1138Q 2002 Estuarine Research Federation

Estuaries Vol. 25, No. 6A, p. 1138–1142 December 2002

Time Series of the Abundance of the Post-larvae of the Crabs

Cancer magister and Cancer spp. on the Southern Oregon Coast

and Their Cross-shelf Transport

JEREMIAH JOHNSON and ALAN L. SHANKS*

Oregon Institute of Marine Biology, University of Oregon, Charleston, Oregon 97420

ABSTRACT: Using stationary zooplankton nets that fished the tidal current we measured the daily abundance of Cancercrab megalopae near the mouth of Coos Bay, Oregon, during the 1997 spring settlement season. During the spring of1997, the coastal waters were dominated by a significant El Nino event. Sea surface temperatures (SST) were higher thannormal, upwelling indices were an order of magnitude smaller than during the two previous springs, and upwellingfavorable winds were weak. Daily catches of Cancer magister megalopae ranged from 0 to 78 with 61% of the total catchoccurring during four pulses. Peak catches tended to occur every 13.6 d close to 13.8 d average period between springtides. Significant cross correlations were found between the maximum daily tidal range and the catch of C. magistermegalopae; large catches tended to occur 4 to 7 d after the spring tide. Daily catches of Cancer oregonensis and Cancerproductus ranged from 0 to 307 with catch significantly positively cross correlated to the maximum daily tidal range at alag of 25 days suggesting that the largest catches tended to occur after the spring tides. We hypothesize that a tidally-generated phenomenon internal waves, transported Cancer megalopae shoreward and caused the observed variation intheir abundance in Coos Bay.

Introduction

Planktonic larval stages are characteristic of thelife histories of many nearshore benthic marine in-vertebrates (Strathmann 1987). While some larvaeremain nearshore, others are regularly carried offthe continental shelf (Lough 1974). At the end ofthe planktonic phase, the larvae need to migrateto a suitable environment in which to settle. Thelarvae of organisms which inhabit estuaries, the in-tertidal zone or the nearshore, may need to mi-grate shoreward great distances.

Since most larvae are probably unable to swimagainst prevailing horizontal currents, the migra-tion to the nearshore is probably accomplished bythe use of shoreward currents. Possible cross-shelftransport mechanisms include wind driven surfacecurrents, shoreward propagating convergences as-sociated with tidally generated internal waves, re-laxation following upwelling events, and currentsgenerated by the density structure over the conti-nental shelf (reviewed in Shanks 1995). The num-ber of larvae transported to the nearshore shouldfluctuate with the physical phenomena causingtransport. If transport were wind driven then onewould expect to see a significant correlation be-tween wind duration and direction and larvalabundance. Time series have been used to infer

* Corresponding author; tele: 541/888-2581 ext. 277; fax:541/888-3250; e-mail: ashanks@oimb.uoregon.edu.

mechanisms of shoreward transport of blue crab,Callinectes sapidus (Rabalais et al. 1995; van Mont-frans et al. 1995; Morgan et al. 1996; Shanks 1998),the lined shore crab, Pachygrapsus crassipes (Shanks1983), barnacles (Shanks 1986; Pineda 1991;Roughgarden et al. 1991), Cancer spp. megalopae(Wing et al. 1995a,b), and larval fish (Thorrold etal. 1994).

Cancer magister supports an economically impor-tant fishery in the northeast Pacific. The fishery ischaracterized by high interannual variability incatch (McConnaughey et al. 1992). Many studieshave tried to explain these variations (Botsford andArmstrong 1989; McConnaughey et al. 1995; Winget al. 1995a). The variability may be caused by var-iations in the number of larvae that migrate fromoffshore back to suitable coastal settlement sites.This study presents the first daily time series of theabundance of Cancer spp. in the northeast Pacific.Using time-series analysis, we compared daily larvalabundance to the physical variables that may causelarval transport.

