This dataset collates available geo-referenced and individual-based isotopic values (δ¹³C and δ¹⁵N) of C. sapidus and its potential animal prey in Mediterranean waters. The isotopic values, included in the dataset, are expressed in delta notation (‰ deviation from atmospheric nitrogen and from Pee Dee Belemnite [PDB] limestone used as standards for N and C, respectively) and δ¹⁵N or δ¹³C = [(R_Sample/R_Standard) – 1] × 1000, where R = ¹⁵N/¹⁴N or ¹³C/¹²C. The analytical precision of measurements for all δ¹³C and δ¹⁵N values was 0.2‰ as calculated by the standard deviation of replicates of the internal standards. This dataset can be used for a variety of comparative analyses including the calculation of the trophic position of the crab and/or metrics and descriptors of its isotopic niche, and it was conceived as one of the input files for the Functional biogeography of invaders workflow of the LifeWatch ERIC Internal Joint Initiative. Specifically, the analytical workflow aims at identifying climatic predictors of the trophic position of two invasive crustaceans, i.e. the blue crab C. sapidus and the Louisiana crayfish Procambarus clarkii. For P. clarkii, the workflow runs on an aggregated dataset resolved at population scale, whereas for C. sapidus, two datasets can be used as input files to run the analyses: (i) an aggregated dataset at the population scale similar to the one built for P. clarkii and (ii) an individual-based dataset with isotopic values of single specimens as described in the present article. All datasets include isotopic information for potential prey to allow the estimation of the trophic position of the invasive species under analysis.

LifeWatch ERIC Internal Joint Initiative - Functional biogeography of invaders: the case of two widely distributed omnivorous crustaceans (https://bit.ly/iji-crustaceans).

Cristina Di Muri, Giorgio Mancinelli, Ilaria Rosati, Lucia Vaira

Coastal and transitional areas of the Mediterranean Sea colonised by C. sapidus. The westernmost records are located in Spain, the northernmost in Croatia, the easternmost in Turkey, and the southernmost in Greece. The majority of records lie in Italy.

The dataset contains geographical and temporal information on the sampling event including country, location, geographical coordinates, type of habitat, year, and month or season in which the sampling occurred. Biological features of the species included are also specified, such as the invasive or native nature of the species for each location and the prey-predator relationship. Such attributes, together with δ¹³C and δ¹⁵N values, can be used for downstream analyses including the calculation of the blue crab trophic position, which can be estimated using two different approaches. The first method estimates the trophic position using the following equation:

Trophic Position δ¹⁵N = (δ¹⁵N_Consumer - δ¹⁵N_Baseline)/Δ¹⁵N + λ

This equation is a generalisation of the formula presented in Jepsen and Winemiller (2002), where δ¹⁵N_Consumer is the nitrogen isotopic value of the blue crab, Δ¹⁵N is the trophic level fractionation of δ¹⁵N, δ¹⁵N_Baseline and λ are the nitrogen isotopic value and the trophic level of the baseline species (e.g. for Phorcus turbinatus, λ = 2). Alternatively, the blue crab trophic position can be estimated using a Bayesian approach implemented in the R package tRophicPosition (Quezada‐Romegialli et al. 2018, R Core Team 2021). In this case, the original δ¹³C and δ¹⁵N values can be back-estimated using mean values, standard deviations, and sample size for each location and species and assuming a normal distribution.

The literature search for compiling this dataset ended on 31^st April 2021.

The online platforms ISI Web of Science and Scopus were searched using multiple search criteria including the terms “Callinectes sapidus” and “stable isotopes” in conjunction with “non-indigenous”, “alien”, “invasive”, “Mediterranean Sea”, and “Black Sea”. The results were integrated with those obtained by querying Google Scholar using the same search criteria, together with the corresponding terms in Spanish or Portuguese (e.g. “jaiba azul”, “cangrejo azul”, “siri azul”) in order to access additional literature published in languages other than English. Google Scholar search results were saved using the freeware Publish or Perish ver. 7.27.2849 (Harzing 2007).

Only records with defined locations whose accuracy was checked using Google Earth were included in the dataset; geographic coordinates were converted to decimal degrees when not originally specified as such. The taxonomic check was performed using the World Register of Marine Species.

The blue crab preys preferentially on bivalves (Hines 2007); accordingly, this taxonomic group was chosen as a reference for the selection of baseline species included in the dataset. M. galloprovincialis was generally used in the dataset given the almost ubiquitous distribution in Mediterranean marine coastal waters. If not available, other bivalves and herbivorous gastropods occurring at the study sites were chosen. On only one occasion, the omnivorous polychaete (Alitta succinea) was used as the baseline species. The trophic level of prey species was assigned, based on their trophic habits as follows: bivalves’ trophic position = 2 (filter feeders); gastropod Phorcus turbinatus trophic position = 2 (herbivore; Aslan and Polito 2021); polychaete A. succinea trophic position = 2.78 (omnivore; Jumars et al. 2015, Como et al. 2018). Both M. galloprovincialis and Arcuatula senhousia are filter feeders and their diets mainly rely on phytoplankton and suspended particulate matter (Inoue and Yamamuro 2000, Ezgeta-Balić et al. 2014); hence, in agreement with the Sea Around Us database, we assumed for both taxa a trophic position = 2. However, it has been also repeatedly indicated that zooplankton can be included in the diet of M. galloprovincialis depending on local conditions, as well as on seasonal variations in resource availability (Ezgeta-Balić et al. 2012, Peharda et al. 2012). Our dataset is freely downloadable and the trophic position of C. sapidus prey can be modified according to the user's specific needs and/or if and when more updated information becomes available. Within our dataset a considerable variation in individual δ¹⁵N values occur for M. galloprovincialis as well as for other baseline species (i.e. Phorcus turbinatus). Such variation could be due to individual-scale differences in feeding habits, ontogeny, and metabolism (Tibbets et al. 2007, Doi et al. 2017). The user is, therefore, free to calculate the trophic position of C. sapidus by adopting, for example, the grand mean of the δ¹⁵N values or any other estimation of central tendency (e.g. mode or median). Alternatively, individual δ¹⁵N values of baseline taxa can be selected by eliminating the outliers or by choosing only a subset of the specimens included (e.g. the lower quartile of the isotopic distribution).

The dataset gathers isotopic values of different Mediterranean areas colonised by C. sapidus including seven study sites in Italy, two study sites in Greece, and one study site in Croatia, Spain, and Turkey (Fig. 1, Table 1). The westernmost records are located in Spain (39.00494; -0.148602), the northernmost in Croatia (43.027423; 17.436056), the easternmost in Turkey (40.157275; 25.96473), and the southernmost in Greece (38.961748; 20.815487).

38.96175 and 43.02742 Latitude; -0.1486 and 25.96473 Longitude.

The dataset is a collection of individual-based isotopic values belonging to C. sapidus and its potential prey including: P. turbinatus, A. succinea, Arcuatula senhousia, and M. galloprovicialis.

Creative Commons Public Domain Waiver (CC-Zero)

This work is licensed under a Creative Commons Attribution (CC-BY) 4.0 Licence.

An individual-based dataset of carbon and nitrogen isotopic data of Callinectes sapidus in invaded Mediterranean waters.

https://doi.org/10.48372/9CD2907F-8F44-4DF6-9070-6B21E1991B94

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