California State University, Northridge Movement and Reproduction in the Chiton Nuttallina Californica
CALIFORNIA STATE UNIVERSITY, NORTHRIDGE
MOVEMENT AND REPRODUCTION IN THE CHITON NUTTALLINA CALIFORNICA
A thesis submitted in partial satisfaction of the requirements for the degree of Master of Science in
Biology
Joel Tiefel
August, 1987 approved:
Dr. Ross Pohlo
Dr. Earl Segal
California State University, Northridge
1 1 ACKNOWLEDGEMENTS
I would 1 iKe to formally thanK the members of my committee: Dr. Ross Pohlo, Dr. Larry Allen and Dr.
Earl Segal, for their valuable comments and help on my manuscript. I especially want to thanK Dr. Segal for bearing with me the past several years and encouraging me to finish the thesis. His demand of excellence and concern with details have been outstanding examples I hope to pass on to my students.
I am extremely grateful to my wife, Jody, whose love and support have been a great encouragement throughout this project.
1 1 1 TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS ••••••••••••••••••••••••••••••••••••
LIST OF FIGURES •••••••••••••••••••••••••••••••••••••• v
LIST OF TABLES ••••••••••••••••••••••••••••••••••••••• v
ABSTRACT •••••••••••••••••••••••••••••••••••••••••••• v
INTRODUCTION •••••••••••••••••••••••••••••••••••••••••• 1 t1ATER I ALS AND METHODS ••••••••••••••••••••••••••••••••• 4
Reproduction ••••••••••••••••••••••••••••••••••••• 7
Homing •••••••••••••••••••••••••••••••••••••••••• 11
RESULTS •••••••••••••••••••••••••••••••••••••••••••••• 1 3
Reproduction •••••••••••••••••••••••••••••••••••• 13
Gross Horphology ••.••••••••.••••••.•.•••.••••..• 20
Homing •••••••••••••••••••••••••••••••••••••••••• 22
0 J SCUSS I ON a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a • a 11 • a a a 11 a a 35
Reproduction •••••••••••••••••••••••••••••••••••• 35
Homing •••••••••••••••••••••••••••••••••••••••••• 37
S UI"11'1A RY • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 4 2
LITERATURE CITED ••••••••••••••••••••••••••••••••••••• 43
APPEND I X ••••••••••••••••••••••••••••••••••••••••••••• 48
lV LIST OF FIGURES
Figure Page
1 • Loc at i on of Nut t a 1 1 i n a c a 1 i for· n i c a study at Marina del Rey, California •••••••••••• 6
2. Dorsal view of gonads and associated organs of Nuttall ina cal ifornica •••••••••••••• 10
3. Micrographs (100 x) of cross section through ovaries and associated organs of female Nuttall ina cal ifornica from March 1986 and December 1985 .••.••••••••••••.• 15
4. Monthly average of stage III oocytes per gram of wet body weight ••••••••••••••••••••••• 17
5. Micrographs <100 x) of cross section through testes and associated organs of ma 1 e Nut t a 1 1 i n a c a 1 i for· n i c a from May 1986 and September 1985 •••••••••••••••••••••• 19
6. The percentage and number of Nuttall ina cal ifornica homing from each home spot type • .•••.••••••••.••.••.••..•....•.••.•••.•.• 26
7. The percentage and number of Nuttallina cal ifornica homing based on size •••••••••••••• 28
8. The percentage of Nuttall ina cal ifornica observed active during substudy B 9. The percentage of Nuttall ina cal ifornica observed active during substudies A and C (July 2, August 29, and Nov ember 1 0 to Nov ember 11 , 1 984) ••••••••••••• 34 v LIST OF TABLES Table Page 1. Ratio of male to female Nuttall ina cal ifornica collected monthly .••••••••••••••.• 21 2. Number and percentage of Nuttall ina cal ifornica showing fidelity to a spot based on homespot type and size of chitons •••.•••••••••••••••••••••••..••.•••••.• 24 3. Number and percentage of Nuttall ina cal ifornica in original spot after stated number of days based on home spot type and animal size ••••••••••••••••••••••••• 29 vi {l ' ABSTRACT MOVEMENT AND REPRODUCTION IN THE CHITON NUTTALLINA CALIFORNICA by Joel Tiefel Master of Science in Biology The reproductive cycle of Nuttall ina cal ifornica was studied from September 1985 until August 1986 and its movements from December 1982 until January 1985 at Marina del Rey, California. A method of analyzing histological sections of ovaries for mature oocytes, previously used on Bivalvia and Asteroidea for determining a reproductive cycle, was used on~ cal ifornica. The results indicate a probable breeding period between March and July. Movements of this species occurred when it was awash or submerged and the time of day appar·en t 1 y made no difference. Nuttall ina cal ifornica~s movements indicate it is a homing species si nee 85/~ of marl vii with the greatest fidelity being to spots alongside other animals and in depressions. viii INTRODUCTION Nuttall ina cal ifornica is one of the most abundant species of chi tons in southern California and possibly all of California. It is found from the Straits of Juan de Fuca, Washington, to the Gulf of California it appears none of the southern California chi tons occupy a higher, more exposed station Prior studies on Nuttall ina cal ifornica from HopKins Marine Station in Pacific Grove, California, have involved the impact of Larus occidental is, the Western Gull, foraging on~ cal ifornica its response to osmotic stress its blood ionic compositon Legard, 1975>. 