Aureoumbra lagunensis

Aureoumbra lagunensis is a unicellular planktonic marine microalga that belongs to the genus Aureoumbra under the class Pelagophyceae. It is similar in morphology and pigments to Aureococcus anophagefferens and Pelagococcus subviridis. The cell shape is spherical to subspherical and is 2.5 to 5.0 μm in diameter. It is golden-coloured and is encapsulated with extracellular polysaccharide layers and has a single chloroplast structure with pigments.

Aureoumbra lagunensis thrives in a warm hypersaline environment as the greatest cell density has been found in water with salinity higher than 40 PSU and with temperatures between 25–30 °C (77–86 °F). Generally, the density of A. lagunensis is in the order of 10⁶ cells mL⁻¹, being higher in the summer months with lower abundance during the winter.

Aureoumbra lagunensis causes harmful algal blooms and was the dominant microalga in the 7 year long brown tide (1990 - 1997) that happened in Laguna Madre, Texas. Its dominance over other coexisting phytoplankton is in part associated with its encapsulating mucus layer of exopolymer secretions (EPS) and its ability to revert from vegetative and resting cell forms. The A. lagunensis blooms cause a substantial increase in light attenuation, which in turn contributes to marine biodiversity loss, particularly phytoplankton communities and benthic invertebrates. A. lagunensis thrives in low-light conditions, where it can maintain high growth rates at 150 umol photons m⁻² s⁻¹, thus an increase in light attenuation causes a positive feedback which further perpetuates blooms.

Aureoumbra lagunensis nutrient uptake is unlike other common microalgae. It uptakes inorganic nitrogen in the form of ammonium (NH₄⁺) and nitrite (NO₂⁻) and organic nitrogen in the form of urea, but does not utilize nitrate (NO₃⁻). It uses environment dissolved organic phosphorus as the sole source to regenerate phosphate for growth.