0 14 DIEL MIGRATION AND RESPONSE TO TURBULENCE IN THE HIGH INTERTIDAL GASTROPOD LITTORINA SCUTULATA (GOULD 1849) JOSEPH W. MCCOY, JR. HOPKINS MARINE STATION STANFORD UNIVERSIT JUNE 1977 ITRODUCTION The small gastropod Littorina scutulata (Gould 1949), is a conspicuous inhabitant of the upper intertidal zone of the West Coast of the United States. Minimal research has been done on its short-term behavior patterns. The only significant works address differential rates of migration in animals of different sizes (Chow, 1975), and migration up or down with the tidal cycle (Glynn, 1965). Preliminary observations of Littorina scutulata in the field at Mussel Point, Pacific Grove, California suggested further study of migration patterns would be desirable. A tendency to move up and out of the high tide pools around dusk, and a tendency to move downward with approaching dawn, were noted. The questions arose, does the L. scutulata population undergo a diurnal migration, and if so how consistent is it, and with what environmental changes are movements correlated? The purpose of this study was to provide data answering these questions. MATERIALS AND METHODS A study site was chosen near the western tip of Mussel Point, on the grounds of Hopkins Marine Station, Pacific Grove, California. The two pools studied were located in a region exposed to strong wave action, but high enough in the intertidal zone (three to four feet above the Balanus-Endocladia belt: see Glynn, 1965) so that high tides and rough surf were necessary for sig- nificant water exchange. A large granite plateau, sloping from the sea, provided a permanent basin for the two pools. Pool #1, the larger pool, was situated furthest from the sea, having the gradually sloping plateau as a bottom. The much smaller Pool #2, positioned very near the seaward edge of the granite plateau, occupied a small depression on the sloping granite surface (see fig. 1). Pool f2 was more frequently disturbed by wave action, and appeared to be a less extreme environment than Pool fl, which was situated at the highest level occupied by L. scutulata. A square wooden quadrat frame (lmx 1m) subdivided into 100 10 x 10cm squares with nylon line was placed about one inch above Pool l in an open area with a gradual slope (see fig. 1). This Quadrat (#1) was positioned so the border line between the third and fourth rows of squares corresponded roughly to the normal water level. An observer could look down over the grid and count the number of snails within each square. Snail counts were made at various times and under various conditions during 24 hour diel cycles and 25 hour tidal cycles, paying particular attention to periods of significant environmental change (eg. dawn, dusk, higher high tide, etc.). A contour map of the quadrat l area was made by measuring depths within each 10 x 10cm square with a ruler (fig. 2), and an average depth for each square calculated (fig. 3). For the smaller pool (Pool #2), the rough terrain prevented the use of a simple quadrat frame. In early experimentation counts were made only of animals in and out of water, and in crevices. For later studies a trans¬ parent plexiglass overlay was cut to fit the pool and surrounding edges, and divided into 4cm x Acm squares. By looking down upon this quadrat (42) snail counts within each square could be made. A contour map was also made for Pool #2 (see fig. 4), and an average depth for each square calculated (see fig. 5). Various environmental parameters were monitored during one or more of the experiments. Initially the Winkler titration method (Carrit and Carpenter, 1966) was used to determine dissolved oxygen concentrations within the tide pools. This method proved unsatisfactory for extended field study and therefore a portable oxygen meter and electrode were later employed (Yellow Springs Instrument Co. model #54). A LI-COR photometer (model LI-185) was used to measure light intensities throughout the diurnal cycle. The salinity of the tide pools was measured using an American Optical Co. refractometer. Temperatures were recorded by a Weather Measure mercury thermometer. I. DIEL MOVEMENTS To study L. scutulata's migration during the diel cycle, one observation was carried out on Pool fl; the results are shown in figure 6. Three additional experiments were carried out on Pool #2. The results for these experiments (f2-4) are presented in figures 7-9. Figure +6 shows that L. scutulata was engaging in a migration correlating with the diel cycle. In the transition from afternoon to darkness (5:30 PM-8:00 PM) a noticeable upward migration of L. scutulata occurred. Note the decrease in population in the 4-7cm depth range and the corresponding increase in animals in the 0-3cm depth range. A reciprocal migration downward in the transition from darkness to dawn is not clear from these data. Pool l was situated in L. scutulata's uppermost intertidal range, and for this reason atypical behavior of its inhabitants was suspected. Pool f2 was used in all further experiments. The results of experiment #2 (see fig. #7) show a definite shift in