Dietary supply with essential lipids affects growth and survival of the amphipod Gammarus roeselii

Growth and survival of benthic macroinvertebrates depend on the availability and the quality of potential food sources. The significance of essential biochemical nutrients, such as sterols and polyunsaturated fatty acids (PUFAs), for benthic invertebrates has been insufficiently studied. We investigated the effects of these essential lipids on growth and survival of the benthic gammarid Gammarus roeselii, a widespread species in streams, rivers and lentic waters of Central Europe, in standardized feeding experiments. Juvenile gammarids were fed a mixture of three cyanobacteria with no evidence of toxin production, either unsupplemented or supplemented with cholesterol or the long-chain PUFA docosahexaenoic acid (DHA) using bovine serum albumin (BSA) to load algal or cyanobacterial cells with single lipid, and a mixture of three eukaryotic algae containing various sterols and long-chain PUFAs. Our results revealed that growth and especially survival of gammarids on the cyanobacterial diet significantly increased upon supplementation with cholesterol and DHA, indicating that the nutritional inadequacy of cyanobacteria for gammarids and potentially other benthic invertebrates is at least partially due to a deficiency in these essential lipids. We propose that the expected increase in the frequency of pelagic cyanobacterial mass developments as a consequence of global warming will also affect benthic food web processes to an as-yet-unknown magnitude.