Kinneret Algae Atlas

Phylum: Dinoflagellata
Class: Dinophyceae
Order: Peridiniales
Habitat: plankton, pelagial, littoral
Distinctive features: mixotroph. Too large to be grazed by zooplankton. Major food source for Cichlid fishes. Performs daily vertical migrations. When it blooms in spring it constitutes > 95% of total phytoplankton biomass. Its bloom can be seen as patches of coffee brown colored water. Peridinium gatunense is certainly the most studied organism in Lake Kinneret, with hundreds of publications addressing it. For a review article see Zohary et al. 2014.
Organization: flagellated single cells
Color: dark brown
Cell shape: prolate sphaeroid (close to a sphere)
Cell diameter (D): 44 - 58 µm, median: 50 µm (N=1230)
Cell length (L): 47 – 60 µm, median: 52 µm (N=423)
Cell biovolume: 44,300 – 99,400 µm³, median: 67,000 µm³.
Biovolume equation: V, µm³ = 1.31 D²·⁷⁸³⁵. Regression eqn. based on >400 measurements of both D and L with V computed for a prolate sphaeroid.

Morphological features

This is the second largest dinoflagellate in Lake Kinneret (after Ceratium hirundinella). Under the light microscope, those large, spherical single cells are distinct by having thick, colorless thecae (shell) enveloping the strongly brown-colored living cell or protoplast (Plate 1a,b). The epitheca and hypotheca, are conical and of similar size. The cingulum is wide, deep, and displaced about one cingular width (Plate 2). The sulcus widens slightly and reaches the antapex. The plates are reticulated or rarely rugose and irregularly arranged. Chloroplasts are numerous and parietal (along cell walls). See Hansen and Flaim (2007) for a more detailed taxonomic description. Under unfavorable conditions the cells shed their thecae, and a naked protoplast emerges which will later excrete new thecae. The thecae are also shed before cell division (Plate 1c). After division, each of the two daughter cells excretes its own new thecae. Mitotic cell division is “phased”: it occurs only at night, between midnight and 4 am (Serruya and Pollingher 1976). Sexual reproduction was never observed in Lake Kinneret, possibly because it also occurs at night. Peridinium gatunense resting cysts are spherical, with a thick and distinct cell wall, and two distinct red spots, or eyespots (Plate 3). Throughout the bloom development period, a small proportion of the cells (~ 1 %, Alster et al. 2006) change their morphology to become resting cysts, which sink to the sediments to remain there as an inoculum for future growth. Vegetative cells emerging from resting cysts keep the two red spots. After cell division each daughter cell keeps one red spot. With later divisions those red spots get diluted. Presence of those red spots are thus an indication of the origin of the cell from a resting cyst.

Plate 1. Peridinium gatunense from Lake Kinneret. (a) abundant cells from a patch, showing dark brown protoplast inside transparent thecae with distinct cingulum. Several empty thecae are also present. (b) A single cell with its flagellum (small cells on left are part of a Microcystis colony). (c) Two daughter cells shortly after cell division and the empty thecae of the mother cell. Daughter cells are of smaller size, still without thecae. Photos: Alla Alster.

Plate 2. Light (left) and SEM (right) microscope photos of Peridinium gatunense showing the wide and deep cingulum that is displaced about one cingular width. Photos: Alla Alster.

Plate 3. Resting cysts of Peridinium gatunense, with two red eyespots, before completely shedding the thecae. Photos: Alla Alster.

Plate 4. (a) Map of the spatial distribution of chlorophyll in Lake Kinneret on 1 May 2020, during the peak of a P. gatunense bloom, showing the patchy distribution of the dinoflagellates. Map, curtesy of Gideon Tibor, IOLR, was created from Sentinel-3 remote sensing data. (b) Air photo of part of a patch of P. gatunense (darker water on bottom left side), curtesy of Asaf Dori, Israel Nature and Parks Authority.

