Spatio-temporal dynamics of coral-macroalgal interactions and their impacts on coral growth on urbanised reefs.

Interactions between corals and macroalgae are important in influencing benthic community structures on coral reefs and have become increasingly common occurrences. However, little is known about their temporal variation as most studies have only documented them from single surveys. To investigate the dynamics of coral-macroalgal interactions, we surveyed three urbanised reefs in Singapore bi-monthly for three years. We found that the frequency of coral-macroalgal interactions varied greatly across sites and seasons. The extent of coral-macroalgal contact was positively correlated with macroalgal abundance, but the correlation differed significantly among macroalgal genera. The growth rates of Goniopora, Montipora and Pavona corals, but not Platygra, were also negatively correlated with the extent of macroalgal interactions. Overall, our results highlight that coral-macroalgal interactions are spatially and temporally dynamic, with varying effects among coral species. It is critical to consider seasonal fluctuations of macroalgae if the overall long-term impacts of macroalgae are to be understood.