Page 30 Vol. 6; Supplement THE VELIGER LITERATURE CITED provided by the papillae and the highly vascularized nature of these papillae. HARRISON, F M. 1961. Some excretory processes in the abalone Haliotis ruf¬ SUMMARY escens. Journ. Exp. Biol. 39 179-192 LEVINSON & MACFATE 1. Tests were performed on the snails, Tegula funebralis 1951. Clinical laboratory diagnosis. 4th ed.; pp. 1 - 1146. and T. brunnea, to determine the nature and quantity of Lea & Febiger, Philadelphia their excretory products and the organs of excretion. NEEDHAM, J. 2. Standard colorimetric assays were used on homo- Problems of nitrogen catabolism in invertebrates, II. 1935. genates prepared from the ctenidium, digestive gland, Correlations between uricotelic metabolism and habitat in the right and left kidneys. Total non-protein nitrogen, ammo¬ phylum Mollusca. Biochem. Journ. 29: 238-251 nia, urea, and uric acid were determined. PICKEN, L. E. R. 3. Uric acid was observed to be the major excretory 1937. The mechanism of urine formation in invertebrates. II. product of these snails. It accounted for 11.8% to 76.6% The excretory mechanism of certain Mollusca. Journ. Exp. of the total non-protein nitrogen in the right kidneys, the Biol. 14: 20 -34 only organs where this waste product was detectable. TODD, SANFORD & STILWELL Only slight traces of ammonia were found in the digestive 1948. Clinical diagnosis by laboratory methods. 11th ed. gland, and no urea was present in the tissues tested. W. B. Saunders Co.; i -xi + 954 pp. The Distribution and Movement of Tegula funebralis in the Intertidal Region of Monterey Bay, California (Mollusca : Gastropoda) WILLIAM M. WARA AND BENJAMIN B. WRIGHT Hopkins Marine Station of Stanford University, Pacific Grove, California (9 Text figures) INTRODUCTION tigated Tegula funebralis' intertidal distribution and move¬ ment patterns in relation to certain biological and physical Tegula funebralis (A. ADAMS, 1854) is very common environmental factors. Before investigating movement pat- along the west coast of California, although little work terns, we wanted an accurate, correlatable distribution has been done on its intertidal distribution. Hewatt (1934) analysis for several areas along Mussel Point, Pacific describes its distribution as between the plus one and plus Grove, California. To do this, we collected information five foot level above mean lower low water. Ricketts and pertaining to numbers and size classes of this snail along Calvin (1962, pp. 352-355) put the population center at with environmental data of the areas, such as vertical level the three foot tide level. Neither reference describes the of collection, algal covering, area configuration, substra¬ distribution extent along the intertidal region. We inves- tum, and wave and current action. Factors that seem to Page 31 Vol. 6; Supplement THE VELIGER resulted in an overall movement pattern which, when com- affect the distribution were then checked by exposing pared with that of other populations, gave information on marked populations to these various conditions and ob¬ the effectiveness of certain factors in influencing popula- serving the movements of the snails. tion distribution. METHODOLOGY POPULATION DISTRIBUTION We selected five areas along Mussel Point, each, as de- Area A is a rocky, open coastline with a heavy algal scribed below, representing a different environmental con- covering. It has no current movement though the outer dition. In each area we marked the exact water level at rocks facing seawards receive heavy wave action. low tide on a very calm day to give correlatable marks, Area B is a rocky, open coastline without an algal cover- whose height was then determined by use of existing ing. It has no current movement though the entire profile benchmarks. At low tide a transect two meters wide was receives the heaviest wave action of all five areas. Mussels extended from shore to the minus two foot tide level in and barnacles almost entirely cover the rock surfaces below each area, and every Tegula funebralis within the transect was counted and measured for the largest basal diameter the plus three foot tidal level, and all Tegula funebralis are found among these animals. of the shell from the lip to the edge of the opposite side. Area C is a semi-protected area with a heavy algal cover- In order to investigate the movement patterns of Tegula ing. The area has a light current flowing through it with a funebralis, we put marked populations into areas which best represented the factor being tested and compared moderate wave surge. Area D is a semi-protected area with a heavy algal cov¬ their movements with the movements of control groups ir ering. There is usually a moderate current flowing through areas where the factor did not exist. A periodic positior it with a moderate wave surge, although the inner third plot of the individuals within the population over time NUMBER OF SNAILS /ME MEAN SIZE (MM.) 1000 (1400) 800 22 SIZE 600 400 