Breakdown of phytoplankton pigments in Baltic sediments: effects of anoxiaand loss of deposit-feeding macrofauna

We examined the decay of chlorophyll a and the carotenoid fucoxanthin iii o xic and anoxic sediment microcosms, with and without the deposit-feeding be nthic amphipod Monoporeia affinis, over 57 days at 5 degrees C, Deep frozen phytoplankton from the Baltic Sea proper was added to all but a few microc osms. The range of chlorophyll a and fucoxanthin decay rate constants obser ved in microcosms with phytoplanton addition was 0.04-0.07 day(-1). The fas test pigment decay and build-up of chlorophyll breakdown products after phy toplankton addition were found in oxic treatments with amphipods. No effect s of amphipods on pigment breakdown were found in anoxic treatments, or in treatments without phytoplankton addition. Greater losses of chlorophyll a in oxic (96%) than in anoxic (80%) treatments after 57 days indicates that preservation of sedimentary organic matter will be enhanced during periods of anoxia. Due to slow recruitment and recolonization in Baltic sediments, a single anoxic event may cause long-term (years) absence of significant ma crobenthos. Anoxic events will thus not only reduce decay of plant pigments , and presumably other organic matter, while they last, but will also have longer-term effects, through elimination of macrofauna, which when present enhance organic matter decomposition. (C) 2000 Elsevier Science B.V. All ri ghts reserved.