THE DISTRIBUTION ili~D REPRODUCTION OF THE
PISHO CLAN, TIVELA STULTORUH, IN NONTEREY BAY
A Thesis Presented to the Graduate Faculty
of
California State University, Ha~vard
In Partial Fulfillment
of the Requirements for the Degree
!'laster of Arts in Biology
By
Mark D. Stephenson
August 19711 Copyright © 1974 by Mark D. Stephenson
. ' TABLE OF CONTENTS
ABSTRACT .... i
LIST OF FIGURES ii
LIST OF TABLES iii
INTRODUCTION . l
SECTION l
Distribution 3 Introduction 3 Methods and Materials 5 Results 10
Discussion 20
Conclusions 24
SECTION 2
Reproductive Cycle 25 Introduction . 25 Methods and Naterials 27 Results 33 Discussion 47
Conclusions 52 ABSTRACT
The distribution and reproductive cycle of the
Pismo clam, Tivela stultorum, were investigated in
Monterey Bay. Pismo clams were found only between the
Salinas River mouth and Santa Cruz. The highest dens
ities of clams 1;ere found at the Monterey Bay Academy beach and Sunset State B~ach, and were somewhat less
to the north and south of these two adjacent 1Jeaches.
The highest densities 1;ere found to be intertidal, while subtidal beds were found to be rare and to have
low densities. Most of the dispersion patterns were
random. The different size classes did not show a vertical stratification.
Pismo clams spawn during their second summer and
their primary spawning period is in September and
October. Both subtidal and intertidal Pismo clams
spawn in Monterey Bay, even though this is near the northern limit of their range. Their sex ratio is
approximately even for all sizes of clams.
i LIST OF FIGURES
Fig. l Hap of Honterey Bay and sampling sites.
Fig. 2 Size frequency distribution of Pismo clams on
selected beaches in 1972 and 1973.
Fig. 3 Vertical distribution of clams at Honterey Bay
Academy.
Fig. 11 Female gonad in the inactive stage.
Fig. 5 Female gonad in the early active stage.
Fig. 6 Female gonad in the late active stage.
Fig. 7 Female gonad in the ripe or mature stage.
Fig. 8 Female gonad in the part spent stage.
Fig. 9 Female gonad in the spent stage.
Fig. 10 Hale gonad in ripe or mature stage.
Fig. ll Hermaphrodite gonad condition.
Fig. 12 Per cent of females in early active stage.
Fig. 13 Per cent of females in late active stage.
Fig. 14 Per cent of females in ripe stage.
Fig. 15 Per cent of females in part spent stage.
Fig. 16 Per cent of females in spent stage.
Fig. 17 Per cent of Pismo clams in inactive stage.
Fig. 18 Per cent of males in ripe stage,
Fig. 19 Size of female, male and immature Pismo clams.
ii LIST OF TABLES
Table l Positions of sampling sites in Honterey Bay.
Table 2 Intertidal ancl subtidal densities of Pismo
clams in Honterey B,ay.
Table 3 Tests of signif.i1q TalJle It Tests of spatial dispersion of Pismo clams at five localities. Table 5 Numbers of clams in each stage of gonadal maturity. Table 6 Temperature, chlorophyll a, phaeo-pigment and stage of gonadal maturity of Pismo clams in Honterey Bay. iii INTRODUCTION The Pismo clam (Tivela stul torum) 1vas first studied early this century by 1veymouth ( 1923) and Baxter ( 1930) at Pismo Beach, California. Since then, California Department of Fish and Game has taken annual surveys to estimate popu lation abundance. These studies along 1rlth the classic Coe and Fitch (1950) study have provided valuable information on the almndance, reproductive cycle, and growth rates of the clams from Pismo Beach to San Diego. Although they are an important sport fishing resource, the Pismo clams in l'lonterey Bay have received little scientific attention. The intent of this study 1vas to determine the local distribution and reproductive cycle of the Pismo clam in l'lonterey Bay. Additional information on their growth rates, preda tion by sea otters, and correlations of numbers of clams with sediment parameters was reported by Nybaklren and Stephenson (l97ll). Ackno1dedgment is given to my major advisor, Dr. James Nybal{l{en, who provided valuable assistance and advice during the course of the study and helped 1rl th the writing of this thesis. The comments and constructive criticism of my thesis committee, Drs. Cailliet, Hartin, and NylJakken, have aided in the final drafting of this thesis. Hany people have provided assistance. In particular, I would lil{e to thank Bill Head, l. --- 2. Gary HcDonald, and Brian Nax;rell for help >vi th the field wurlr and Signe Johnsen for making all of the histological preparations of the gonad tissues. Financial assistance .vas provided from U. S, Army Corps of Engineers Contract No. D.A.C.\1', 72-72-C-0016. . SECTION l DISTRIBUTION INTRODUCTION Before the present study 1vas initiated little was lmown about the clistribution o"f Pismo clams in Monterey Bay. Perhaps the most informative qualitative data is from a Cali- fornia Department of Fish ancl Game survey of Honterey Bay conducted during a low· tide on January 15, 1969. At that time 87 clammers w·ere found lJetiveen the Salinas River mouth and Elkhorn Slough, 57 betifeen Elkhorn Slough and the Pajaro River, 156 betifeen the Pajaro River and Honterey Bay Academy beach, and 62 lJet\Yeen Monterey Bay Academy beach and Rio del Har (Dahlstrom, personal communication). Assuming that the clammers are found iVhere the clams are, one can quickly ob- tain a rough estimate of the location of clams in Honterey Bay. The only quantitative data came from the California Department of Fish and Game. The method employed to obtain these data was to dig a six-inch 1vide by six-inch deep trench from high tide level do1m to lmv tide level. The length of clams and the location 1vi thin the transect where the clams ifere found 1vere recorded. In 1968, using the transect method of sampling, they obtained six clams at Sunset State Beach, four clams approximately one mile south of Sunset State Beach, six clams approximately l. 5 miles south of Slmset State Beach, 3. and three clams at Zm~ldmvslci State Beach (Dahlstrom, personal conununicati on) . Unfortunately, this transect method 1vas of limited value for estimating the density and dispersion pat terns