2 More extensively Kues (1969) examined several aspects of the ecology of Nuttall ina cal ifornica including movements in two locations in La Jolla, California. Vesco <1980) examined the relationship between~ cal ifornica and organisms in a coralline algal community at Whites Point, Los Angeles, California, including movement studies. Louda (1972> looKed at the effect different densities of~ cal ifornica have on its associated intertidal community in Santa Barbara, California. While a number of studies on reproduction in various species of chitons have been carried out, a study on Nuttall ina cal ifornica has not been among them. The reproductive cycle has been determined for many chitons including: Cryptoconchus porosus from New Zealand (Brewin, 1942>; Katharina tunicata, Mopal ia hindsi i Cryptochiton stelleri from the west coast of the United States The development of oocytes and associated cells has been studied in the chi tons Mopal ia mucosa and Chaetopleura apiculata (Anderson, 196?) from the United States, in Sypharochiton septentriones from Australia, in Chiton tuberculatum (Cowden, 1961) from Bermuda, and in Acanthopleura spiniger Sea. The lacK of reproductive information on Nuttall ina cal ifornica, incomplete observations on its movements, the ease of access to it at low tide, and its relative abundance prompted this present study. MATERIALS AND METHODS Nuttall ina cal ifornica Some refer to it as Nuttall ina fluxa when it is located south of Point Conception and Nuttall ina cal ifornica when it is found north of the Point MacGinitie, 1968; McLean, 1969). However, several investigators question this distinction believing them to be the same species 1980). It will be referred to in this paper as Nut t a 1 1 i n a cal i for· n i ca. The location for this study was Marina del Rey, California <33°58'10"N, 118°26'40"W). The area used was along the south side of the marina along the levee/jetty separating the marina from La Ballona CreeK. The area extended from BOO meters east of the west end of the jetty, where the Pacific Avenue bridge crosses over the creeK to the jetty, to about 670 meters east primarily hard granitic and conglomerate composition maKe up this jetty. Nuttall ina cal ifornica is found on the sides and tops of these boulders in natural depressions, alongside other animals, and in the open from the upper intertidal area to the middle intertidal area 4 5 Fig. 1. Location of Nuttall ina cal ifornica study at Marina del Rey, California. Study area marked. •D 41 A.'- I ~ I~ <,' ~-~~;,','• /h(,_AlTL 'lllarina de/ f:?e'J .:, ·£..:.,_...~'- ·--~ • . ..(" :·/;J~··.··--.. o.,,R•£ ./_.,/• ...-\,,.- · . ---.l..., trp"~lr( \ ~/ ,. /''- 125 . . . _ Vrq,., t. \;;;;J 9}-' ·: --~~~~~v.. '"'• '· ,.. <· Ll ~-~-'~v..._~~ ~,\~g~ 103 0 ~·- ..... #. '\\ ~(;+'"" """ -t '. ' \ 102 1C • 18 \ <' I ,. t \, ~~ --~_.!-__.!_ ---- t: .. ~' G .-:/\ ...... c ,.. _,.."--;::' .. \: ~\ . t> . ·l·~O J ~~0 -- '' ' ' '' ' ,.,. •• ''' ' '' J . ·''-. \ -"'•AOu""' ,.., ' \ ;"/. \ . ' \ \· :r \v .. , ' \ \• ~: .,o· ... ,, -- of)'- .... \ \ ; ... ,~ ·~.. -.- ,, \.. ,"' o+ \\ \\ ; ,_., \· ' -;'"? ~~(; \". '' " 'f ,, \. "' / \ ~-iQRTH-.rs; ~ / \ PA~S&G~~--~~----~--- ' ,_._ CAPT.t.p.,c:. 6• .. ' 510111 c.'" • 65· \' / / .· _-' / .' / ~,..- ,·-~·'. . ' ./ . . ~ ~ ./ ~ ~~;-:t, . ' ·f ~- '"'y,\ ' ' ;/'\. •...... o ';?~ ~ 0 '2000' \. . . \ I I I ~h . - '· 1000' '~..,. \ 7 occuring below 0.0 datum. The other major animals found in this study area with~ cal ifornica include Co 1 1 i se 11 a d i g i t a 1 i s, Co 11 i se 1 1 a 1 i rna t u 1 a, Co 1 1 i se 1 1 a scabra (finger, file and rough 1 impets>, Chthamalus fissus (small acorn barnacle>, Pachygrapsus crassipes, snail>, Anthopleura xanthogrammica (giant green anemone>, Serpulorbis sguamigerus Mytilus edul is (bay mussel>, and Mopal ia muscosa (mossy chiton). Reproduction Fourteen animals were collected monthly during daylight hours and low tide from September 1985 until August 1986. The length of each animal was recorded. Only animals longer than 25 mm were selected since results from a preliminary study indicated the smallest female with mature oocytes was 23 mm in length. The animals were taKen to laboratory facilities at MoorparK High School where the valves were removed, the bodies damp dried, and weighed to the nearest mg solution (6 parts 95% ethyl alcohol, 3 parts 45% formal in and 1 part glacial acetic acid) and after three days, transferred to 70% ethanol where they remained for a mininum of two weeKs. 