Ecology

From the beginning of monitoring in Lake Kinneret in the 1960s, the regular late-winter-spring bloom of P. gatunense was the most salient feature of the Kinneret phytoplankton (Zohary et al. 2014). Those intense blooms could be observed as large patches of coffee-brown colored water (Plate 4), reaching up to several square kilometers in area. At the bloom peak P. gatunense reached mean epilimnion concentrations > 500 cells mL⁻¹ (Figs. 1, 2), or 150-250 g m⁻² of wet weight biomass and comprised >95% of total phytoplankton biomass. The blooms declined sharply in May-June (Fig. 2), shortly after water temperature exceeded 25ºC, thermal stratification was established, and nutrients became scarce, leaving behind resting cysts on the lake sediments. During the summer months P. gatunense concentrations in the water column were low, usually <5 cells mL⁻¹ (Fig. 2). Autumn turnover caused re-suspension of the cysts from the sediments, leading to their excystation and the initiation of the next year’s bloom. After many years of recorded constancy, in the mid-1990s, the regular pattern of late-winter spring P. gatunense blooms broke down, P. gatunense blooms have become irregular (Fig. 1) occurring only in high-rainfall years (Zohary et al. 2012), and in more recent years, not even in all of them. As in several other Kinneret dinoflagellates, cell size varies seasonally (Fig. 2), with largest sizes recorded in January-February, when nutrients are most plentiful, and smallest sizes in summer, after the bloom crash. In 2019 and 2020, when the lake’s water level rose after several years of being remarkably low and inundated for the first time shores that were overgrown by dense vegetation – exceptionally dense patches of P. gatunense (~1600 cells mL⁻¹) developed between flooded Tamarix trees (Zohary et al. 2026). Peridinium gatunense cells are too large to be grazed by crustacean zooplankton (Hambright et al. 2007). The native Cichlid fish feed primarily on Peridinium (Zohary et al. 1994) but overall, grazing has only a minor impact on the population. The primary loss of cells is due to death and decomposition in the water column. Second in importance is sinking to bottom sediments, where decomposition processes prevail but some grazing also takes place. An additional, less important losses is by parasitism by chytrid fungi in the water column (Alster and Zohary 2007).

Physiological features

Because Peridinium gatunense is a large cell, its growth rate is slow compared with that of other microalgae, with ambient doubling (turnover) time of ~7 days (Table 1). Lab experiments have shown maximal growth rates at 20-23 °C at light intensities ranging 50-200 μmol photons m-2 s-1. Growth rates decline at 25-27 °C (Berman and Dubinsky 1985). The specific photosynthetic rates (per unit chlorophyll) of P. gatunense are low (Table 1) in comparison with other phytoplankton prevailing in Lake Kinneret. But daily vertical migration and accumulation close to the surface in daytime (Berman and Rhode 1971) enhances photosynthesis. With darkness, the motile cells migrate down the water column to depths with higher nutrient concentrations. When CO2 levels become limiting (under intense bloom conditions), the dinoflagellates responded with higher levels of external and internal carbonic anhydrase activity and internal storage of inorganic C by means of a C concentrating mechanism (Berman-Frank et al. 1994). C content of P. gatunense, 45% of dry weight, is relatively high due to the thecae made of polyglucan, with practically no N, P. Allelopathic interactions between Peridinium gatunense and the bloom forming toxic cyanobacterium, Microcystis sp. were reported by Sukenik et al. (2002).
Table 1. Physiological parameters for Peridinium gatunense based on field measurements (from monitoring data using only dates when P. gatunense comprised > 90% of total phytoplankton biomass).

Physiological parameter	Average ± SD	N	Reference
C:Chl ratio	58.3 ± 19.3	243	Yacobi and Zohary (2010)
Assimilation number (at depth of max photosynthesis), mg C mg Chl⁻¹ h⁻¹	1.56 ±0.80	36	Yacobi and Zohary (2010)
Turnover time, d	7.44±5.05	36	Yacobi and Zohary (2010)
C content, % dry weight	45.6±4.7	54	J Erez lab, HUJ
N Content, % dry weight	4.3±0.6	54	J Erez lab, HUJ
C:P	464±150		Wynne et al. 1982

Environmental conditions

Peridinium gatunense biomass > 100 g m⁻² (considered a bloom) was associated with all incidences of Secchi depth < 1.5 m (Fig. 3) and TSS> 10 mg L⁻¹ (not shown), 70% of all incidences of turbidity > 4 NTU (not shown), 80% of all incidences with pH > 9.1 (Fig. 3), over 80% of the cases of excessive oxygen super-saturation (DO >13 mg L⁻¹, Fig. 3) and of TP> 0.05 mg L⁻¹, and over 60% of all cases where TN exceeded 1 mg L⁻¹, demonstrating how a single dominant species can modify the light conditions and chemical properties of its own environment. Factors that may have impacted P. gatunense biomass may have been salinity (no blooms at chloride> 280 mg L⁻¹) and availability of particulate organic N (Norg-part) for a mixotrophic species (Fig. 3). Its environmental preferences included temperature range of 16-23 °C, and probably particulate organic matter as a source of nutrients. This explains its proliferation in dense patches among inundated shore vegetation.

Additional figures

Figure 1. Time series of Peridinium gatunense depth-integrated wet-weight biomass (g m⁻²), Lake Kinneret, 1970-2020.

Figure 2. Box plots showing the seasonal pattern of statistics of water column cell abundance (left) and volume per cell (right) for Peridinium gatunense.

Figure 3. Peridinium gatunense abundance (cells mL⁻¹) vs. environmental parameters recorded at the site and time of sampling.

Cite this record as: Tamar Zohary, Alla Alster. 7 May 2026. Electronic publication. Israel Oceanographic & Limnological Research. https://kinneret-algae-atlas.org/ Searched on —.

Peridinium gatunense Nygaard 1925

Morphological features

Ecology

Physiological features

Environmental conditions

Additional figures

Further reading