Tracking seasonal food web dynamics and isotopic niche shifts in wild chubbyhead barb Enteromius anoplus within a southern temperate headwater stream

In temperate headwater streams, intra-annual variation in energy input is critical in influencing aquatic food webs. We used stable isotope analysis to explore how seasonal variation in energy sources likely influenced invertebrate composition together with isotopic niche patterns of a cyprinid minnow, the chubbyhead barb Enteromius anoplus within a southern temperate headwater stream. Basal food sources had lower carbon and nitrogen stable isotope values in winter and spring compared to summer and autumn. Seasonal variations in the aquatic invertebrate communities were depicted by differences in the composition of gatherer and predator groups together with occurrence of scrapers in summer. Temporal changes in the isotopic values of these invertebrate groups appeared to coincide with that of basal food resources. The chubbyhead barb exhibited seasonal variation that was characterised by larger isotopic niches in winter compared to summer. Tissue-specific comparisons revealed larger isotope niche size based on fin tissue than muscle tissue during the cold period but comparable isotope niche sizes in the warm period. Contrasting inter-tissue isotopic niche patterns, the cold period suggested the likelihood of tissue physiological differences. Comparable isotopic niche patterns in summer and autumn suggested the possibility of synchronised physiological processes for both tissues. This suggested the potential for fin tissue as non-lethal alternative when inferring food web dynamics for this species.