A general expression describing tliis depth-related burrowing intensity may 

 be stated: 



1=1 

 (1)I,= S DYiBTYi+Y2-Y„ 

 i = n 



where I„ is the depth-related burrowing intensity, Dw- is the mean length of 

 burrowing by the i year class (from Figure 20-6), Bj is the 

 temperature-dependent burrowing rate (Figure 20-7) and Y^ is the size of the 

 2nd year class. 



The influence of A'^ 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 = l 

 (2)S.A.L=2 Lyj Cy^ + Cy^ • • • Cyn 



i = n 



where S.A.t is the burrow lumen wall surface area of a population ofN. incisa, 

 Ly: is the mean burrow length of the Yi year class and Cyj^ is the mean 

 circumference of the burrow of the nth year class. 



Burrow irrigation by A', 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 liglit 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: 



P)0Ar.,„o« = 2 VhaloTYl+Y2--Y„1 

 i = n -' 



where is the quantity of oxygen-containing sediment. Vj^ j^ 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 Nephtys, 

 virtually singular in its sand-dwelling, predaceous life mode. This departure in 



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