Fig. 5. Relationship between animal positioning (frequency distribution at
different depths shown by the grey bars; scale, lower x axis) and
O2 profiles (one symbol type per O2 profile; scale,
upper x axis) as a function of sediment depth in naturally occurring
(open and closed triangles, circles and open squares, left panel) and
experimentally manipulated O2-gradients (water column
PO2=21 or 40 kPa). Analyses were performed at
days (d) 0, 4, 7 and 11. As O2 penetration velocity varied from
core to core for the same water column, values of
PO2, O2 profiles are grouped by
similar near anoxic-zone depths (thickness, 1 mm; dotted lines) independent of
exposure time. The animal's position followed the O2 profiles, and
were independent of sediment depth and time. N is the number of
analysed cores per O2 profile penetration depth.