T. Zohary et al., SEASONALITY OF STABLE CARBON ISOTOPES WITHIN THE PELAGIC FOOD-WEB OF LAKE KINNERET, Limnology and oceanography, 39(5), 1994, pp. 1030-1043
Seasonal variations in the carbon isotope composition of components of
the pelagic food web in Lake Kinneret were recorded and compared with
those recorded for bulk plankton from the lake in the early 1970s. In
dividual planktonic components as well as bulk plankton were isotopica
lly lightest shortly after overturn in January and heaviest in May, af
ter the peak of the annual bloom of the dinoflagellate Peridinium gatu
nense. The range of deltaC-13 values observed over an annual cycle and
the annual and seasonal means varied considerably between taxa. Withi
n the primary producers, P. gatunense (range, - 23.2 to - 17.9 parts p
er thousand) was significantly C-13-enriched relative to concurrent na
noplankton (- 27.4 to - 19.0 parts per thousand). Zooplankton deltaC-1
3 showed indistinct taxon-specific differences but greater seasonal va
riation (- 33.8 to -19.8 parts per thousand) than any phytoplankton co
mponent examined. Adult fish exhibited smaller deltaC-13 variability t
han the planktonic components. End-member isotope compositions confirm
ed the linkages nanoplankton --> zooplankton --> Kinneret sardines, an
d Peridinium --> Sarotherodon galilaeus. Likely grazing of zooplankton
on isotopically heavy Peridiniopsis spp. in spring and on a yet undet
ected light component in winter were implicated. The data demonstrate
that the deltaC-13 of bulk particulate organic matter samples provides
only a simplified view of a complex picture of deltaC-13 dynamics wit
hin the pelagic food web of a freshwater system.