due to the small area surveyed and the lack of repli cates. It 1vas necessary to devise a ne1v system to adequately sample the clams so that estimates of density and dispersion patterns could be made. Since the California Department of Fish and Game surveys covered only a few· areas, it 1vas also necessary to sample representative sites all over the Bay to ascertain the presence of the clams. Although there 1vere rumors of extensive subtidal populations of clams in various Monterey Bay localities, no documentation of such beds existed. Determining the exist ence of subtidal lJeds 1vas of interest for they might be the major source of recruitment to the heavily clammed interticlal areas. The only evidence of the occurrence of such beds 1vas from Fitch (1965), who reported that large numbers of sulJtidal clams 1vere found at one location in southern California. The intent in this phase of the study was to estimate the density and analyze the dispersion pattern and vertical distribution of Pismo clams at several locations in Monterey Bay. 5. HETHODS AND MATERIALS Intertidal samples 1vere taken at ten locations in Honterey Bay (Fig. 1, Table l). The sampling locations were initially selected randomly. How·ever, some of the locations .vere inaccessalJle. Therefore, __ some sampling sites had to be relocated to the nearest accessable site. At eight loca tions the first sampling took place during the months of June, July and August of 1972. At the Salinas River mouth station (117, Fig. 1) the sample 1vas taken in November. Fort Ord (119, Fig. 1) was sampled in December 1972. Rio del Nar, Honterey Bay Academy, Sunset State Beach, Zmudo.vski State Beach, and Hoss Landing Beach >Vere resampled during June and July 1973. Pismo Beach was sampled in December 1973. At each station, 20 one square meter samples 1vere selected randomly >vi thin a sixty by eighty foot grid placed so the lo.vest edge 1ffiS at approximately the -1.0 foot tidal level. Each square meter was raked wt th a small hand ralce set wt th tines that .vere spaced 12 rum apart and that penetrated six inches deep. A quarter-square meter area 1vas subsampled by talcing 13-.018 2 m cores that penetrated six inches into the substrate (Oliver and Slattery, 1973). The contents were emptied into a sieve box and sieved in the surf. The rakes gave adequate samples for clams greater than 39 rum in length as these clams could not fit bet>Veen the tines sidew-ays. The cores obtained quanti tative samples for clams from 39 mm do1m to about 10 mm. The lmver linli t of 10 llllll >Vas determined by the mesh size in the FIGURE 1 HAP OF MONTEREY BAY AND SM!PLING SITES 6 . 0 NAUTICAL MILES 10 F=l'-';==', o!;=', ~~~=r!==r1. L, 0 KILOMETERS 20 I. Santo Cruz 2. Rio del Mar 3. Monterey Boy Academy 4. Sunset State Beach 5. Zmudowski State Beach 6. Moss Landing Beach 7. Salinas River Mouth 8. Morino Beach 9. Fort Ord 10. Monterey 9 30' 10 50' 7. TABLE l Positions of the stations sampled in the distribution studies. Location Latitude (N.) Longitude (if. ) Santa Cruz 36° 57.7 1 122° 0,1 1 Rio del Har 36° 57.6 1 121° 511.8 1 I 1 Monterey Bay Academy 36° 55.2 121° 5J.. 2 I 1 Sunset State Beach 36° 511.8 121° 119 • 7 I ZmudowBld State Beach 36° 50,2 I 121° /18, 2 I Hoss Landing 36° 47,6 I 121° 47.5 1 Salinas River mouth 36° 45.6 1 121° !18 , 2 I Marina 36° liJ.. 9 I 121° /18,6 I Fort Ord 36° 110 , 0 I 121° 50,8 I Honterey 36° 36,1 I 121° 53.1 1 B. sieve box. Each clam 1vas measured, the quadrat of occurrence noted, and then reburied. A one 1vay analysis of variance test (Woolf, 1968) was used to test for significant deviations of mean densities be tween the years 1972 and 1973 at each location. Another test, a Student-Newman-Keuls multiple range test (lvoolf, 1968) was used to test for significant deviations of densities among the different locations. Subtidal samples were taken offshore of each inter tidal sampling station at the -15 foot tidal level. This was the shallmvest depth at which sampling could be done from a boat because of 1vave action. The sampling 1vas done in July, August and September of 1972, except for the Fort Ord station, which was not sampled due to heavy surf. Subtidal stations were not resampled because of the low· number of clams found in 1972. The sampling device 1vas a modified portable gold dredge (Brett, 19611). This device 1vas recently used to con duct surveys for macrofauna (Hughes and Thomas, 1971) and was compared with other benthic samplers (Hodgson, unpub lished) . The gold dredge consisted of a seven horsepower pump that pumped high pressure water down to the diver belmv. The water entered the middle of an L-shaped tube six inches in diameter and shot out one end. This caused a pmverful suction at the other end which coulcl be used to vacuum up sediment and clams. A bag of 3 mm nylon mesh was attached to the end opposite the suction. The clams.and sediment - 9. were sucked up through the tube ancl into the mesh bag. The sediment was expelled through the mesh, leaving only the clams and larger particles. At each station, 20 one square meter samples were sampled to a depth of six inches. The sample locations were selected haphazardly in that the diver would sample a square meter area and move approximately ten to fifteen feet mvay to take the next sample. The divers probably did not introduce bias in selection of sample sites because the visihili ty 1vas usually limited to five feet or less and the bottom was extremely homogenous. Further, siphons ,,.ere not visible, although they have been reported elsew-here (Fitch, 1965). After the sample 1vas collected in the mesh bag, it was brought up to the boat above, where it was sorted for clams. The clams 1mre measured and returned. The spatial dispersion of Pismo clams at each of the locations surveyed 1vas determined by using the variance to mean ratio, chi square test (Elliot, 1971). Clams were sep arated into small clams ( <39 mm maximum length) and large clams (> 39 mm maximum length) for testing dispersion because different sized sampling units w·ere used for the two sizes of clams, and to determine if the small clams had a differ- ent clispersion pattern than the large clams. 