Impact of Fish Aquaculture Effluent on Reef-Associated Microbial Communities & Coral Health

While demand for aquaculture continues to increase, little attention has been given to its potential effects on coral reefs and other nearshore habitats. For this reason, the Disease Working Group conducted experiments in Bolinao, Philippines utilizing transplant experiments, water quality analyses, immunological assays, and microbial community characterizations to investigate how aquaculture effluent influences coral health and disease.

Work undertaken by Prof. Farooq Azam (CDWG) and his doctoral students, Melissa Garren and Steven Smirga, confirmed the presence of strong nutrient and microbial gradients extending from fish pens to adjacent reefs. Increased nutrient concentrations, in turn, led to algal blooms that persisted throughout both wet and dry seasons.

Their results also indicate that water-associated bacteria from fish pen effluent can become associated with corals and that corals transplanted near fish pens undergo rapid changes in microbial community structure. Further analyses are being conducted to identify the mechanism by which coral microbial communities shift in response to effluent and whether this shift affects coral health. Data collected by Prof. Laurie Raymundo (CDWG) and Dr. James Guest (RRWG) show corals transplanted closer to fish pens initially lost tissue and showed higher mortality than those in cleaner water. Data collected by Prof. Drew Harvell's (CDWG) doctoral students, Courtney Couch and Morgan Mouchka, suggest that effluent may exacerbate coral oxidative stress and suppress immune function following transplantation. This could have significant ramifications on the coral's ability to mount an effective innate immune response against Porites Ulcerative White Spot (PUWS), a common disease on the surrounding reefs, or potential pathogenic microbes within the effluent itself.

A larger experiment is planned, which we hope will elucidate the effects of long-term exposure to aquaculture effluent and explain the complete loss of once-viable coral reefs in the Bolinao fish pen area. The overall objective of the project is to produce scientific knowledge that might feed directly into policy in an area of developing concern: sustainability of aquaculture adjacent to coastal ecosystems.

Aquaculture farm - Bolinao
Aquaculture - Bolinao

    
 
 
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