A general expression describing this depth-related burrowing intensity may 
be stated: 
i = 1 
0)i z = 2 
‘ B t y i + Y 2 
i = n 
where I z is the depth-related burrowing intensity, Dyj is the mean length of 
burrowing by the i^ 1 year class (from Figure 20-6), Bj is the 
temperature-dependent burrowing rate (Figure 20-7) and Y 2 is the size of the 
2nd year class. 
The influence of N. incisa on increasing the sediment-water interface surface 
area is best described by computing the surface area of the burrow wall since 
the burrow is continuously irrigated and may be stated: 
i = 1 
(2) S.A. l = 2 L Yi C Yj + C Y 2 '' ’ C Yn 
i = n 
where S.A.^ is the burrow lumen wall surface area of a population of N. incisa , 
Lyj is the mean burrow length of the Yi year class and Cy n is the mean 
circumference of the burrow of the nth year class. 
Burrow irrigation by N. incisa results in the oxidation of surrounding 
sediment. The degree of oxidation has only been expressed in a qualitative 
sense here. However, since the thickness of the sediment “halo” is virtually 
identical to the oxidized zone at the sediment-water interface, the influence of 
N. incisa on oxygenating subsurface sediment can be quantititively expressed 
by calculating the volume of light brown aerobic sediment surrounding the 
burrow for each year (size) class and extrapolating this figure over the density 
of that size class in a square meter of sediment: 
i = 1 
(3) ®N. incisa ~ ^ ^halo 
i = n 
where 0 is the quantity of oxygen-containing sediment. Vj ia j 0 is the volume of 
the oxygenated halo (Figure 20-8) and Y| is the density of the 1st year class in 
worms/m". 
The silt-clay habitat of N. incisa is unique within the genus Nepktys , 
virtually singular in its sand-dwelling, predaceous life mode. This departure in 
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