FISHERY BULLETIN: VOL. 81, NO. 3 



10- 

 5" 



V) 



CO 



O 



i_ 



o> 5 



So 



Ma co ma spp. 



N = 46 



A//ff truncata 



N = 65 



  



4 



\ 



15- 



10- 

 5- 

 







"tt- 

 10 



20 



Serripes groenlandicus 



N=I57 



40 50 60 70 



Shell Length mm 



80 



90 



FIGURE 5. — Shell size of three groups of clams consumed around Nome, Alaska. Shells are from the benthic feeding record. 



Island, the small ophiuroid, Amphiodia craterodmeta 

 (disc diameter = 1-4 cm) was the most abundant 

 species, and there was a record of furrowed sediment 

 and Macoma shells (Table 1). Qualitative obser- 

 vations indicated few large, living bivalves, mostly 

 Macoma spp. and fewer Mya truncata. Instead of a 

 visually conspicuous tube mat of polychaetes, the 

 bottom was covered with a dense carpet of inter- 

 woven ophiuroid arms. At Cape Nome, Myriochele 

 oculata; the tube-building amphipod crustacean, 

 Protomedeia fasciata; and the infaunal tunicate, 

 Rhlzomogula sp., were relatively abundant. Mya trun- 

 cata was the major walrus prey taken at Cape Nome 

 (Table 1 ) and was the only abundant large bivalve liv- 

 ing here (>5/m 2 ). The number of sea stars, primarily 

 Asterias amurensis, increased from Cape Rodney to 

 Cape Nome. They were the predominant large 

 epifaunal animals. 



The feeding activities of walrus produced similar 

 changes in the structure of these different benthic 

 communities. The feeding excavations we dis- 

 covered probably were <1 mo old (see section on 

 Study Area), and occurred in highly mixed gravel and 

 sand, in sand, and in sandy mud. Sediments were 

 significantly less consolidated {t — 10.2, P<0. 0001) in 

 Mya pits (penetration = 1 1.9 cm; n = 15) than in un- 

 disturbed sediments (penetration = 4.4 cm; n — 15). 

 The biogenic structure of surface sediments in ex- 



cavations was poorly developed compared with the 

 adjacent bottom. 



Despite differences in the structure of nonprey com- 

 munities, most infauna were less abundant inside the 

 recent walrus excavations from all feeding sites. With 

 few exceptions, the abundances of major groups (Fig. 

 6) and numerically dominant species (Fig. 7) were 

 lower inside pits (Cape Rodney, Nome, Cape Nome) 

 and furrows (Sledge Island). One exception was the 

 polychaete worm Myriochele oculata at one Sledge 

 Island site (Figs. 6, 7). These individuals were not 

 recently settled, but were large adults in well- de- 

 veloped tubes. Because this species was relatively 

 immobile, tubes probably were concentrated pas- 

 sively in the furrow bottom during walrus feeding. 

 The small (diameter <1 cm) infaunal tunicate Rhizo- 

 mogula sp. was very abundant in the Cape Nome 

 region, and apparently rolled into Mya pits during 

 and after excavation. Its abundance was significantly 

 higher (t = 5.1, P<0.01) in the bottoms of pits (X = 

 576 per core inside, 251 outside; n = 6). One or two 

 larger epifaunal anemones also occurred in many ex- 

 cavations. We observed several of these individuals 

 rolling across the sediment surface in strong cur- 

 rents. Scavenging lysianassid amphipods were abun- 

 dant in only two cores from recent excavations at 

 Cape Nome (61 and 43/core; 1/133 m 2 ). These 

 amphipods were rare in most core samples (< 1/core; 



508 



