Triple stable isotope analysis to estimate the diet of the Velvet Scoter (Melanitta fusca) in the Baltic Sea

Abstract

This study quantifies contributions of different food sources in the winter diet of the Velvet Scoter (Melanitta fusca) in coastal waters of the Lithuanian Baltic Sea using non-lethal avian sampling. We highlight the application of stable sulphur isotope ratios as complementary to stable carbon and nitrogen isotope analysis in order to discriminate sandy bottom macrozoobenthos organisms as potential food sources for the Velvet Scoter. Selection of the most relevant trophic enrichment factors and Monte Carlo simulations in order to choose the best fitted model were undertaken. The stable isotope mixing model revealed the main contributions of a group of bivalves, Mya arenaria and Cerastoderma glaucum, to be 46–54%, and while the crustacean, Saduria entomon, comprised 26–35% of the diet.

Sulfur isotopic discrimination factors differ among avian tissues and diets: Insights from a case study in Gentoo Penguins

“…The whole catfish fed to cormorants had an average δ 34 S value of 2.0 ± 2.2‰ (Craig et al 2015), while whole herring fed to penguins had an average δ 34 S value of 18.9 ± 0.2‰ (Table 1). This is a reflection of freshwater prey fish generally having lower δ 34 S values (Hesslein et al 1991, Connolly et al 2004) compared to marine species (Moreno et al 2010, Morkune et al 2018).…”

“…The whole catfish fed to cormorants had an average δ 34 S value of 2.0 ± 2.2‰ (Craig et al 2015), while whole herring fed to penguins had an average δ 34 S value of 18.9 ± 0.2‰ (Table 1). This is a reflection of freshwater prey fish generally having lower δ 34 S values (Hesslein et al 1991, Connolly et al 2004) compared to marine species (Moreno et al 2010, Morkune et al 2018. Florin et al (2011) obtained a very strong inverse relationship between dietary δ 34 S values and diet-tissue discrimination factors (Δ 34 S diet-tissue ) in mammalian blood, plasma, and serum.…”

“…In the absence of species and tissue-specific Δ 34 S diet-tissue values studies using sulfur isotopes in dietary mixing models researchers have applied the discrimination factors reported by Craig et al (2015) for Double-crested Cormorants ( Phalacrocorax auritus ) fed on freshwater catfish to other bird species (Peterson et al 2017). Other studies have used discrimination factors derived from invertebrates, fish, and/or mammals (Winiarski et al 2012) or assumed no differences in δ 34 S values between diets and avian tissues (Morkune et al 2018). This is of potential concern, as mixing model results are highly sensitive to variation in discrimination factors and the use of inappropriate values can bias estimates of avian diets (Bond and Diamond 2011).…”

“…While limited, avian studies have exploited the ability of δ 34 S values to discriminate between marine and terrestrial resource and habitat use (Hobson et al 1997(Hobson et al , 2015, due to the generally higher δ 34 S values observed in primary producers from marine relative to terrestrial/aquatic ecosystems (Connolly et al 2004). Prior studies have also used δ 34 S values in birds to discriminate between benthic vs. pelagic prey resources (Morkune et al 2018), identify the salinity zones of foraging locations (Yohannes et al 2014), infer the relative importance of capital vs. income nutrient source to egg production (Jones et al 2022), trace the dietary sources of environmental contaminants (Ramos et al 2013), and quantify the use of anthropogenic-derived resources (Abdennadher et al 2014). However, δ 34 S measurements on biological material such as avian tissues are analytically complex and expensive relative to other light elements.…”

Historical faunal exchange between the Pontocaspian Basin and North America

“…The second scenario considers historical dispersal across the Mediterranean Sea/northern Atlantic by either current-mediated transport of veliger larvae (Scheltema, 1966(Scheltema, , 1971) and rafting individuals (Thiel & Haye, 2006), or bird-mediated transport (steppingstone or long-distance dispersal). In fact, mud snails may be carried in the gut of birds (Morkūnė, Lesutienė, Morkūnas, & Barisevičiūtė, 2018;van Leeuwen, Velde, Lith, & Klaassen, 2012;Wada, Kawakami, & Chiba, 2012) and fish (Aarnio & Bonsdorff, 1997) and are able to survive this passage through the digestive system. In addition, van Leeuwen and van der Velde (2012) suggested passive dispersal by water birds, in which young individuals or eggs are attached to feathers, feet, or bill.…”