Contributions to Our Knowledge Tryonia Imitator (Pilsbry 1899)

CONTRIBUTIONS TO OUR KNOWLEDGE TRYONIA IMITATOR (PILSBRY 1899)

A thesis submitted to the faculty of San Francisco State University in partial fulfillment of the requirements for the degree

Master of Arts in Biology: Marine Biology

by MICHAEL G. KELLOGG San Francisco, lifornia December 1985 Copyright by Michael G. Kellogg 1985 I OUR (PI )

Michael G. logg n Francisco State Universi 1985

Once thought confined 3 localities and proposed as an species, Tryonia imitator is confirmed or reasonably a survi

1 12 localities from the Petaluma River marsh (38°09 N) to n

1 Diego River (32Q46 N). Nineteen historical populations

I to 31°52 N) have apparently been extirpated mostly i habitat modifications. Tryonia imitator inhabits coastal strand habitats tolerate wide fluctuations of environmental parameters a occur on variety of substrata. They are immergent, desi (LD-50 approximately 6 days in both desicca relative humidity) do not ly explain is i habitats. typically occur in densi es

a as both deposit and c ingesting surface lms. They are and shore a are rasiti

that is a on of this ny e most t i ion ir and encouragement ng the term this Two e, vid Lindberg and rry Roth, ve been especially generous ir and advice. Of my many friends at Moss nding Marine es several were of particular help in the eld and/or contri thoughtful discussion; these include Mark Silberstein who population in Parson•s Slough to my attention and much more, lliam Wright, Chris Jong, and many others. services la Baldridge, Librarian Moss Landing Marine Laboratories were indispensable. Her abilities extend the usefulness a small li beyond measure. The members of my committee have considerable latitude and patience which I truly appreci is is particularly of James Nybakken who in it ion i and advice during my stay at Moss ng. Several people generously of ir knowl James T.. Carl pro vi i s notebooks on west American lus Much on concerning imitator s 1 or some of locali records

i him the Department of I ce available me through cou

1oan imens, some of whi were ki y i 1i

v e S. i n, I am 1 H. n

nty seum ra 1 Hi i 1 ia Academy of 1 iences, Thomas ller, Uni onal Museum, and liner U. li ia Sciences. My greatest of gratitude goes to my wi Li 11 for her help in the field and thout whom I am sure this would never have been completed.

vi E

LI ii

LI f J GURES e o e e e e o e e e o a e e e e e o e o e e e e o e e e e e e e e e e e e e e e e e e e e i LIST OF ABBREVIATIONS ••••••.••••••••••••••••••••.••••••••••••••••••

I NTRQDUCT I ONe e e e e e e e o e e e e e e e e o e e e e e e e e e e e e e e e e e e e e e e o e e e e e e e e e e e

TaX 0 nomy •• e •• e ...... e ••• G •••••• e •• 0 ••••••••• 0 ••••••••• @I ••• METHODS AND MATERIALS ..••••••••••••.•••••••••••••••••••••••••.••••

Samp 1 i ng ...... 8 Distribution •••••••••••••••••••••••••••••••••••••••••••

Experiments .•••••••••••••••••••••••••••••• 411 ••••••••••••••••• RESULTS AND DISCUSSION •••••••••••••••••••••••••••••••••••••• Distribution Historical Distribution •••••••••••••••••••••••••••••• Present Distribution •••••••••••••••••••••••

Di spersa 1 •••••••••••••••••••••••••••••••• o ••••••••••

ogy ••••••••••••••• e ••••• 0 e ••••••••••••• 0 0 0 •••••• e 0 0 Habi ic erance to Desiccation ••••••••••••••••

Symbioses •••••••••••••• SUMMARY CONCLUSIONS ••••••••••••••••••••••• LI c ,.7

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1.. Field si ng is

2. Recent (non-fossil} locali records status imitator populations in California and northern Mexico ••••••••

3. Results of tolerance to desiccated sediment experi

4. Results of tolerance to 100% relative humidi

5. Results of laboratory predation experiments ••••••••••••••

6. Results of field predation experiments ••••••••••••••••••••

7. Analyses of Three-spined sti eback 1 1

viii LI FI

Fi re 1. Experimenta 1 for iccation experiments...... • ••• 15

2. Experimental set-up for laboratory predation

3. Experimental set-up for field predation experiments ••••

4. Map of the Recent (non-fossil) locality records for ...... lL--- imitator in California and northern Mexico •••••••••••••••••

5. Benthic diatoms and sediment grains in a squash on the digestive tract of a male Tryonia imitator 1 in in Bennett Slough •••••••••••••••••••••••••••••••••••••••••••

6. Tolerance imitator to desi ng i ons: survival in iccated iment; B) survi in 100% ve humi ......

7. Frequency distri on of on 1

8. trematode cerca a from 1 ssue male 1 in

ix LI ABBREV IONS

ANSP - Academy of Natural Sciences, Phil phia CASIZ - Department of Invertebrate Zoology, California Sciences, San Francisco

LACM - Los Ange~es County Museum of Natural History, es SU - Stanford University, Stanford UCMP - Museum of Paleontology, University of Cali ia, USNM- United States National Museum (Smithsonian I on), Washington, D.C.

X I" I

Shore-dwelling iid snails are found in most areas world and ically occur in unct popul ons as high as 100,000 or more individuals per m2 (~-~· 1 Winterbourn 1970). They compose one of the most important g deposit-feeding invertebrates in northern estuaries ( ) are considerable current interest to systematists e ler

Da vi s 19 80 ; Da vi s , e t ~.. 19 82) •

The European shore-dwelling hydrobiid fauna s i studied by ecologists e.~. Anderson 19 ; Barnes 1975a,b, 1976; Fenchel; et !l· 1975; Fenchel & Kofoed 1 1 1975; Lassen & Hylleberg Kristensen 1978; Levinton & & Nix 1976; Lopez & Levinton 1978; Seigismund 1982; Simpson 1 Walters 1980). Such is not the case with the poorl American hydrobiid fauna with about 25 genera and 175 ies in United States (Thompson 1968), mostly in freshwater.

exceptions (Mazurkiewicz 1 ; Wells 1978; Hershler & s 1 a

is, __ 1982) 1 i e s on can dwelling i ids 11 y none on west ies .. Consistent with this 1 1 ion on Y west coast shore-dwelling

1899) is sparse. Li re s are 1 imi a c

and na 1 1 i or 1 ). evi eld

1 surveys, published li , a museum records indi t hi cal is ies was di in most ti 1 lagoons a mouth of Salmon , Sonoma County, lifornia to California Norte, Mexico. However, some of these are upon unknown sources and many others had not been confirmed in years. The apparent restriction T.. imitator to y localities led the U.S. Fish &Wildlife Service to propose l· ______as an endangered species in 1977 [Federal Regi 42(8): , 12 n 1977]. Because the time limit, created by the ies

Amendments of 1978, expired before a final rule could i imitator was officially withdrawn from consideration in November 1 Today the snail is known or reasonably assumed to survive 12 localities (present study), and it is currently consi a 1 candidate species in category 2 (l. Eng, pers. comm. i to the Federal Register [49(100): 664, 22 May 2 comprises taxa for ich information now in .. s. Fish & Wildli ] Service i icates that i 1 i ies as enda or threatened is sibly appropri conclusive data on biological ili a ( s) are

cu y avail e ...... Dl .. It is largely two reasons - 1 a

vani ing opportunity - I undertook is i 1e ion surviving popul ons 11 la upon adequate protection remaini coa a over opment and reclamation, knowledge of snail •s bi is essential in formula is ions eva i on .. present study was : 1) critically assess cal a present di tion T. imitator and 2) make sic ons on i habi t and ogy.

