Tetraselmis cordiformis – Kinneret Algae Atlas

Phylum: Chlorophyta
Class: Chlorodendrophyceae
Order: Chlorodendrales
Habitat: plankton
Distinctive features: relatively large cell size with 4 .
Organization: flagellated single cells
Color: green
Cell shape: sphaeroid
Cell diameter (D): 10.2–15.9 μm, median: 13.1 μm (N=526).
Cell length (L): 13.4–18.7 μm, median: 15.9 μm (N=526)
Cell biovolume: 730-2400 μm³, median: 1400 μm³.
Biovolume equation: prolate spheroid V, μm³ = 4/3 p L/2 (D/2)² (or: regression eqn. based on >500 measurements of both D and L with V computed for a prolate sphaeroid: V= 1.9507*D^2.5651

Morphological features

One of the larger flagellated species of Lake Kinneret (after the dinoflagellates), and the only one with four flagella (Plate1). It is heart-shaped (=cordiform, as it’s name) or cherry-shaped, ellipsoidal or almost sphaerical, never twisted, with four equal-length flagella emerging out of a pit or depression in the upper side of the cell (Plate 1). It has a red or , and a single cup-shaped chloroplast usually with a basal . Two contractile vacuoles are present near the base of the flagella.

Plate 1. Tetraselmis cordiformis (live material) seen with its heart or cherry-shape, 4 flagella and reddish-brown eyespot. A, B, D – front view. C - Specimen viewed looking at its “bottom” side with only the ends of the four flagella visible. Photos: Alla alster.

Plate 2. A massive bloom of Tetraselmis cordiformis on 19 February 1996: the entire lake water turned grass green, as seen in the green trail of water behind our sampling boat and as seen more closely in a hand-held beaker of lake water (inset). Photos: Tamar Zohary.

Ecology

Tetraselmis cordiformis usually occurs in the Kinnret plankton in small numbers of < 50 cells/mL (Fig. 1) and biomas not more than 4 g m^-2 (not shown). It is more abundant between February and April and again from August till November but absent in July and rare in December and January (Fig. 2). A technician-effect is noted in our data: a technician was replaced on 1 Jan 2013. It is evident in Fig. 1 that the newer technician counted this species more frequqently than the previous one. On a single unusual occassion in February 1996 Tetraselmis cordiformis formed an intense bloom that colored the entire lake with a strong grass-green color. This intense bloom disappeared within a few days and was missed by our weekly sampling, but photographic records remain (Plate 2). On another occassion, a massive bloom of this flagellated alga took place in a series of experimental tanks behind the Kinneret Limnological Institute. Again the bloom was short lived and disappeared within days. A distinct annual cycle of cell size is evident from our data: cells are smaller size in summer, larger in winter (Figs. 2, 3A). Cell size correlates well with water temperature (R²=0.48, Fig. 3B).

Environmental conditions

T. cordiformis occurred at the full range of water temperatures occurring in the lake, at > 1000 μS cm^-1 and Chloride > 210 mg L^-1, when Secchi transparency was 2-4 m, euphotic zone depth > 5 m, mostly at pH between 8–9, Chlorophyll < 400 mg m^-2, at > 100 mg L^-1, when NH₄ was low but NO₃, Norg and DON were moderate (Fig. 4).

Additional figures

Figure 1. Time series of Tetraselmis cordiformis abundance (cells mL^-1), Lake Kinneret, 1992-2020. The greater frequency of observations of the species from 2013 onwards is likely due to change of the technician doing the microscope counts on 1 Jan 2013.

Figure 2. The annual pattern of water column cell abundance (left) and volume per cell (right) P. elpatiewskyi, based on data for 1992-2020. Statistics shown are: median – middle line; 25th to 75th percentiles – box content; 90th and 10th percentiles - top and bottom bars, respectively.

Figure 3. A. Time series of measured cell size, 2006-2012, showing largest size around January-February each year (grid lines indicate 1 January of each year). B. Regression of cell size against water temperature.

Figure 4. Tetraselmis cordiformis abundance (cells mL^-1) vs. selected environmental parameters recorded at the site and time of sampling.

Cite this record as: Dr. Tamar Zohary, Dr. Alla Alster. 16 June 2026. Electronic publication. Israel Oceanographic & Limnological Research. https://kinneret-algae-atlas.org/ Searched on —.