Distribution and sources of cyclic pheophorbides in the marine environment

The labile chlorophyll alpha (Chl alpha(1)) degradation product, 13(2), 17(3)-cyclopheophorbide alpha enol (CPP516), was only recently found in marine sediments, where it can contribute a significant fraction to solvent-extractable sedimentary chlorins. We developed a new chromatographic method for the analysis of CPP516 to study its distribution and sources in the marine environment. We found high concentrations of CPP516 in surficial sediments and particulate matter collected in sediment traps. It contributed 40 to 70% to the sum of all Chl alpha(1) degradation products in fecal material from herbivorous microzooplankton and macrozooplankton. We did not find CPP516 in exponentially growing or stationary phase algal cultures. These data suggest that a major source of CPP516 is herbivores feeding on phytoplankton. We also found a series of compounds similar to CPP516 in sediments and sediment-trap samples. Mass-spectrometric and ultraviolet(UV)/visible-spectrometric analyses suggest that these are CPP516 analogs of divinyl-Chl alpha and Chl bs and Chl cs, conclusions that have to be confirmed by synthesis. CPP516, dissolved in organic solvents, easily degrades to 13(2)-oxopyropheophorbide alpha and chlorophyllone alpha under oxic conditions. When associated with particles, CPP516 is stable in oxic aquatic environments on a timescale of days, possibly stabilized by the chelation of metal cations. The chromophore of CPP516 differs substantially from that of other Chl alpha(1) degradation products; it has absorption maxima at 360, 426, and 688 nm CPP516 does not fluoresce as other Chl alpha(1) degradation products. As a consequence, it is invisible to fluorescence-based analyses of "pheopigments." Thus, rates of grazing and growth derived from such measurements, as used in conjunction with the gut fluorescence and the Chi-budget method, will be underestimates of true rates when CPP516 contributes significantly to total chlorins.