Meeting Abstract

S7-1.2  Saturday, Jan. 5  The role of spatial and ontogenetic morphological variability in the spread of a tropical alga across barrier reefs and oceanic islands STEWART, H.L.; Friday Harbor Labs, University of Washington hstewart@u.washington.edu

Hydrodynamic conditions on barrier reef systems range from wave-driven flow on the forereef to slow unidirectional flow in protected lagoons. This hydrodynamic gradient presents challenges to reef organisms; those in lagoons may face mass transfer limitation due to slow delivery of nutrients and gases in oligotropic water, while forereef organisms struggle to stay attached in the face of high drag forces under waves. The distribution of the macroalga Turbinaria ornata thrives across all areas of barrier reefs in the South Pacific. A combination of field and lab experiments showed that this alga exhibits morphological variability that enables it to cope with the challenges presented by different hydrodynamic conditions across the reef. Lagoon plants are flexible and produce airbladders that make them buoyant, whereas forereef plants are not buoyant, but strong and stiff. Production of bladders and resulting buoyancy was found to be a phenotypically plastic trait in response to water motion that confers advantages to lagoon plants but also plays an important role in dispersal. Further investigation revealed that ontogenetic variation of buoyancy, material properties, and reproductive capacity is part of a dispersal strategy whereby fertile, buoyant fronds drift between oceanic islands forming new populations, contributing to the recent range expansion of T. ornata across French Polynesia.