Chroococcus minutus – Kinneret Algae Atlas

Phylum: Cyanobacteriophyta
Class: Cyanophyceae
Order: Chroococcales
Habitat: planktonic
Distinctive features: single spherical cells or couples of hemispherical cells after cell division, surrounded by a wide colorless homogeneous sheath.
Organization: single cells or colonies of 2 (most common) to 8 cells
Color: blue-green
Cell shape: sphere
Colony shape: spherical
Cell diameter (D): 3 – 10 μm, median: 5.9 μm (N=1500). Cell diameter varies significantly over an annual cycle, making it necessary to measure it routinely.
Cell biovolume: 20 – 500 μm³, median: 110 μm³. Larger cell size in winter, smaller in summer (see Fig. 2).
Biovolume equation: Sphere V, μm³ = 4/3 π (D/2)³.

Morphological features

Individual spherical blue-green colored cells are surrounded by a wide colorless homogeneous sheath (Plate 1). The species is polymorphic with numerous morpho-and ecotypes. Chroococcus turgidus and Chroococcus minutus are difficult to tell apart. The most notable difference is that the sheath of C. minutus is usually homogeneous with no layering while that of C. turgidus is laminated (layered). Furthermore, on average C. minutus cells are smaller, but both species show large size variation and the sizes overlap.

Plate 1. Chroococcus minutus from the pelagic waters of Lake Kinneret, showing a single cell with its typical thick homogeneous sheath (bottom) and two cell couples with their shared sheath. The right couple of cells are infected by bateria. Photo by Alla Alster, July 2026.

Ecology

An alanlyst effect is apparent in the long-term record of C. minutus and C. turgidus shown in Fig. 1. In particular, it is evident that Analyst 5 (1996-2012) counted more C. minutus whereas Analyst 6 (2013-2020) counted more C. turgidus, probably due to different taxon names given to the same organisms. Chroococcus minutus / turgidus has always been common in lake Kinneret, with long periods of thousands of (mostly 2-celled) colonies mL^-1 (Fig. 1). Prior to the decline of Peridinium gatunense and appearance of nostocalean cyanobacteria in the mid 1990s Chroococcus was the most abundant Kinneret cyanobacterial taxon. Peak abundance is from August to October (Fig. 2). Like several other Kinneret species, cells are smaller in summer, larger in winter (Fig. 2).

Environmental conditions

Advantaged by high water temperatures (>25^oC) and a well-stratified water column. Indifferent to chloride concentrations.

Additional figures

Figure 1. Time series of Chroococcus turgidus and Chroococcus minutus mean epilimnion colony abundance (colonies mL^-1) Lake Kinneret, 1987–2020, showing a distinct Analyst Effect.

Figure 2. The annual pattern of water column cell abundance (left) and volume per cell (middle) and number of cells per colony (right) of Chroococcus minutus, based on data for 2004-2012 (Analyst 5 only). Statistics shown are: median – middle line; 25th to 75th percentiles – box content; 90th and 10th percentiles - top and bottom bars, respectively.

Cite this record as: Dr. Tamar Zohary, Dr. Alla Alster. 21 July 2026. Electronic publication. Israel Oceanographic & Limnological Research. https://kinneret-algae-atlas.org/ Searched on —.