8 All females and at least one male from each month/s collection were processed for histological analysis. A preliminary study indicated the reproductive state of male chitons could not be clearly determined from histological preparations of testes since the testes were essentially identical in appearance. The internal organs were then dissected out 10p. Because of the length of the gonad and somewhat irregular shape, sections were taKen at the anterior, middle, and posterior end Micrographs of oocyte stages from other ~hitons were compared to Nuttall ina cal ifornica to maKe initial differentiation of its oocytes. An ocular micrometer was used to determine a size range for the oocyte stages. Mean oocyte di ameter·s were calculated as the average of measurements along the longest and shortest axes of 325 randomly selected oocytes Gustafson, 1987>. Each section of a slide was then examined and the number of stage Ill oocytes counted. The section having the highest number of stage III oocytes was used 9 Fig. 2. Dorsal view of gonads and associated organs of Nu t t a 1 1 i n a c a 1 i for n i c a . ------represents area where cuts were made for histological sections 10 . I - --t:::::::::::;;;;;tt-::; OVa r3 +~-trs dorsa1 L--J-~t::r aorta fEMALE.. I I in calculating an oocyte to g~am of wet body weight ~atio fo~ that animal. Monthly ave~ages ove~ the yea~ of the oocyte to g~am wet body weight ~atio we~e plotted and a two-sample Student-'s "t" test was applied to dete~mine if the~e was any significance in the va~iation of monthly ave~ages Homing F~om Decembe~ 1982 until Janua~y 1985 a study was conducted involving 146 Nuttall ina cal ifo~nica. Du~ing low tides the chitons we~e obse~ved and numbe~ed with a fast-d~ying o~ange enamel paint. The home spot of each chiton was ma~ked with the same numbe~. Each animal"s o~iginal home spot, the compass di~ection its head was facing, and its body length in mm were ~ecorded. Three substudies--two day-long, low-tide to low-tide observations 11/10/85>--we~e included in this study. Movement was checked and recorded at 24-hour in terva 1 s (the second consecutive 1 ow tide> in the study and also every one to three hours in substudies A, B, and C above. When chitons were found occupying new spots during a low tide, these too were marked with the animal"s number and dots to indicate it being the second, thi~d, or other home spot. 1 2 Du~ing substudy A, a face masK and sno~Kel we~e used to obse~ve the chitons when subme~ged. In addition to this equipment, a wet suit and a wate~p~oof flashlight with a ~ed lens to avoid any 1 ight distu~bance to the animals (Smith, 1975; Lyman, 1975) were added to substudy C. Reco~ds we~e Kept of <1> the numbe~ and length of animals leaving and ~etu~ning to each spot and <2> the numbe~ and length of animals ~emaining at each spot fo~ at least 24 hou~s. Compa~isons we~e then made conside~ing all facto~s in the two catego~ies. Fidelity to a home spot was based on the total numbe~ of chitons that eithe~ ~etu~ned to a spot afte~ leaving o~ ~emained in a spot fo~ 24 o~ mo~e hou~s. @ ' RESULTS Reproduction Calculations of the mean diameters of the randomly selected oocytes clearly showed three stages. Stage I oocytes ranged from 20 to 52)U, stage II oocytes from 52 to 98)/, and stage III from 98 to 188~· A graph of the ratio of average number of stage III oocytes per gram of wet body weight versus month of the year can be seen in Fig. 4. The means of the months of March-July were significantly higher than the means of the seven other months There is, therefore, a high probability of a breeding season for Nuttal ina cal ifornica during the months of March through July. As from a preliminary study, examination of the histological preparations of testes indicated the majority of the individuals were identical in appearance. Spermatozoa were present in all specimens including a few where the testes were partially spent I 3 14 Fig. 3a-b. Micrographs <100 x) of cross section through ovaries and associated organs of female Nuttall ina cal ifornica from March 1986 and December 1985. Stage I, II, and III oocytes and the gut or intestinal tract are labeled. IS a b 16 Fig. 4. Monthly average of stage III oocytes per gram of wet body weight. AVG.S.III OOCYTES/GRAM ~ t-..:l lJ..I _,... t.n 0') 0 0 o o a C> 0 t..) SEP.B5 OCT.B5 )~1',) N0'./.8.5 DEC.B5 ~~:;. ~;n ,/./'/' ...... ,JAN.B6 0 FEB.B6 ~ --...... _ rrl t -~ ...... ~ (A M.AR.86 -...., APR.B6 "7~ MA.Y 86 1 JUN.B6 ...... "">~ / ...... - / JUL.86 / /~· / .. AUG.B6 +"".~- ~ 18 Fig. Sa-b. Micrographs (100 x) of cross section through testes and associated organs of male Nuttall ina cal ifornica from May 1986 and September 1985. Upper micrograph shows testis full of spermatozoa while the lower micrograph shows testis partially spent. 