiwan, 71% of the cages were locatedwithin 100mfroma reef. This pattern
is nonrandom and could not be explained by the natural distribution of coral reefs; only 5% of the Vietnamese
coast harbors coral reefs, and sea cage farms are present in these areas only. This indicates that the farms require
similar conditions as the reefs including clear and shallowwaters and protection against storms andwave action.
We found that turf algal overgrowth decreased at 287m±54 m, dead coral at 1446m±154 m, live coral cover
increased at 566 ± 221 m and branching corals increased at 867 m ± 140 m from the cage farms. We conclude
that proximity to coral reefs should be considered when planning future developments of sea cage aquaculture,
and recommend that distances of at least 1.5 km should be kept.
Statement of relevance: Consider coral reefs when planning sea cage aquaculture site.