Test for allelopathic interactions between two marine microalgal species grown in intensive cultures [Phaeodactylum tricornutum, Dunaliella tertiolecta]

Both high pH and cell senescence are believed to lead to the production of toxic extracellular metabolites in freshwater microalgae. However, there was no evidence for allelopathic suppression of photosynthesis when filtrates of either of two marine microalgae, Phaeodactylum tricornutum and Dunaliella tertiolecta , were mixed with whole cultures of the other species. This was true even when filtrate of P. tricornutum sample was derived from a culture at high pH or from one in various stages of senescence. It is believed that the major factor leading to the dominance of P. tricornutum in intensive outdoor cultures is the unique ability of this alga to tolerate pH levels above 9.5, not the allelopathic inhibition of competing species.