Marine microalgae isolated from coastal environments are unlikely to be optimally adapted to the new pond environment. Therefore, genetic selection may significantly improve productivities of the algal mass cultures. For example, when a single limiting factor exists such as the nutrient source, genetic selection will offer a greater advantage for growth. If two organisms differ through a hereditable genetic difference to utilize the same limiting substance, then the one that is better in capturing the limiting nutrient will prevail in that environment. Eventually competition for one limiting factor will result in a single type of dominant organism. There are many factors that determine the species dominance which include: (i) resource-growth rate relationships for different algae, (ii) variable environmental conditions, (iii) inhibition of one organism by another through excreted allelopathic substances, and (iv) loss of growth due to predation or sinking. Free fatty acids, cell wall degradation products, exo-metabolites produced by algae and cyanobacteria, such as cyanobacterin (Gleason and Paulson 1984; Gleason and Baxa 1986) and fischerellin (Gross et al. 1991; Hagmann and Jüttner 1996) could also have allelopathic potential. Simple mathematical competition models can be designed for two organisms that compete in the pond. The above factors can be included as terms in the model.