In order to test the hypothesis that the microbial enrichment in the sea-surface microlayer (SML) over coral reefs is significant, we investigated the abundance and production of the microbial community in the SML and sub-surface water (SSW) at a fringing coral reef of Malaysia. Samples were taken at 2 coral sites with different live coral coverage as well as one offshore site. We detected substantially high enrichment factors (EFs) in abundance (where EF = SML/SSW: the ratio of microbial abundance in the SML relative to SSW) for all biological groups at all sites: up to 6.0 for heterotrophic bacteria, 4.2 for cyanobacteria, 18.8 for autotrophic nanoflagellates and 22.6 for heterotrophic nanoflagellates. We also found that the enrichment factors of microorganisms in coral reefs were remarkably higher than in other marine ecosystems, and a higher concentration of microorganisms was observed in the higher coral coverage site, probably due to higher organic matter released by corals. The higher microbial abundance in the SML over coral reefs may enhance gaseous exchange and carbon flow in the food web through the air-sea interface.

Previous studies have suggested that Crown-of-Thorns starfish (COTS) larvae may be able to survive in the absence of abundant phytoplankton resources suggesting that they may be able to utilize alternative food sources. Here, we tested the hypothesis that COTS larvae are able to feed on coral-derived organic matter using labeled stable isotope tracers ( 13 C and 15 N). Our results show that coral-derived organic matter (coral mucus and associated microorganisms) can be assimilated by COTS larvae and may be an important alternative or additional food resource for COTS larvae through periods of low phytoplankton biomass. This additional food resource could potentially facilitate COTS outbreaks by reducing resource limitation.

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Okinawa Prefectural Government implemented a public program entitled "Comprehensive management program of Crown-of-Thorns Starfish (COTS) outbreaks in Okinawa" during the period between 2012 and 2018 in order to develop new policies for the future coral reef management. The program involved scientific research on the major causal factors of COTS outbreaks and monitoring surveys for establishing prediction method of outbreaks in Okinawa Island. The results of the program suggested: 1) COTS larval dispersion leading to successful recruitment is likely to be limited to a local scale, 2) COTS larvae can utilize detritus and coral mucus as supplemental food sources in addition to phytoplankton, 3) food availability of COTS larvae quickly increases to the level at which larval growth and survival is supported by terrestrial runoffs from heavy rainfall, 4) prediction of COTS outbreaks is thought to be feasible by monitoring alga-eating juvenile densities. The Okinawa government proposed based on these results that the future COTS outbreaks should cope with short-and long-term efforts, consisting of juvenile monitoring, repeated removal in a limited area and water quality improvement in the coastal areas.