TAXONOMY

Systematics within the Hydrobiidae is by no means e. the characters commonly used in gastropod systematics are 1 use within the famil For example, the radula is diagnostic at family level, but not for species. The shells are all small ( 11 under 5 mm) and can be virtually identical between ies even genera. In historical usage, the Hydrobiidae sensu lato compri genera and more than 1,000 species distri ted worl er Davis 1980). Grouped prima lyon basis res 1, radula, operculum, a penis - this la s elded a satisfactory assi cation to ( is ) . as 4 son s as subfamilies ( or 1966b) have i

ssi ion zi superfami 1y ini

ne lies and 11 i is [1 ]) nor .. A monumental step in ari on id ics was made by Davis (1 ). He showed t morphology all n terns, ontogeny, a zoogeographic the Hydrobii sensu lato are clea y c a the Hydrobii sensu cto primarily the northern a the Pomatiopsidae primarily of the southern hemisphere. In provided diagnoses of both families and defined the hydrobioid organization within the superfamily Rissoacea. Because re available concerning the anatomy of most species it is cu y impossible to ace all hydrobioids in their proper families. The following classification reflects dominant u family level categories are not without nomencl F Baker 1928; H.B. Baker 1960; Davis 1979; Thompson 1969). is as complete and critical as possible. All references li been examined and references included in Taylor (1975), t included, here have been determined not to refer imitator ..

urn Class GASTROPODA ier 1 SubClass PROSOBRANCH Milne Order

Superfamily RISSOACEA ~uu ... ~ Family HYDROBIIDAE

Tryonia imitator ( 1 ) 1899:121 23, 1 1 e 918:138. Keep & ily 1 1964:173. udestrina curta Arnold 1903:22-23, 28, , 305; Schuchert 1905:480. Arnold 1906:36. Hannibal 1 1912b:186. Oldroyd 1924:17. Burch 1947:18. Woodri 1946:66-67. Kanakoff & Emerson 1959:31.

Hydrobia imitator (Pilsbry). Berry 1947:59. or ' 1 132.

Amnicola (?). Light, et ~- 1954:254. Assiminea ?. Gordon 1979:245.

Bythinea sp. Mudie, --~· 1979: Tryonia imitator (Pilsbry). Taylor 1966b:160, 197. 1967:257, 206-207. MacDonald 1969:41-42. Kern 7 Bishop & Bishop 1973:147. Carlton 1974:55. 1975:504. Taylor 1975:102. Taylor 1978. Wol , ...... ,...et ____,..._ 19-21, A-10, A-23, A-27. Kellogg 1980. Quammen 78. Taylor 1981:153. Kellogg 1982. Quammen 1984:532, DESCRIPTION: Shell minute (up to 4.5 mm}, elongate to conic;

whorls (4-6 in number) well rounded, suture y nuclea whorls planorboid, apex blunt. Peritreme se narrowly umbilicate non-umbili (occasi ly wi ne axial es); scul re 1 consi ng ne spiral , occasionally eros

raised growth lines. Color li brown, in 1 i urn light , corneous, in i ral .. HOLOTYPE: 62670a PARATYPES: ANSP 62670,

longer extant]

DISCUSSION: Most shells ofT. imitator I seen are u mm in 1 length a consi a 4 .. 5 whorls .. sional s 1 grow to 4.5 or 5.0 mm 5 .. 5 - 6 whorls are i y more attenuate. I concur th Taylor (1966a) Paludestrina --cu Arnold 1903, descri as a eistocene sil, is a synonym T.. imitator Pilsbry. Exami ion of both holotypes and numerous museum specimens reveals the two names are equivalant.

(along with f· curta has been synonymized with Paludestrina --~~~ (Gould 1855) by Hannibal (1912a, 1912b) and as f. _cu___ it was synonymized with Tryonia protea (Gould 1855) by Woodri al .. (1946); it is distinct from both of those taxa as di (1966a). The fossil record ofT. imitator is apparently the Pleistocene. Reports from the Upper Miocene-Lower Canyon Formation (Kew 1924; Oakeshott 1958) are misi ons an undescribed freshwater hydrobiid. It does occur in

Bay Point Formation (Kern 1971) and in other 1i ia

eistocene locali es i as P.. --cu REMARKS: or ( ) no ca on assigned ies to ' systematics thin the Hydrobii depends anatomy which is unavail T..

type species the s.. In i on, are highly sculptured unli those T .. imi y li i 1 characteristics (see Stearns 1901), and or s access

anatomical knowledge of most western hydrobiid ies ( & or 1965:104), so I low ) assignment t ea until more ta become available. I I.

Sampling

easiest consisted of hand picking specimens from al l ma or shaking the mats in a ket of water. Similarl can obtained by stripping blades of Ruppia maritima (Linnaeus 1 fingers. Specimens were obtained from the sediment by scoopi a sieving with a hand-held sieve of 0.5 mm mesh size. ils d a so be obtained from sediment samples by allowing them to in a container of seawater and picking the snails from si vessel over a period of several days. Quantitative samples i estimates were obtained either with 2 lb coffee cans (123 cm 2) or plastic coring tubes (7 cm 2) and sieved through a 0.25 mm screen ..

These samples were then washed wi seawater into museum i had been added a few drops of clove oil rose 1" 1 rs the was from these rs a ethyl alcohol. The samples were 1 nocular dis microscope. Alternati sorted immedi y si ng i recogni on of live coll snails .. i obtai and extrapol to m2 values. lini were made with a hand-held American cal Compa refractometer ..

