Deep-burrowing crustaceans – density dependent effects on sediment chemistry Some thalassinidian crustaceans burrow exceptionally deep into the anoxic part of marine sediment where molecular diffusion normally dominates chemical transport. In this study we use tracers and microsensors to monitor the impact of such deep bioturbation. By introducing oxygen as well as advective transport to the buried material a large volume of the sediment is affected by one single burrow, and as animal density increases overlapping effects on sediment chemistry are inevitable. The relationship between burrow density and chemical impact are thus studied and modeled. Combined effect of sediment-associated compounds on marine benthic macrofauna This project investigates sub-lethal effects of complex chemical mixtures in both pristine and contaminated marine sediments. Bioturbated sediment comprises a spatially and temporally dynamic mosaic of redox reactions. By using voltammetric microelectrodes that concurrently measure, in situ, a suite of compounds involved in early diagenesis it is possible to obtain the resolution needed to study such complex and dynamic systems. The combined effects of sediment-associated compounds are primarily studied on two marine mud-shrimps, Calocaris macandreae and Upogebia deltaura. The animals’ behavioral and toxicological responses to dynamic solute matrices and associated (scavenged) anthropogenic heavy metals are studied in boxcore (microcosm) experiments. Particular attention is given to quantifying concentration-response relationships and thresholds, and in identifying physiological mechanisms, with respect to ecologically relevant chemical mixtures. Effects of chemical mixtures on the embryonic development in lobster eggs Here we look at the combined effect of diagenetically generated solutes on the embryos of two decapod lobster species, Homarus gammarus and Nephrops norvegicus. Chemical dynamics in and around egg clutches are studied in detail, using microsensor-technology. Physiological and morphological parameters are monitored to estimate effects on development in embryos exposed to chemical mixtures both in vivo and in vitro. Adult female behavioral response, genetic and ecological differences are also investigated.