Evaluation of Energy-Dispersive X-ray Spectrometry (EDX) for Analysis of Gut-contents of Megabenthos

Abstract

Energy-Dispersive X-ray spectrometry (EDX) was applied to the gut-content analysis of benthic animals, and its validity for easier estimation of the origin of gutcontents was evaluated. We analyzed the elemental composition of various reference samples and compared it with the elemental composition of the gut-contents. EDX analysis showed eight principal elements and five scarce elements. We used eight principal elements for analysis which were characteristic of the origin of gut-contents. We could not discriminate flocculent material of supposedly planktonic origin from bottom sediment because both were rich in iron, aluminum, and silicon. We could, however, easily distinguish sea floor sediment mainly composed of inorganic substances from fresh sediment that is rich in bioelements such as calcium, phosphorus, potassium, and sulfur. The calcium content was especially high in crustaceans, and sulfur in fish muscle. Six-rayed radar charts, with the weight percentages of Ca, S, P, K, and Mg (representative bioelements) and Fe+A1+Si (representing sediment) as the ordinates, showed three characteristic patterns for different sets of items. Geodesic similarity indices of the food items of six deep-sea fishes and nine control items were calculated. The UPGMA showed three distinct clusters, i.e., stomach contents with sediment remains, Ca-rich contents, and supposedly protein-rich contents. The present method could elucidate the fishes' general food habits objectively, and it has wide scope of applicability independent of location, season, and prey species.