Burrow-Sediment Relations 
The sediment color along present and past burrows was also useful in 
semi-quantifying the role of N. incisa in 1) aeration of sediment and 2) in 
increasing the effective surface area of the sediment-water interface into the 
benthos. There is always some oxygen diffusion across any sediment-water 
interface, assuming the overlying water is oxygenated. Wherever burrows 
penetrate the sediment and are irrigated with oxygenated water, a halo of light 
brown or yellow oxygenated sediment soon develops around the burrow. The 
transition of yellow-brown to black, 2-5 cm deep, approximates the limit of 
oxygen penetration. Thus an increase in “aerobic” sediment is described by the 
expression: 
^halo ^burrow-halo system ' ^burrow 
This volume was estimated here by measuring the light brown oxidized zone 
visible against the thin, sediment-filled glass aquaria using planimetry. This 
subsurface oxygenation persists for some time after a worm abandons the 
burrow, since efferent oxygenated irrigation water typically continues to 
course through old burrows. The rate of increase in sediment aeration 
following introduction of a single worm in a thin aquarium at 18°C is 
summarized in Figure 20-8. The 2-5 mm thick “aerobic” halo is continuous 
with and as thick as the aerobic zone at the sediment-water interface (see 
Figure 20-3). The dotted line in Figure 20-8 represents the depth of aerobic 
sediment in an aquarium without any worm present, that is, the aerobic zone 
at the sediment surface. Any increase above this level represents that resulting 
as a consequence of burrow irrigation activities. By comparing the aeration 
rates depicted in Figure 20-8, it is apparent that the slope of the curve increases 
with water temperature. This rise in sediment aeration eventually levels off in 
time as an equilibrium develops between oxygenation of new burrow sediment 
and chemical reduction of oxygenated sediment along old abandoned burrows. 
Figure 20-8 summarizes the relationship between temperature and rate of 
Nephtys sediment aeration observed in laboratory in situ thin aquaria. It is 
apparent that the extent of sediment oxygenation is positively correlated with 
temperature, i.e. more oxygen is delivered to deeper layers during warmer 
seasons. Hence, even though oxygen demand by the benthos is at its maximum 
during warm periods, the actual sediment aeration through Nephtys burrowing 
and irrigation can be even greater. 
DISCUSSION 
N. incisa burrows through sediment using adaptations previously described 
for other Nephtys and Nereis species (Schafer, 1962) and for Arenicola marina 
(Wells, 1952). This specialized locomotion called “bolting” refers to the head 
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