UCLA

Coral reefs experience natural and anthropogenic disturbances that can shift reefs from coral to algal domination, with concurrent loss of ecosystem functions and services. Pulse (transient) disturbances, such as storms, can alter the regime of environmental drivers in reefs negatively affecting corals. However, little is known of the resilience of the shifted macroalgal community, motivating my research into the effects of storm-associated disturbance on macroalgae. Here I investigate 1) how dominant macroalgae respond to changes in environmental drivers such as light, sediment, and nutrients and 2) how light and sediment disturbances affect species interactions and resilience. First, I explored the response of a green calcifying alga to changes in light, nutrients, and sediment. In the field, increased nutrients reduced growth, but only with added sediment, while ambient nutrients and reduced light increased growth. In microcosms, sediment acts as a buffer in high light, increasing growth. Thus, different combinations of environmental drivers produce complex interactions that can ameliorate negative effects of changes in certain environmental drivers. Second, I examined the effects of short-term disturbances in sediment and light on growth and species interactions of two macroalgae (calcifying vs non-calcifying), demonstrating environmental drivers can have independent rather than interactive effects depending on species assemblage. Intra-specifically, light reduction negatively affected the calcifying species and had negligible effects on non-calcifying species. However, interspecifically, light reductions resulted in negative responses for both algae, with differential performance suggesting species interactions. Thus, both species and community context are needed to improve predictions for coral reefs in the Anthropocene. Last, I studied the resilience of these macroalgae to storm-associated light and sediment disturbances. While disturbance negatively affected growth for both species, the capacity for resilience differed substantially. The calcifying species recovered quickly while the other did not; further, recovery rate was dependent on the presence of the other species, suggesting community context can affect species resilience. Overall, this work reveals the importance of studying species-specific responses of dominant macroalgae and their interactions to short-term disturbances as these responses can be shaped by community and environmental contexts, both of which are expected to continue to change in the Anthropocene.