population upward and out of the pool during the transition from day to night. This migration correlates reasonably well with the temperature curve. the temperature decreasing abruptly with the onset of dark- ness as the snails move upward. The increase in temperature at dawn is considerably more gradual, and the correlation with the snail's downward migration less distinct. The high tides at this date occurred near dawn and dusk. Does the tidal cycle itself influence L. scutulata's migration? If it does, a bimodal curve might be expected, with upwardmove- ment accompanying the two high tides and downward movement accompanying the two low tides as reported by Glynn (1965). However, the migration data show no downward migration at the high low tide at 12:45 AM, and a downward migration at the low high tide 6:30 AM, while there was an upward move- ment at the high-high tide the preceding evening. Experiment #3 results were gathered using a plexiglass overlay. The population (see fig. 8) migrated downward with approaching dawn, as is evident in the population changes at the 1-2cm depth range and the 3-Acm depth range; the snails were already in their normal position by 5:00 PM the previous evening. Snail movements show some correlation with changes in temperature and oxygen concentration. However, the observations were preceded by rough seas, high tides, and considerable flooding of Pool #2. Wave splash into Pool #2 also occurred during the period 8:00 PM tol midnight of the first day, which may have inhibited normal migratory behavior. Experiment 4 was similar to #3 except that very little flooding of Pool +2 preceded the observations and no splash occurred during the experiment itself. The population (see fig. 9) shows a very obvious migration upward at dusk and downward at dawn. Note particularly the progressive con- centration of the snail population in the 0-2cm depth range at nightfall, and the significant shift downward in the early morning hours. This migration, once again, parallels fluctuations in light intensity, oxygen concentration, and tidal levels. The foregoing observations show that numerous pool- dwelling L. scutulata migrate upward in the evening and downward at dawn, a movement correlated well with the light regime as well as other physical parameters that vary accordingly. Any correlation between tidal cycle (semi¬ diurnal) and the snail's migration pattern (diurnal) seems to be coincidental. II. RESPONSE TO TURBULENCE To separate the effects of turbulence and water ex- change from those of other factors that might influence the diel cycle of movement in L. scutulata, an experiment was performed. At a high tide period on May 19, 1:30 PM, arti- ficial turbulence was induced by flooding Pool #2 with approximately one quart of fresh seawater every 30 seconds. dumped in from the seaward side. In this attempt to simulate natural water exchange, the distribution of the snail pop- ulation was recorded every half hour for three hours. The results for this experiment (45) are shown in figures 10 and 11. The snails show a marked migration from the O-2cm depth range to the greatest depths of Pool #2, which correlates well with the continual artificial turbulence. The major pathways of migration are schematically represented in figure 11. Note the population is concentrated at very shallow depths at 1:30 PM and shifts to the greatest depths by 4:00 PM. This migration is particularly significant since no major migration of L. scutulata was ever seen in the early afternoon under normal conditions. Other changing environmental parameters correlated with snail movements here might possibly influence snail behavior, Salinity decreases from 45%0 to 35 %0, and there is a similar drop in temperature (160 to 11°0.). Oxygen con¬ centration decreased from 15.9 ppm to 11.2 ppm. These parameters may be important especially when considering that most snails are normally submerged at 1:30 PM in the afternoon. The migration of L. scutulata into the more protected region of the pool with increased turbulence and related effects in experiment #5 may be of selective advantage. It would help the snails avoid displacement by wave action to an environment not suited for L. scutulata. SUMMARY 1. Studies of diel cycles of migration and of responses to turbulence were made on the marine snail Littorina scutulata at Pacific Grove, California. 2. Snail populations in pools undergo an upward migration correlating well with approaching darkness and a reciprocal downward migration correlating with dawn. Some other physical parameters fluctuate with the light cycle (e.g. oxygen concentration, temperature, etc.) and these might also influence the migration. 