10. RESULTS The mean intertidal densities from 1972 to 1973 were not significantly different at any location (Table 2). In each year the highest intertidal densities w·ere found at Honterey Bay Academy and Sunset State Beaches. North and south of these beaches the density decreased. To the north, Santa Cruz had only a single juvenile clam and to the south, Harina, Fort Orcl, and Nonterey had no clams. Honterey Bay Academy was significantly higher in density than the other locations, with the exception that it did not differ significantly from Sunset Beach in the density of small clams in 1972 and the large clams in 1973 ( TalJle 3). Sunset State Beach 1vas next highest in density with the exception that it was not significantly higher than Rio del l'!ar for the density of large clams in 1972 and it 1vas not significantly higher in density of small clams than any location in 1973. A survey 1vas also made of Pismo clams at Pismo Beach to compare the density with the densities found in Honterey Bay. The mean density of large 2 clams at Pismo Beach ;vas . 7 clams/m (95% C.L . .._ .116) which ;vas significantly lmver than the 1973 densities at Sunset and Honterey Bay Academy, but not significantly different from the densities at Rio del Har, Jvloss Landing or Zmudmrski (P <.Ol). The mean density of small clams at Pismo Beach was . 5 clams / 41 m2 ( 95% C. L ..± .11 6) , which was significantly lug. l1e r than the 1973 mean densities at Hoss Landing, Sunset and Rio del Har, but not significantly different from the densities 11. at Honterey Bay Academy or Zmudowski (P < .Ol). In the smmner of 1972 small clams bet1reen 10 nllll and 35 mm 1-rere found abundantly at Honterey Bay Academy and at Sunset State Beach, but not at other beaches (Figure 2). Host of these clams probably w·ere spmmed during the summer of 1970. In 1973 these clams probably comprised the !tO mm to 70 mm size class on these lJeaches. The numlJer of young clams betw·een 10 mm and 35 mm 1vas significantly l01ver in 1973 than in 1972 on these t1vo beaches (Hann 1Vhi tney U test, p ( .05), suggesting a poor year for recruitment. To determine the vertical distribution of clams, seven intertidal heights 1-rere sampled ranging from the -. 2 to the 3 .1! foot tidal level at Honterey Bay Academy to deter- mine if the clams 1rere more abundant at some tide levels than others. There w·ere no clams found above the 2.6 foot level (Figure 3). The densities of clams from level -.2 to 2.6 did not deviate significantly among levels (Student-Newman Keuls multiple range test, P < .05, ifoolf, 1968). The depth below the sand at which the clams occur was olJserved to be less than six inches from the top of the shell to the surface of the sand. This w-as cletermined at each survey by probing the sand remaining under the area 2 1vhere our six inch deep of m core sample 1ms taken. At no time w·ere clams found at a depth greater than that sampled by the cores. 12. All the small clams less than 39 mm in length apparently randomly dispersed (Table 4). Most of the large clams greater than 39 nun in length persed, the exceptions being an apparently contagious dis persion of clams from Rio del Har in 1972 and Honterey Bay Academy in 1973. The variance/mean ratio test employed in these analyses can only be employed effectively as a compar ative index of dispersion individuals are similar for each sample (Elliot, 1971). Since the means and total number of individuals the same in these samples, comparisons cannot be made among the various beaches. Also, it is not possible to ascertain the degree of clumping in the samples dispersion patterns. Therefore, it appears most of the clams does not appear to be the case, there ditional data to test the significance or degree of departure from randomness. Subtidal densities were lmmr than interticlal dens ities in all cases (Table 2). Moss Landing had the largest subtidal population square meters. --- TABLE 2 INTERTIDAL DENSITIES OF PISHO CLAHS IN HONTEREY BAY Density of Clams/H2 +95% Confidence Limits 1972 1973 Location II Clams X 95% C.L. II Clams X 95% C.L. Santa Cruz 1 • 05 ± .41 Rio del Har 28 1.40 ± .88 28 1. 40 ± .83 Honterey Bay Academy 164 8.45 ±2.97 133 6. 65 ±2. 28 Sunset State Beach 117 5.85 ±1. 76 71 3.55 ±1.45 Zmudowski State Beach 24 1.20 ± .56 44 2.20 ±1.33 Hoss Landing Beach 14 1. 70 ± .35 16 • 80 ± .69 Salinas River Hauth 4 .20 ± .13 Harina Beach 0 0 Fort Ord 0 0 Honterey 0 0 SUBTIDAL DENSITIES OF PISHO CLAHS IN HONTEREY BAY Density of Clams/m2 ±95% Confidence Limits 1972 Location II Clams X 95% C.L. Santa Cruz 0 0 Rio del Har 0 0 Honterey Bay Academy 3 .15 ± .23 Sunset State Beach 0 0 Zmudowski State Beach 0 0 Hoss Landing Beach 8 .40 ± .47 Salinas River Hauth 1 • 05 ± .17 Marina 0 0 Fort Ord Honterey 0 0 TABLE 3 Tests of significance of differences among densities of Pismo clams from different areas using the Student-Nemnan Keuls multiple range test (Hoolf, 1968). A line under the means indicates that these means do not deviate signifi cantly (P ~ <.01). Small Clams less than 39 mm in length in 1972 Location: Rio del Mar Zmudowski Sunset Honterey Bay Academy Density: .10 .10 1.05 1.45 (Clams/>;; m2) Small Clams less than 39 mm in length in 1973 Monterey Bay Location: Hoss Landing Rio del Mar Sunset Zmudowski Academy Density: .10 .25 • 25 .40 .75 (Clams/!,; m2) Large Clams greater than 39 rom in length in 1972 Monterey Moss Rio Bay Location: Salinas River Landing Zmudmvski del Mar Sunset Academy Density: .20 .70 .75 1.00 1.65 2.65 (Clams/m2) Large Clams greater than 39 mm in length in 1973 Monterey Bay Location: Rio del Mar Moss Landing Zmudowski Sunset Academy Density: .40 .45 .55 2.75 3. 65 (Clams/m2) ..._ FIGURE 2 SIZE FREQUENCY DISTRIBUTION OF PISHO CLA.HS ON SELECTED BEACHES IN 1972 AL\fD 1973 15. SIZE FREQUENCY DISTRIBUTIONS OF PISMO CU\MS ON MAJOR SAMPLING BEACHES, I972-·!9T3 X= 1.40 Rio dal Ma,· t 14 June 1972 .