Diet of the intertidal callianassid shrimps Biffarius arenosus and Trypea australiensis (Decapoda:Thalassinidea) in Western Port (southern Australia), determined with multiple stable-isotope analyses

Abstract

Biffarius arenosus had a mean δ¹³C of –15·4 ± 0·2‰ and a mean δ¹⁵N of 5·9 ± 0·1‰ (n = 38), and Trypea australiensis had a mean δ¹³C of –16·3 ± 0·3 and a mean δ¹⁵N of 7·6 ± 0·1 (n = 20). The δ¹³C signatures of the only mangrove species present (Avicennia marina) and the most abundant saltmarsh plant (Sarcocornia quinqueflora) indicated that they were not major food sources. Seagrasses, predominantly Heterozostera tasmanica, had mean ^δ13C and δ¹⁵N values of –11·7 ± 0·2‰ (n = 65) and 3·9 ± 0·2‰ (n = 62), respectively. Seagrass epiphytes had mean δ¹³C and δ¹⁵N values of –17·9 ± 0·4‰ and 4·6 ± 0·3‰ (n = 27), respectively. A mixture of seagrasses and their epiphytes was the most likely source of organic carbon for B. arenosus. Benthic microalgae, such as diatoms, were a possible food source, but phospholipid biomarkers indicated a meagre abundance of diatoms in the sediments, and microscopy of shrimp guts revealed few or no diatom frustules. For T. australiensis, food sources were less easily distinguished than for B. arenosus, but they could include seagrass epiphytes plus the green macroalgae Enteromorpha spp. and/or the brown alga Chordaria cladisiphon.