Non‐lethal sampling does not misrepresent trophic level or dietary sources for Sagmariasus verreauxi (eastern rock lobster)

Abstract

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 δ 13 C and δ 15 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 δ 13 C values to be lower than other tissues by 0.3 ± 0.2‰ for antennae tissue and 0.1 ± 0.2‰ δ 13 C for leg tissues, whereas for δ 15 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 δ 13 C and 3.0‰-4.0‰ for δ 15 N. Conclusions:We show that S. verreauxi can be sampled non-lethally with mathematical corrections applied for δ 13 C, whereas any tissue is suitable for δ 15 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.

Fatty acid analysis reveals the trophic interactions among organisms in the Zhelin Bay Marine Ranch

“…Stable isotope ratios of carbon and nitrogen can accurately determine the trophic position and the contribution of food source of organisms in a food web (Schoo et al, 2018). Due to different metabolic rates of different tissues, isotope fractionation will exist in tissues of marine organisms, such as fish (Blanco et al, 2009), crustaceans (Day et al, 2023), mollusks (Cabanellas-Reboredo et al, 2009;Deudero et al, 2009), and macroalgae (Viana et al, 2015); the distribution of stable isotopes may be different among organs, which will bias the results of the survey. The promising new methods are DNA-based methods for detecting prey DNA that is contained in the stomach/gut of predator.…”