__I--,--,-----J--t-1~ n. ..~-.,.----,-----..--+-'P--W..Jb-J--L-L.-ni..-J..f-LflTI..J..l-Jhil,_m,-, X = 1.40 Rio del Mar 29 June 1973 p X= 8.60 Monterey Bay Academy 12 July 1972 ..._____...l...l-1-1...\J....L...1...J.~.w....y...w-.J...f..l.-l--'-'-f-I-'....J....j-J-1--'-r-'--'--'-·-P 0 1-0hp o ~ 12r X= 5.65 Sunset Beach 2.9 June /.97.;2 m q [l n r x= 3.75 Sunset Beach 30 June /973 lh- 1-..--/II"'MI I n n I ' ' X=I.IO Zmudows.ti Beach 28 June 1972 VJ 12 ::E :5 x= 2.15 Zmudowski Beach u 8 u. 0 3 July /973 5 4 Cil ::E :::> zor---,---,--L~~~L--fLLLY~--ru~.---,---,----r---rr--~10 o 20 40 so so roo 120 SIZE OF CLAM (mm.) 17. SIZE FREOU.ENCY DISTRIBUTIONS OF PISMO CLAMS ON MAJOR SAMPLING BEACHES, 1972-1973 X= 0.65 Moss Landing II July 1972 rq 0 p 0 p - X = 0.85 Moss Landing ·--.---· !- .,-1.r+·nL-~--~--LY~~~~~-2-rJu_/_y_/~9-73--,---+L~ W o:rfl rn r r "'12... r _,:< (.) 8 X= 0.65 Moss Landing [54 II Oct. 1973 rll :; ::> z 0 ·-·- '-'--;---...,.-'-"---r·-·__o-,---r_--r_~, 0 ZC! 40 60 00 100' 120 SIZE OF CLAM (mm.) FIGUHE 3 VEHTICAL DISTHIBUTION OF CLANS AT HONTEHEY BAY ACADEHY 13. VERTICAL DISTRIBUTION OF CLAMS AT MONTEREY BAY ACADEMY X= 0 clams/m.2 T-IDE LEVEL (ft.) 3.4 X=2.5 2.6 r:p 0 q m X= 2.75 1.8 X=7.5 1.2 X=3.75 0.7 x,;,s.2s 0.4 (/) ::!' <( ...J u 8 ~ 6 X=4.o [5 4 -0.2 !11 2 ~ - rn z or--~~--=-F=~+--~~~roWJ~,~n~~Y.~~~~q+: __ wn~,~----===r•----~~~~-rr~-~n~, 0 20 40 60 80 100 120 LENGTH OF CLAM (mm.l 19. IlESULTS OF TESTS OF SPATIAL DISPEHSION OF INTERTIDAL PISHO CLANS Host Probable Dispersion Pattern Small Clams Large Clams Local:L ty Year ( ( 39 mm) ( > 39 mm) Rio del Nar 1972 Random Contagious Rio del Nar 1973 nan c1 om nandom Honterey Bny Academy 1972 Hanel om llandom Nonterey flay Academy 1973 Random Contagions Sunset 1972 nand om !land om Sunset 1973 Random Handom Zmudowski 1972 Random Random Zmudmvski 1973 Random nand om Hoss Landing 1972 nand om Hand om Hoss Landing 1973 nand om Random -- 20. DISCUSSION Pismo clams in Monterey Bay ~Vere distributed between the Salinas River and Hio del Nar 1d th the heaviest concen trations occurring at Sunset State Beach and Nonterey Bay Academy. No clams 1vere found south of the Salinas Hiver and only one clam ~Vas found at Santa Cruz. The aerial survey of Hontercy Bay conclnctccl by the California Department of Fish ancl Game (Dahlstrom, personal communication) sh01ved a similar distribution of clammers. Host of the clammers 1vere con centrated near the beaches on ~Vhich the highest densities of clams Here found. No clammers 1vere found at Santa Cruz or south of the Salinas Hiver. Surprisingly, the density of large Pismo clams >39 nun in length at Pismo Beach 1vas significantly loH·er than at t1vo of the beaches in Honterey Day, especially since Pismo Beach has alHays been kno1vn among sports fishermen for its large populations of clams. The reason for the l01ver density found in the survey at Pismo Beach is not kno1m, but it may be speculated that it was a result of the heavier fishing pressure (personal observation) or that not enough samples Here taken to adequately estimate the density. Although the density ~Vas lo~Ver at Pismo Beach, the total number of clams available to clammers may be much greater clue to the larger surface area exposed during l01v tides. The larger area exposed is a result of the flatter slope of the beaeh at Pismo Beach as compared to Nonterey Day beaches. 21. Hy feelings ·an the reliability of' the sampling tech nique were that one could estimate the density effectively if certain sources of error were minimized. One source of' error was that in 1972 the sampling tidal heights were determined by using tid.c tables to predict the height of the water. On some of the surveys the weather 1vas rougher, hence it affected the accuracy of' selecting the height to sample. Another source of error was that it was not always possible to re survey the exact same spot on the beach, even though the spot could lJe 1 oca ted from eli stance measurements to lanclmarlcs taken during the original survey. This was a result of the sampling site being submerged clue to sand erosion. In such cases it was necessary to sample an adjacent site. Realiz ing that sampling variability might have lJeen introduced clue to the selection of the wrong sampling height or not resamp ling the same spot in subsequent surveys, the best approach to assess the relialJili ty of the technique 1ms to subjectively look at the data obtained at each area in 1972 and 1973 (Fig ure 2). In both years the highest intertidal densities were fDlmcl at Monterey Bay Academy, with Sunset Beach second highest in density. Moss Lancling hacl the lowest density in hath years. The size frequency distributions of the clams obtained at each location wer.e somewhat similar in 1972 ancl 1973 also (l"igurq 2). Since lJoth years' results 1;ere similar, the variability clue to the sampling technique, although aclmowleclgecl, was considered to be minimal. &>~ 22. The densl.tie·s of Pismo clams w·ere found not to deviate significantly from each other at six different intertidal heights; however, only one beach was sampled and only 4 meter squares were sampled at each height. \1eymouth ( 1923) and Baxter (1961) have reported that Pismo clams 15 to 30 tmn l.n length were found mainly in the middle part of the inter- tidal range, but they did not state what tide level height the m1cldle part of the tidal range corresponded to. 1vhen this survey 1ms eonclueted, very fe1v clams of that size were found at any level (Figure 3), but that may be mainly an artifact of sampling only one beach. No clams were found above the 2.6 foot tidal level in Monterey Bay. In most of the areas surveyed Pismo clams were ran- domly dispersed. This type of dispersion has been found in other bivalves such as Serobicularia plana (Hughes, 1970), Nulina lateralis (Jackson, 1968), Gemma @;emma (Jackson, 1968), Cardium edule (Kosler, 1968), and Hacoma baltica (Kosler, 1968). At a few of the locations large