19 a b "; 20 the highest number of females for any month was eight and the lowest was four. The highest number of males for any month was ten and the lowest number, six. The total numbers collected for the year were 96 males and 72 females. This is a ratio of 1.33 to 1 Gross Morphology Dissection of Nuttall ina cal ifornica revealed it to be dioecious, but no external sexual dimorphism can be seen. Internally, males can be distinguished from females by gonad color. In females the color is darK green to 1 ight yellow while in males it is orange-yellow to red. This color distinction was borne out by the fact that only those animals with darK green to 1 ight yellow gonads possessed oocytes and only those with orange-yellow to red gonads possessed sperm. The gonad is located in the median dorsa~ region just anterior to the pericardium beneath the muscles supporting and holding the third to sixth valves and in some cases extending to the seventh. It is narrowly attached along its mid-dorsal 1 ine to the under side of these muscles by way of the dorsal aorta. The gonad wall is highly folded except dorsally. In females these folds contain developing oocytes. These folds, with the accompanying oocytes, are often entwined with the intestine and midgut glands or 1 iver il ' 2 I Table 1.--Ratio of male to female Nuttall ina cal ifornica collected monthly Month Number of Males Number of Females Sep. 85 6 8 Oct. 85 8 6 Nov. 85 7 7 Dec. 85. 8 6 Jan. 86 9 5 Feb. 86 8 6 Mar. 86 7 7 Apr. 86 9 5 May 86 9 5 Jun. 86 7 7 Ju 1 • 86 10 4 Aug. 86 8 6 Totals 96 72 Ratio of males to females: 1.33 1 22 imposssible to remove intact. The reproductive anatomy of Nuttall ina cal ifornica was found to be essentially identical to that of other chitons described by Hyman (1967). Homing The 146 chitons used over the course of the study were found to be in three different types of home spots: depressions, alongside other animals, or in the open. A "depression" refers to a hole of any kind in the rock that ~ould either be the shape of the chiton's body or larger and varied in depth from less than the height of the chiton to several times its height. "Alongside other animals" refers to the chiton being located by or under one of four different animals: Serpulorbis sguamigerous, Chthamalus fissus, Anthopleura xanthogr·ammica, and Myti lus edul is. •In the open" means there was no apparent covering or depression under which or near which the chiton could be found. A comparison between home spot type and number of chitons homing revealed 43 of the 146 animals <29%) left and returned to the same spot--thus homed. This number represents 29% of the animals found in depressions, 33% of those alongside other animals and 23% of those in the open. Eighty-two additional animals (56%) remained at the same spot for at least 24 23 hours, i.e. they were not observed leaving and returning. This number represents 57% of the animals in depressions, 57% of those alongside other animal~ and 46% of those found in the open. Combining the 29% that left and returned and the 56% that remained for at least 24 hours indicates that 85% showed fidelity to a particular spot A comparison was also made between size of the animals and the number homing. The size range was from 15 to 40 mm with the animals arranged into two size groupings: one from 15 to 28 mm and the other, 29 to 40 mm. In the first group 24 (27%> homed by leaving and returning and 53 (60%) could be found at the same spot for at least 24 hours. In the second group 19 <3Z/.> homed by leaving and returning, and 29 (50%> were at home after 24 hours Table 3 shows the number and percentage of chitons in their original home from one to nine days after first observations were made. Those chitons in depressions have the highest number and percentage remaining in the same spot after each day. Further, the smaller chitons, less than 29 mm, also have a higher number and percentage in the original spot after each day's observation. In addition to homing, other movements were seen. Ten chitons were seen occupying spots previously occupied by other chitons. Two of these actually 24 Table 2.-- Number and percentage of Nut t i>.ll ina c a 1 if or n i c a !:hOtoJ i ng f i de 1 i t >' to a spot bc>.sed on home spot type c>.nd size of c h i tons. II A % B % c % D % E /. F In depre!:ions 100 27 27 2 2 54 54 3 3 86 86 II Alongside other animals 33 10 30 3 9 27 10 30 30 91 3 In the Open 13 3 23 0 0 3 23 3 23 9 69 3 Totals 146 40 27 3 2 66 45 16 1 1 125 86 17 Less than 29 mm 88 23 26 45 51 8 9 77 88 11 Grec>.ter than 28 mm 58 17 29 2 3 21 36 8 14 48 83 6 Total:- 146 40 27 3 2 66 45 16 1 1 125 86 17 Key to column letters: A: Number of chi tons observed lec>.ving c>.nd returning at lec>.st once to origin<>.! spot. 8: Number of chi tons ob!:e>r·ved lec>.ving c>.nd returning to another but not to first spot. C: l'lumbe>r of chi tons rem<>.ining in origiroc>-1 spot c>.t le<>.st 24 hours. Does not incl•Jde those in column A D: Number of chi tons at anot.he>r !:-pot for 24 hours. Doe>s not include those in column c. . E: Tote>. 1 shot.•Jing f i d"' 1 i t )' to a !:pOt. F: 1-Jumbe r of chi tons at both origin a 1 and 2nd spot at 1 e c>.s t 24 loours. 