Sequestrichnia – an ethological category of marine trace fossils recording the collection and stowage of nutritional material within burrows

Abstract

Morphologically diverse trace fossils belonging to different ichnogenera share similar characteristics in that their producers: 1) sequester organic-rich sediment from the seafloor, or from suspension when plenty of benthic food is available; 2) transfer it downward; 3) stow it in a burrow; and 4) utilize it later during times when benthic food availability is restricted. Organic matter delivery to the seafloor is subject to pronounced seasonal fluctuations. Storage is optimal if the cache is located in anoxic sediment and beyond the reach of competing burrowers. Since the most reactive (i.e., nutritional) organic substances become oxidized first, refractory organic matter is enriched deeper in the substrate. If, however, reactive organic matter is brought in contact with refractory organic matter, priming may take place. Priming refers to enhanced microbial remineralization of refractory organic matter, typically up to 30%. This process is especially efficient where fresh organic matter is transferred into anoxic deposits. In addition, if an open burrow is produced within anoxic sediment, microbial activity is stimulated by the steep geochemical gradient between anoxic host sediment and oxygenated water in the lumen. The microbes and/or their metabolic products may also serve as food source. Consequently, stowing behaviour is an efficient nutritional and survival strategy for animals living in settings that experience strongly fluctuating delivery of benthic food, by conserving food resources during times of plenty to be used when starving.