PYROLYSIS MASS-SPECTROMETRY OF A BENTHIC MARINE ECOSYSTEM - THE INFLUENCE OF ARENICOLA MARINA ON THE ORGANIC-MATTER CYCLE

Curie-point pyrolysis mass spectrometry (pyMs) was used as analytical technique to analyze the organic matter from sediments. Mass pyrograms (fingerprints of sedimentary organic matter) were obtained from sediments, fecal pellets and blue-green algae of an experimental laboratory scale marine benthic ecosystem, designed from the study of the effects of bioturbation by A. marina on marine biota. A decomposition of surface sediment was performed under aerobic and anaerobic conditions to compare the organic matter in the decomposition stages, as shown by pyMs, with the compositions found in the ecosystem. The upper millimeter of the surface sediment showed many pyrolysis products of proteins, polysaccharides and N-acetyl-amino sugars derived from the algal matter. Lower layers showed a composition intermediate between those found in the aerobic and anaerobic decomposition experiment. The mass pyrogram of fecal pellets and of sediment digested by Arenicola for long periods of time is similar to the one of aerobic microbial decomposition after 6 wk. Two types of Arenicola burrow systems, a relatively slow and a rapid sediment recycling system, were compared by pyMs. Almost no difference is seen between the mass pyrograms of funnel sediment, burrow sediments and feces. The high feeding rate may be related to the relatively poor quality of the sedimentary organic matter. The many pyrolysis fragments of biopolymers in the valleys caused by the slow recycling burrow and their diminuation in the burrow sediments points to processes of microbial digestion before ingestion by the worm. The feces is depleted even more in biopolymers, and the furan type organic matter becomes predominant. The slow pace of food ingestion points to an ample supply of digestible organic matter for the adult worm.