8 Attempts ze snails fi ion were unsuccessful .. ove (useful for other benthic isms iled as did standard methods for molluscs such as magnesium propylene phenoxytol, and menthol c ls. Later attempts at microwave fixation (Berg & Adams 1984) also failed to kill snails in a relaxed condition. To study possible predators, sterosteus aculeatus Linnaeus 1 were collected for faecal analysis from Moro Cojo Slough, County, by dip net. Often more sh were snagged on mats picked up by the net than captured in the net itself. were placed in TeaBoy plastic containers (0.2 mm mesh) in n aquarium with running seawater. Faeces were collected from containers and examined under a binocular dissecting mi

Distribution

determine the distribution of I su eld sites (table 1). i onal locali i 1 i whi or [1975, 1 i {8):2507, 12 n 1977] were icul museum coll ons .. For the latter I studi the ifornia Academy Sciences, Universi 1 i and obtained on loan rna from es Natural History and Academy of Natural iences il i e 1 Fi d sites su

SONOMA COUNTY MONTEREY COUNTY Salmon Creek Bennett Slough Bodega Harbor Elkhorn Slough i Petaluma River marsh Elkhorn Slough ( Parson's Slough MARIN COUNTY Moro Cojo Slough Estero de San Antonio Old Salinas River Walker Creek Carmel River Tomales Bay China Camp State Park SAN LUIS OBISPO COUNTY Corte Madera los Osos Creek Richardson's Bay Sweet Springs Morro Bay SAN MATEO COUNTY Oceano Half Moon Bay San Gregorio Creek SAN DIEGO COUNTY Pomponio Creek Agua Hedionda lagoon Pescadero Marsh Buena Vista lagoon San Elijo SANTA CRUZ COUNTY Batiquitos Waddell Creek San Dieguito Scott Creek Los Penasquitos Santa Cruz San Diego River Soquel Watsonville Slough erance siccation was in both desi and exposure to air under conditions of 100% relative humi the former set of experiments sediment was obtained from Slough, sieved through a 0.5 mm mesh screen to remove most infauna, and equal amounts were placed in 34 10-cm diameter ass finger bowls. Each bowl was then filled to the top with seawater. The water in the experimental bowls was allowed away and sampling began when the water had evaporated from all experimental bowls (7-8 days later). These finger bowls were a on a bench in the laboratory beneath open windows (fi re 1). Tryonia imitator were added to each finger bowl. desiccation on male and female snails were tested sepa aci either males or females in alternating bowls. bowls

~0 s with females were selected by use a random e to serve as controls. control fresh One es one les were each od. The sediment from bowls was si a snails removed and placed in fresh r a ing snail was as alive ve snail s dead. The order of sampling was determi a ra male and female bowls were randomi i ze i e posi on on the bench. after two consecutive days of 0% survival in s. is experiment was run three times. erance 100% relative humidi was determi aci si snails in osed petri dishes in i toweling to the bottom and th seawater to maintain humidi dishes. Control dishes were up in same manner, with seawater. Male and female snails were again tested survival was determined as described above. This was 1 so repeated three times.

Because some mortality occurred before the onset i in both sets of desiccation experiments, the results were i setting the highest number of snails surviving equal Student•s t-test significance was used to compare the ion coefficients of the males and females in each set of as well as the experimental results with their respective controls.

To test whether shore crabs prey upon ___,..___ foll ng experiments were designed. Shore crabs, ---~1.--- oregonensis (Dana 1851), .!:!_ .. nudus (Dana 1851), and _ __,l~L....lll:-....li--

11 1839, were coll s held in an aquarium were conducted by placi one in a em seawa and i imens T.. imi oregonensis i 1y preyed upon snails in experiments concentrated on is ies.

Five were and measu i in the large nger bowl of fresh seawater .. One 1-i_emi graesus oregonensis was also sexed a measu a bowl ining snails. A ski was in ace arou outsi the bowl to reduce t (figure 2). An arbi ry time limit 40 minutes (determi preliminary experiments) was allowed for the crabs to snails The time apsed before the first snail was eaten and the me before the last snail was eaten were recorded. The order in whi snails were eaten was also recorded when that could be determi

This experiment was run th 22 different specimens of H. _-a.:___ _

Field experiments were conducted by constructing 5 gallon plastic buckets. The bottoms of the buckets were a

large "windows 11 were cut in their sides. Nylon screen 1 .. 0 mm size was afixed over these windows with silicone cement. experiments were conducted in the Old Salinas River a hi

population of l· imitator is evidenced by empty shells~ live T imi cannot found there now. The cages were approximately 12 em into sediment ( gure 3). a c nched th holes) was over escape the du ng hi tides. salinity of the water was the same inside

cages were always placed in irs one i i snails only (either 60 or 120) and the other same irs were i s time. contents ca by scooping the sediment from bottom the a approxima y 12 em) into another bucket. is was si a 0.25 mm mesh screen a a bi ar dis microscope so t number snails surviving in coul counted and compa Figure 1

Experimental set-up for desiccation experiments. Petrie 100% relative humidi experiments can be seen behind the s desiccating sediment. 1 Figure 2

Experimental set~up for laboratory predation experiments. A of Tryonia imitator (Pilsbry) can be seen in the left a is Hemigrapsus oregonensis (Dana).

Figure 3

Experimental set-up for eld predation experiments. are in channel of the Old Salinas River marsh, just north·

I I. DI

DI I ON

Snails minute, nondescript shells are seldom 1 collectors and are often overlooked even by malacologi a resu it can be difficult to accurately determine the ra a ies .. This problem is compounded when, as in the case of----:"---- ____, i

becomes desirable to know the species• range before man-i i modifications eliminated entire populations. What is T.. imitator•s distribution is summarized in figure 4 e 2.

Historical Distribution

The data indicate an original range from mon ' 8 County (38°21 N), to Ensenada, a California N) .. Nineteen historical ons

these, two 1 oca 1 i es in (8 : 12 Jan 1 lupe i Lagoon, are sources unknown to me. The locali au is although it might to ei 1 in southern San isco or the vicini Ba ra County, perhaps nea mouth a i of te coll ion at several localities can inferred from knowl l e, IZ specimens from were proba y lected in last as the collector R.E.C. rns ed in 1909 at the ( 73}; while from Alviso were probably collected ea yin is century as the collector H. Hannibal was born near viso in a began collecting at an early age (Taylor & Smith 1971). from Oakland, all collected by H. Hemphill (probably in 1 century- he died in 1914 at the age of 84 [Abbott 1973]}, are variously labeled: 11 0akland, Cal .. 11 (ANSP 27964; CASIZ ex collection; UCMP 855), 11 brackish water near Oakland Ca1 11 7

11 11 ex SU), near Oakland Cal .. , brackish water, Lake Merritt ( Z ex Hemphill collection), "Oakland, San Francisco B.. , Cali

206188) and 11 0akland Cal., Lake Merritt" (CASIZ 0521 }, me a single collection from which Hemphill sent specimens museums and pri collectors, the lots are 1 consi represent a single 1 ity. The elimination T. imitator ons s 1

to three causes: 1) road on cutting rna the ocean creating freshwater habi amation marsh itats for resi development; and 3) dredgi wa navi opment. sewhere (Kellogg 1 ), I shells from the salt pond area of khorn 1 i that lived there commercial salt (Gordon 1979), and that the shells from from n 1908 and ich is period version linas River mou and present harbor nee (Gordon 1979). I sagree th ld's (1967, 1969) conclusion that the shells in Old linas ver downstream from freshwater sources. This idea seems to result misapplication of Taylor•s (1966b) data for the distribution genus Tryonia specifically to T. imitator (see MacDonald Extirpation of the population at Salmon Creek, Sonoma been due to a spill of pesticides that occurred there in 8 s (D.W. Taylor, pers. comm. 1980).

