The term “white algae” is not a formal scientific classification, but a confusing descriptor for various colorless organisms or materials found in aquatic environments. True algae perform photosynthesis, a process fundamentally linked to the presence of colorful pigments. A biological definition of “white algae” involves two categories: organisms that have lost their color and organisms that never possessed it. This clarifies what the public often encounters and mislabels, from distressed coral symbionts to specific pathogens.
Biological Identity and Pigmentation
Most organisms classified as algae are photoautotrophs, using sunlight to create food through photosynthesis. This process requires chloroplasts, which contain light-capturing pigments. The primary pigment is chlorophyll a, which absorbs red and blue light while reflecting green light, giving most algae a greenish hue.
Different groups of algae possess accessory pigments that absorb wavelengths chlorophyll cannot, allowing them to thrive in diverse light conditions. For example, brown algae use fucoxanthin, and red algae utilize phycobilins like phycoerythrin, which mask the green color. Since classification is based on dominant color, an organism that appears white or colorless lacks the apparatus for the primary metabolic function of most algae.
The Two Definitions of “White Algae”
The concept of “white algae” involves two biological scenarios: algae that have lost their color and organisms that are naturally colorless but related to algae. The first scenario, known as bleaching, involves losing pigmentation due to severe environmental stress. This happens when photosynthetic algae expel pigmented symbiotic partners or degrade their own pigments because of high temperatures, chemical exposure, or intense light.
Coral bleaching is a prominent example, where corals expel colorful microalgae (zooxanthellae), leaving the tissue translucent and the white skeleton visible. Algae in swimming pools may also be chemically bleached by high concentrations of chlorine, which destroys chlorophyll and turns the growth white. In these cases, the whiteness signals distress, dormancy, or death in an organism that was once pigmented.
The second definition refers to intrinsically colorless organisms, such as the genus Prototheca. These unique microalgae are closely related to green algae like Chlorella, but they have lost their chloroplasts and their ability to photosynthesize. Prototheca species function as obligate heterotrophs, acquiring nutrients from their environment instead of using sunlight. Their genetic lineage places them within the algal family, despite being biologically different from typical algae.
Common Misidentifications and Practical Contexts
In real-world settings, the term “white algae” is often applied to materials that are not algae. In swimming pools, a white, tissue-like growth is commonly labeled “white water mold,” which is actually a fungus or a bacterial biofilm. Other white residues, such as undissolved pool chemicals or mineral scale from high water hardness, are also frequently mistaken for organic growth.
Prototheca, a true colorless alga, is a rare opportunistic pathogen in vertebrates associated with the disease protothecosis. Prototheca wickerhamii is often implicated in human cases, while Prototheca bovis causes mastitis in cattle. These infections are a serious health implication linked to the colorless species sometimes grouped under the “white algae” umbrella.
The cosmetic industry uses “white algae extract,” which refers to an extract from a naturally pigmented seaweed, such as Corallina officinalis. These extracts are processed into a white or colorless form for use in lotions and creams, valued for non-pigment properties like antioxidant or moisturizing benefits. The marketing term focuses on the final appearance of the extract, not the original color of the marine organism.