200 NUMBERS METERS FROM 6 FT. TIDE LEVEL HEIGHT (FT.) 2 Rock YSHELL FRAGMENTS ROCKS ROCKS AND SHELL FRAGMENTS Endoclodig Gigartino 2(-) - Rolfsio Iridaea — —Lithothamnion 94 00 02000 % Tegulo funebralis with Acmoeo asmi Figure 1: Distribution in numbers and size classes of Tegula funebralis in Area A Vol. 6; Supplement THE VELIGER Page 32 NUMBER OF SNAILS /ME MEAN SIZE (MM.) 221 300 200 S12E 100 NUMBER —10 METERS FROM 6 FT. TIDE LEVEL HEIGHT (FT.) LARGE ROCKS LONG ROCKY CREVICE ROCKY POOL Ralfsia Lithothamnion ooooo- % Tegula funebralis with Acmaea asmi Figure 2: Distribution in numbers and size classes of Tegula funebralis in Area B of this profile has relatively quiet water. pends to some extent on the amount of open rock surface Area E is a protected area with a sparse algal covering. available. Rocky areas which have little algal covering have a larger number of snails on them than a heavily cov¬ It has no current movement and little wave surge. Pools in this area are very crowded at low tide and some of the ered rocky area. The reason for this distribution may be Tegula funebralis move about on the fine sand bottom of that rock surfaces provide the main food source for their the pools. Only in these pools were the snails found to be grazing. Two notable exceptions are found, one in Area C grazing on dead algae, periodically cast up at high tide. at the twenty-eight meter mark (Fig. 3) where outer rocks In all five areas Tegula tends to be clumped in places are washed by heavy surge, reducing the density of snails that have a sparse algal covering and usually is dispersed in this area, and the other in Area D at the fifteen meter in areas of dense coverage. mark (Fig. 5) where a shell fragment substrate decreases the population density. DISCUSSION AND CONCLUSIONS The mean size of the animals increases with the degree (Distribution) of algal covering. The larger snails are found in the heavy algal covering more often than in protected crevices. THE COLLECTING of Tegula funebralis was done at low Moderate current does not affect the Tegula funebralis tide; small irregularities in population numbers due to sub¬ distribution, as the higher densities found along rock faces strate irregularities smooth out at high tide when the bordering the channel in Area D at thirty-eight meters snails disperse from their clumps in the crevices. In plotting are similar to the densities found shoreward at four meters their distribution in relation to certain environmental in quiet water (Fig. 5). factors, we found relationships which indicate that certain Population densities are reduced in areas of heavy wa¬ biological and physical factors may control population ter turbulence. Area B with its heavy surf is relatively distribution. barren of Tegula funebralis (Fig. 2). The outer rocks in The population density decreases as the amount of algal Area C which receive heavy wave action are also sparsely covering increases, indicating that population density de¬ Vol. 6; Supplement Page 33 THE VELIGER MEAN SIZE (MM.) 25 [NUMBER OF SNAILS /ME SIZE 300 200 NUMBERS 25 METERS FROM 6FT. TIDE LEVEL HEIGHT (FT.) PROCK OUTCROP ROCKS AND SHELL 2 SAND LARGE ROCKS FRAGMENTS Felvetia o Endoclodio Endocladig Gigartina — —Rolfsio 2(-) Tridgea — Lithothamnion 0 40 40 40 40 % Tegula funebrolis with Acmded asmi Figure 3: Distribution in numbers and size classes of Tegula funebralis in Area C populated, while similar areas closer to shore in calmer decreases with increase in the vertical height along the water have higher densities of snails (Fig. 3). transects with the largest snails rarely found at the sea¬ Vertical height clearly affects the population density ward edge of the transect (Fig. 7). quite aside from the maximum height of zero feet and POPULATION MOVEMENTS plus six feet (Fig. 8). Between these limits similar heights in different places show different numbers of in- Population I (marked in the size classes 0-15 mm, 15-20 dividuals as found in Area A between seven and sixteen mm, and over 20 mm), was placed in Area D on outer meters from shore (Fig. 1), in Area C between eleven rocks at the plus two foot tidal level. Water at high tide and twenty-five meters (Fig. 3), and in Area D (Fig. 5) was turbulent with little current movement. This popula¬ Different vertical heights having similar population den¬ tion was plotted for fifteen days (Fig. 9). sities are found in Area C twelve and twenty-seven meters Population II (marked as in Population I), was placed from shore, in area D between forty-two and fifty-four in Area D on inner rocks at the plus three foot tidal meters, and in Area D between forty-two and fifty-four level. Water at high tide was calm without current move- meters, and in Area E between five and nine meters (Fig ment. This population was plotted for 19 days (Fig. 9), 4). The greatest population density is at the plus two to Population III was placed in Area D at the plus three four foot tidal level (Fig. 8). The mean size