25 Fig. 6. The percentage and number of Nuttall ina cal ifornica homing from each home spot type. * indicates number of animals 26 Percentage of Anirnals 0 Depression I 0 3 In Open ~/ ~'!I ~~ r ::t1 a!> (b 0s. 3 :;) 0 &0 5' 0 5' :;) &D Q 0 ;::u ~ a:. :I c.-1 0 .... 3 =- (b 10=- 0 ' ' ' 27 Fig. 7. The percentage and number of Nuttall ina cal ifornica homing based on size. * indicates number of animals 28 Percentage of Animals --' 0 0 0 &, ~rn rn ..... ::r 0 ;:) 1'0 (,() )> :::l 3 3 3 0 G) (/) ..... ('[l N 0 rl" ~~~ ~,9 ~~ r a:> ~ s:.0 3 :> 0 10 :;)' :;)' 0 10 a:::::0 0...... ::::0 a:> :I c,..-t 0 ..... 3 Table 3a.--Number and percentage of Nut ta 11 ina cal i forn i ca in or i gina 1 spot after stated number of dars based on home spot type. Number of Days 2 3 4 5 6 7 8 9 In Depressions 54 43 28 27 24 7 6 6 5 Alongside Animals 9 6 4 4 4 In the Open 3 2 0 0 0 Totals 66 51 33 32 2$' 9 7 7 6 /. In Depressions 54 43 28 27 24 7 6 6 5 /. Alongside Animals 27 18 12 12 12 3 3 3 3 /. In the Open 23 15 8 8 8 8 0 0 ·o Tot. /. (ltchi tons/146 tot.> 45 35 23 22 20 6 5 5 4 Table 3b.--Number and percentage of Nuttall ina c a 1 i for n i c a in original <:pot after stated number of days based oro size. Number of Days 2 3 4 5 6 7 8 9 Less than 29 mm 45 32 22 22 21 8 6 6 5 Greatt-r than 28 mm 21 19 11 10 8 Totals 66 51 33 32 29 9 7 7 6 /. Lt-ss than 29 mm 51 36 25 25 24 9 7 7 6 /. Grt- a tt-r than 28 mm 36 33 19 17 14 2 2 2 2 Tot. /. Ulch i tons/146 tot.> 45 35 23 22 20 6 5 5 4 30 exchanged spots. Three chitons were also seen moving while exposed. One of these moved three em and turned 180°. The other two moved less than two em. A summary of chiton activity level during substudies A, B, and C is presented in Fig. 8 and Fig. 9. Any individual not in its original home spot or turning within its home spot was considered active. The diagrams indicate all activity occurs when the animals are either awash or submerged. The highest percentage of animals active was recorded during one awash period on an outgoing tide (8/29/84>. In both substudies A and B, the highest percentage of animals active was du~ing or within one hour of awash periods. Substudy C also revealed activity at or near awash periods, but a higher percentage of chitons were found moving several hours after submergence. 3 I Fig. Sa-b. The pe~centage of Nuttall ina cal ifo~nica obse~ved active du~ing substudy B a. 100 4/19/84 90 eo g! 70 ...... 'i!60 gso"' ...... e 4o N 30 20 10 600 E I A s b. 100 6/19/84 90 80 II 70 ...... > ...:u 60 "'c 50 ...... 0 e 4o N 30 2t.% 20 187. 187. ui A I s lll\'i 33 Fig. 9a-c. The percentage of Nuttall ina cal ifornica observed active during substudies A and C (July 2, August 29, and November 10-11, 1984). E =emerged or uncovered, A= awash, S = submerged or covered, ( ) = number of animals. 34 a. 100 90 712184 eo -~ 70 .... .'i!60 §so"' .... 6 40 30 29% 20 17% 10 6't I (I) ['" 600 700 BOO 900 1000 1100 1200 1300 1400 1500 1600 1700 I BOO 1900 Hours E s E b. 100 8129184 90 8 % eo 7 % .::.. 70 .... .';j 60 "'g so .... II) 13) 6 40 30 20 13% 10 7% 2) I) 500 600 700 BOO 900 1000 1100 1200 1300 1400 1500 1600 1700 !BOO Hours E s A E II II i"Wi DAY c. 100 IIIlO- 11111184 90 eo ....~ 70 ...... ';! 60 "'c ~ so .... 437. 6 40 30 9) 20 10 E I A I s I A IE lA Is IV I I I I I II I II I II I I I 11111111 I 1111111111111 I INIGIT 11111111111 I 11111111 I IIIII I II I I 11111111 I I I I§ DISCUSSirn~ Reproduction The relative size of the gonads of many chitons shows regular annual fluctuations. Many investigators have made use of this in a gonad index Tucker and Boolootian, 1959; Tucker and Giese, 1962). A different method, analyzing histological sections of the ovaries for oocytes, was employed with Nuttall ina cal ifornica. This method, though to my knowledge not used before in chitons, has been used with other invertebrates, e.g. Bivalvia Asteroidea 1987). At least three distinct stages of oocyte development have been identified in other chitons according to cytochemical and ultrastructural characteristics 1968). Anderson <1969>, described the sizes of stage I and mature oocytes in Mopal ia muscosa and Chaetopleura apiculata. In the former, stage I is 20pin diameter and mature oocytes range from 225 to 250}/. In~ apiculata stage I oocytes are also 20p in diameter and mature oocytes are 180-190~. Boolootian <1964>, 35 36 however, indicates the size range of mature oocytes in ~ muscosa to be 140 to 168)/. The results of measurements on the randomly selected oocytes of Nuttall ina cal ifornica also show three stages of development. Since it is the stage III oocytes that are released during spawning The spawning period for Nuttall ina cal ifornica, according to monthly stage III oocyte per gram wet weight averages, is between March and July. The months of September through February are a probable period of oocyte formation and growth with August being a resting or inactive phase of the gonads. Other chitons whose reproductive cycles have been studied indicate a variety of patterns. Katharina