Materials and MethodsOrganisms that passed through the mouth of the

Coos estuary in southwestern Oregon, U.S.(438209100N, 124820900W) were sampled fromApril 8 through July 1, 1997, the period when mostC. magister megalopae appear to return to shore(Terwilliger and Rumrill personal communica-tion). Samples were collected with a pair of neus-

Abundance and Transport of Cancer Megalopae 1139

ton nets. Neuston nets were used because in estu-arine waters megalopae of C. magister have beenshown to be in greatest abundance at the surface(Eggleston et al. 1998). The net mesh was 500 mm.Each net had a mouth opening of 16 3 33 cm andthen expanded out to 0.25 m diameter before theytailed off in a conical shape. To sample separatelythe flood and ebb tides, the nets were placed sideby side facing opposite directions in a PVC frame.The PVC frame was held in position with ropes toa buoy in the channel and the shore. To quantifywater filtered, the nets were equipped with flowmeters mounted so that when current flow was op-posed to the net opening, the nets collapsed ontothe flow meter preventing rotation of the rotor. Toreduce larval loss during periods when each netwas not sampling, the cod ends bend at a 908 angleso that during non-sampling currents the cod endspinched the back of the net closed.

Plankton samples were removed from the netsduring slack tide at every other low tide. Nets werepulled ashore, washed down with freshwater, andsamples were preserved with 10% buffered for-malin. Megalopae were identified using the de-scriptions in Lough (1974) and enumerated undera dissecting microscope. It was impossible to dif-ferentiate Cancer orgenensis from Cancer productus sothey were counted together (DeBrosse et al. 1990).

Wind speed and direction were obtained fromthe National Oceanic and Atmospheric Adminis-tration Cape Arago Weather Station (CARO3) lo-cated 3.6 km south of the sample site. The winddata were used to calculate cross-shore and along-shore wind stress (Pedlosky 1987). A ten-degreecorrection was added to the wind directions (ap-proximating the angle of the coast) prior to thecalculation of wind stresses. Seawater temperaturewas obtained from a Hobo temperature logger setapproximately 3 m below mean lower low water atNorton Gulch located 4 km south of the mouth ofCoos Bay. Predicted tides for Coos Bay were ob-tained from the Harbor Master software. The max-imum daily tidal range was calculated as the dif-ference between the highest high tide and the ad-jacent low tide during each collection period. Dataare reported as daily averages.

Catches in the ebb and flood nets were com-bined, and the data log-transformed (log10 x11)prior to statistical analysis (Thorrold et al. 1994).Data for sample dates that were missed (days 15,16, 56, and 80) were estimated by taking the av-erage of the prior and successive data points. Toinvestigate relationships among the variables, crosscorrelations (6 7 d lag) were run between thephysical time series and the physical and biologicaltime series. To account for the effects of autocor-relations in the time series, the corrected standard

errors of the cross correlation coefficients werecomputed (Wing et al. 1995a). This corrected stan-dard error was used when it was more conservativethan the white noise standard error calculated dur-ing the cross correlation analysis. If significant au-tocorrelations were found, ARIMA (AutoregressiveIntegrated Moving Averages) models were fitted tothe data using standard techniques ( Jassby andPowell 1990; Dunstan 1993). Cross correlationswere run between the residuals of the ARIMAs. Pe-riodicity in the data was investigated using Fourieranalysis.

ResultsDuring the spring of 1997, the coastal waters

were dominated by a significant El Nino event. Seasurface temperatures (SST) were higher than nor-mal with anomalies ranging from 11.118C to12.778C (Pacific Fisheries Environmental Labora-tory 1998). Over the course of the study, SST in-creased from 118C to 168C. The upwelling indicesfor 458N, 1258W (the nearest point to our studylocation for which an upwelling index is calculat-ed) were an order of magnitude smaller for thespring of 1997 than they were for the two previoussprings (Pacific Fisheries Environmental Labora-tory 1998). The northwest winds which persist dur-ing the spring and summer were not as strong in1997 as normal (Pacific Fisheries EnvironmentalLaboratory 1998).