Present Distribution

Eleven populations have been confirmed livi is (table 2, figure 4); one more popul ion in a western arm of Mugu Lagoon, is assumed on si collections. indi a cu ra

I luma ver marsh, Sonoma nty (38°09 N),

I Diego County (32°46 N}. locali es in museum 1 ons ( ls been revisited a are therefore i ica in e 2 re as s uncertain .. Figure 4

Map of the Recent (non-fossil) locali records for ~~-- (Pilsbry) in California and northern Mexico. Numbers entries in Table 2. 8 Living ns Hist pulat Status Uncertain Table 2

Recent (non-fossil) locality records and status of ----IL..o.--- Pilsbry) populations in ifornia and northern Mexico. correspond to those in figure 4. e 2 locality and source(s) of known occurrence locali s a

SONOMA COUNTY

1. 1945 Salmon k Berry lagoon 2. 1897 Petaluma River ANSP 73997 ving marsh Pilsbry 1899 nd MARIN COUNTY 3. 1879 San Rafael USNM 47881 CASIZ 052116 ALAMEDA COUNTY 4. ? near Oakland ANSP 27964 ( ke Merritt) CASIZ 051098 CASIZ 05211 052119 UCMP 855 USNM 206188 Federal Regi 5. 1947 Bay Farm I and D.W .. Taylor

CLARA 6.. ? so USNM 252215

7.. ? Guadal 1 i (also see Barbara Cou e 2 ( i ) locali and source(s) known occurrence locali ta s a

SAN MATEO COUNTY 8. 1960 north end Half D.W .. Taylor Moon Bay Federal Register 9. 1966 marsh at mouth D.W .. Taylor living popul of Pescadero and Federal Register found this Butano creeks ..

SANTA CRUZ COUNTY 10. 1885 Santa Cruz ANSP 27963 Exti ANSP 62670 ANSP 73993 CASIZ 051099 UCMP 6253 USNM 153427, 526415 Pilsbry 1899 Federal Register

11. ? Soquel Marsh D.W .. Taylor Federal Regi MONTEREY COUNTY 1965 Old inas MacDonald 1967, River 1969 ls'

1976 Bennett ough D.. W.. Taylor Regi

7 Moro Cojo ough IZ 1

15. 1978 khorn (salt ls' e 2 ( i 1oca 1 i ty and da source(s) rst known occurrence locality s a

MONTEREY COUNTY (continued) . 1979 Elkhorn Slough sent study Extirpated? (Hudson•s Landing) empty ( appeari ) have been 17. 1984 Parson°s Slough present study Living popul found this

SAN LUIS OBISPO COUNTY 18. 1972 Los Osos Creek Taylor 1978 ving marsh (Morro found is Bay) Listed as in the Regi

? lagoon at Oceano Taylor 1978

SANTA BARBARA COUNTY

7. ? Guadalupe 1 i (see also Clara

20 .. 1966 lagoon IZ 1097 UC Sa Barbara

VENTURA COUNTY 21. 1979 Mugu lagoon CASIZ 020785 (west arm) 54209 now; no 1 ons locality and te source(s) rst known occurrence locality s a

LOS ANGEL COUNTY 22. 1974 Ballona LACM 10572 Status record empty shells, no subsequent lections ..

23. ? San Pedro USNM 153426 Pilsbry 1899 Taylor 1978 Federal Register

ORANGE COUNTY 24. 1968 Balsa Chica LACM 10571 Status Slough record empty ls, subsequent call ons. 25. 1971 Upper Newport or 1978 Status in Bay

SAN DIEGO COUNTY 26. 1970 Agua Hedi Lagoon

1958 Buena Vi or 1978 Lagoon

28. 1970 San ijo or Lagoon 1970 tiqui or 1978 Lagoon e 2 ( locality and te known occurrence s a

30. 1958 San Dieguito Taylor 1978 Living popul Lagoon found this (= De 1 r of Taylor, not him in 1) 31. 1959 Los Penasquitos Taylor 1978 Living popul Lagoon found this (= Pines Lagoon found

32. 1971 mouth of San Bishop & Bishop ving Diego River 1973 found Taylor 1978 Federal Register 33. 1912 Tijuana River Taylor 1978 (Imperial Beach) ICO Baja California

? inada 1 1 i The ism(s) s a i i di bution is unknown. There is good evidence that the a ion i Bennett ough was not present prior to 1946 (Kellogg 1980) its time and method of establishment is unknown. ssive shorebirds and waterfowl may be an important dispersal mecha phenomenon has been documented for mollusks by lone (1965a ) Rees (1965), and others, and implicated for hydrobiid snails Bondesen & Kaiser (1949) and Hunter, et !l· (1964). ils attached to or lodged in the feet and feathers of birds a once removed from water some may retain their viability long insects can be ive short distance dispersal small snails and clams (Rees 1965). i es containing T. each year visited by many thousand migratory wa several ies (Browning, et !l· 1 al .. d ; Quammen ) . bi coast moving freely between areas

t don•t. Birds that are commonl seen ng i i areas of dense T. imitator popul ons at ng marbl godwits, black-necked , American

ews, nlin, dowitchers, a American coots. i 1e undocumented, occasional nsport T.. imi feathers, mud stuck to the bird•s , or even in {Malone 1966) is li y occur. ven t females i embryos through di development logg 1980; or }, a single brooding female is all t is necessary (theoreti ly at least) successful colonization after dispersal to a sui e habitat. Over a sufficient period of time occasional of I· imitator by birds could account for its dispersal to i and down the coast. A mechanism of transport that is known to occur is that while floating upside down on the surface tension of is mechanism is more likely to serve as a means of dispersion in a population or between populations of one marsh than it is snails between separate marshes. eating snails are ca out to sea by wind and tidal currents, but the chance ir remaining afloat long enough to return to a suitable i seem great. Floating does, however, provide a means snails could become lodged in the feathers wading or swimmi eating is also known occur in vae ( in

northern Europe. Newell ( , 1964) thought that H vae represented part of a cyclic ior that in

the popula on's i on within 1 i on

an important food resource ingestion lm .. is i has been challenged by Little & Nix (

H. ulvae is an accidental phenomenon, not associ c behavior, that probably ai in dispersal. is evi that the probability of floating may be vely increa H. ulvae at least in some ci nces ( 1; Newell ) . floating is a y or ssi ined is but they can seen to ingest su lms in the 1 floating is common enough that a number of snails can usually so situated in nature.

