Figure 1.
The principal component analysis of δ13CAAn values of different producers show a range of different isotope patterns between bacteria, fungi, vascular plant and algae.
None of the microalgal or macroalgal group clustered separately from one another. Values in parentheses are the percentage variation accounted by each axes. The first axis separates the photoautotrophs from the microbes, and the second axis separates vascular plants from algae, and fungi from bacteria. The fairly similar vector lengths show that almost all amino acids were important for the variations of the two first ordination components. See Table S4 for analytical details.
Figure 2.
Linear discriminant function analysis based on the δ13CEAAvalues (Ile, Leu, Lys, Phe, Thr, Val) of bacteria, fungi, algae and terrestrial plants.
In the left figure (a) displaying the scores of the first two discriminant axes, fungi and terrestrial plants each cluster separately from algae and bacteria. In the right figure (b) displaying the second and third discriminant axes, bacteria are separated apart from the algae, fungi and terrestrial plants. The dotted lines represent confidence ranges at P = 0.5. See Table S6 for details.
Figure 3.
Linear discriminant function analysis with the δ13CEAAvalues (Ile, Leu, Lys, Phe, Val) from the three algal groups.
It separates all seagrass samples from the three algal groups. The majority of the algal samples classified correctly within their own groups (Table S7). The dotted lines represent confidence ranges at P = 0.5; confidence ranges are only displayed in the left figure (a) because the third linear discriminant in right figure (b) only explained 14%.
Figure 4.
Bars representing the maximum range for individual amino acid δ13Cn values (normalized to their means) and bulk δ13C values across five giant kelp samples (Macrocystis pyrifera) or five seagrass samples (Posidonia oceanica).
The bars for the amino acids represent the mean and standard deviations of either five non-essential (NEAA) or six essential (EAA) amino acids.
Figure 5.
Application of source diagnostic δ13CEAA patterns in food web studies across three different ecosystems.
(a) In oligotrophic arctic lakes in Alaska, Daphinia sp. and seston cluster closely to each other, and their EAAs appear to derive predominantly from microalgae although a part of their EAAs may have come from foods reworked by bacteria or from allochtonous sources (i.e soils). (b) In the central North Pacific Ocean the EAAs of the carnivorous fish species (opah; Lampris guttatus, common dolphinfish; Coryphaena hippurus, broadbill swordfish; Xiphias gladius) resembled microalgae rather than EAAs from bacteria and fungi. (c) In a complex littoral marine system by the Californian shore, the δ13CEAA fingerprints of California mussel (Mytilus californianus) resemble microalgae and not bacteria or brown algae, i.e. kelp. In the figure legend, ‘Pr’ signifies predicted samples. See Table S8 for analytical details.
Figure 6.
A boxplot generated with the FRUITS mixing model showing the contribution of essential amino acids (Leu, Lys, and Val) from three diets (bacteria; n = 12, kelp; n = 5, microalgae; n = 27) to the California mussel (Mytilus californianus; average value of two samples).
The boxes provide a 68% confidence interval (corresponding to the 16th and 84th percentiles) and the whiskers provide a 95% confidence interval. The horizontal continuous line indicates the average while the horizontal discontinuous line indicates the median (50th percentile). See Appendix S1 for detailed information.