Pismo clams were not randomly dispersed. Departure from randomness has been re- ported for other bivalves. Tellina tennis, for example, is regularly dispersed in low densities and randomly dispersed in high densities (Holme, 1950), and Mya arenaria shows a clumped dispersion pattern (Gaucher, 1965). No sediment data or other data were available to explain the contagious distributions. Large numbers of subtidal Pismo clams were not found in Monterey Bay simiiar to those found by Fitch (1965) at 2 Zuma Beach. The highest density of .011 clams/m 1ms found at Hoss Landing, ~Vhich is considerably lo~Ver than the six <) clams/m~ found by 1°itch (1965) at Zuma Beach. The density 2 at Hoss Landing n1ay have heen greater than the 0.4 clams/m found during the survey, since as many as six clams !Vere fre- quently collected from an area of approximately one square meter ~Vhen clams ~Vere collected for the reproductive stucly. At Pismo Bench large numhers of subtidal clams !Vere also found. TlVenty clams ~ 'rhc highest intertidal dcnsi ties of Pismo clams in Monterey Bay were found at Monterey Bay Academy and Sunset State Beaches. The density of clams decreased to the north and to the south of these beaches. No clams were found south of the Salinas River and only one juvenile clam was found at Santa Cruz. 'rhe clensi ty of large clams at Pismo Beach was significantly low·er than the densities at Monterey Bay Acad- emy or Sunset State Beaches. The mean densities of Pismo clams at seven intertidal heights did not differ significantly indicating there was no vertical stratification. In most of the surveys the clams were randomly dispersed. Subtidal clams were not numerous and occurred at a maximum density of 0. 11 2 clams/m (95% C.L. = ,117) at Hoss Landing. . SECTION 2 REPRODUCTIVE CYCLE INTRODUCTION Most previous studies on reproduction in Pisn1o clams have been done in southern California or farther south off Baja California (Coe, 191!7; Coe and f'itch, 1950). All sug gested that the duration of the reproductive cycle in Pismo clams was extended in the southern part of its range, and was somewhat restrictecl in the northern part of its range. A re stricted spawning season in the northern part of an animal 1 s range was not uncommon in many intertidal animals (Giese, 1959) and 1vas found in the bivalves Hya arenaria (Ropes and Stickney, 1965), and Hercenaria mercenaria (Porter, 1964). Since Nonterey Bay is near the northern limit of the Pismo clam's range, it is possible that spawning might occur only during the 1varmest years or that spawning would not occur at all, and that the clams might depend on recruitment from the more southerly populations. The only information concerning the reproductive cycle of Pismo clams in Nonterey Bay 1vas from a one year study lJy Giese, et al. ( 1967), 1rhich showed that the 1\Teight of the gonad increased in size during the spring, reached a maximum from June to September, and there after decreased rapidly. No evidence was presented to shmv that the clams spawned their gametes in contrast to resorb ing them, nor 1rere the subtidal populations of clams studied. Large numbers of subtidal clams 1rere found at Zuma Beach 25. 26. (Fitch, 1965) and at Pismo Beach and Hoss Landing (see Sec tion 1). If these subtidal populations were the major source of gametes, it could prove to be essential to keep them at their present levels to provide recruitment for the heavily clanuncd intorLiclul area. 27. NETHODS AND HATElUALS Seventeen to tw·enty clams 1vere collected monthly from four locations to determine the degree of gonadal maturity. Clams 1vere collected intertidally near the north end of Nan- resa State Beach from November 1971 to October 1973. Collec- tions were made from ~loss Landing intertidally from February 1972 to October 1973 and from Noss Landing sulJtidally from FelJruary 1972 to September 1973. From June 1973 to October 1973 collections 1vere made subtidally at Pismo Beach. The collections were then brought back to the Noss Landing Harine LalJOratories and either processed immediately or put into running sea ;vater and processed wtthin l18 hours. Processing involved removing the clam from the shell and preserving it in formalin. A small block 1vas later dissected from a stand- ard location in the lower part of the foot 1vhere the gonad was located. The tissue blocks were 1mshecl overnight in water, dehydrated 1vith alcohol, and infiltrated 1vith paraffin. From the paraffin they were poured into molds and sectioned at seven microns. The sections were mounted on slides and stained 1vi th eosin and hematoxylin. The slides were examined and categorized as to the degree of gonadal maturity, follow- ing a classification modified from Ropes, et al. (1965). This classification called the female gonad inactive if the fol- licles were collapsed and had no gametes in them (Figure 4), early active if small oocytes w·ere starting to be formed on the follicle \Valls (Figure 5), late active if the oocytes 28. were rounded with well developed nuclei and still attached to the follicle walls (Figure 6), mature or ripe if the major ity of the oocytes were weLl developed and lying free within the follicle (Figure 7), part spent if the follicles were partly emptied or mature oocytes (F'igure 8), and spent if the follicles were mostly empty but had residual oocytes in them (Figure 9). Hales were classified as ripe if the spermatozoa had flagella and completely filled the follicles (Figure 10), No other male stages .vere classified because of the extreme difficulties in separating the various maturation stages of the spermatozoa, 29. FIGURE 4 Female in the inactive stage, 40X magnification . . FIGURE 5 Female in the early active stage, 40X magnification 30. FIGURE 6 Female in the late active stage, ItO X magnification FIGURE 7 Female in the ripe or mature stage, 40X magnification 31. FIGURE 8 Female in the part spent stage, l10X magnification FIGURE 9 Female in the spent stage, !fOX magnification 32. FIGURE 10 Male