Trophic and growth baseline of dominant subtidal gastropods in contrasting subtropical marine environments

Using ¹³C/¹²C, ¹⁵N/¹⁴N and ¹⁸O/¹⁶O isotopes, the trophic relationship and growth estimation were analyzed in gastropods Nassarius siquijorensis, Murex trapa and Turritella bacillum and their potential food sources and predators in summer and winter from estuarine and oceanic environments in subtropical Hong Kong. Results of δ¹³C and δ¹⁵N values and isotopic mixing model revealed N. siquijorensis and M. trapa were one trophic level higher than T. bacillum, in which its main food source was particulate organic matter (POM) whereas N. siquijorensis largely consumed POM and polychaetes and M. trapa also preyed on other gastropods. Crabs were the major predator of gastropods. Organisms collected from oceanic waters were more ¹³C enriched than from estuarine waters, reflecting different carbon food sources from marine or terrestrial origin. The δ¹⁸O profile from shell carbonate suggested these gastropods were one to two years old. T. bacillum exhibited faster summer growth than the other two species.