Background:

Algal blooms have increased in frequency and intensity in recent decades. Excess nutrients of anthropogenic origin may be an essential factor that gives rise to these blooms.

Goals:

This work aimed to study an unusual bloom of the chlorophyte Chlamydomonas in an urban lake from a morphological and chemical approach.

Methods:

The study site was a small lake located in Cantera Oriente, Mexico City. Sampling was performed in February 2016 (the cold-dry season); environmental variables were measured in situ, and surface samples were obtained for organism abundance and chlorophyll-a concentration. An additional sample was freeze-dried for chemical analyses, and another sample was fixed in glutaraldehyde for ultrastructural studies by SEM, TEM, LM, and confocal microscopy, using the stain Nile red to detect the presence of intracellular lipids.

Results:

The results of morphological observations agreed with the characteristics of the description of C. reinhardtii. The bloom abundance values were high (6.98 x 105 ± 1.37 x 105 cells mL-1), confirmed by the high values of chlorophyll-a concentration (5548 ± 796 µg L-1). The carbohydrate:protein ratio of the cells (0.15) indicates high protein synthesis during the enormous algal proliferation. The low lipid content (6.5 %) is associated with the absence of intracellular lipid granules and may be related to the availability of nitrogen and phosphorus and high vegetative multiplication. C. reinhardtii synthesizes essential fatty acids, such as alpha-linolenic acid (Omega 3), a precursor of beneficial lipids in human cardiovascular and neurological health.

Conclusions:

The bloom consisted mainly of Chlamydomonas reinhardtii and it significantly correlated with the chlorophyll a concentration, indicating high photosynthetic capacity and active cell division. Linoleic acid (Omega 3), an important substance for human health, was present in the alga composition. A controlled culture of this alga could improve the Omega 3 concentration offering a biotechnological resource for the future.