Self-organized pattern formation of a common tropical alga.

Recent in-situ observations within a tropical coral reef have revealed novel polygonal patterns of the calcifying green alga Halimeda. The observed patterns showed no evidence of a matching exogenous template in structural reef morphology, distribution of biological competitors for space, or other environmental factors, suggesting that pattern formation is consistent with endogenous, nonlinear dynamics. A simplified, spatially explicit numerical model is proposed that simulates a feedback whereby Halimeda preferentially grows in regions less conducive to the growth of corals (when corals are the dominant spatial competitor), and coral growth is inhibited in regions of dense Halimeda. Model results reveal self-organized emergent polygons of Halimeda cover that qualitatively match observations.