PAUL and FEDER: LITTLENECK CLAM IN GALENA BAY 



that the number of 0-age group cockles (C. 

 edule) appeared to be poorlj^ correlated with 

 abundance of spawning stock. He also observed 

 that poor to moderate settlements followed 

 years of good to exceptional recruitment. If 

 larval production and settlement of P. staminea 

 is affected by year-class densities in a similar 

 manner, it is possible that the strong year 

 classes of 1966, 1967, and 1968 are responsible 

 for the moderate to poor recruitment observed 

 in Galena Bay during the following years 

 (Figures 7, 8). 



P. staminea does not move horizontally 

 (Feder and Paul, unpubl. data); therefore, the 

 only source of recruitment of this species to an 

 area is the annual settlement of veligers. Thus, 

 the large number of clams 20 mm in length 

 and longer that are found between the tidal 

 heights of +0.43 and -0.43 m must be the 

 result of relatively good survival of these larvae 

 (Figure 9). 



Very few littleneck clams were located above 

 the tidal height of +0.43 m (Figure 9); the 

 number of clams observed is probably the 

 result of environmental stresses which act on 

 young clams at the upper, more frequently 

 exposed portions of a beach. The 2-foot uplift 

 of land in Galena Bay following the Alaska 

 Earthquake in March 1964 (National Research 

 Council, 1971) may have affected settlement 

 and/or survival of clams at the upper limits 

 of their intertidal distribution during that year 

 (Figures 7, 8). The time of the year for settle- 

 ment of P. staminea veligers in Prince William 

 Sound is not known. 



Strong tidal currents may affect the numbers 

 of settling veligers in the intertidal zone (Fraser 

 and Smith, 1928). On Shell Beach, the study 

 site with the strongest currents (Table 1), the 

 number of clams under 5 yr of age (seven clams 

 per 0.25 m-) was consistently lower than that 

 found on the Indian Creek Mudflat (23 clams 

 per 0.25 m-) where the shore was relatively 

 undisturbed by wave action and currents. 



On most beaches and flats of Prince William 

 Sound, there are many temporary and perma- 

 nent streams fed by rain, melting snow, and 

 glacial ice. P. staminea is rarely encountered 

 in areas where permanent freshwater streams 

 flow over or percolate through beach sediments 



at low tide (Feder and Paul, unpubl. data). 

 Mortality resulting from rainfall on exposed 

 beaches is negligible; however, heavy rainfall 

 affects distribution of P. staminea by altering 

 beach topography. Freshwater runoff after a 

 period of prolonged rainfall is often responsible 

 for the active transport of beach sediments; 

 in such areas clams are washed away with 

 these sediments (Feder and Paul, unpubl. data). 



Throughout its range P. stami)iea is found 

 within 15 cm of the sediment surface and 

 occasionally at the surface (Amos, 1966). In 

 areas of Prince William Sound examined by us, 

 clams through 4 yr of age are essentially 

 epifaunal in their distribution while older 

 individuals are subsurface dwellers. Siphon 

 length is almost certainly the limiting factor 

 in determining the depth at which various 

 sizes of clams occur. Sieve analysis of sediment 

 from Eater and Shell Beaches shows that 

 coarse gravel at the beach surface covers med- 

 ium gravel and finer sediment (Figure 2). 

 The geology of such gravel beaches affords 

 young P. stami)iea protection from predation, 

 exposure, and ice scouring by providing spaces 

 between the gravels in which the clams can 

 lodge themselves. These spaces, filled with water 

 at high tide, provide a haven for young clams. 

 Here they can remain and feed below the 

 level of the beach surface at a depth greater 

 than their siphon length. On the Indian Creek 

 Flat, sediment fills the intergravel spaces 

 (Figure 2), thereby forcing young P. staminea 

 to remain closer to the surface for longer 

 periods of time than if they had settled on a 

 gravel beach. Clams on mud flats such as 

 Indian Creek are then more vulnerable when 

 young, and this may, in part, explain better 

 survival of clams on gravel beaches. 



In Galena Bay few individuals that settle 

 between the tidal heights of -0.43 and -0.76 m 

 survive beyond their fourth year, despite the 

 fact that it is here that the heaviest concentra- 

 tions of young clams occur (Figure 10). This 

 distribution may be the result of selective 

 settlement by veliger larvae (Thorson, 1957, 

 1966), hydrographic concentrations of larvae 

 in the plankton at time of settlement (see 

 Ryther, 1968 for discussion), or some form of 

 selective mortality such as predation (see 



675 



