MEPS 509:181-191 (2014)  -  DOI: https://doi.org/10.3354/meps10880

ABSTRACT: Both global- and regional-scale stressors are contributing to the decline of corals on reefs across the planet. Even though many factors affect corals, we have very little data on the relationship between multiple co-occurring stressors and their compounding effects on these critical ecosystem engineers. We provide evidence that under short-term exposure, the presence of the brown alga Dictyota menstrualis has direct negative consequences for coral survival and recruitment, while seawater elevated to +3.5°C causes sub-lethal stress and compromises coral health. Three life-history stages (larvae, 6 wk-old juveniles [~0.15 cm²], and 1-2 yr-old colonies [0.8-45 cm²]) of the common Caribbean coral Porites astreoides were exposed to each stressor alone and in combination. Exposure to D. menstrualis reduced the survival of P. astreoides larvae and 6 wk-old juveniles by ~40% and caused partial mortality in 1-2 yr-old colonies. Elevated temperature did not cause mortality, but induced sub-lethal stress that was disparate among coral life-history stages. These stressors in combination predominately impacted corals in an independent manner. However, extended exposure resulted in a synergistic enhancement of oxidative damage (lipid peroxidation) in P. astreoides larvae. Our results suggest that benthic macroalgae can greatly inhibit coral recruitment, and this pressure combined with rising sea-surface temperatures represents a significant threat to the health of coral reef ecosystems. These results highlight the importance of local- and global-scale stressors acting in concert to impact coral demographics during critical early life-history stages.

KEY WORDS: Macroalgal presence · Thermal stress · Recruitment · Porites astreoides