in ripe or mature stage, 40X magnification FIGURE ll Hermaphrodite clam, 40X magnification 33. RESULTS Pismo clam females in Nonterey Bay were in the early active stage from January to July (Table 5 and Figure 12). In 1973 clams attained this stage about one month later than in 1972. Intertidal clams at Nanresa reached this stage one month earlier than clams at Noss Landing and the subtidal clams at Noss Landing stayed in this stage one month longer than the clams at the other two localities. The late active stage of females ;vas attained in the period from March to July, and the number of clams in this stage reached a maximum between April and June (Figure 13) . This stage was reached one month later in 1973 than in 1972. The intertidal clams at Manresa reached this stage first, followed by subtidal clams from Noss Landing one month later. The :r;ipe stage of females was found from Jvlay to Sep tember (Figure 111). Clams at Jvloss Landing reached this stage one month later in 1973 than in 1972. Clams at Jvlanresa de veloped into the ripe stage in Hay of both years. Subtidal clams at Noss Landing reached this stage one month later than intertidal clams from Noss Landing or Nanresa. Inter tidal clams at Nanresa and subtidal clams at Pismo Beach developed into the ripe stage one month earlier than inter tidal or subtidal clams at Noss Landing. crhe part spent stage (Figure 15) was important be- cause it indicated onset of spawning. It ;vas difficult to 34. distinguish between .this stage and the late active stage be cause in both these stages the follicles were not completely full of gametes. There 1vas a possibility that some errors 1vere made, but most of the determinations 1vere certainly correct. Most of the clams in the partially spent stage were found from Hay to December, but the greatest numbers occurred in this stage from June to September (Figure 15). Some female clams were in the spent stage throughout the year, but this stage was dominant in the period from October to December (Figure 16). The few ova that remained in some of the females were usually completely resorbed by April. The exception was the subtidal clams from Moss Land ing. In these clams the ova persisted longer and in a few cases. ova were found in individuals that were in the early stage of gametogenesis. The inactive stage of females dominated from December to Harch, but some individuals were in this stage from October .to Nay (Figure 17). The ripe stage of males dominated from April to Sep tember, just as it did in the females (Figure 18). In order to correlate the gonal cycle of the Pismo clam and both temperature and food data, temperature, chloro phyll a, phaeo-pigment and stage of gonadal maturity data were compiled on a monthly lJasis (Table 8). Chlorophyll a has been used as an indicator of phytoplankton standing crop and phaeo-pigment could be an indication of phytoplankton --- 35. detritus (Lorenzen, i967). From a total of 286 clams, 142 Here male and lllil Here female (Figure 19). The small clams ( the large clams () lt4 mm in length) had a sex ratio that Has not significantly different from 1:1 (Chi square, .50> P> .30) suggesting that these clams Here not protandric. Most of the clams first developed ripe gametes and hence reached maturity at 20 !Iilli in length (Figure 19) ; hoH ever, one female clam reachecl maturity at 13 mm. Three hermaphrodites (less than 1%, Figure ll) Here found during the study, but it must be emphasized that they Hete not specifically looked for. Only a small block of gonad tissue Has dissected from the foot as in all the other clams. A complete cross-section of the foot Hould have to be examined to adequately check for hermaphroditism since usually only a feH follicles are of the opposite sex (Coe, 19117). TABLE 5 NilllBERS OF CLAHS IN EACH STAGE OF GONADAL HATURITY 1971 1972 1973 N D J F H A H J J A s 0 N D J F H A H J J A s 0 Hanresa Intertidal Inactive 5 14 10 2 1 3 3 16 20 14 2 2 3 Early active 1 10 7 6 1 3 9 8 Late active 2 4 4 5 7 1 Ripe 6 5 7 6 5 2 7 5 5 1 Part spent 1 1 4 5 8 2 1 6 1 4 12 3 Spent 7 4 5 1 1 1 6 8 2 7 Hales 8 1 3 10 10 16 9 15 7 9 511 7 1 9 5 10 4 14 11 7 7 Total 20 20 19 20 20 20 20 20 18 20 20 20 20 20 20 17 20 20 19 18 ' 20 20 20 20 Hoss Landing Intertidal Inactive 10 4 3 11 13 15 13 11 1 Early active 4 8 4 3 6 5 1 Late active 2 5 1 4 Ripe 5 14 2 10 8 2 3 7 3 Part spent 3 2 5 2 1 1 9 1 6 13 5 Spent 1 2 6 3 5 4 5 1 2 Hales 5 8 14 6 5 15 8 5 7 5 2 1 2 3 13 12 8 12 11 611 Total 20 20 20 19 19 20 20 20 18 20 20 20 20 20 20 20 20 20 20 20 18 '-'' 0'\ FIGURE 12 PER CENT Ol' FEHALES IN EARLY ACTIVE STAGE PERCENT OF FEMALES IN EARLY ACTIVE STAGE 100, Manressa --- Mc.ss Landing (intertidal) -- Moss Lending ( subtidiJI) - ~ - Pismo Beach (\ 'I \ 80 f- 1\ ,, I\ ,1, \ \ I I \ I \ ' I I Ji I \ II I I 60 1- I I if I I I I \ '( I I I I I \ 0/o I I : I I I I I I I I \ I I I I ,' I I 401- I I \ I I I I I I I I \ I I I / I I \ I I I I I I I 'I \ 20 1- I I I ,' I I I I I I I I I I I \ \ \1 A b) \ ~ \ \\ \-~ 0 ·--.! N D J F M A M J J A s 0 N D J F M A M J J A s 0 -1971 1972 . 1973 FIGURE 13 PER CENT OF FEHALES IN LATE ACTIVE STAGE PERCENT OF FEMALES IN LATE ACTIVE STAGE 100 Monressa --- Moss Landing {inlertidal) -- -- Moss Landing {subtidal) 80 - ~ - Pismo Beach . GO o/o 1, I ~·~ I \ 40 II I \ "I I d \ I ll 11 \ I I \ 20 I I I I I 1\ I I II / .I \\ \ \ 1\ I I I I 0 ·I I I . I V1 I ' m N D J F M A M J J A S 0 N D J F M A M J J A S 0 N -1971 1972 1973 ------FIGURE 111 PER CENT OF FEHALES IN RIPE S'.rAC',E PERCENT OF FEMALES IN RIPE STAGE roo Monressa - -- Moss Landing (intertidal) I -- Moss LondinQ (subtidal) 1 1 1 I - • - Pismo Beach d\ \ A 80 I'II' I ,''I r/\1 : I ~ II 'II' I I 60 il 1\ ~ \ '\ \' I I 1 1 11 / \' I I .1 I I 0/o 1 '1\\ 1 I I il \\ 1 1\\ I \I 40 'I l\ 1 \' 'I .\I I I I '1 .1'1 I I I I I ~\ 1 I I I I \' :1 \ \i I / I I I ~ ,- --'I \ ~~ I 20 I I I I \ I I ·\.\ I I I I I I I I ;, . I I ·.___,, 'I I \1 I I I~ I !/ o~.--..-.--.--.-~~r-.--+--.-.--1--~-.--.-.--.--~-+r-.-.--.--.