Dinoflagellate bloom development and collapse in Lake Kinneret: a sediment trap study

Warm monomictic Lake Kinneret, Israel, is characterized by awinter–spring water bloom of the large (~50 µm diameter)dinoflagellate Peridinium gatunense Nygaard. Usually the P.gatunense bloom declines in May–June and a less prominentbloom of smaller dinoflagellates (mostly Peridiniopsis spp.of ~20–30 µm diameter) develops. Water column abundancesand sedimentation losses to those dinoflagellates were followedthroughout 1994 and 1995. The objective was to quantify thevariables that describe population dynamics, that in turn willshed more light on the seasonal patterns of bloom dynamics.Sedimentation losses were measured by means of sediment trapswith and without a preservative (formaldehyde) that were exposedfor 24 h once every 2–3 weeks. Annual sedimentation lossesof Peridinium (hypolimnetic trap catches) were 209 g wet wtm^-2 year^-1 in 1994 and 187 g wet wt m^-2 year^-1 in 1995, whichconstituted 16 and 23% of Peridinium production in those years,respectively. This study revealed that increased death ratespreceded a mass sedimentation flux of Peridinium and causedthe decline of the bloom in Lake Kinneret. Annual sedimentationlosses of Peridiniopsis were 55 g wet wt m^-2 year^-1 in 1994and 34 g wet wt m^-2 year^-1 in 1995. In contrast to live Peridiniumcells, Peridiniopsis cells continued to swim to the lower trapafter the onset of thermal stratification, possibly taking advantageof the higher nutrient concentrations below the thermocline,at a time when the lake is already stratified and the epilimnionis nutrient depleted. This could be an important factor allowingPeridiniopsis spp. to peak after the decline of Peridinium.