Trophic connectivity between intertidal and offshore food webs in Mirs Bay, China

Summary: Trophic interactions are common worldwide, both within and between ecosystems. This study elucidated the trophic connectivity between intertidal and offshore zone, in Mirs Bay, China. The contributions of offshore suspended particulate organic matter (SPOM), intertidal macroalgae and epiphytes to consumer biomass were assessed, and the trophic pathways were identified through the use of stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) of basal sources and consumers. Mean δ13C values of basal sources had a wide range (−19.6‰ to −11.8‰) and were generally well separated in Mirs Bay. The average δ13C of consumers in Mirs Bay ranged from −19.2‰ to −11.8‰, reflecting a carbon source integrated from different primary producer signals. IsoSource model solutions indicated consumers assimilated organic carbon from a mixture of basal sources. Offshore SPOM carbon was the primary carbon source supporting most consumers in both intertidal and offshore zones. Intertidal macroalgae and epiphytes also accounted for a large fraction for some consumers. δ15N data indicated 5 trophic levels in Mirs Bay. Intertidal consumers, except for Capitulum mitella, had a TP (trophic position) between 2 and 3, and mainly included filter-feeders and grazers. In contrast, almost all offshore consumers had a TP of between 3 and 4 except for filter-feeders (zooplankton), planktivores (Clupanodon punctatus and Sardinella aurita) and piscivores (Gymnura japonica). The basal sources fueled consumers through two trophic pathways, each of which involved organisms of both intertidal and offshore zones, implying trophic connectivity between them in the Mirs Bay ecosystem. Keywords: Food webs, Trophic connectivity, Carbon pathways, Stable isotopes, Mirs Ba