Sediment, light, and interspecific interactions have strong but independent species-specific effects on two dominant coral reef macroalgae
摘要
Storms are predicted to increase with climate change in the South Pacific, resulting in reductions in light levels and increases in sedimentation for marine communities. In coral reef ecosystems, light is a limiting resource to primary producers while sediment is generally considered a stressor. To test these hypotheses, we examined growth and structural responses of two macroalgae, Padina boryana and Sargassum pacificum, in response to experimental manipulations of sediment addition and light reduction on a fringing reef in Mo’orea, French Polynesia (17.491918 oS 149.850036 oW) from April - May 2019. This experiment was first conducted on two monospecific assemblages, P. boryana and S. pacificum, respectively, and then on interspecific assemblages. In monospecific assemblages, shade reduced P. boryana growth by 68% with no effect of sediment, while added sediment increased S. pacificum growth by 40.4% with no effect of light. While carbonate content of P. boryana appeared higher in ambient light and with added sediment, this pattern was insignificant. Further, neither factor affected thallus toughness of S. pacificum. In interspecific assemblages, growth of P. boryana was higher and calcification was overall lower than in monoculture. S. pacificum reduced growth in response to reduced light when grown with P. boryana, suggesting species interactions. Our study suggests P. boryana and S. pacificum have species-specific growth responses to changes in light and sediment that may occur with short-term disturbances associated with storms. Further, understanding the responses of species and influence of community context on these responses will strengthen coral reef predictions in the Anthropocene.