Lipid content of stream macroinvertebrates

Abstract

Total lipid content of freshwater macroinvertebrates from different orders and with different life histories was investigated. Lipids were determined as HIP-extractable lipids (HIP = hexane: isopropanol). Macroinvertebrate taxa were assigned to different feeding guilds, and life histories for insect taxa: Gammarus pulex (Amphipoda/shredder), Ecdyonurus sp. (Ephemeroptera/hemimetabolous/grazer), Perla sp. (Plecoptera/hemimetabolous/predator), Hydrophsyche sp. (Trichoptera/holometabolous/ suspension feeder), and Atherix ibis (Diptera/holometabolous/predator). Animals were collected in two streams in Switzerland bimonthly between October 1994 and October 1995. Lipids, expressed as percent dry mass (dm), were estimated using two techniques: (1) as total lipid content, determined by the sulphophosphovanilline method; (2) as total fatty acids (= sum of fatty acids), determined by gas chromatography. The annual average total lipid contents for G. pulex, Ecdyonurus and Perla were 6.1 %, 7.0 % and 6.0 % dm, respectively. The two holometabolous insects, Hydropsyche (8.0 %) and A. ibis (9.3 %), exhibited the highest total lipid content. Total fatty acids as a percentage of total lipids was lowest in G. pulex (62 %), followed by Ecdyonurus (64 %), Perla (73 %), Hydropsyche (80 %), and A. ibis (85 %), The dry mass of holometabolous insects (Hydropsyche and A. ibis) related positively with lipids, indicating an increase in body concentration during larval growth. No or only a weak positive relationship with dry mass was found for the hemimetabolous Ecdyonurus and Perla. Gammarus pulex, in contrast, showed a negative relationship. Male G. pulex attained a larger size and contained less fat than juveniles and adult females. Seasonal changes in total lipid content were recognisable only as weak trends because of high variation among individuals. Gammarus pulex had higher total lipid content in spring, while Perla and Hydropsyche maxima occurred in summer. No seasonal trends in total lipid content could be observed in Ecdyonurus and A. ibis.