A significant positive cross correlation was foundbetween the along-shore and cross-shore windstress at 0 d lag (r 5 0.4519; p , 0.05). No othersignificant correlations were found between any ofthe other physical forcing mechanisms.

A total of 305 C. magister megalopae were caught.Daily catches ranged from 0 to 78 and were highlyvariable with 61% of the total catch occurring dur-ing four pulses (Fig. 1). Catches of C. magister werenot significantly correlated with water filteredthrough the nets. A peak in the Fourier analysisperiodogram of the daily abundance of C. magistermegalopae was found at 13.6 d (Fig. 2). During thestudy, the average number of days between springtides was 13.8 d. The similarity between the peaksin the periodogram of C. magister catches, and theaverage number of days between spring tides sug-gests that C. magister catches were fluctuating withthe fortnightly tidal cycle. Significant cross corre-lations were found between the maximum daily tid-al range and the catch of C. magister megalopae(Fig. 2); large catches tended to occur 4 to 7 dafter the spring tide. Variations in C. magister catchwas not significantly cross correlated with any oth-er physical variable.

A total of 987 C. oregonensis and C. productus me-galopae were caught. Daily catches ranged from 0

1140 J. Johnson and A. L. Shanks

Fig. 1. Variation in the number of megalopae caught d21

(solid line) plotted with the maximum daily tidal range (dashedline). Sampling started on April 8, 1997 and ran through July1. The maximum daily tidal range is the difference between thehighest high tide and the adjacent low tide.

Fig. 2. Results of time-series analysis of the daily abundanceof crab megalopae caught at the mouth of Coos Bay. On theleft are the results of Fourier analysis of the daily abundance.On the right are the results of cross correlations between themaximum daily tidal range and the log-transformed daily abun-dance of megalopae. The dashed lines indicate r values neededfor significance (p , 0.05).

to 307 (Fig. 1). No large peaks in the Fourier anal-ysis of C. oregonensis and C. productus abundancewere found (Fig. 2). The catch was, however, at alag of 25 d significantly and positively cross cor-related to the maximum daily tidal range suggest-ing that the largest catches tended to occur afterthe spring tides (Fig. 2). There were no other sig-nificant cross correlations found.

DiscussionThe El Nino of 1997 altered the oceanography

of the Oregon shelf (Smith et al. 1999). These wa-ters are normally characterized by intermittent up-welling caused by strong northwest winds and briefrelaxation events associated with southerly winds(Strub et al. 1987; Huyer et al. 1991). In the springof 1997, the northwest winds were weak, the SSTwas high, and the upwelling indices were low. Con-ditions were anomalous and conclusions from thisstudy may not apply to non-El Nino years.

Both the fortnightly periodicity in the peakcatches of C. magister and the significant cross cor-relations between the abundance of C. magister, C.oregonensis and C. productus and the maximum dailytidal range, indicate that the abundance of thesemegalopae fluctuated with the spring to neap tidalcycle. Data similar to these were used by Shanks(1983) to develop the hypothesis that larvae canbe transported shoreward in the surface conver-gences over tidally-generated internal waves.

In southern California, the abundance of a va-riety of megalopae and intertidal barnacles variesover a fortnight; peak settlement tends to occurseveral days before spring tides (Shanks 1983,1986; Pineda 1991, 1994). Pineda found this cycleof settlement peaks correlated with the cycle of tid-ally-generated internal bores, large internal wavesthat break and cause local upwelling (Pineda

1991). He hypothesized that shoreward transportof larvae resulted from the internal bores. Sets oflarge internal waves are associated with the inter-nal bores (Cairns 1967; Winant 1974). Conver-gence zones are generated over the trough of theinternal waves (LaFond 1959). Shanks demonstrat-ed that these convergences transport larvae shore-ward and hypothesized that the fortnightly patternof settlement was caused by these large internalwaves.