ECOLOGY

Tryonia imitator inhabits coastal lagoons, creeks, marshes. These coastal strand habitats are typically la fluctuations of environmental parameters on both a sea il basis. Although T. imitator has been characateri as a water species, these habitats are often hypersaline ring and late Fall and hyposaline during the Winter. 1 fluctuations occur, such as at creek mouths, i ties can va dramatically on a ily basis. In addi on, low ions where T. imitator occurs show wide temperature on seasonal and daily basis. iments in va sil muds to muddy sands and coarse sands s. 1

nd i are ical 1 i i worldwi [ stensen [Denmark]; Thompson 1968 [ ]; s ]; Winterbourn 1970 [New and]). Also typical of shore-dwelling id snails, di l· imitator within any habitat where it occurs is ities are high .. di bution a a it ing marine i tes is usually s sediment in size, higher organic and hi mi ial omass (Lopez & inton 1978), but Fenchel (1975a:1 ) s concluded that the actual distribution patterns of hydrobiid snails result from interplay between habitat selection, dispersal a colonization, biotic interactions, and extinctions which ~~ ••• are in part functions of local geographical features, habitat sizes a unpredictable climatic factors".. Walters (1980) ls {1 shown that no single environmental parameter or simple combi parameters can predict the distribution or abundance 1 i hydrobiids. One biotic interaction which might and abundance ofT. imitator and perhaps shore-dwelling ii on world-wide basis (Kellogg 1982) is predation ns (see section on predation).

Habitat

imitator is not occur i 11 is immergent it is red with co a 1 i in

(Winterbourn ) ' South ca (G .. M.. .. comm .. probably sewhere .. It is typical i snai s can be wi the interti 1 habit 1 i hydrobiids, in rticular, antic i i d imitator inhabit coastal lagoons, creeks, oughs, licornia- domi rna s areas of wa nds ng mats snails can be found crawling on the sediment surface, on R. maritima, on submerged stems of Salicornia spp., amongst rna of green algae, on submerged rocks and debris, a oating i on the surface tension of the water. At the Petaluma River marsh, Sonoma County, I· imitator were abundant on R. maritima and mats of Enteromorpha sp. in a llow of 0.2 m water depth. Other invertebrates present were s ostracods, amphipods, and insects. Several small ______. __ oregonensis (Dana 1851) were observed in the main channel Petaluma River, but no signs of crabs were seen in inner marsh where T. imitator occurs. At the mouth Butane and scadero Creeks, n imitator is found in the inner rna on sil mud, mouth they were livi in sand. Sali ties 1 i es in marsh on an ebbi ti 6 Jan 1980 were 4, 5, 8 values must be appreci y hi duri a ially the creek mouth, i i ng T.. imi a consi e fl on in salini on a sis .. Bennett Slough, is ne silt and c 1 is less i es genera 11 y range from 28-38 t can consi y less times of heavy rainfall and runoff .. in areas imitator is 0.5 m or less low ti temperature at surface can va 13 or more in a si e (12 - a 1630 on 26 Nov 1980}. Here, l· imitator occurs at a 20,000/m2 with several introduced and native invertebrates i Foraminifera, 1879, ostracods, Nebalia pugettensis (Clark 1932), Orchestia gemma (Totten 1834), Batillaria attramentaria (Sowerby ), a Aplysiopsis smi i (Marcus 1961). Hemigrapsus oregonensis ( na 1 H. nudus (Dana 1851}, and Pachygrapsus crassipes Randall found in Bennett Slough near the culvert connecting it s landing Harbor, but not in the areas harboring T. _i_m_i ____ The sediments of Moro Cojo Slough, Monterey County, very fine sands to cl (Hansen 1976), water depth is 0.5 m or ess and the salinity can vary from as low as 4 ppt ng the (Gordon 1979) to as high as ppt during summer (

The history ofT. imitator in Moro 0 ough logg (1980). Other i i lid ychaetes, copepods,

Orchestia sp .. , Trichocorixa .. ' . ' .. larvae .. In more than 2 rs on one sma Hemi9rapsus s been found in At the Los Osos Creek rna in Morro is i T.. imi was wi nsennella sp .. , ca 1837, Cerithidea californica (Haldeman 1840}, ---- 1855), and Haminoea vesicula (Gould 1855). In a i on, J.T. ( per s . c omm . 1 ) nd capi lid and Orchestia sp. in same area, all which compose a 1 assortment native stream-mouth • The introduced lmona snail Ovatella myosotis (Draparnaud 1801) was not found al it occurs elsewhere in Morro Bay. samples taken in a 1 meander through the marsh with a silty mud bottom and salini ppt yielded density estimates of 4,000- 37,000/m2• was also found in the main channel of Los Osos Creek wi a sali 32 ppt and sediment of gravel with a ne sand and silt cover.

Wolfe, et ~- (1979) report abundant Tryonia imitator in reaches of the western arm of Mugu Lagoon where they so nematodes, Capitella capitata (Fabricius 1780), unidenti polychaetes, tubificid oligochaetes, calanoid copepods, ostracods, Corophium sp., Acteocina inculta, a 1 opisthobranchs. also report Hemigrapsus _....:.:..,._ ___ lower reaches of western arm, not near ons di T.. imitator .. At itos Lagoon, n Di County, oati rna

Enteromorpha large, i abundant T.. ----imi shore near the mouth of the lagoon, ie

--~· (1979) describe the lagoon as mostly less n 5 in wa th salinities that ically icall from summer highs (50 ppt or in 1a lows less than 10 ppt). They report the following i i goon, i (Linnaeus 1758}, ------.....1._ __._____ ---- (linnaeus 1758), (Fabricius 1780), -!....----- _....____ -----a'------(Schmarda 1861), Pachygrapsus crassipes, Callianassa _c_a_l1_· _____...;... Dana 1854, Trichocorixidae, Assiminea californica (Tryon .....M...--- sp. (a misspelling of and undoubtedly a misidentification ofT. imita , and Haminoea vesicula. At San ijo lagoon, San Diego County, abundant I· imi were found on R. maritima; no other invertebrates except amphipods were observed ..

Mudie, et ~· (1979) describe San Dieguito Lagoon, n County, where I· imi tor was also abundant, as 3-6 i western end with a hard sandy bottom and also subject seasonal fluctuations in salinity (greater than 35 ppt in summer, less ppt in winter). They report Polydora socialis, hoppers 11 (probably Orchestia sp.), Trichocorixi

1 i a misi on T.. imitator .. At squi abundant on Enteromorpha mats a a were observed nea Mudie, __a_l. several marine and estua ne i lagoon i i salinities are usually slightly higher n ocean 44 in low channels T.. imi occurs .. In the San ego River, llow (approxima y 0.5 m) s near I 5 overcrossi

Trophic

i 1 a ve utilizes a broad trophic resource base, acting as both a and epiphytic grazer. Microscopic examination of sli the digestive tract of individuals from Bennett Slough reveal grains and benthic diatoms ( gure 5). Bacteria microorganisms coating sediment and organic parti es are an food source for deposit feeding invertebrates. They are utilized by northern ropean and eastern American ~--- (Kofoed 1975a,b; Levinton & Lopez 1977; Newell 1965), a utilized by T. imitator as well. Kofoed {1975a) s diatoms and bacteria are assimil H. ci (60-75%) than bl al (8-50%}" (in sense organic debris) is much less importa id snails ia and microorganisms se much of the assimilated or is ( ) . i nton ( ) a however, sms assimilated as ci y in the 1 suggest that microorganisms remai ng es are from di on, so that digestion rs be constrained ili snail sms the particles. Benthic diatoms may be most importa resource Figure 5

