OLIVER ET AL.: RELATIONSHIPS BETWEEN WAVE DISTURBANCE AND ZONATION 



hour at the laboratory. Biomass was calculated 

 from samples taken with a hydraulic suction 

 dredge (Brett 1964) in August 1972. Vertical 

 layers were excavated from a 0.25 m^ cylinder and 

 collected separately in 1 mm mesh bags. Animals 

 were weighed after being removed from 709c 

 ethanol and air-dried for 10 min. These weights 

 were converted to grams of organic material with 

 the conversion factors of Lie ( 1968). 



Animals swimming near the bottom were sam- 

 pled with a funnel trap, an inverted funnel ( 20 cm 

 in diameter) with the spout leading up and into a 

 holding jar. Legs held the traps within several 

 centimeters of the bottom. These traps were set 

 periodically throughout the entire year, primarily 

 at M-2 (Figure 1; 9 m). 



The availability of polychaete larvae was esti- 

 mated by the settlement of larvae into plastic col- 

 lecting jars. The jars were wide-mouth gallon con- 

 tainers (mouth diameter = 10.5 cm; volume = 4.5 

 1) held vertically in a rack at a height of 1 m from 

 the bottom. Jars were collected at 14-day intervals 

 from September 1972 to June 1975 at station M-4 

 (Figure 1; 18 m). No sediment was placed in the 

 jars, but a 1 or 2 cm layer of seston accumulated 

 during each interval. The jars were covered with a 

 galvanized mesh ( 1 cm square) to prevent the en- 

 trance offish. The jar contents were washed over a 

 0.25 mm screen and preserved in 49c formalde- 

 hyde. Postsettlement polychaetes were identified 

 to species. 



Diver observations of sediment movements and 

 current patterns were frequent. Direct measure- 

 ments of wave height and wave period were also 

 made in the northern bay from September 1971 to 

 February 1973. They were recorded by the Corps 

 of Engineers from Santa Cruz Pier approximately 

 18 km from the study area. Although wave heights 

 were generally greater in the central bay, the sea- 

 sonal patterns were similar throughout the bay. 



Feeding and burrowing observations were made 

 in the laboratory and gut contents were examined 

 under a compound microscope. If an animal con- 

 tained only sediment, it was called a deposit 

 feeder. Some deposit feeders also preyed on other 

 infauna in an aquarium. 



ENVIRONMENTAL SETTING 



Central Monterey Bay is characterized by 

 high-energy beaches (sensu Clifton et al. 1971) 

 that have a relatively gentle seaward slope and a 

 well-developed winter berm. The most distinct 



physiographic feature is the large Monterey Sub- 

 marine Canyon (Figure 1). Prevailing wind and 

 wave direction is from the northwest. Wave re- 

 fraction in relation to bottom topography concen- 

 trates wave energy on the northern sandflat and 

 disperses wave energy in the canyon head and 

 along a portion of the adjacent southern sandflat. 

 Width of the breaker zone and wave height in- 

 crease dramatically to the north and south of the 

 canyon head (Gordon 1974). 



Wave-generated bottom currents have primary 

 control over the sedimentary environment of a 

 beach. Clifton etal. (1971) gave a detailed descrip- 

 tion of wave-generated depositional structures in 

 the high energy-nearshore environment along the 

 southern coast of Oregon. The same major deposi- 

 tional structures and zones were present in central 

 Monterey Bay. The relative position of the near- 

 shore and offshore is illustrated in Figure 2. The 

 bulk of the faunal sampling and other field obser- 

 vations was performed in the offshore area ( Figure 

 2). 



Strong longshore tidal currents can produce lin- 

 goid and undulatory small ripples (Reineck and 

 Singh 1973) that trend perpendicular to the rip- 

 ples produced by oscillating wave-generated cur- 

 rents. Both types were observed at the stations in 

 18 m of water and deeper, and often resulted in a 

 complicated maze of discontinuous ripple crests. 

 In shallower water, wave-generated currents were 

 more intense and dominated the depositional 

 structure. They produced ripple crests in the fine 

 sand that were more or less continuous and nor- 

 mal to the direction of wave arrival. During 

 periods of large winter swell, conditions at the 9 m 

 station were very similar to those described for the 

 "outer planner facies" of the nearshore by Clifton 

 et al. (1971). Here, ripple marks were obliterated 

 by wave currents and the sediment moved in sheet 

 flow. Fager (1968) observed similar "miniature 

 sandstorms" on the sandflats adjacent to the 

 Scripps Institution of Oceanography in southern 

 California. 



The bottom threshold velocity of sediment 

 movement is highly dependent on water depth. 

 Given the narrow range of grain size distributions 

 among the sandflat stations ( Table 1 ) , the predom- 

 inant factors controlling the threshold of sediment 

 movement along the sandflat transects were un- 

 doubtedly water depth, wave height, and wave 

 period (Komar 1976). Since unidirectional 

 longshore currents had a decreasing impact on the 

 surface sedimentary structures with decreasing 



439 