Both hypotheses predict that peaks in settlementshould occur during periods of peak internal waveactivity that in Pineda’s (1991, 1995) data are in-dicated by anomalous drops in SST relative to thelong-term average SST. In southern California,these temperature drops occur several days beforethe spring tides and concurrent with settlementpeaks. At Neah Bay in the Pacific northwest, anom-alous decreases in SST occur from several days af-ter the spring tide to just prior to the neap tide(Pineda 1995). In Coos Bay, peaks in Cancer me-galopae abundance occurred 4 to 7 d after thespring tides suggesting that these megalopae aretransported shoreward by internal waves.

Large tidally-generated internal waves, compo-nents of the internal tide, are common features ofthe continental shelf environment the world over.They have been regularly observed off northernCalifornia and Oregon (Curtin and Mooers 1975;Howell and Brown 1985; Stantion and Ostrovsky1998; Trevorrow 1998; Kropfli et al. 1999). Trans-port by an internal-wave convergence requires or-ganisms to inhabit the neuston. Buoyant particlesor larvae that have strong swimming abilities canbe entrained in the convergence zone above inter-nal waves (Franks 1992) and transported shore-ward with the convergence zone. Megalopae of C.magister, C. oregonensis, and C. productus inhabit theneuston (Lough 1974; Reilly 1983; Shenker 1988)

Abundance and Transport of Cancer Megalopae 1141

and are strong swimmers (Fernandez et al. 1994).Shenker (1988) and Wickham (1979) observedlarge numbers of C. magister megalopae in conver-gences over the Oregon and northern Californiacontinental shelves. Shanks (personal communi-cation) observed numerous C. magister megalopaein convergences over internal waves near themouth of Coos Bay.

Wing et al. (1995a,b) presented time series ofCancer megalopae abundance along the northernCalifornia coast. Their analysis suggests that peaksin abundance resulted from upwelling relaxationevents that transporting megalopae shoreward. Incontrast, we found abundance to vary only with thetidal range. The difference in conclusions maystem from differences in sampling frequency, re-gional differences in transport mechanisms, andannual differences in transport mechanisms.

We sampled daily while Wing et al. (1995a,b)sampled weekly. Weekly sampling, because of alias-ing, cannot resolve a signal with a period # 14 d(Emery and Thomson 1997). It is impossible forthem to find a relationship between catch and tidalrange. Because of aliasing, it is also questionablewhether they can attribute variations in megalopaeabundance to relaxation events. Wing et al.(1995a,b) speculate that local variations in upwell-ing circulation and coastal topography may causelocal differences in the temporal pattern of settle-ment. Transport mechanisms may vary betweenyears. Our data were collected during El Nino con-ditions characterized by weak upwelling and warm-er than usual SST. Weak upwelling might have pre-vented us from seeing settlement peaks associatedwith relaxation events and a strong shallow ther-mocline (Shanks unpublished data) might haveenhanced transport by internal tidal waves.

Shoreward transport of larvae by slicks associat-ed with convergences over internal waves has beendemonstrated in many locations around the world(Zeldis and Jellett 1982; Shanks 1983, 1988; Kings-ford and Choat 1986; Shanks and Wright 1987; Pi-neda 1999). Settlement patterns of organismstransported by internal waves tend to vary with thefortnightly tidal cycle (Shanks 1983, 1986, 1998;Montfrans et al. 1990; Pineda 1991, 1994; Boylandand Wenner 1993; Mense et al. 1995; Metcalf et al.1995). We hypothesize that a tidally-generated phe-nomenon, internal waves, transported Cancer me-galopae shoreward and caused the observed vari-ation in their abundance in Coos Bay.

LITERATURE CITED

BOTSFORD, L. AND D. ARMSTRONG. 1989. Oceanographic Influ-ences on the dynamics of commercially fished populations, p.511–565. In M. Landry and B. Hickey (eds.). Coastal Ocean-

ography of Washington and Oregon. Elsevier, Amsterdam,The Netherlands.

BOYLAND, J. M. AND E. L. WENNER. 1993. Settlement of Brachy-uran megalopae in a South Carolina, USA, estuary. MarineEcology Progress Series 97:237–246.