Benthic diatoms and sediment grains in a squash prepa on digestive tract of a male Tryonia imitator collected in Photomicrograph 400x with nomarski optics and polarizi 1

(at least seasonall a di i a ve ir nee in e size sel ion , et a 1. ) . An a i onal trophic resource is organic film on significance of these lms. su films (Newell 1962) and Tryonia imitator can also i these films while oating on the surface tension. Di on of nutrients such as amino acids may so be possi e (

Tolerance to Desiccation

Lassen & Hylleberg Kristensen (1978) used { .. , dose 11 at whi 50% mortality occurs or in this case 50% survival) to compare tolerances n ----- spp. to environmental Similar were erances on se the on that snails are in areas permanent water. The resul for es i significa y in i ( IS or 100% relative humidi (Student•s p<0.5) so ir resul are summarized in es 3 & 4 6 .. i 1 s in i ng iment show lly ra d 1 i an average LD-50 ju over 6 ( snails survived beyond 11 days and this di si ifica y • s p).. ) from ly snails i a 80% survival over same values determined ssen & leberg Kristensen ( ) ventrosa (j ) re slightly higher than for.!. .. imitator and both the --x...-- .. are known from intertidal habitats. Similarly, snails exposed to air at 100% rel ve humidi so exhibit high mortality, with an average LD-50 of just u 6 (figure 6) .. No experimental snails survived beyond 10 is differed significantly (Student 1 s t-test; p ).0001) from permanently submerged control snails which averaged 81% survival the same period. Tryonia imitator survi in 100% ve di is comparable to Hydrobia ventrosa (LD-50 about 6 neglecta (LD-50 about 18 days) or H. ulvae ssen & Hylleberg Kristensen ) . 1 1 species occur intertidally .. T.. unable to when submerged, the results i here ( .. Wi

some of the pre-sampling i es 3 & 4).. so the compa son ues, it would seem imitator from i 1 is more

rvation desi on .. p T.. from areas sea ic

desiccation. bi t r suitable 11 be if they dry out occasionally. e 3 lts erance icca iment live snails sampling combi males a females surviving from a 20 snails ( sex) ..

days of number live snails mean number desiccation exp I exp II exp III snails (SD)

1 8 .0 (3 .. ) 2 11 13 13 .. 3 (1 .. 15) 3 11 11 11 11 .. 0 (0 .. ) 4 7 7 .. 0 ---- 5 7 7 4 6 .. 0 (1. ) 6 5 5 .. 0 7 7 2 4 .. 5 8 9 6 7 .. 5 9 3 5 2 3.3 10 1 1 0 0.7 11 4 0 1 1.7 12 0 17,1 0 16 .. 5 13 15 .. 5 ' ' e 4 1 erance 1 ve di

number live snails ea i i number males a females surviving from a 1 12 snails si sex) .. days of number live snails mean number 100% RH exp I exp II exp III snails (SO)

1 12 9 12 11 .. 0 (1 .. ) 2 10 8 10 9 .. 3 (1 .. 15) .. 5 3 7 7 10 8 .. 0 (1.. 73) .. 7 4 9 9 .. 0 ---- .. 8 5 5 4 8 5.7 (2. ) .8 6 6 6 .. 0 .. 5 7 2 4 3.0 ( 1. ..3 8 1 3 2 .. 0 ( 1" .. 2 9 2 1 1 1 .. 3 (0 .. 11 .. 8 10 2 0 * 2 1 .. 3 (1 .. 15 11 .. 11 0 4,6 0 5 .. 0 (1 .. * 12 4, 5, 4.8 (0 .. 50

s Figure 6

Tolerance imitator to desiccating condi ons: A) survival in desiccated sediment; and B) per cent survival to air of 100% relative humidi (RH). ~ 0 u u (f) Q) u

'-4- 0

0 u

0 0 0 :tuaJJad 9

Predators

Consi ng sities 1 ons one would expect them to serve as a trophic resource for invertebrate and vertebrate predators. Known predators i c fish, and birds, while several other tors may be Amongst the latter are flatworms and gastropods. Reynol & (1963} describe how a freshwater clad attacks and consumes ii snails. Coastal flatworms should be equally capable, al not collected any when sampling T. imitator. The cephala i sa obtusa Brown 1827 feeds upon hydrobiid snails which are swall (Thompson & Brown 1976). Tryonia imitator co-occurs th a ler cephalaspidean, Acteocina inculta (Gould 1855), in ia but a predator-prey relationship between~· incul s not been established. Shonman & Nybakken (1978} ve offshore species, Acteocina tella (Gould 1853),

most exclusi y and same may A. ---i p tion shore ght be important in li local distribution and ndance of tor at a one locali situation is icula y suggestive i where the snails are in Bennett, , a s

Sloughs, but absent in Moss ing Harbor, El 51 linas River .. crabs -~__,,L..--..- Pachygrapsus a to a lesser H.. s are Moss Landing Harbor, Elkhorn Slough, and Old linas River, es ally in slou s T. ----tor .. Accordingl iments were ne if i on T. imitator a if they have al dis ion. Other possibilities may explain the i tterns, but considering the range of physical natural populations of I· imitator (described in on on habitat) it is not likely that salinity, tempera re, or characteristics -- those factors which most often correla distribution of estuarine organisms -- can be responsi e. S dispersal barriers are not likely (see section on di ) i considering the fact that localities with hundreds shells of I· imitator (of unknown age) found in Elkhorn Slou a Old Salinas River indicate that the snail has reached areas one means or another. Preliminary experiments on crab ies occur on the periphery Hemigrapsus ily eat l .. _i_m_i __ in la H. nudus and do or i ls P.. an occasional T.. imi tor, in H.. nudus paid little a ion snails .. due the small number a ir u condi on, a dietary ant (

1980) ' or their lack famil iari th T.. imi as a Hemigrapsus nudus is never common or abunda on and would therefore seldom encounter T. imitator. ies ions i 1 zone it so is i y to encou T.. and it co-occurs the smaller, less aggressive.!:!_. P.. di aces i downwa interti lly (Willason 1981). Further experiments on Hemigrapsus oregonensis reveal male and female crabs within the size range (11-33 mm) eat I· imitator without regard to the size or sex the snail ( 5). The data are highly variable and yield no discernable The time taken until the first snail was eaten ranged 23:06 minutes, the time until the last snail was eaten ra 21:50 to 39:53 minutes, and the total time taken to eat all ve snai ranged from 10:17 to :23 minutes. The frequency distri on these times is presented in gure 7. There is no relationship the size and sex of the crab and any of those times, nor size in which the snails were ( could ) " Once it was determined 1 an see if the crabs were equally cient in eld .. ils or snails crabs were aced in in the d ver, T imitator does not now live, H.. -...... ~~:.----- results, shown in Table 6, reveal mortality a much higher n crabs. Clea y I cannot argue from these oregonensis is y ible the lack in the Old Salinas River, but it is just as clear t on shore crabs s i a 1 a di tion T.. imi tor. , evi t 11 y 11 circumstanti Although not in is it for shore era and T. imitator to coexist; however, I i imitator populations doing so would at much lower i es those that occur where crabs are not Crustaceans are known to eat hydrobiid snails el example Smidt (1951} reports that crustaceans prey upon _...._ __ _ in Denmark, and Hylleberg {1975:287) made the followi ...... I have found mud snails [northern European ----- sensitive to predation, especially by crustaceans. a rna I find it a challenging question why hydrobiids are absent from la areas harbouring all the species associated with ii [crustaceans] are abundant. The patchy occurrence snails well be caused predators .. 81

