Particulate fatty acids in two small Siberian reservoirs dominated by different groups of phytoplankton

Abstract

SUMMARY 1. We studied the composition of fatty acids (FAs) in the seston from two small freshwater reservoirs (Bugach and Lesnoi) with distinct periodicity of domination by cyanobacteria and eukaryotic algae during the growth season. 2. The diatoms in the both reservoirs were characterised by a high content of 14:0 and C16 unsaturated acids, whereas that of the essential FA 20:5ω3 [eicosapentanoic acid (EPA)] was low. The correlation between this polyunsaturated FA (PUFA) and diatom biomass was not significant in either reservoir. The percentage of 20:5ω3 in seston significantly correlated with the biomass of euglenophyta in Bugach and dinophyta in Lesnoi. Hence the diatoms, usually referred as a valuable food for zooplankton, were not an important source of the essential PUFA in these systems. 3. The dominant cyanobacteria in Bugach, and the green algae in Lesnoi, both contained the same marker acids: 18:3ω3 and 18:2ω6. Hence, a discrimination between these two phytoplanktonic groups on the basis of FA biomarkers may be difficult in some cases. 4. We found no significant correlation between the content of 20:5ω3 in seston and the biomass of the dominant daphniids in either reservoir. This is contrary to expectations, based on the literature, that EPA is generally important. Rather, the biomass of the two dominant Daphnia species in Bugach correlated strongly with the content of 18:3ω3 in the seston. The cyanobacteria were a probable source of this ω3 FA for Daphnia. We conclude that EPA is not always important for Daphnia populations although, in such cases, some other PUFA (e.g. 18:3ω3) might be related to their growth.

Efficiency of transfer of essential polyunsaturated fatty acids versus organic carbon from producers to consumers in a eutrophic reservoir

“…PUFA were represented by the sum of x-3 acids: 18:3x-3, 18:4x-3, 20:3x-3, 20:4x-3, 20:5x-3, 22:5x-3 and 22:6x-3. The same was done for the non-essential C16-PUFA, which were represented by the sum of 16:2x-4, 16:3x-4, and 16:4x-1, characteristic of diatom algae, and of 16:2x-6, 16:3x-3, and 16:4x-3, characteristic of green algae (Ahlgren et al 1992;Sushchik et al 2003a). …”

Feeding spectra of Arctodiaptomus salinus (Calanoida, Copepoda) using fatty acid trophic markers in seston food in two salt lakes in South Siberia (Khakasia, Russia)

“…Commonly, 20:5x3 and x7, x4 and x1 C16 PUFAs are considered as diatom markers (Brett et al 2009). However, Sushchik et al (2004) have demonstrated that summer diatom populations can be low in PUFA compared with the spring ones, while 14:0 and 16:1x7 together are good predictors of both summer and spring populations of diatoms (Sushchik et al 2003a). Diatoms are reported in both lakes in summer (Gaevsky et al 2002), with lower occurrence in L. Shira, that is in good accord with the lower percentages of FATM 14:0 and 16:1x7, observed in our study.…”

“…However, it is known that 18:3x3 is also synthesized by Cyanobacteria, especially filamentous species (Gugger et al 2002). Moreover, Sushchik et al (2003a) have shown in a freshwater reservoir that 18:3x3 indicates dominance of both green algae and Cyanobacteria. We have noted that in summer period Cyanobacteria Lyngbya contorta, a non-identified small-sized cyanobacterial species, and green algae of Dictyospherium genus dominate phytoplankton in Lake Shira (Gaevsky et al 2002).…”

Seasonal correlations of elemental and ω3 PUFA composition of seston and dominant phytoplankton species in a eutrophic Siberian Reservoir

“…Its surface area is 0.32 km 2 , and its maximum depth is 7 m, and the mean depth is~2 m. Mean seasonal concentrations of dissolved inorganic phosphorus in 2002, 2003 and 2004 were 0.014 mg l )1 , 0.005 mg l )1 and 0.008 mg l )1 , respectively, and mean concentrations of NH 4 -N were 0.163 mg l )1 , 0.254 mg l )1 and 0.221 mg l )1 , respectively. Detailed descriptions of the Reservoir are given elsewhere (Sushchik et al 2003a(Sushchik et al , 2004.…”

“…It should be noted, that while initially the core role of EPA in nutrition of some zooplankton species (population) has been emphasized, we consider also the sum of x3-PUFA, like in some other studies (Park et al 2002;Von Elert 2004), because recently there is strong evidences has been obtained concerning the importance of diverse x3 species for zooplankton growth, such as a-linolenic, 18:3x3 (Wacker and Von Elert 2001;Sushchik et al 2003a), stearidonic, 18:4x3, (Ravet et al, 2003) and eicosatetraenoic, 20:4x3 (Becker et al 2004) acids. We found Sx3-PUFA better related with the whole elemental composition (stoichiometry) of seston, than any single PUFA species.…”