CAIRNS, J. L. 1967. Asymmetry of internal tidal waves in shallowcoastal waters. Journal of Geophysical Research 72:35–63.

CURTIN, T. B. AND C. N. K. MOOERS. 1975. Observation andinterpretation of a high-frequency internal wave packet andsurface slick pattern. Journal of Geophysical Research 80:882–894.

DEBROSSE, G. A., A. J. BALDINGER, AND P. A. MCLAUGHLIN. 1990.A comparative study of the megalopal stages of Cancer orego-nensis Dana and C. productus Randall (Decapoda: Brachyura:Cancridae) from the northeastern Pacific. Fisheries Bulletin 88:39–49.

DUNSTAN, F. D. J. 1993. Time series analysis, p. 243–310. In J. C.Fry (ed.). Biological Data Analysis: A Practical Approach. Ox-ford University Press, New York.

EGGLESTON, D., D. ARMSTRONG, W. ELIS, AND W. PATTON. 1998.Estuarine fronts as conduits for larval transport: Hydrodynam-ics and spatial distribution of Dungeness crab postlarvae. Ma-rine Ecology Progress Series 164:73–82.

EMERY, W. J. AND R. E. THOMSON. 1997. Data Analysis Methodsin Physical Oceanography. Elsevier Science, Inc., New York.

FERNANDEZ, M., O. O. IRIBARNE, AND D. A. ARMSTRONG. 1994.Swimming behavior of Dungeness crab, Cancer magister Dana,megalopae in still and moving water. Estuaries 17:271–275.

FRANKS, P. J. S. 1992. Sink or swim: Accumulation of biomass atfronts. Marine Ecology Progress Series 82:1–12.

HOWELL, T. L. AND W. A. BROWN. 1985. Nonlinear internal waveson the California continental shelf. Journal of Geophysical Re-search 90:7256–7264.

HUYER, A., P. M. KOSRO, J. FLEISCHBEIN, S. R. RAMP, T. STANTON,L. WASHBURN, F. P. CHAVEZ, T. J. COWLES, S. D. PIERCE, AND

R. L. SMITH. 1991. Currents and water masses of the coastaltransition zone off northern California, June to August 1988.Journal of Geophysical Research 96:809–831.

JASSBY, A. D. AND T. M. POWELL. 1990. Detecting changes inecological time series. Ecology 71:2044–2052.

KINGSFORD, M. J. AND J. H. CHOAT. 1986. The influence of sur-face slicks on the distribution and onshore movement of smallfish. Marine Biology 91:161–171.

KROPFLI, R. A., L. A. OSTROVSKI, T. P. STANTON, E. A. SKIRTA, A.N. KEANE, AND V. IRISOV. 1999. Relationships between stronginternal waves in the coastal zone and their radar and radio-metric signatures. Journal of Geophysical Research 104:3133–3148.

LAFOND, E. C. 1959. Slicks and Temperature Structure in theSea. Navel Electronics Laboratory, San Diego, California.

LOUGH, R. G. 1974. Dynamics of Crab Larvae (Anomura, Brach-yura) off the Central Oregon Coast, 1969–1971. Oregon StateUniversity, Corvalis, Oregon.

MCCONNAUGHEY, R. A., D. A. ARMSTRONG, AND B. M. HICKEY.1995. Dungeness crab (Cancer magister) recruitment variabilityand Ekman transport of larvae. ICES Marine Science Symposium199:167–174.

MCCONNAUGHEY, R. A., D. A. ARMSTRONG, B. M. HICKEY, AND D.R. GUNDERSON. 1992. Juvenile Dungeness crab (Cancer magis-ter) recruitment variability and oceanic transport during thepelagic larval phase. Canadian Journal of Fisheries and AquaticScience 49:2028–2044.

MENSE, D. J., M. H. POSEY, T. WEST, AND T. KINCHELOE. 1995.Settlement of brachyuran postlarvae along the North Caroli-na coast. Bulletin of Marine Science 57:793–806.

