Do fatty acid profiles help to explain sesarmid crabs food choice

We evaluate the use of the combination approach of fatty acid (FA) profiles and Carbon/Nitrogen ratios to investigate the feeding preference of the sesarmid crab Perisesarma bidens on different diets. The alga Enteromorpha intestinalis, Kandelia obovata leaves and propagules were used in a laboratory feeding assay. Consumption rates of P. bidens were higher in the order of algae= leaves>propagules. C/N ratios indicate that P. bidens significantly assimilates both nitrogen and carbon from algae, nitrogen but not carbon from brown leaves, and only carbon from propagules. A comparison of FAs in tissues and faeces indicated that crabs efficiently assimilate essential FAs (EFAs) from a given diet in the order of algae>leaves>propagules. Results of higher EFA ratios ( 3/ 6) match with that of low C/N ratios indicating that algae had higher nutritional value than leaves and propagules. FA profiles suggested that brown leaf palatability was due to decomposing activity by bacteria and fungi in the leaf tissues. These data suggest that the combination of FA profiles and C/N ratios provides a better understanding of the diet choice by sesarmid crabs.