The negative correlation I ve

shore and T. imitator s d at all localities I able visit. These ions along th Hylleberg•s {1975) similar on 1 me ea ier ( 1

1982) to suggest the ion in hi i es of shore-dwelling hydrobii tion crustaceans, especially , a is mi 1 snai itats not sui e to themselves .. are present where I· imi tor occurs be i i Table 5

Results of laboratory predation All times are in minutes. e 5 ------crab snails time time 1 me sex size sex ze sna i 1 sna i 1 ea (mm) (mm) eaten eaten ea all snai ------M 10.9 F 1.2 X 0.9 4 13:48 39:47 M 1.7 X 1.2 3 F 2 .. 1 X 1.5 5 F 2. 6 X 1.6 1 M 3.1 X 1.7 2

F 12 .. 2 M 1 .. 0 X 1.7 1 16:25 M 1 .. 3 X 1 .. 0 M 1 .. 8x1 .. 2 F 2 .. 2 X 1 .. 5 2 F 3 .. 1 X 1.9

F 12 .. 5 M 1 .. 1 X 0.9 1 8:48 M 1.3 X 1 .. 0 3 M 1. 8 X 1 .. 2 4 F 2.0 X 1 .. 4 5 F 3.2 X 1.9 2

F 13 .. 8 F 1.2 X 1.0 10:58 38:35 F 1.8 X 1 .. 3 M 2.1 X 1 .. 3 M 2.1 X 1 .. 5 F 3.2 X 2 .. 1

M 15 .. 3 M 1.1 X 0.8 2 8: M 1 .. 8 X 1 .. 1 F 2 .. 2 X 1 .. 4 M 2 .. 2 X 1 .. 6 1 F 3 .. 1 X 1 .. 9 3

M 15.8 F 1 .. 3 X 1 .. 1 3 16:46 F 1 .. 4 X 1 .. 0 1 F 2 .. 2 X 1 .. 4 F 2 .. 9 X 1 .. 8 2 F 3 .. 1 X 1 .. 9

M 16 .. 3 M 1.5 X 1 .. 1 2 M 1 .. 8 X 1 .. 2 5 F 2.1 X 1.4 3 F 2.4 X 1 .. 7 4 F 3. 0 X 1.7 1 e 5 ( ------crab snails 1 sex size sex size snail eat (mm) (mm) eaten ea all snai s ------M .. 8 F 1.3 X 1.2 5 23:06 38:53 5: F 1.4 X 1.0 3 M 1.9 X 1 .. 2 1 M 2.2 X 1 .. 5 4 F 2.8 X 1 .. 7 2

F 17.0 F 1 .. 5 X 1.1 5:30 26: F 2 .. 3 X 1 .. 6 F 2.4 X 1.1 F 2 .. 6 X 1 .. 6 M 3.3 X 2 .. 0

F 17 .. 7 M 1 .. 5 X 1 .. 1 17:27 M 1 .. 8 X 1 .. 3 F 1 .. 8 X 1.3 F 1 .. 9 X 1 .. 3 F 1.9 X 1.4

F 18.6 M 1.5 X 1 .. 1 6:57 37: F 1 .. 8 X 1 .. 2 F 2.8 X 1 .. 7 F 2 .. 9 X 1 .. 8 F 3 .. 0 X 1 .. 9

M 19.3 M 1 .. 0 X 1 .. 7 1 2: 9: M 1.5 X 1 .. 1 4 M 1 .. 8x1 .. 2 3 F 2.2 X 1 .. 5 5 F 3.0x1 .. 7 2

M 20 .. 8 M 1 .. 1 X 0 .. 9 :35 F 1.3 X 1 .. 1 M 1 .. 8 X 1 .. 2 F 2.9 X 1 .. 8 F 3 .. 1 X 1 .. 9

F 22.0 M 1 .. 5 X 1 .. 1 4 :11 1: M 1 .. 5 X 1 .. 2 5 F 2.7 X 1 .. 7 2 F 2 .. 9 X 1 .. 7 3 F 3.0 X 1.8 1 e 5 ( i ) ------crab snails time me sex size sex size eat (mm) (mm) eaten all snail ------~ F 23 .. 8 M 1 .. 5 X 1 .. 1 2 17:52 28:09 :17 F 1.8 X 1 .. 2 4 F 2 .. 3 X 1 .. 5 1 F 2.8 X 1.7 5 F 3 .. 0 X 1 .. 9 3

M 24 .. 5 F 1 .. 1 X 0.9 5 4:29 35: M 1 .. 5 X 1.0 4 F 1 .. 8 X 1.2 3 F 2 .. 4 X 1 .. 5 1 F 2 .. 9 X 1 .. 8 2

M 26.0 M 1.1 X 0 .. 8 3 18:18 19: 2 F 1 .. 2 X 1 .. 0 5 M 1.8 X 1.1 1 M 2 .. 1 X 1 .. 3 4 F 3.1 X 1.9 2

M 27 .. 2 F 1 .. 3 X 1.2 5 23:00 39:08 16: M 1.5 X 1.1 3 M 1.9 X 1.2 4 M 2 .. 2 X 1 .. 6 2 M 3 .. 1 X 1 .. 8 1

F 28.1 M 1 .. 0 X 0 .. 9 8: F 1.3 X 1 .. 1 M 1.5 X 1 .. 1 F 2 .. 9 X 1 .. 7 F 3 .. 0 X 1 .. 8

F 29 .. 5 F 1.3 X 1 .. 1 4 6: M 1 .. 8 X 1 .. 2 2 M 1 .. 9 X 1 .. 3 3 F 2.0 X 1 .. 4 1 F 3 .. 1 X 1 .. 9 5

M 30.7 M 1 .. 8 X 1 .. 2 11: M 1.8 X 1 .. 3 F 2 .. 3 X 1.6 F 2.4 X 1 .. 7 F 2.9 X 1 .. 9 snails sex size sex size sna i 1 (mm) (mm) ea

M .8 M 1.5 X 1.1 1 5:29 M 1.8 X 1.2 3 M 2.2 X 1.5 2 F 2.6 X 1.6 5 F 3.2 X 1.8 4 Figure 7