-~-, '-" '.0 N D J F M A M J J A S 0 N D J F M A M J J A S 0 ~ -1971 1972 1973------FIGURE 15 PER CENT OF' F'E"l~LES IN PART SPENT STAGE PERCENT OF FEMALES 11\J PART SPENT STAGE 100 Manressa Moss LandimJ (intertidal) Moss Landing (subtidal) - · - Pismo Beach 80 I I I) ,, j~ I I /1 •\ ·1,1 ~~~ 60 I' I I 1,,. . I I I • 1 C:'o 1; \ ; \ I ( I I, J, ' n ' ' i I·1 ' \ I 40 I' I I I ' I • / ' I . I \ I i I 'i II \ ) I I" \ I . I 'I i I' I ! \ I I I' ' I I I I I ' I .'I ',· 1 20 I, I \, I I' ',1 1 \ I ·I" 1 0 I'1 ' I ' I I I • I I lo \ I I • I I ~ NDJFMAMJJAS ONDJ FMAMJ JASON 0 -1971 1972 1973------• FIGURE 16 PER CENT OF FEHALES IN THE SPENT STAGE l l. I • z ·-· ·- ·-·- . - =::--;=-:::-~_--·- . '-'\.. '<( ..., t "") 0 g~------~~g~--~--~-:g~----:---~0~------:------__j~ v 0C\J FIGUTIE 17 PE!l CENT OF PISHO CLANS IN INACTIVE STAGE PERCENT OF PISMO CLAMS IN INACTIVE STAGE !00 Monresso --- Moss Landin!J {intertidal) - -- Moss Landin9 (subtidal) - • - Pismo Beach I 80 I ...... _._ I f\ I ' I I I \ 1/ I 60 \ ' I A ' I 0/o ,\ II I 1\ /1 I I 40 1\ '\ I I I I ,\ \\ I I 'II . '\I I j I II 20 1\ I I '\ \\ 1\ //; \ ' OL--,-,--.--r--r-~~--.--r~,-~~--.--r~r-,--.--.-~-4,-,--.--~-.-, NDJFMAMJJASONDJ FMAM.JJ A S 0 N ..,. I\:> -1971 1972 1973------FIGUTIE 18 PER. CENT OF HALES IN HIPE STAGE PERCENT MALES IN RIPE STAGE Manressa --- Moss Landing G!lterti:laD 100 r r-n1 ~ --Moss Land inc SIZE OF I<'EMALE, ~l~LE AND HINATURE PISMO CLAHS SIZE OF FEMALE, MALE, AND IMMATURE PISMO CLAMS Females= 144 Males= 142 (f) :2' -' u"' ~ l lmm""" ~: Jiil :> Q0 z 0 j f I l I I l 0 20 40 60 80 100 120 140 160 ..,. LENGTH {mm.) TABLE 6 TENPERATURE, CHLOROPHYLL a, PHAEO-PlG}lENT AND STAGE OF GONADAL NATURITY IN NONTEREY BAY Hean, Standard Stage of Deviation, and Range of Gonadal Sources of TemEerature Data All Temperature Data Chlorophl11 a PhaeoEigments Haturity Std. 1 2 3 4 5 6 7 Nean Dev. Range Nean Range Nean Range Jan -- 10.67 10.55 11.96 13.7 10.5 10.6 11.33 1.29 10.5-11.96 9.42 5.1-15.2 12.34 5.7-22.4 Feb 10.8 11.64 11.66 13.65 15.2 11.6 11.4 10.74 1.48 10.8-15.2 8.04 1.1-16.4 6.76 1. 2-12.6 t'j Har 11.0 12.09 12.04 11.98 14.7 12.5 11.7 12.28 1.16 11.0-14.7 35.74 22.3-49.0 36.08 18.1-49.4 :»r;--" " ,.... t" rt '¢> " Apr 10.8 11.94 11.01 13.86 -- 12.8 11.6 12.00 1.15 10.8-13.86 46.42 35.9-56.8 41.43 28.2-52.2 t-'· ["l rt ~ rt (D (D t-'· Nay 12.0 12.81 12.02 13.63 15.8 12.5 11.9 12.95 1.40 12.0-15.8 34.18 20.8-52.2 35.98 18.4-79.5 ~ ---ro Jun 13.9 14.42 13.33 12.79 16.7 13.4 12.4 13.84 1.43 12.4-16.7 53.58 20.7-81.8 63.76 21.2-100.2 Ju1 13.6 15.64 14.85 17.39 16.6 15.9 14.5 15.49 1.30 13.6-17.39 12.58 9.5-18.7 13.04 3.5-19.0 i"!.UJ~"' 'd 'd rt (D (D Aug 15.4 15.14 14.37 15.60 16.3 15.3 14.2 15.18 .93 14.2-16.3 10.48 8.6-13.5 11.28 9.3-14.9 ::l rt Sep 15.0 14.97 14.04 14.40 16.4 14.9 14.1 14.84 .81 14.04-16.4 64.98 39.6-94.7 23.36 21.6-25.3--UJ 'd Oct 12.3 16.09 15.83 17.29 15.7 15.5 15.4 15.44 1.53 12.3-17.29 10.16 3.5-20.8 5.24 1. 6- 8. 9 (D ::l Nov 12.2 13.54 13.60 -- -- 13.8 13.4 13.30 .62 12.2-13.8 4.44 1.3-7.4 2.66 1.8- 4.3 rt Dec 10.0 11.63 11.42 -- -- 12.4 12.6 11.62 1.10 10.0-12.6 9.82 3.6-15.6 2.56 1.9 3.1 -"" Vl 46. Sources of cl'emperattire Data Given in Table 6: l. Smethie ( 1973) - means of monthly temperatures talcen in the upper 10 meters of water at four stations in northern ~Iontcrey Bay (1150, 1153, 1154, 1159) in 1971-1972. 2. Droenkow and Benz (1973) -means of monthly surface temperatures taken at Jive stations in northern Nont ercy llay (1101, no::;, 1105, 1150, 11511) in 1972-1973. ::;. Broenkow and Benz (1973) -means of monthly tempera tures at 5 meters in depth at five stations in Itorth ern Monterey Day (1101, 110::;, 1105, 1150, ll51t) in 1972-1973. 4. Kaiser Nonitoring program (unpublished) - means of monthly surface temperatures talcen at two stat:lons (Krl and Kr2) at Noss Landing in 1972-1973. 5. Data I have collected -means of monthly surface temperatures talcen at Hoss Landing ancl Jvlanresa State Beacl1 in 1973-1974. 6. Data Archives (1973) - means of daily surface tempera tures taken at North Point Lobos, California, in 1972-1973. Sources of Chlorophyll a ancl Phaeo-pigment Data: Waidelich (unpul)lishecl) - Chlorophyll a andC)Phaeo pigment data are expressed in units of mg/m~ and are means of monthly values at five stations in northern Honterey Bay (1101, 1103, 1105, 1150, 1153) taken in 1972-1973. 1t7. DISCUSSION Some spawning of Pismo clams occurred in the period Jrom .June to August at Pismo !leach and Nontoroy Day, hut the main spmming period occurred cluring Sep Lember and October. Similar x·esults were obtained by Coo (19~7) Jor Pismo clams at San Diego. This is in contrast to the late spring or summer spawning common in other members of' the f'amily Vene ridae. Ansel (1961) reported that spawning occurred in Venus orata and Venus casina in Nay, Venus fasciata f'rom February to .July, and Venus striatula in summer. Nercenaria merce naria spawned in summer (Loosanoff', 1937; Porter, 1964), Venerupis japonica and Protothaca standnia spawned in late spring (Quayle and Bourne, 1972), Venus pullastra spawned in ,June (Quayle, 1952), and Saxidomus giganteus spmmed in April and Nay (Frazer and Smith, 1928). A similar late spring or summer spmming period also has been reported f'or many other Pacific Coast bivalves in cluding Ostrea lurida (Coe, 1932), Donax gouldi (Coe, 1953), Pododesnms cepio (Leonard, 1969), Siliqua patula (Quayle and Bourne, 1972), and Clinocardium nnttalli (Quayle and Bourne, 1972). A rarer michvinter spmming period was reported f'or Nyti1us edulis (Hoare and lleish, 1969) and Nytilus calif'orn icus (Young, 19112). The common occurrence of late spring or summer spa1m ing, when the temperature was near its maximum, sug,gested that temperature may be an important factor in governing the reproductive cycle. ·Orton (1920) and Nelson (1928) first suggested that each species had a critical minimum tempera ture requirement, below 1vhich it 1vill not spa1m. That temp erature was important to the time of spmming is further indicated by Loosanorf and Davis ( 1963), 1v!to have been able to condition many bivalve species for out of season spawning at almost any time or the year. Sufficient food was found to be a necessary require ment for gametogenesis and spmming by Sastry (1966, 1968). The sources of rood for Tivela have been studied by Coe (1947), who found they are capable of digesting naked dino flagellates, small diatoms, and detritus. He found that most of the phytoplanlcton ingested 1ms not fully digested and that the principal source of nutrition was detritus. Temperature, chlorophyll a, and phaeo-pigments in creased during the months from F'ebruary to June in Honterey Bay (Table 6). If the phytoplankton pigment data are indica- tive of an increase of utilizable food for Pismo clams, the clams may use and require this increase in rood for develop ment or their gonads. 