Marine food web trophic interaction of trace elements and stable isotopes of carbon and nitrogen in Rabigh lagoon, Red Sea, Saudi Arabia

Abstract

The increase in heavy metal pollution in mangrove ecosystems due to anthropogenic activities has been on the increase and has been studied previously. However, there is a need for a better understanding of the use of stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) to establish trophic levels (TL) and their contamination in the food web. In this study, samples of sediment, mangrove, algae, seagrasses, crustacean, poriferans, echinoderms, molluscs, cnidarian and fishes were collected for determination of trace elements (Fe, Mn, Cu, Zn, Cd, Cr, Pb, Ni and Co) and stable isotopes. Varian 720-ES inductively coupled plasma-optical emission spectrometer (ICP-OES) and Thermo elementary analyser–ConFlo IV–Delta V Advantage mass spectrometer were used for the analysis of metals and stable isotopes respectively. The food web structure of Rabigh lagoon mangrove comprises a group of organisms such as crustacean (crab), porifera (sponges), echinoderm (starfish), mollusc (aquatic snails) and cnidarian (coral) in the second trophic level (TL = 1.0–2.0). For the third trophic level (TL = 2–3), Platycephalus bassensis (TL = 2.96) and Scomber sp. (TL = 2.30) belonging to the taxonomic group fishes are the two organisms in this trophic level. However, from the 9 trace elements determined, only Cd and Pb recorded excessive bioconcentration in the species. In terms of Total Magnification Factor (TMF) and metal concentrations, there was significant biodilution of all trace elements determined in this study except for Pb (TMF = 0.72; p > 0.05) and Co across the extracted food web consisting of molluscs, crustacean and fishes. Biodilution of Pb was not significant across the trophic levels of the food web. This study provides baseline information on the food web structure and transfer of trace elements across the food web of Rabigh mangrove, Red Sea, Saudi Arabia.