Food sources and trophic niches of dominant benthic organisms especially ophiuroids in the Yellow Sea: An assessment using stable isotopes and fatty acid markers

Ophiuroids are ecologically important echinoderms that occupy important trophic roles in marine food webs. However, the feeding ecology of dominant ophiuroid species in the Yellow Sea remains unclear. This study employed stable isotope and fatty acid analyses to characterize food sources and trophic niches of three dominant ophiuroids in the Yellow Sea and Zhangzi Island. Ophiura sarsii vadicola, Stegophiura sladeni and Ophiopholis mirabilis exhibited broad and overlapping stable isotope ranges, implying diverse dietary compositions. Significant positive correlations were found between the δ15N values and disc diameter in O. sarsii vadicola and O. mirabilis (p < 0.05). The δ13C values showed significant correlations with disc diameter, positively in S. sladeni and negatively in O. sarsii vadicola and O. mirabilis, indicating ontogenetic dietary shifts. In Zhangzi Island, seven species were categorized as carnivorous or suspension-feeding based on dietary probabilities. Carnivorous species showed higher utilization of sedimentary organic matter (SOM), while suspension feeders primarily consumed particulate organic matter (POM). O. sarsii vadicola exhibited a unique feeding pattern combining suspension feeding and carnivory. Fatty acid profiles revealed a predominance of saturated fatty acids (SFAs) in ophiuroids, with differential abundance of unsaturated fatty acids across species. Carnivorous ophiuroids displayed significant differences in monounsaturated (MUFAs) and polyunsaturated fatty acids (PUFAs) compared to suspension feeders and whelks. Fatty acid trophic biomarkers indicated diverse diets among ophiuroids, and O. sarsii vadicola exhibited relatively strong omnivorous characteristics. Additionally, additional samples of ophiuroids (including various size classes) and other benthic organisms with diverse trophic niches are needed for further assess the food chain.