tunicata shows a clear breeding season during the early summer, but Mopal ia hindsi i from the same area shows an almost reciprocal cycle with maximum activity in the winter Mopal ia muscosa, a co-occurring chiton with Nuttall ina cal ifornica, the data on spawning was not clear and may indicate different breeding months for populations in slightly different areas Cryptochiton stelleri breeds in February or March (A~ey and C~ozie~, 1919>; Chaetopleu~a apiculata, June, July, and August Homing Many aspects of the behavio~al ecology of inte~tidal chitons have been ~epo~ted since the fi~st study of A~ey and C~ozie~ <1919> on Chiton tube~culatus. Seve~al species studied show a "homing behavio~" simila~ to the movement patte~n desc~ibed in p~osob~anch and pulmonate 1 impets and in opisthob~anchs. Though homing behavio~ has been desc~ibed in ove~ eight chitons 1919; Chelazzi et al., 1983; Glynn, 1970; Lyman, 1975; Mille~ and Batt, 1973; Schmidt-Effing it has also been used to mean ~etu~ning to a gene~al a~ea o~ app~oximately the same site with a diffe~ent o~ientation 1975>. This assumption is based on p~io~ obse~vations of the vast majo~ity of the animals maKing fo~aging o~ othe~ movements sometime du~ing each daily tidal cycle Vesco (1980) observed foraging in Nuttall ina cal ifornica and determined that most do maKe feeding forays each day since 90% of the chitons from one community and 77% from another had full gastrointestinal tracts while no tracts were less than half full. A general consensus from the many studies investigated is that at least half of the animals should be seen leaving and returning to their home spot or be seen in their home spot after 24 hours if they are to be called a homing species. Therefore, Nuttall ina cal ifornica is another homing species as a total of 85% displayed one or the other types of homing behavior. Some chitons that do return to a specific location may change their home after a few days. Seventeen <1?/.) of the chitons I observed occupied at least two homes. Some of the reasons for this may be: <1> lacK of suitable food in the former area, <2> occupancy of its spot by another chiton, and (3) the second home may merely be a resting or stopover place until it returns to its original home. Though others have found Nuttall ina cal ifornica only occupying depressions as home spots ( Kues, 1969; MacGinitie and MacGinitie, 1968; Nishi, 1975; Vesco, 1980>, the results of this study show a number occupy other types of homes. The majority of the 146 chitons 39 occupied depressions (68%>; but others occupied spots alongside other animals (23%>, and still others were found in the open (9%). Andrus and Legard (1975) similarly found~ cal ifornica, in Central California, located alongside other animals such as Tetracl ita squamosa rubescens, Poll icipes polymerus, and Mytilus cal ifornianus. The significance of these home spot types to homing indicates a preference of Nuttall ina cal ifornica for depressions and homes alongside other animals. It will home to all three types of homes I delineated, but shows the greatest fidelity to spots alongside other animals with depressions very close behind. Kues <1969) showed the importance of a depression as a home spot by comparing amounts of water lost by chitons in depressions to those removed from depressions and attached to flat rock surfaces. After six hours the average water loss for those in depressions was 9.5% while that for those out of depressions was 54.3%. The depressions help to trap some water and keep the animals from desiccating. A spot alongside other animals may serve the same purp~se. In agreement with Kues (1969), Nuttall ina cal ifornica was found to move when awash or submerged. The time of day made no apparent difference in chiton movement since the controlling factor was the presence of water. In only a very few cases were animals found 40 moving when exposed and then distances of three em or less. Perhaps moving when awash or submerged serves a similar function-- prevention of desiccation. Cranoplax hartwegi i and Mopal ia muscosa, whose ranges overlap Nuttall ina cal ifornica in Central California have different activity patterns. Cranoplax hartwegi i was found, unliKe ~cal ifornica, to be most active when exposed or awash 1 iKe~ cal ifornica, was active when awash or submerged dessication since its movements were primarily under macroalgae. Some of the explanations that have been offered on the advantages of homing in 1 impets and chi tons include protection from dislodgment 1975; Collins, 1977; Lindberg and Dwyer, 1983), predator avoidance Wells, 1980>, location near suitable food resources and protection from desiccation 1969; Lyman, 1975; Vesco, 1980; Verderber et al ., 1983>. Although I observed no predation on Nuttall ina cal ifornica, Moore <1975> noted that the Western Gull may consume up to 15/. of a local population during its 90-day breeding season. The