Combined effects of sedimentation and water temperature on the growth and development of coral spat (2013)

Undergraduates: Kelly Speare, Dr. Gretchen Goodbody-Gringley and Dr. John F. Bruno

Faculty Advisor: John Bruno
Department: Biology

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Coral reefs are threatened by anthropogenic impacts worldwide, resulting in widespread reef degradation. Resilience and recovery of reefs are, in part, dependent on recruitment of juvenile corals. Here we investigated the impacts of two known stressors to coral reefs, sedimentation and increased water temperature, on juvenile coral spat. Favia fragum spat were exposed to four experimental treatments: warm-filtered (~30¿C; 5μm filer), warm-unfiltered, ambient-filtered (~25¿C; 5μm filter), and ambient-unfiltered. After 8-weeks, growth and zooxanthellae density were highest in the ambient-filtered treatment compared to all other treatments. Zooxanthellae chlorophyll concentration increased in single stress treatments (warm-filtered and ambient-unfiltered) relative to the ambient-filtered treatment, suggesting that increased chlorophyll is a mechanism of photosynthetic compensation for zooxanthellae loss. Notably, there was no difference in survival between the ambient-filtered (86.2%), ambient-unfiltered (91.7%), and warm-filtered treatments (89.1%), indicating that coral spat may be able to tolerate exposure to sedimentation and increased temperature in isolation. Survival was significantly reduced, however, in the warm-unfiltered treatment (54.4%), demonstrating that the combined effects of sedimentation and increased temperature may have a greater impact on survival than either individual stress.