of animals foot tidal level on an outer rock face bordering the current Vol. 6; Supplement Page 34 THE VELIGER NUMBER OF SNAILS /M 400 MEAN SIZE (MM.) 300 200 NUMBERS 100 SIZE 13 25 20 METERS FROM 6 FT. TIDE LEVEL 4 HEIGHT (FT.) ROCKS ROCK ROCKS AND ROCKS SANOT SACHE SAND ROCKS AND SAND Endocladio Gigartino Ralfsia 48796oaooaooo % Tegula funebrolis with Acmoea asmi Figure 4: Distribution in numbers and size classes of Tegula funebralis in Area E (*sandy beach extends shoreward eleven meters to the plus six foot level) channel. At high tide a moderate current runs through moved down; all snails moved down at the first light of this channel. This population was plotted for fourteen dawn. On nights of heavy wave surge the numbers on days. After the first fourteen day study was completed. the rock tops were one tenth those normally found on the Population III was placed in the current channel at the rocks for dark nights. This vertical movement was noted minus one foot tidal level, directly out from the point of at many places along Mussel Point. its original placement and was found after five days to Population V (two groups, one taken from the zero to have dispersed much as on the fifth day of the first period plus one foot level and the other from the plus four to (Fig. 9). five foot level) was marked and placed at the plus two Population IV, clustered under three rocks at the plus foot level in a crevice of a rock outcrop. The rocks extend four foot tidal level, was marked and its vertical move¬ from a sandy substrate at zero feet to plus seven feet. The ment was followed during rising and falling tides over two groups, plotted for fourteen days, showed no vertical periods of 24 hours. During daylight hours at high tide, or horizontal separation. However, sixteen individuals the population remained beneath the rocks with individ¬ were found beyond four meters down current and only uals rarely on rock tops. At night during high tides the nine beyond this distance up current. population moved to the rock tops in large numbers. They DISCUSSION AND CONCLUSIONS moved up as soon after twilight as the tide permitted, in numbers dependent on the intensity of the moonlight. (Movement) On bright moonlit nights the density on rock tops was Tegula funebralis moves up to rock tops during the night half that found during dark overcast nights. During the high tide, but not during the daylight high tides. The low tide periods at night about four-fifths of the snails Page 35 Vol. 6; Supplement THE VELIGER NUMBER OF SNAILS /ME 000 (1200) MEAN SIZE (MM.) 800 600 SIZE 400 200 NUMSERS 62 42 TERS FROM GET TIDE LEVEL HEIGHT (FT.) ROCK OUTCROP ROCKY CREVICE ROCkS SHELL FRAGUENTS SHELI FRAGMENTS Pelvetia SAND Endocladia Gigartino Ralfsig — 2(-) — — ridaea 00 4.9 8.5 7.7 100 % Tegula funebralis with Acmaea asmi Figure 5: Distribution in numbers and size classes of Tegula funebralis in Area D As shown by the movement of Population V, there upward movement seems to be light-dependent with the seems to be no vertical specificity for Tegula funebralis threshold level inhibiting this movement at the light in- but a random dispersal. tensity of the full moon. The movements of Tegula funebralis do not appear to Tegula funebralis movements seem to be directed by differ with size; the three size classes were intermixed water current to some extent, as slightly more of the in throughout the dispersal of Populations I and II. dividuals in Populations III and V were found down current than up current. Page 36 250 NONSER 200 150 100 TOTAL OF ALL FIVE AREAS 50 OO NUMBER AREA O AREA E 20 AREA B S0 NUMBER AREA A 40 a 20 2 16 20 24 28 S12E (M4.) Figure 6: The relationship between numbers of animals and size classes for each of the five areas plus a total for all five areas LITERATURE CITED HEWATT, W. G. 1934. Ecological studies on selected marine intertidal commun¬ ities of Monterey Bay. unpubl. Ph. D. Thesis, Stanford Univ. Stanford, California. RICKETTS, EDWARD F., & JACK CALVIN 1962. Between Pacific tides. 3rd. Ed. Stanford Univ. Press, xi + 518 pp.; Stanford, Calif. THE VELIGER Vol. 6; Supplement SIZE MEAN (MM.) 24 21 5 2 3 HEIGHT (ET) Figure 7: The range, standard deviation, and mean of Tegula funebralis shell size. At each depth the vertical line indicates the total range; the broad portion of the line indicates that ninety-five percent of the individuals fall within this range (2 g); the crossbar indicates the mean NUMBERS 400 300 200 100 L HEIGHT (ET.) Figure 8: The number of Tegula funebralis per square meter found at each vertical height level above mean lower low water 0 Vol. 6; Supplement THE VELIGER POPULATION T POPULATION II POPULATION III SEAWARO SEAWARO SAwARO KOcK Wders CURREN 02 eu au e 220 sHel Bocks s FRAGMENT SUE STRATE Dat DAV Dar Dar dar DAY L DAY 15 DAY 19 DAY 14 Figure 9: The redistribution of Tegula funebralis populations over various time periods. At Day 1 populations were placed in the center of the concentric circles Page 37