Seasonal variations in food quality for pelagic and benthic invertebrates in Lake Erken – the role of fatty acids

Abstract

1. Plankton net samples and sedimenting matter in traps from mesotrophic Lake Erken, Sweden, were analysed for carbon (C), nitrogen (N), phosphorus (P), total lipids and fatty acid (FA) content to determine what differences and seasonal changes might exist in the quality of food available to pelagic zooplankters and benthic invertebrates. 2. Matter collected in a plankton net was assumed to correspond to food available to pelagic grazers, while matter collected in sedimentation traps provided a measure of food available to benthic invertebrates. Furthermore, food quality was assumed to be related to polyunsaturated fatty acid (PUFA) content. 3. The results suggest that suspended particulate matter, collected with a plankton net, is a much higher‐quality food resource than sedimenting matter. Our data also show that only during the spring and autumn do the benthic fauna have access to high‐quality food, because of the dominance of diatoms during these periods. During summer, pelagic grazer production was probably limited by food quantity, whereas benthic invertebrate production was probably limited by food quality. 4. Plankton net samples showed consistently higher values than trap samples (% of dry weight, DW, or mg g–1 DW) for nearly all variables analysed: C, N, P, saturated FA (SAFA), monounsaturated FA (MUFA), PUFA, ω3 FA and ω6 FA. If N and P were expressed per C, the differences decreased and both data sets indicated moderate to no N or P limitation. N/P also showed well‐balanced ratios throughout most of the season, on average 10 and 7 (by weight), respectively. The largest differences between the two food resources occurred in the PUFA content, including the important FA of the ω3 type. The only FA with higher levels in the trap samples were some unidentified FA of relatively short chain lengths. Seasonal variation for most variables was also very large in both net and trap samples. 5. PUFA and ω3 FA showed good relationships with the P content of net samples, but not with that of trap samples. Eicosapentaenoic acid alone did not give a good relationship with P. Thus, P seems to be a good predictor of food quality in living phytoplankton but not in dead matter or detritus.

Disentangling food quantity and quality effects in zooplankton response to P‐enrichment and UV radiation

“…A P-normalized v3-PUFA index offered the best prediction for macrozooplankton nutrient limitation. This finding may be explained by the interconnected metabolisms of v3-PUFA and P in autotrophs (Ahlgren et al 1997) and their irreplaceable role for herbivorous consumers (Sterner and Elser 2002), and is congruent with results of the metaanalysis which support the relevance of PUFA and P as single constituents for zooplankton growth (Table 7). The positive slope of the regressions between v3-PUFA:P and macrozooplankton growth may have resulted from a greater influence of v3-PUFA on algal food quality relative to P below the seston C : P threshold of 350 (Becker and Boersma 2003), from an excessively P-rich seston akin to Elser's 'stoichiometric knife edge' hypothesis (Elser et al 2005), or from a combination of both.…”

“…The seston fatty acid composition observed in this experiment was well explained by the dominance of the green algae Dyctiosphaerium chlorelloides (. 95% biomass in all enclosures; Delgado-Molina et al 2009), a relatively poor algae in EPA and DHA content (Ahlgren et al 1997). Likewise, Penrichment reduced highly unsaturated fatty acids (HUFA), although the effects varied between UVR treatments.…”

Spatial variation in nutrient excretion by macrozoobenthos in a Chinese large shallow lake (Lake Taihu)

“…Due to the frequent cyanobacterial blooms, substantial algal mats deposited in sediments might enhance food conditions for macrozoobenthos (Wen et al 2009). The caloric energy of muddy sediments was lower compared with that of sedimenting phytoplankton, due to bacterial decomposition (Ahlgren et al 1997). In addition, living benthic algae could excrete extracellularly polysaccharides and glycoproteins, which might be used as suitable food sources by macrozoobenthos (Madsen et al 1993;Underwood & Paterson 1993).…”

The dependencies between the abundance of Chironomus f. l. plumosus and bream (Abramis brama) net catches in a lowland reservoir (Zegrzyński Reservoir, central Poland)

“…Phytoplankton sedimenting onto a reservoir bottom is a favorite food for Chironomus. The diatoms that, in spring, constitute a major proportion of the phytoplankton in rivers feeding Zegrzyński Reservoir (Bubień 1989) exhibit a very high nutritive value, because of high concentrations of unsaturated fatty acids (Johannson and Beaver 1983, Rasmussen 1984, Goedkoop and Johnson 1996, Ahlgren et al 1997, Goedkoop et al 2000. A continuous supply of sedimenting tripton, rich in diatoms, is probably the main cause of the high numbers of Chironomus observed during the spring peak.…”