Frequency distribution of predation times from la t e when snaU e

when h 8 e en t al t e to e sna e 6 Resul eld ion

---~------no. sna i 1s no. and per cent no .. a r duration per cage survival w/o crabs survival

4 days 120 72.5% 9 7 .. 11 days 60 24 40.0% 0 0 .. 0 21 days 120 33 27 .. 5% 0 0.0 1 month 60 3 5 .. 0% 0 0 0 also are n 1951), ' Linnaeus 1758, is i y minor. Three-spined ckl G aculeatus occur th T. imitator in the marsh at the mouth Pescadero and Butano Creeks, San Mateo County, in Moro Cojo Monterey County, and probably elsewhere. Three-spined sti strictly visual predators (Beukema 1963) that feed mostly in column, but their diet often includes a benthic on i i mollusks (Hynes 1950; Moyle 1976). Because these fi were inadvertently collected while sampling T. imitator, and se G. aculeatus is known to eat hydrobiid snails in Bri in ( ) ' possibility of a predator-prey relationship was expl The that Gasterosteus aculeatus swallow e (Hynes 1950} allowed the detection ofT. ----imi ls ir faecal materi di 0 consi primarily copepods, ostracods, and r coll in October and December 1980 ea the snails (table 7). Anal is G.. s from Moro o Sl lar of 25 T.. imi r in 1 snails were found in 1 s imi rs an important di three-spined stickl c sh snails contained several e Three-spined stickl ks may become i e 7

Anal ree- c k 1 rna a 1 ..

------date of sh collection number food item ------10 Oct 1980 1 Trichocorixa sp .. 2 Copepoda, Ostracoda, Trichocorixa 3 Copepoda, Ostracoda, Tryonia imita (6)

4 Dec 1980 4 Copepoda, Trichocorixa sp. 7 Copepoda, undetermined fine materi 8 Copepoda, Ostracoda, Trichocorixa 9 Ostracoda, Trichocorixa sp., Tryonia 10 Ostracoda, Trichocorixa sp .. , Tryonia .....-...-:--~- 11 Copepoda, undetermined fine material 12 Copepoda, undetermined fine materi

13 Ostracoda, Trichocorixa sp .. , ---..l"--- 14 Trichocorixa sp .. 17 Copepoda, Ostracoda, undetermi a 18 Copepoda, undetermined ne rna 20 Copepoda i r di so t to consi y eat same i and require a 1earni for new ( ) . It s possi e t sh with T. imitator in ir s lea eat snail (perhaps king oating snails or

accidently while pursuing other prey into gal mats or ----1-'--- while the other fish continue to pursue more conventional This hypothesis could be tested tagging, releasing, and fish whose diet has been determined by the method of 1 is used in this study. Hynes (1950} found that hydrobii occu in diet of British~· aculeatus mainly in winter when normally a specimens were found in each fish. He attributed this scarci preferred food during the winter and a similar seasonali in consumption of l· imitator may be indicated (Table 7; lang Shore birds and probably other waterfowl are of Tryonia _im_,_· __ I was unable to ir 1 s in droppings and pell that I 1 even could observe llets, rna ed godwits, 1 ca avocets, long-billed curlews, dunlin, dowi vely feeding in areas of T. imitator (1980, 1 ), , reported resul

T.. i mi tor composed a nt i a 1 ( ) dowitchers, western sa i nl in, a can arm Mugu lagoon. also il i r 1 s in her analyses bi i i ng that samples re necessary. Tryonia imitator has not been found ng anal wes rn sandpi 11 l at nding (B. Ramer, .. c omm . 19 85 ) ,

ing in areas i T. imita or to coll on. su singl hydrobiids can also an important component in of ropean waterfowl (Goss-Custard 1969; 01 1965).

Symbioses

---..l"--- imitator in Bennett Slough, Monterey Cou found parasitized by unidentified cercariae of a digenetic (figure 8). According toW. Sousa (pers. comm. 1984) are extremely similar to the species infecting Cerithidea ica Bolinas Lagoon, Marin County. If they do prove to the same, birds are the most likely final host for this parasi The Bennett ough popul on is also host a s cili similar species of chodina a i Hi d (1949). ip is unknown, t protozoans can movi in

rna over idermis no detrimental snail. shells ofT .. imi are and/or bl al Shells small round (approxima y 0.5 mm diameter) and unknown ni a to them. 1 Pescadero marsh, San Mateo County, had a small lacu s lman on i 1. is is i America it also occurs on shells iid snails salsa {Pil ) a Amnicola Pil 2) in Maine {Davis, __ __ Figure 8

Unidentified trematode cercaria from the gonadal tissue a rna Tryonia imitator collected in Bennett Slough. Photomi with nomarski optics and a polarizing 1

IV .. AND CONCLUSI

1 .. 1 1899) s been la i si its ginal ption. An exception is the proposal Fish & Wildli Service in 1977 to list T. imitator as an species due to its apparent restriction three locali es. present study was begun to: 1) critically assess the hi cal a present distribution of I· imitator and 2) make basic ons its habitat and ecology.

2. To determine I· imitator•s Recent distribution, si Sonoma County to San Diego County were surveyed. seum 1 ons and literature reports were also critically exami

3. The historical indicate a range from lmon

1 County (38°21 N), to Ensenada, Baja li a N). Nineteen historical populations ve y

largely due to man-i habi i ons ..

4. Today the snail is or reasonably a su ive 12 locali es from Petaluma ver rna to the San Di River, Diego N) ..

5 .. licornia na rna se i are tions environmental rameters on both a seasonal a a sis ..

6. ____.....___ imitator utilize a broad trophic resource se, as both deposit feeders and epiphytic grazers, ingest su as well ..

7 .. Desiccation experiments were conducted tote d observations.. They yielded LD-50 values of just over 6 in desiccated sediment and just under 6 days in 100% humidi do not readily explain the absence of Tryonia imitator from i i habitats, but do help to explain their absence in habi seasonal or occasional drying.

8. d The distribution of ----l"--- imitator in a negatively wi the distribution shore 1 es .. Many factors, possi y in combination, mi accou is tory field experiments ily eat the snails a lea potential to affect their di but ion although is s demons conclusi y .. sali and/or sediment cha ics may more on

the tolerances exhibi na ral 1 case. The nic the sediment also Critical experiments are needed. 9.. Fi nt y one this nor

Shore bi and waterfowl are i in dispersal feed in areas dense T. imitator populations and {1980, 1984) indicate the snails can importa in dowitchers, western sandpipers, dunlin, and American in southern lifornia.

11. imitator is parasitized by cercariae an unidentified digenetic trematode, the affects of whi studied.

12. Tryonia imitator shares many features with dwelling hydrobiid snails that make them ecologically i important organisms. These incl 1 i , hi density populations, trophic resource se, avail li s susceptibili to si sm.. It is ly c in a it it th most i hydrobiids and which can be The phylogenetic distri on is it explored .. l CI

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