The evaluation of symbiotic microbial communities occurring in the intestinal tract of animals has received great interest in recent years. However, little is known about gut microbial communities in cetaceans, despite their relevance in the ecology of marine communities. Here, we report an investigation using 16S rRNA gene amplicon sequencing of the resident gut microbiota of the two cetacean species Stenella coeruleoalba and Tursiops truncatus by sampling intestinal mucosa from specimens retrieved stranded along the Tyrrhenian coast of Tuscany (Italy). We found an abundance of members from Clostridiaceae and Fusobacteriaceae, which in total accounted for more than 50% of reads, in agreement with gut microbiota composition of other carnivorous mammals. Probably due to the limited number of samples available, sex, preservation status and also species, did not correlate with overall differences in the microbiota. Indeed, a high similarity of the taxonomic (family-level) composition between the gut microbiota of the two species was found. However, Pedobacter spp. was found abundant in amplicon sequencing libraries from S. coeruleoalba, while clostridia were more abundant from T. truncatus samples. Our results shed some light on the gut microbiota composition of two dolphin (S. coeruleoalba and T. truncatus) species, with specimens collected in the wild. Studies with a larger number of individuals are now needed to confirm these first results and evaluate the interspecific differences in relation to sex and age.

Cetacean stranding reports in the North Aegean Sea were recorded since 1998 from Strimonikos Gulf in Chalkidiki up to Alexandroupoli on the Turkish border and in a few northern Aegean islands. On site, the specimens were examined to identify species, gender, approximate age and, when possible, cause for stranding. A total of 26 filled stomachs of five cetacean species collected since 2002 were analysed: bottlenose dolphins Tursiops truncatus (N = 8), common dolphins Delphinus delphis (N = 8), harbour porpoises Phocoena phocoena (N = 5), striped dolphins Stenella coeruleoalba (N = 4) and Risso's dolphins Grampus griseus (N = 1). From the analysed stomachs it was found that the bottlenose dolphins fed mainly on snake blenny Ophidion barbatum (34%), bogue Boops boops (22%) and round sardinella Sardinella aurita (13%); common dolphins on round sardinella (17%), picarels Spicara spp. (10%) and Cocco's lantern fish Lobianchia gemellaris (9%); harbour porpoises on Gobidae (four-spotted goby Deltentosteus quadrimaculatus 41% and black goby Gobius niger 37%) and round sardinella (7%); striped dolphins on Myctophydae (Madeira lantern fish Ceratoscopelus maderensis 51%), and on Pfeffer's enople squid Abraliopsis morisii (10%) and bogue (8%); and Risso's dolphin exclusively on Teuthidae (31%), the umbrella squid Histioteuthis bonellii (30%) and the reverse jewel squid H. reversa (14%). The present work represents the first attempt to investigate the diet up to species level for several cetaceans in Greek waters and for harbour porpoises stranded in the Mediterranean Sea.

Stomach contents of six striped dolphins taken as by-catch in the swordfish fishery in the eastern Mediterranean Sea off the Turkish coast were examined. In total, 29 taxa were identified to species or family and 1777 individual food items (1394 bony fishes, 289 cephalopods, 94 crustaceans) were counted. Diaphus spp. and Ceratoscopelus maderensis were the most remarkable ones, as they accounted for 70.45% of the total number of fishes. Onychoteuthis banksii, on the other hand, was the only cephalopod species found in all stomach content analyses and represented 38.06% of the total number of cephalopods. Bony fish species: Myctophum punctatum, Notoscopelus elongatus, Electrona risso, Sudis hyalina, Moridae sp., Phycidae sp., Sternoptychidae sp. and cephalopods: Pterygioteuthis giardi and Chtenopteryx sicula were reported the first time in the stomach contents of striped dolphin in the Mediterranean Sea.

