title: Resilience of coral-associated bacterial communities exposed to fish farm effluent.
abstract: BACKGROUND
  The coral holobiont includes the coral animal, algal symbionts, and associated microbial community. These microbes help maintain the holobiont homeostasis; thus, sustaining robust mutualistic microbial communities is a fundamental part of long-term coral reef survival. Coastal pollution is one major threat to reefs, and intensive fish farming is a rapidly growing source of this pollution.
  
  
  RESULTS
  We investigated the susceptibility and resilience of the bacterial communities associated with a common reef-building coral, Porites cylindrica, to coastal pollution by performing a clonally replicated transplantation experiment in Bolinao, Philippines adjacent to intensive fish farming. Ten fragments from each of four colonies (total of 40 fragments) were followed for 22 days across five sites: a well-flushed reference site (the original fragment source); two sites with low exposure to milkfish (Chanos chanos) aquaculture effluent; and two sites with high exposure. Elevated levels of dissolved organic carbon (DOC), chlorophyll a, total heterotrophic and autotrophic bacteria abundance, virus like particle (VLP) abundances, and culturable Vibrio abundance characterized the high effluent sites. Based on 16S rRNA clone libraries and denaturing gradient gel electrophoresis (DGGE) analysis, we observed rapid, dramatic changes in the coral-associated bacterial communities within five days of high effluent exposure. The community composition on fragments at these high effluent sites shifted towards known human and coral pathogens (i.e. Arcobacter, Fusobacterium, and Desulfovibrio) without the host corals showing signs of disease. The communities shifted back towards their original composition by day 22 without reduction in effluent levels.
  
  
  CONCLUSIONS
  This study reveals fish farms as a likely source of pathogens with the potential to proliferate on corals and an unexpected short-term resilience of coral-associated bacterial communities to eutrophication pressure. These data highlight a need for improved aquaculture practices that can achieve both sustainable industry goals and long-term coral reef survival.
authors.affiliation: Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, United States of America. mgarren@ucsd.edu
authors.forename: Melissa
authors.initials: M
authors.lastname: Garren
authors.forename: Laurie
authors.initials: L
authors.lastname: Raymundo
authors.forename: James
authors.initials: J
authors.lastname: Guest
authors.forename: C Drew
authors.initials: CD
authors.lastname: Harvell
authors.forename: Farooq
authors.initials: F
authors.lastname: Azam
mesh_terms: D000818:Animals; D037421:Anthozoa / Q000382:microbiology*; D017756:Aquaculture; D001419:Bacteria / Q000254:growth & development*; D002244:Carbon; D002734:Chlorophyll / Q000737:chemistry; D017753:Ecosystem; D004784:Environmental Monitoring; D004785:Environmental Pollutants; D005399:Fishes; D019015:Geologic Sediments; D014871:Water Microbiology; D014874:Water Pollutants, Chemical
chemical_list: D004785:Environmental Pollutants; D014874:Water Pollutants, Chemical; D002734:Chlorophyll; D002244:Carbon