METCALF, K. S., J. VAN MONTFRANS, R. N. LIPCIUS, AND R. J. ORTH.1995. Settlement indices for blue crab megalopae in the YorkRiver, Virginia: Temporal relationships and statistical efficien-cy. Bulletin of Marine Science 57:781–792.

1142 J. Johnson and A. L. Shanks

MONTFRANS, J. V., C. A. PEERY, AND R. J. ORTH. 1990. Daily,monthly, and annual settlement patterns by Callinectes sapidusand Neopanope sayi megalopae on artificial collectors deployedin the York River, Virginia: 1985–1988. Bulletin of Marine Sci-ence 46:214–229.

MORGAN, S. G., R. K. ZIMMER-FAUST, K. L. HECK, JR., AND L. D.COEN. 1996. Population regulation of blue crabs Callinectessapidus in the northern Gulf of Mexico: Postlarval supply. Ma-rine Ecology Progress Series 133:73–88.

PACIFIC FISHERIES ENVIRONMENTAL LABORATORY. 1998. PacificFisheries Environmental Laboratory, Volume 1998. NationalOceanic and Atmospheric Administration.

PEDLOSKY, J. 1987. Geophysical Fluid Dynamics. Springer-Verlag,New York.

PINEDA, J. 1991. Predictable upwelling and the shoreward trans-port of planktonic larvae by internal tidal bores. Science 253:548–551.

PINEDA, J. 1994. Spatial and temporal patterns in barnacle set-tlement rate along a southern California rocky shore. MarineEcology Progress Series 107:125–138.

PINEDA, J. 1995. An internal tidal bore regime at nearshore sta-tions along western U.S.A.: Predictable upwelling within thelunar cycle. Continental Shelf Research 15:1023–1041.

PINEDA, J. 1999. Circulation and larval distribution in internaltidal bore warm fronts. Limnology and Oceanography 44:1400–1414.

RABALAIS, N. N., F. R. J. BURDITT, L. D. COEN, B. E. COLE, C.ELEUTERIUS, K. L. J. HECK, T. A. MCTIGUE, S. G. MORGAN, H.M. PERRY, F. M. TRUESDALE, R. K. ZIMMER-FAUST, AND R. J.ZIMMERMAN. 1995. Settlement of Callinectes sapidus megalopaeon artificial collectors in four Gulf of Mexico estuaries. Bul-letin of Marine Science 57:855–876.

REILLY, P. N. 1983. Dynamics of Dungeness crab, Cancer magister,larvae off central and northern California, p. 57–84. In P. W.Wild and R. N. Tasto (eds.), Life History, Environment, andMariculture Studies of the Dungeness Crab, Cancer magister,With Emphasis on the Central California Fishery Resource.California Department of Fish and Game, Sacramento, Cali-fornia.

ROUGHGARDEN, J., J. T. PENNINGTON, D. STONER, S. ALEXANDER,AND K. MILLER. 1991. Collisions of upwelling fronts with theintertidal zone: The cause of recruitment pulses in barnaclepopulations of central California. Acta OEcologia 12:35–51.

SHANKS, A. L. 1983. Surface slicks associated with tidally forcedinternal waves may transport pelagic larvae of benthic inver-tebrates and fishes shoreward. Marine Ecology Progress Series 13:311–315.

SHANKS, A. L. 1986. Tidal periodicity in the daily settlement ofintertidal barnacle larvae and an hypothesized mechanism forthe cross-shelf transport of cyprids. Biological Bulletin 170:429–440.

SHANKS, A. L. 1988. Further support for the hypothesis that in-ternal waves can transport larvae of invertebrates and fish on-shore. Fisheries Bulletin 86:703–714.

SHANKS, A. L. 1995. Mechanisms of cross-shelf dispersal of larvalinvertebrates and fish, p. 324–367. In L. R. McEdward (ed.).Ecology of Marine Invertebrate Larvae. CRC Press, Boca Ra-ton, Florida.

SHANKS, A. L. 1998. Abundance of post-larval Callinectes sapidus,Penaeus spp., Uca spp., and Labinia spp. collected at an outercoastal site and their cross-shelf transport. Marine Ecology Pro-gress Series 168:57–69.

