Dopamine release by Ulvaria obscura (Chlorophyta): environmental triggers and impacts on photosynthesis,growth, and survival of the releaser

In the NE Pacific, Ulvaria obscura is a common component of “green tide” blooms. It is also the only alga known to produce dopamine, which is released into seawater on sunny days when Ulvaria is emersed and then rehydrated. To better understand the mechanisms associated with dopamine release, we experimentally determined whether light quantity and quality, desiccation, temperature, exudates from conspecifics, and dissolved dopamine caused dopamine release. We also examined the effects of desiccation on Ulvaria's ability to photosynthesize, grow, and survive. Desiccation was the only factor that caused significant amounts of dopamine to be lost from U. obscura tissues. The loss of water from Ulvaria tissues was strongly and positively correlated with the loss of dopamine after rehydration. Only 56% of desiccated algae survived for 1 week, compared to 100% of undesiccated control algae. Desiccated algae lost 77% of their pigmented surface area and grew only 15% as much as undesiccated algae, which remained fully pigmented. The oxygen saturation of water containing Ulvaria that was desiccated and then rehydrated was significantly lower than that of seawater containing undesiccated algae. Thus, desiccation, which is coupled with dopamine release, is associated with the deterioration and death of some, but not all, tissues in Ulvaria. Although dopamine released into seawater can reduce the survival or growth of potential competitors, its release is associated with significant physiological stress and tissue mortality. However, the survival and continued growth of some Ulvaria tissues indicates that a net fitness benefit to release dopamine following desiccation cannot be ruled out.