Use of stable isotopes to understand food webs in Macao wetlands

In this study, components of the food-web in Macao wetlands were quantified using stable isotope ratio techniques based on carbon and nitrogen values. The d13C and d15N values of particulate organic matter (d13CPOM and d15NPOM, respectively) ranged from -30.64 ± 1.0 to -28.1 ± 0.7 %, and from -1.11 ± 0.8 to 3.98 ± 0.7 %, respectively. The d13C values of consumer species ranged from -33.94 to -16.92 %, showing a wide range fromlower values in a freshwater lake and inner bay to higher values in a mangrove forest. The distinct dietary habits of consumer species and the location-specific food source composition were the main factors affecting the d13C values. The consumer 15N-isotope enrichment values suggested that there were three trophic levels; primary, secondary, and tertiary. The primary consumer trophic level was represented by freshwater herbivorous gastropods, filter-feeding bivalves, and plankton-feeding fish, with a mean d15N value of 5.052 %. The secondary consumer level included four deposit-feeding fish species distributed in Fai Chi Kei Bay and depositfeeding gastropods in the Lotus Flower Bridge flat, with a mean d15N value of 6.794 %. The tertiary consumers group consisted of four crab species, one shrimp species, and four fish species in the Lotus Flower Bridge Flat, with a mean d15N value of 13.473 %. Their diet mainly comprised organic debris, bottom fauna, and rotten animal tissues. This study confirms the applicability of the isotopic approach in food web studies.