'l'hey must require substantial amounts of energy since the gonad increased from 12% of the body tissue weight in January to 28% in September (Giese, et al., 1967). Some other sources of food that were non-planktonic in origin may be important in supplying the necessary energy for gonad development, such as macro-algae detritus, but no estimates or their abundance or seasonal variations were !mown to the author: Host of the gametes were shed in September and October wbcn tl1e temperature was at its maximum and chloro~ phyll a and phaeo-pigment values reached their fall maximums. 'I'he trigger that initiated spmming could have been the in crease in food and/or temperature in the fall; however, other factors migl1t have been important such as lunar periodicity (Koringa, 1947; }!ason, 1958; Hileikovsky, 1970), or various dissolved organic substances (Galtsoff, 1961). Regardless of what factor or factors triggered spawning, it might have been advantageous for the clams to spa1m in the i'all so that their pelagic larvae would have food from the i'all phyto plankton bloom. Coe and Fitch (1950) reported that Pismo clams in Baja California have an extended spawning season in compari son to Pismo clams i'rom San Diego and Pismo Beach. They did not, however, show any restriction of their spawning season through the increase in latitude i'rom San Diego to Monterey Day. '!'he majGri.ty oi' gametes were shed in September and October at San Diego (Coe, 1947), Pismo Beach and Monterey Bay, even though Monterey Day was near the northern limit oi' their range. The temperature dii'i'erence between San Diego and Pacii'ic Grove, Calii'ornia, i'or the 1nonths oi' Septen~er and October when spawning occurs averaged 4.82° C (range 2.61 to 6.99) based on daily temperatures taken over an eighteen year period (U.S. Department oi' Coum1erce, 1956). Hence, 50. Pismo clams spmmed at different temperatures at the t~VO locaU.ons. This data suggested that there ~Vas not a single critical spmming. temperature for all populations of Pismo clams. It does not rule out, ho~Vever, that the clams may have spawned in response to the yearly maximum temperatures in all areas, which occurred in September and October. Th~ time of spawning could also be delayed in San Diego because spawning was governed by the change in temperature over the year and 1vas not dependent on any specific time of spmming. Another possible explanation may be that different popula tions of Tivela 11ere genetically adapted to spmm at differ ent temperatures as has been found to be the case with Crassostrea virginica (Loosanoff, 1969). In Nonterey Bay (Figure 19) and in San Diego (Coe, 1947), Tivela stultorum first developed mature gonads ~Vhen about 20 mm in length. Ho1vever, because of a s1o~Ver gro~Vth rate for juvenile clams in Honterey Bay in comparison ~Vith San Dieko, clams developed mature gonads their first summer in San Diego (Coe, 1947) and their second summer in Honterey. This rapid maturity ~Vas in contrast ~Vith other Pacific Coast bivalves such as Saxidomus giganteus which matured at 40 mm when it ~Vas from three to five years of age, and from Clino cardium nuttalli ~Vhich matured at 110 nun at tHo years of age (Quayle and Bourne, 1972). Pismo clams were first thought to be hermaphroditic by 1veymouth ( 1923), but Coe ( l9LJ7) later cletcrminerl that 51. they were dioecious"with less than one per cent hermaphro ditic. In samples from Monterey Bay and Pismo Beach less than 011e percent were hermaphroditic. Small percentages of hermaphrodites are probably not uncommon in dioccious bivalves (Loosanoff, 1936; !lopes, 1966). '!'he sex ratio of Pismo cloms in Monterey Bay was not significantly different from l: l in large ( ) !Jll mm in length) and small ( < !JIJ mm in length) clams. I11 adult clams in San Diego, Coe (1947) found a sex rat:Lo for adult clams of 180 females to 1119 males ~Vhich ~Vas more nearly significantly different from a l:l ratio (Chi square, . l > P > . 0 4) . 52. CONCLUSIONS (}ametogenesis started in February and a majority of clams 1mre ripe in Nay or June. They remained in this stage throughout the summer ~Vi til some partial spmming. Complete spawning occttrred mainly during Septe~1er and October in Monterey Day and Pismo Beach. Clams reached the ripe stags earliest at Nanresa Beach and Pismo Beach and latest at the subtidal Moss Landing station. Intertidal Noss Landing clams reached the ripe stage at an intermediate time. (}ametogen esis and time of spmming may be correlated with temperature and phytoplanlcton abundance in Nonterey Bay. The sex ratio for large and small clams did not differ significantly from 1:1. Clams matured at 20 mm in Nonterey Bay and San Diego, lmt because of slo~Ver growth rates for young clams at Monterey Bay, they developed ripe gonacls a year later than clams in San Diego. 53. LI'l'ERATU!lE CI'l'ED Anonymous. '1973. Surf-ace water temperatures. Scripps In stitute of Oceanography. Ansell, A. D. 1961. Heproduction, growth and mortality of Venus striatula (da Costa) in Kames Bay, Millport. J. ~lar. Biol. Assn. U.K. 41:191-215. Baxter, J. 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