SHANKS, A. L. AND W. G. WRIGHT. 1987. Internal-wave-mediated

shoreward transport of cyprids, megalopae, and gammaridsand correlated longhsore differences in the settling rate ofintertidal barnacles. Journal of Experimental Marine Biology andEcology 114:1–13.

SHENKER, J. M. 1988. Oceanographic associations of neustoniclarval and juvenile fishers and Dungeness crab megalopae offOregon. Fisheries Bulletin 86:299–319.

SMITH, R., A. HUYER, P. KOSRO, AND J. BARTH. 1999. Observationsof El Nino off Oregon: July 1997 to present (October 1998),p. 33–37. In Proceedings of the 1998 Science Board Sympo-sium on the Impacts of the 1997/98 El Nino Event on theNorth Pacific Ocean and its Marginal Seas, Volume 10. NorthPacific Marine Science Organization (PICES), Sidney, BritishColumbia, Canada.

STANTION, T. P. AND L. A. OSTROVSKY. 1998. Observations ofhighly nonlinear internal solitons over the continental shelf.Geophysical Research Letters 25:2695–2698.

STRATHMANN, M. F. 1987. Reproduction and Development ofMarine Invertebrates of the Northern Pacific Coast. Universityof Washington, Seattle, Washington.

STRUB, P., J. ALLEN, A. HUYER, AND R. SMITH. 1987. Large-scalestructure of the spring transition in the coastal ocean off west-ern North America. Journal of Geophysical Research 92:1527–1544.

THORROLD, S. R., J. M. SHENKER, E. D. MADDOX, R. MOJICA, AND

E. WISHINSKI. 1994. Larval supply of shorefishes to nurseryhabitats around Lee Stocking Island, Bahamas. II. Lunar andoceanographic influences. Marine Biology 118:567–578.

TREVORROW, M. V. 1998. Observations of internal solitary wavesnear the Oregon coast with an inverted echo sounder. Journalof Geophysical Research 103:7671–7680.

VAN MONTFRANS, J., C. E. EPIFANIO, D. M. KNOTT, R. N. LIPCIUS,D. J. MENSE, K. S. METCALF, E. J. I. OLMI, R. J. ORTH, M. H.POSEY, E. L. WENNER, AND T. L. WEST. 1995. Settlement of bluecrab postlarvae in western north Atlantic estuaries. Bulletin ofMarine Science 57:834–854.

WICKHAM, D. E. 1979. The relationship between megalopae ofthe Dungeness crab, Cancer magister, and the hydroid, Velellavelella, and its influence on abundance estimates of C. magistermegalopae. California Fish and Game Quarterly 65:184–186.

WINANT, C. D. 1974. Internal surges in coastal waters. Journal ofGeophysical Research 79:4523–4526.

WING, S. R., L. W. BOTSFORD, J. L. LARGIER, AND L. E. MORGAN.1995a. Spatial structure of relaxation events and crab settle-ment in the northern California upwelling system. MarineEcology Progress Series 128:199–211.

WING, S. R., J. L. LARGIER, L. W. BOTSFORD, AND J. F. QUINN.1995b. Settlement and transport of benthic invertebrates inan intermittent upwelling region. Limnology and Oceanography40:316–329.

ZELDIS, J. R. AND J. B. JELLETT. 1982. Aggregation of pelagicMunida gregaria (Fabricius) (Decapoda, Anomura) by coastalfronts and internal waves. Journal of Plankton Research 4:839–857.

SOURCES OF UNPUBLISHED MATERIALS

RUMRILL, S. Personal Communication. South Slough EstuarineResearch Reserve, P.O. Box 5389, Charleston, Oregon 97420.

TERWILLIGER, N. Personal Communication. Oregon Institute ofMarine Biology, P.O. Box 5389, Charleston, Oregon 97420.

Received for consideration, April 5, 2001Accepted for publication, May 1, 2002