Flow of terrestrial carbon though aquatic ecosystems (allochthony) is an important but underestimated component of the global carbon cycle. A lack of clear consensus about the importance of allochthonous (terrestrial) organic carbon is sometimes attributed to uncertainties associated with conventional ‘bulk’ isotope data, the most widely used ecological tracer. Amino acid‐specific isotope analysis is an emerging research method promising to address existing limitations of bulk C and N isotope analyses. We tested the efficacy of amino acid δ13C data as a generalizable measure of allochthony by analysing an aggregated dataset (n = 168) of primary and secondary data of carbon sources from disparate geographical locations across the globe. We found the δ13C fingerprints amino acids to be consistently distinct between allochthonous (terrestrial) and autochthonous (aquatic) carbon sources. We also found that our approach is most effective when we use only essential amino acid tracers (i.e. isoleucine, leucine, phenylalanine, threonine and valine). Predictive trends in δ13C fingerprints appear to be largely compatible across studies and/or laboratories. As a case study, we used this approach to quantify the contribution of terrestrial carbon to an endemic cavefish, Cryptotora thamicola, and found that its biomass was comprised largely of autochthonous carbon (~75%).

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Toxicity (extreme weakness, body temperature drop, cyanosis, some slow deaths) in test mice, upon intraperitoneal injection of standardmethod paralytic shellfish poison (PSP) extracts of some PSP-free oysters, is consistent with the relatively high levels of zinc in these extracts. As a rough guideline, the threshold for a toxic response corresponds to a drained tissue zinc level of over 900 μg/g. The identification of zinc as the substance responsible has been supported by inducing toxicity in control extracts by spiking with nontoxic levels of zinc, and by eliminating toxicity from toxic extracts by chemical removal (precipitation, ion exchange) of metals.

Quantifying the trophic basis of production for freshwater metazoa at broad spatial scales is key to understanding ecosystem function and has been a research priority for decades. However, previous lotic food web studies have been limited by geographic coverage or methodological constraints. We used compound‐specific stable carbon isotope analysis of amino acids (AAs) to estimate basal resource contributions to fish consumers in streams spanning grassland, montane and semi‐arid ecoregions of the temperate steppe biome on two continents. Across a range of stream sizes and light regimes, we found consistent trophic importance of aquatic resources. Essential AAs of heterotrophic microbial origin generally provided secondary support for fishes, while terrestrial carbon did not seem to provide significant, direct support. These findings provide strong evidence for the dominant contribution of carbon to higher‐order consumers by aquatic autochthonous resources (primarily) and heterotrophic microbial communities (secondarily) in temperate steppe streams.