Conspicuous current activity is also asso- 

 ciated with the Nyckel Ridge forming the 

 south (right) bank of Wilmington Canyon. 

 Water movement on the upper part of this 

 ridge appears to be directed up-slope (west and 

 west-northwest). A northerly current sense is 

 indicated on the more deeply submerged por- 

 tion of this ridge at depths of 1000 to 1200 

 fms. Additional evidence of current activity on 

 this outer ridge are provided by the observa- 

 tion of a firm bottom of stiff clay at Station 41. 

 Samples of similar lithology have been recov- 

 ered from this region by the Woods Hole 

 Oceanographic Institution (Sample 2109B, in 

 Hathaway, 1966) suggesting removal or non- 

 deposition of recent finegrained sediment in 

 this sector. Strong northwest-flowing currents 

 capable of moulding sand and gravel into rip- 

 ples are also noted on the Nyckel Ridge at Sta- 

 tion 43 (Plates 27. 28). 



Benthic Organisms 



Benthic organisms, like bottom currents, ap- 

 pear to modify bottom sediments in the Wil- 

 mington submarine canyon and adjacent areas. 

 The lateral distribution of the more important 

 groups of organisms detected in the photo- 

 graphic survey are shown on Figures 9 and 10. 



Shell material forms a large part of the 

 coarse sediment fraction on the shelf edge at 

 depths less than 100 fms, particularly on the 

 northern and eastern margins of the canyon 

 head (Fig. 9). Shell material of coarse sand to 

 pebble size is often aligned in bands concen- 

 trated in ripple mark troughs. Many of the 

 shells, sometimes distinct enough to be recog- 

 nized as pelecypod valves of scallops and other 

 forms, lie concave up and are often partially 

 buried or filled with sediment. The shell con- 

 tent decreases from over 30 percent on sectors 

 of the shelf to about 1 percent at depths of 

 about 200 to 300 fms. Pelecypod valves of 

 probable shelf origin have, however, been en- 



countered in cores collected in the canyon and 

 on the continental rise (Stanley and Kelling, 

 1968b, Fig. 8). 



Echinoderms are also locally important on 

 the shelf and include starfish, sand dollars and 

 sea urchins (Fig. 9). Crabs and lobsters also 

 abound in this area (Fig. 10). This environ- 

 ment is one of high sand and shell content. 

 Crustaceans apepar to be more abundant in the 

 immediate vicinity of the canyon area than on 

 the adjacent slope. 



The area covered by burrowing organisms 

 increases progressively at depths greater than 

 75 fms. Burrows, tracks, mounds, and other 

 forms of bioturbation are recorded at almost 

 every station below this depth, with the excep- 

 tion of Station 43 (Fig. 10). Pencil-like tubes of 

 polychaete worms [probably Hyalinoecia tubi- 

 cola (Muller)], a common form on the conti- 

 nental slope of northeast North America (Wig- 

 ley and Emery, 1967), are locally important. 

 Numerous forms of bathyal echinoderms (Fig. 

 10), including brittle stars and asteroid star- 

 fish, become important below depths of about 

 500 fms. These, as well as crabs and sea spi- 

 ders leave distinctive markings in the soft mud 

 bottom and otherwise modify the sediment as a 

 result of their movement and their feeding 

 habits. 



Equally spectacular are bottom markings 

 produced by benthic fish (Fig. 9) ; these appear 

 to be most abundant on the slope between 100 

 to 1000 fms. The soft undulating mud at some 

 localities has been entirely moulded by fish 

 that form shallow depressions (resting-places 

 or "nests"), and by fin marks. Holothurians 

 are important because of the trails they make 

 and because of the abundance of their faecal 

 deposits which cover extensive areas of the 

 bottom (Table II). Coelenterates, including 

 sea-anemones and possible soft corals, are re- 

 corded at four localities but are generally less 

 common than the preceding forms (Fig. 10). 



87 



