RESUMO
RATIONALE: Isotope analysis can be used to investigate the diets of predators based on assimilation of nitrogen and carbon isotopes from prey. Recent work has shown that tissues taken from legs, antennae or abdomen of lobsters can give different indications of diet, but this has never been evaluated for Sagmariasus verreauxi (eastern rock lobster). Work is now needed to prevent erroneous conclusions being drawn about lobster food webs, and undertaking this work could lead to developing non-lethal sampling methodologies. Non-lethal sampling for lobsters is valuable both ethically and for areas of conservation significance such as marine reserves. METHOD: We evaluated this by dissecting 76 lobsters and comparing δ13 C and δ15 N isotope values in antennae, leg and abdomen tissue from the same individuals ranging from 104 to 137 mm carapace length. Stable isotope values were determined using a Europa EA GSL elemental analyser coupled with Hydra 20-20 Isoprime IRMS. RESULTS: We found the abdomen δ13 C values to be lower than other tissues by 0.3 ± 0.2 for antennae tissue and 0.1 ± 0.2 δ13 C for leg tissues, whereas for δ15 N, no significant difference between tissues was observed. There was no significant effect of lobster size or sex, though we did observe interactions between month and tissue type, indicating that differences may be seasonal. Importantly, the detected range of isotopic variability between tissues is within the range of uncertainty used for discrimination factors in isotopic Bayesian modelling of 0-1.0 for δ13 C and 3.0-4.0 for δ15 N. CONCLUSIONS: We show that S. verreauxi can be sampled non-lethally with mathematical corrections applied for δ13 C, whereas any tissue is suitable for δ15 N. Our results indicate that a walking leg is most favourable and would also be the least intrusive for the lobster. The application of non-lethal sampling provides avenues for the contribution of citizen science to understanding lobster food webs and to undertake fieldwork in ecologically sensitive areas such as marine reserves.