homing of ~ cal ifornica to depressions and alongside other animals when exposed p • 4 I may prevent some of this predation. Homing, as a means of locating near suitable food resources, may be true in~ cal ifornica as the vast majority of homes were located in denser areas of microalgae. Nishi (1975> and Vesco (1980) have already shown microalgae to be a food source for this chiton. According to Connor and Quinn (1984>, the slime trail left by two homing 1 impet species traps and actually stimulates the growth of microalgae. As they move bacK over these trails they receive the benefit from the action of their mucus. Although not yet investigated, the regular pattern of homing movements of~ cal ifornica may have the same effect and thus Keep it near its food resources. SUMMARY 1. A reproductive cycle was determined for Nuttall ina cal ifornica based on histological examination of ovaries for the number of mature oocytes. This method has not previously been used in chitons. 2. The breeding season for ~cal ifornica, based on this method, is March through July. 3. Nuttall ina cal ifornica is another homing species since 85% of the animals marked either left and returned to the same spot or remained at that spot for at least 24 hours. 4. Three major types of home spots were identified for t::L. c a 1 if or n i c a: in depressions, alongside other animals, and in the open. I t w i 1 1 horne to a 1 1 three but shows the greatest fidelity to spots alongside other animals with depressions a close second. 5. Movement in t::L. cal ifornica occurs when the animal is awash or submerged. In only a few rare cases was a small amount of movement seen when the animal was uncovered. 6. Homing in t::L. cal ifornica is probably advantageous in preventing dessication stress, in predator avoidance, and in location near food resources. 42 LITERATURE CITED Anderson, E. 1969. Oocyte-foll i c 1 e ce 11 differentiation in two species of amphineurans Andrus, J. K., and W. B. Legard. 1975. Description of the habitats of several intertidal chitons Arey, A. L. and W. J. Crozier. 1919. The sensory responses of~ tuberculatum. J. Exp. Zool. 29:157-260. Boolootian, R. A. 1964. Growth, feeding and reproduction in the chiton Mopal ia muscosa of Santa Monica Bay. Helgol will. Meeresunters. 11 : 1 86-199 • Brewin, B. I. 1942. The breeding habits of Cryotoconchus porosus Burghardt, G. E., and L. E. Burghardt. 1969. A collector~s guide to west coast chitons. San Francisco Aquarium Soc. Inc., San Francisco. Spec. Publ. No. 4. 45 pp. Chelazzi, G.; S. Focardi, and J. L. Deneubourg. 1983. A comparative study on the movement patterns of two sympatric tropical chitons Christiansen, M. E. 1954. The life history of Lepidopleurus asellus. Nat. Mag. Zool. 2:52-72. Collins, L. S. 1977. Substrate angle, movement and orientation of two sympatric species of limpets, Coll isella digital is and Coll isella scabra. The Vel iger 20:43-48. Connor, V. M., and J. F. Quinn. 1984. Stimulation of food species growth by 1 impet mucus. Science 225:843-844. Cowden, R. R. 1961. A cytochemical investigation of oogenesis and development to the swimming larval stage in Chiton tuberculatum. Biol. Bull. mar. biol. Lab., Woods Hole 120:313-325. 43 44 Giese, A. C.; J. S. Tucker, and R. A. Boolootian. 1959. Annual reproductive cycles of the chitons Katherina tunicata and Mopal ia hindsi i. Biol. Bull. mar. biol. Lab., Woods Hole 117:81-88. Glynn, P. W. 1970. The ecology of the Caribbean chitons Acanthopleura oranulata and Chiton tuber c u 1 at us, dens i t y, mort a 1 i t y, feed i n g, reproduction and growth. Smith. Con tr i b. Zool • 66:1-21. Gomez, R. L. 1975. An association between Nuttall ina cal ifornica and Cyanoplax dentiens, two West coast polyplacophorans Grant, A. and P.A. Tyler. 1983. The analysis of data in studies of invertebrate reproduction. I. Introduction and statistical analysis of gonad indices and maturity indices. Inter. J. Invert. Reprod. 6:259-269. Grant, A. and P.A. Tyler. 1983. The analysis of data in studies of invertebrate reproduction. II. The analysis of oocyte size/frequency data, and comparison of different types of data. Inter. J. Invert. Reprod. 6:271-283. Grave, B. H. 1922. An analysis of the spawning habits and spawning stimuli of Chaetopleura apiculata. B i o 1 • Bu 1 1 • mar • b i o 1 • Lab. , Woods Ho 1 e 42:234-256. Gustafson, R. and B. D. Gustafson. 1987. Cont)nuous reproduction in the protobranch bivalve Solemya reidi Heath, H. 1905. The breeding habits of the chitons of the California coast. Zool. Anz. 29:390-393. Hyman, L. H. 1967. The Invertebrates. Volume 6. Mollusca 1. Aplacophora, Polyplacophora, Monoplacophora, Gastropoda, the coelomate Bilateria. McGraw-Hill Book Co., New York. 792 pp. Kues, B. S. 1969. The chi tons of southern California including some aspects of the ecology of Nuttall ina fluxa Carpenter. M. S. Thesis, University of California, San Diego. 192 pp. 45 Lindbe~g, D. and K. Dwye~. 