Pheophorbide and pheophytin a-like pigments as useful markers for intertidal microphytobenthos grazing by Hydrobia ulvae

Pigment degradation by Hydrobia ulvae, feeding on an intertidal mudflat dominated by diatoms, was studied in the laboratory. HPLC analysis identified significantly higher amounts of pheopigments in grazed sediment and a decrease in the concentrations of major chlorophylls (a and c1+c2) and carotenoides (fucoxanthin, diadinoxanthin, and b-carotene). Grazing by H. ulvae leads to a stronger pheophorbide a accumulation relative to pheophytin a. Dominant chlorophyll a degradation products were the less polar pheophorbide a4 and pheophytin a2. These pigments were identified in very high concentrations in H. ulvae faecal pellets. Although a major disadvantage of the HPLC method is the uncertainty regarding the extent and rate of pigment conversion into colourless products, these data strongly suggest the possible use of pheophorbide a4 and pheophytin a2 as useful markers for intertidal microphytobenthos grazing by H. ulvae.