commonly observed in the field. Experimental worm density was one per 

 experimental aquarium or one worm/28 cm". The aquaria were kept in the 

 dark except for a two-minute interval once weekly when both sides of the 

 squaria were photographed. 



Patterns and rates of burrowing and sediment aeration were described from 

 sequential photographs of the worm burrows constructed against the glass wall 

 of the sediment-filled thin aquarium. Sediment aeration by local burrowing and 

 irrigation was indicated by a change in sediment color from dark to hglit and 

 provided a record of the worm's present or past location. Tliis method relies on 

 oxygen-sediment-color relationships proposed by Fenchel and Riedl (1970), 

 Hayes (1964), Teal and Kanwisher (1961), Rhoads, Aller and Goldhaber 

 (1977), and Aller and Yingst (1978). The absence of oxygen generally leads to 

 a dominance of reduction reactions (eH<0) including formation of iron 

 sulfides which blacken the sediment. At the point of change from dark to light 

 color in the sediment, values for both eH (volts) and dissolved oxygen (mg/1) 

 begin to increase from 0.0. Presence of oxygen is key to substrate oxidation 

 reactions (eH<0). By quantifying the development of this color discontinuity 

 against the thin aquarium glass wall where worms are burrowing, it is possible 

 to document three parameters of burrowing activity: 1) the spatial-temporal 

 extent of burrowing, 2) the effective new surface area of the sediment-water 

 interface, and 3) the extent of sediment aeration. This record, visible against 

 the aquarium wall, can be photographed at appropriate time intervals and 

 activity quantified by counting burrows, measuring the surface area of burrow 

 linings and by planimetry, measuring the volume of aerated sediment. 

 Horizontal burrowing patterns were also described by recording temporal and 

 spatial appearance of new burrow openings at the sediment surface in large 

 sediment-filled dishes (single .2-. 3 g worms in 3 x 6 x 4" deep sediment trays). 



RESULTS 



Description of the Burrow 



Nephtys incisa actively penetrates fine sediments and establishes an 

 open-ended burrow with no visible modification of the burrow wall except 

 packing. It is not known if mucous, exuded onto parapodial setae during 

 feeding (Davis, 1979b), is present in the burrow wall. The burrow is often 

 W-shaped, but many variations exist. Back and forth motion of the worm with 

 packing of the burrow wall by setal bundles creates a section which is closely 

 fitted to the front and mid section of the worm. This precise fit permits 

 flow-through irrigation by the parapodial ciUa (Davis, 1979c). The occupied 

 burrow is often continuous with a recently abandoned burrow posteriorly, 

 which then continues to receive oxygenated water before it returns to the 

 surface. Abandoned burrow segments gradually fill with suspended particulates 



307 