1983. The topog~aphy, fo~mation and ~ole of the home dep~ession of Coll isella scab~a Linsenmeye~, T. A. 1975. The ~esistance of five species of polyplacopho~ans to ~emoval f~om natu~al and a~tificial su~faces. The Vel ige~ 18 Louda, S. M. 1972. The abundance and dist~ibution of a chi ton, Nuttall ina fl uxa Lyman, B. W. 1975. Activity patte~ns of the chiton Cyanoplax ha~twegi i MacGinitie, G. E., and N. MacGinitie. 1968. Natu~al histo~y of marine animals. New Yo~k: McG~aw-Hill Book Co. 523 PP• MacKay, D. A. and A. J. Unde~wood. 1977. Expe~imental studies in the inte~tidal pate11 id 1 impet Cellana t~amose~ica Mclean, J. H. 1969. Ma~ine shells of southe~n Cal ifo~nia. Revised ed. Nat. Hist. Mus. Los Angeles Cty., Sci. Se~. 24:1-104. M i 1 1 e ~ , M. and G. Bat t. 1 973 • Reef and beach 1 i f e of New Zealand. Hong Kong: Collins. 141 pp. Hook, D. 1983. Homing in the West Indian Chiton Acanthopleu~a g~anulata Gmel in, 1791. The Vel ige~ 26:101-105. Moo~e, M. M. 1975. Fo~aging of the weste~n gull, La~us occidental is and its impact on the chiton, Nuttall ina cal ifo~nica. The Vel ige~ 18 Nishi, R. 1975. The diet and feeding habits of Nuttall ina cal ifo~nica (Reeve, 1847> f~om two cont~asting habitats in cent~al Cal ifo~nia. The Vel ige~ 18(Suppl.> :30-33. Pipe~, S. 1975. The effects of ai~ exposu~e and exte~nal salinity change on the blood ionic composition of Nuttall ina cal ifo~nica. The Vel ige~ 18(Suppl.) :103-108. 46 Robbins, B. 1975. Aerial and Aquatic Respiration in the chi tons Nuttall ina cal ifornica and Tonicella 1 ineata. The Vel iger 18 Selwood, L • 1968. Interrelationships between developing oocytes and ovarian tissues in the chiton Sypharochiton. J. Morph. 125:71-104. Simonsen, M. 1975. Response to osmotic stress in vertically separated populations of an intertidal chiton, Nuttall ina cal ifornica. The Vel iger 18 Smith, A. G. 1977. Rectification of West Coast chiton nomenclature Smith, S. Y. 1975. Temporal and spatial activity patterns of the intertidal chiton Mopal ia muscosa. The Vel iger 18 Soliman, G. N. and A. N. lsKander. 1982. The reproduction and development of the common rocK chitons Acanthopleura spiniger Thorne, M. J. 1967. Homing in the chiton Acanthozostera gemmata Thorne, M. J. 1968. Studies on homing in the chitons Acar.thozostera gemmata. Aust. J. Mar. Fresh. Res. 19: 151-160. TucKer, J. S. and A. C. Giese. 1962. Reproductive cycle of Cryptochiton stelleri. J. Ex p • Zoo 1 • 150:33-43. Verderber, G. W.; S. B. CooK and C. B. CooK. 1983. The role of the home scar in reducing water loss during aerial exposure of the pulmonate 1 impet Siphonaria alternata Vesco, L. L. 1980. Interactions between the rocKy intertidal chiton Nutallina fluxa Wells, R. A. 1980. Activity pattern as a mechanism of predator avoidance in two species of acmaeid 1 impet. J. exp. mar. Biol. Ecol. 48:151-168. ' . 47 Za~, J. H. 1974. Biostatistical Analysis. New Je~sey: P~ent ice Hall, Inc. 620 pp. APPENDIX REPRODUCTIVE TABLE FOR FEMALE NUTTALL INA CALI FORIH CA DATE chi ton .. tiS. II I oocyt~s w~t wt. 9 Oocyhs/g Sep. 85 1 4 1. 02 3.91 2 II .80 13.83 8 32 .64 50.06 n=8 9 55 .77 71.70 10 27 I • 41 19.20 11 25 1 • 16 21 .46 12 12 I • 15 10.43 13 45 1 • 21 37.27 AI.'ERAGES: 26 1. 02 28.48 Oct. 85 5 25 1 • 16 21.46 8 36 .65 5'5. 1 0 9 14 .62 22.40 n=6 11 56 .85 65.71 12 20 1. 24 16. 18 13 14 .77 18.25 AVERAGES: 28 .88 33.18 Nov. 85 2 3 .7'8 3.84 3 56 1. 02 54.76 4 30 I .16 25.76 n=7 10 8 1. 0 I 7. ~·3 11 6 1. 56 3.84 12 17 .94 18. 13 14 47 1 • 51 ~:1. 22 AlJERAGES 24 1 • 14 20.78 DO?c. 85 2 3·;. 1. 09 35. 6~· 8 !e. 1 • 1 I 14.44 ? =~ 1. 08 34.27 n=6 I 0 90 1 • -~.( 7 50. 2·;· 11 43 I. 25 34.40 12 65 1. 58 4!. 23 AI.'ERAGES 48 I .32 35.05 Jan. 86 3 I 7 I .42 I I . 97' 6 40 I • I 2 35 ..~5 7 2~· I . 04 2'5.07 n=5 II !':' 2.14 8.86 13 21 1.80 I I. 64 A'JERAGES 25 1 • 51 18.64 Feb. 86 I • 51 4.6'5 4 37 1. 4":' .<.4.81 8 5 1 • 24 4.05 !4.78 n=6 ? 17., I , 15 13 _, .77 6.52 14 22 1. 32 1-:0 •.65 A'v'ERAGES 16 1. 2~· II • 91 Mar. 86 2 8-5 I. 36 .:.3. 07 4 69 I. 70 40.48 7 9 I .32 6.81 9 15 1 .25 12.00 n=7 10 19 I .22 15.55 11 100 1. 42 70.40 12 100 I. 49 e.7. os AVERAGES ..._,, - 1. 40 39.34 48 49 REPRODUCTIVE TABLE FOR FEMALE NUTTALL INA CALIFORNICA DATE chiton It ItS. I I I oocytes Wet wt. g Oocytes/g Apr. 86 7 65 .92 70.40 8 42 1. 04 40.50 10 80 1. 25 64.00 n=5 11 100 1.42 70.40 13 54 1. 28 42.24 AVERAGES 68 1.18 57.51 May 86 3 50 1 • 18 42.41 4 46 1.11 41 .52 n=5 6 92 1.36 67.4:- 7 62 1. 9.~ 31.63 11 85 1. 48 57.54 AVERAGES 67 1. 42 48.11 Jun. 86 3 90 1 • 14 79.20 6 100 1. 53 65.19 9 80 1.35 5'"'.28 10 27 1. 32 20.44 n=7 12. 87 1. 51 57.78 13 100 1. 42 70.40 14 90 1 . 19 75.43 AVERAGES 82 1. 35 61 .1 0 Jyl. 86 4 80 1 .43 55.76 5 100 1. (.~ 56.77 n=4 7 38 1. 83 20.74 14 29 1 .53 1:3. -r·o AVERAGES 62 1. 64 38.04 Aug. 86 1 1? I. 14 16.7 2 14 1 . 0 9 12.8 3 18 I .14 15.8 n=6 4 18 1. 34 13.4 7 9 .81 II .I 14 .22 1 .';;·2 11 .4 AVERAGES 17 1. 24 13.5 .
.