Chlorophyll degradation and absorption throughout the digestive system of the blue mussel Mytilus edulis L.

Abstract

Ingested chlorophyll α and its degradation products were monitored concurrently with total organics to investigate the separate processes of digestion and absorption in Mytilus edulis L. fed mixed algal ( Phaeodactylum tricornutum Bohlin) and silt diets of either high or low ash content (82 and 10% of total dry wt, respectively). High performance liquid chromatography showed that, relative to chlorophyllide or phaeophytin, phaeophorbide α-like pigments are the primary indicators of feeding processes when using chlorophyll derivatives as natural markers. As much as 82% of ingested chlorophyll was absorbed, with all such uptake occurring prior to the hind-gut/intestine. Substantial absorption of > 50% of what was implied to be non-chlorophyll organics did, however, continue whilst matter was processed in the intestine. Net absorption efficiencies computed from the relative composition of food and faeces were reduced ( P < 0.05) among mussels fed diet of high relative to low ash content. Such reductions were more pronounced for total organics (− 43.2 ± 22.6 vs. 80.6 ± 6.3 %) (± 2 se) than for chloropigments (45.9 ± 26.7 vs. 81.9 ± 4.2%). This was at least partially due to net enrichment of the stomach contents by non-chlorophyll-associated organics of metabolic origin, and demonstrates the utility of chlorophyll as a diet-specific marker of ingested matter. Despite different absorption efficiencies, relative indices of digestive efficiency based on the amount of residual chlorophyll degraded were similar ( P > 0.05) for diets of high (80.6 ± 13.0%) and low (89.9 ± 3.0%) ash content. There is thus a potential for variable coupling between the separate efficiencies of digestion and absorption according to dietary ash content, with associated changes in the metabolic benefit per unit cost of digestion.