4. A migration of snails to the depths of a tide pool subjected experimentally to turbulence was noted. This response may be of adaptive advantage in avoiding displacement in unfavorable situations. ACKNOWLEDGEMENT! I would like to thank Dr. D.P. Abbott for his inspriation, enthusiasm and in aluable assistance. In addition, I would like to extend thanks to Dr. Robin Burnett for his time and assistance. TERATURE CITED . .. - Glynn, P.W. "Community, Composition, Structure of the Endocladia-Balanus Association in Monterey Bay, " Beaufortia 12: 1-198 1965. Calif Chow, V. "The Importance of Size in the Intertidal Distribution of Littorina scutulata" Veliger 18 pp. 69-78 1975. Carritt and Carpenter "Comparison and Evaluation of Currently Employed Modifications of the Wimkler Method for Determining Dissolved Oxygen Concentration In Seawater" Journal Marine Research 24 (3) pp. 286-289 1966. GUR SOINO PLATEAU 2 200 ANOS OA RE — 8 Fot 8 2 11 N t - S — — BA — S — — oo — —7. + 2 AING i S EMERGENEROCS LARGE + E 8 + EIGURE 8 8 — — X 2 2 S AP D O 9 Se He + Oer Ser Ger S —8 e A + IGURE OC — L — — 8 — — S — RE — 5 — 8 —— 0 3 L 0 50 30 123 — 50 1 50 — — — S 2 X — 8 —— 2 ) X — — — — —— — -- — A — 10. 2 A 111 N +/ — — —1— E — ——.- 1 a 1 / J -.------ U —- — 1 1 — i 0 1-. — . -... .... .. — .. — —— — —————— 1. ElGUf 1 + - —.— +1 — — . ++ IGURE 0 0 — RI- — — — H —10- 1 + — — 20 S 14 1 S +1 — 1 . —— — — e 1 — 1 S — — — + H — 5 I 0 — —— : 0 -- 8 — 14. +0 -7 I S t 7 + — — — — — + null IGURE 30 21 25 OTALROE ++ 0 + — 10 5Uf QUTOEA 8 ++ en —+ 8 S X E + —+ t 8 + S —9 —1011 /2 21 3 4 0 2- M ++ IPIEFOEDA + EGHE DARK e — LI — t + — — E S 50 5 R FIG 118 POPULATION — T TRIS IILITTE DARE LSNE — . E — + X 8 — 8 t E 0 0 804 5.30 i S HEE 8 477 ehe NOEXCHANOE SPEA 2 — — — — tt — — + i E H ok S d Ht GURE : + 9 POPULATIONTDISTRIELTON DAR + 4 44 NO 8 2 — — — S + 125 26 116H 1304 —0 I EIGURE TURB ULENCE E ATIONEDISTRIBUTIO — . S — — — E E 2 X 1 —+1 - — —9.1 — O UUE 0 2100 30 EEE JOEEDA + 0 0 NCE LUR — + — 8 — 0/ 33 H0 /00 ALIEE 0 MDE EHATURE 0 FrL +— + HCONG XVE 15. ++++ i : 119 —— — —+ L ( . tt FIGURE I. . . . . . . L . . . . * 1 . * * . . . * 0 . -. FIGURE 1-- Schematic view of experimental site: Pool l with permanent site of quadrat fl designated (100:10cmx 10cm.). Profile of perimental site on granite plateau on Mussel Point, Pacific Grove, California. c FIGURE 2-- Topographical map of Quadrat f (100:1Ocmx 10cm. squares) made from depth measurements every ten centimeters. Line of constant depth on right side of figure. Quadrat row numbers on left side of figure. Note water level at 3-4 border for experiment #l. FIGURE Average depth plot of Quadrat fl for every lOcm.x 10cm. square as calculated rom topographical map of Quadrat l (see fig. 2). Note water level at 3-4 border. 0 . .. FIGURE 4- Topographical map of Pool #2 with lines of equal depth in centimeters. Quadrat #2 (plexiglass overlay) is plotted over topographical map (4cm. x 4cm. squares). FIGURE 5-- Average depth plot of Quadrat #2 for every 4cm. x 4cm. square as calculated from topographical map of Quadrat f2 (see fig. 4). FIGURE 6-- Population distribution plot of Experiment fl April 25-26, 1977. Average depth on vertical axis for every integral depth as taken from average depth plot of Quadrat #l (see fig. 3). Time of day on horizontal axis in intervals corresponding to sampling times of above population distribution. Population densit at eight depth ranges (eg. 0-1cm., 1-2cm., etc.) plotted horizontally at corresponding depth for a specific sampling time. Qualitative light cycle plotted at top of figure. Water exchange data bar and tidal level at bottom of figure. FIGURE 7-- Population plot of Experiment #2 May 10-11, 1977. Actual snail population on vertical axis and time of day on horizontal axis. Three populations: those snails submerged at sampling time, those snails out of water and not in crevices, and those snails in crevices as calculated from total population. Qualitative light cycle, temperature plot, and tidal level plot located below figure. ... FIGURE 8-- Population distribution plot of Experiment #3 May 17-18, 1977. Average depth on vertical axis for every integral depth as taken from average depth plot of Quadrat #2 (see fig. 5). Qualitative light cycle located above figure. Water exchange data bar, light intensity plot. oxygen concentration plot, and tidal level plot located below figure. FIGURE 9-- Population distribution plot of Experiment # May 25-26, 1977. Average depth on vertical axis for every integral depth as taken from average depth plot of Quadrat #2 (see fig. 5). Qualitative light cycle located above figure. Water exchange data bar, light intensity plot, oxygen concentration plot, and tidal level plot located below figure. 0 FIGURE 10-- Population distribution plot of Experiment Average depth on vertical axis May 19, 1977. for every integral depth as taken from average depth plot of Quadrat #2 (see fig. 5). Note starting time of artificial flooding at 1:30 PM, time of high tide for May 19, 197! Salinity, temperature and oxygen concentration changes are listed below. FIGURE 11- Schematic view of major changes in population density throughout Experiment #5 May 19, 1977. Only quadrat squares with snail populations greater than two snails are considered. See legend for pattern of plot for specific sampling times. 0 APPENDIX Actual data sheets from experiments 3-5 are presented. 0 O od 9 X L — LI 1 a -Lu 83 —-— 1 + .. 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