The feeding ecology of striped dolphin, Stenella coeruleoalba, in the north-western Mediterranean Sea was studied using stable isotope analyses. Carbon and nitrogen stable isotope ratios were measured in skin and muscle tissues of stranded and by-caught dolphins from six geographical areas in the Mediterranean Sea and Atlantic Ocean. Variation in δ15N in relation to dolphin size is attributed to changes in diet. Nursing calves have a higher trophic level than weaned animals and their δ15N values decrease progressively until weaning, estimated to be at a body length of around 155 cm. δ15N values then increased for larger individuals which suggests changes in diet for mature dolphins. Geographical differences in diet were apparent between the Atlantic and the Mediterranean, although no clear differences were apparent between the five Mediterranean areas. Comparisons of the nitrogen isotope ratios of skin and muscle highlighted a higher fractionation in skin compared to the muscle tissue. Values of δ13C also increased with body length although it appears that this is not only driven by trophic level enrichment. δ13C increases before weaning and the difference in trophic level between newly-weaned and mature dolphins was twice as high for carbon as for nitrogen. Ontogenetic changes in carbon isotope composition may therefore be driven by feeding on deep water prey and dolphin movements outside the coastal feeding grounds. Indeed, seasonal variations in δ13C are suspected to be driven by migration within the Mediterranean basin.

The present contribution reports for the first time the sessile barnacle Xenobalanus globicipitis as an epizoic of the striped dolphin Stenella coeruleoalba in the oligotrophic waters of north-eastern Brazil. One barnacle specimen was found on a dead cetacean in Ceará State, north-eastern Brazil. Diagnosis and figures of the barnacle are provided and the relationship between the epizoic and the host discussed.

The striped dolphin (Stenella coeruleoalba) is a small, pelagic and cosmopolitan cetacean. Though it is the most common dolphin species in the Mediterranean Sea, it is not considered resident in the Croatian part of the Adriatic Sea. Fifteen striped dolphins were found dead in the Croatian part of the Adriatic Sea in the last eight years (1999–2007). More specimens were found in southern than in the northern part of the Adriatic. Analysis of twelve microsatellite loci and sequencing of 882 base pair (bp) fragment of the mitochondrial DNA (mtDNA) control region were performed for genetic characterization. The mean allelic diversity (7±0.78) and mean expected heterozygosity (0.727±0.05) reveal high genetic variation. Significant deviation from Hardy–Weinberg equilibrium was observed at two loci. Sequence analysis of the mtDNA control region identified seven unique haplotypes with 22 polymorphic sites in ten individuals. The haplotype diversity (0.911±0.077) was high, while nucleotide diversity was strikingly low (0.006±0.003). Results presented here support the notion of the striped dolphin not being resident species in Croatian part of the Adriatic Sea.

We compared the distribution of the digenean Pholeter gastrophilus in the stomach of 27 harbour porpoises, Phocoena phocoena, 27 striped dolphins, Stenella coeruleoalba, 18 bottlenose dolphins, Tursiops truncatus, and 100 long-finned pilot whales, Globicephala melas. The stomach of these species is composed of 4 chambers of different size, structure and function. In all species, P. gastrophilus was largely restricted to the glandular region of the stomach, but the parasite tended to favour the fundic chamber in bottlenose dolphins and harbour porpoises, the pyloric chamber in pilot whales, and none in striped dolphins. However, predictability at infrapopulation level was generally low, suggesting a weak preference of P. gastrophilus for any of the chambers. Three hypotheses were tested to investigate a common cause for the distribution of P. gastrophilus in all host species, namely, colonization of chambers was (1) sequential, (2) dependent on chamber size, or (3) dependent on the passage time of food through the whole stomach. The latter hypothesis was indirectly tested by assuming, based on previous evidence from other vertebrates, that the greater the size of the stomach and/or the energy content of prey, the greater the delay of food passage. We found no compelling evidence that chamber colonization was sequential, or related to chamber size in any species. However, the distribution of P. gastrophilus was significantly more anteriad when the host species had larger stomachs and, particularly, when hosts fed on prey with higher caloric content. Accordingly, the stomach distribution of P. gastrophilus at this scale seems to be passively driven by features of the diet and digestive physiology of each host species. This study provides a general framework to formulate null hypotheses in future studies on microhabitat choice by parasites.