ABS TRAC T Comparative aspects of the ecology of three (: ) from different locations in Barbados, W. l. by Geoffrey Richard Chislett The growth, breeding, and feeding of N. peloronta, N. versicolor, and N. tesselata were studied at contrasting locations on the rocky shores of Barbados. The growth of aIl three species was found to be more rapid at the more sheltered station on the north west of the island. lnterspecific growth rates were as follows: N. peloronta grew fastest, with N. versicolor next, and N. tesselata slowest. There appeared to be no significant seasonal variations in growth ra te. AlI three species were shown to breed aIl year, with marked increaaesand decreases. Available moisture appeared to be an influencing factor. There was no correlation of breeding cycles in any of the species between the two stations. Sex

ratios were calculated also. 1 Feeding studies showed that the- animaIs at the more sheltered station apparently were able to begin feeding sooner :i than at the more exposed station; also feeding seemed to be " restricted mainly to the night time.

Zoology Department ; :Master of Science t ~;\ Comparison of sorne ecological aspects of three Nerita species. CHISLETT COMPARATIVE ASPECTS OF THE ECOLOGY OF THREE NERITA (MOLLUSCA:GASTROPODA) SPECIES FROM DIFFERENT LOCATIONS IN BARBADOS. W. :r.

by

Geoffrey Richard Chislett

A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfilment of the requirements for the degree of Master of Science.

Zoology Depàrtment McGill University Montreal. June 1969.

\ ® Geoffrey Richard Chislett 1970

" - 11 -

ACKNOWLEDGEMENTS

l should likë to thank Dr. J.B. Lewis of the Bellairs Research Institute of McGill University in Barbados for his help in directing this project. l am also grateful to Dr. P. Grant of the Zoology Department, McGill University for advice on statistical procedures and the use of his computer programme. Dr. H. Tyson and Dr. J. Stanley of the Genetics Department also provided valuable advice on statistical procedures. Thanks is also due to Mr. A. Richards of Bellairs for his help in surveying the three stations used in this study. Finally l am indebted to my wife for unfailing help and encouragement, and also for the typing of the thesis. This research project was supported by grant NONR 4939(00) from the Office of Naval Researc~, Washington, D.C., to Dr. J.B. Lewis. - iii - TABLE OF CONTENTS PAGE

ACKNOWLEDGEMENTS •...... ~ ...... ii LIST OF FIGURES ••••••••••••••• ...... iv LIST OF TABLES ••••••••••••••• ...... vi PREFACE •• ...... 1 PART 1. FIELD STATIONS Little Bay...... 3 Harrison's Lighthouse...... 3 South Point...... 5

Il. ENVIRO~ŒNTAL OBSERVATIONS Microclimate Data...... 12 Weather Station Data...... 12 Ill. GROWTH Introduction ••• ,...... 16 ~~terials and Methods...... 20 Results...... 24 Discussion...... 31 IV. BREEDING Introduction ••••••••••••••••••••••• 37 Materials and Methode •••••••••••••• 40 Re sul ts ...... 43 Discussion •••••••• ...... 55 V. FEE DING Introduction ••••••••••••••••••••••• 59 Materials and Methods •••••••••••••• 62 Re sul ts ...... 64 Discussion •••.• ...... 68 Vl. SUJ'illVLARY •• ...... 70

BIBLIOGR~PHY •••.••• • • • • • • • • • • • • • • • • 0 • • • • • • • • • • • 72 - iv -

LIST OF .FIGURES FIGURES -PAGE 1. Map of Barbados showing stations and wind rose...... 4 2. Photograph, map, and profile of station at Little Bay ••.••.•••••••••••.•••••••• 6 & 7 Photograph, map, and profile of station at South Point ••••••••••••••••••••••••• 8 & 9 4. Photograph, map, and profile of station at Harrison's Lighthouse •••••••••••••••• 10 & 11 Hourly means of microclimate observations in the intertidal zone ••••••••••••••••• 14 6. Means of five environmental parameters measured throughout the year at Little Bay, South Point, and Harrison's Ligh thouse •.....•...... ••.••.•.•. 15 Photograph of a tagged specimen of N. peloronta showing axis along which growth measurements were taken ••••••••• 21

8. Manzer and Taylor plot for~. peloronta representing growth rate for a one year period ••..••.•.••••.••.••••••••••• 26 Manzer and Taylor plot for N. versicolor representing growth rate for a one year period...... 27 10. Manzer and Taylor plot for N. tesselata representing growth rate for a six month period...... 28 11. Manzer and Taylor plots for N. peloronta, N. versicolor, and N. tessëlata. Regression lines represent monthly growth rates...... 30 12. Breeding cycles for the three Nerita species from Little Bay and South Point. 48 13. Correlation between percentages of N. peloronta in spawning condition at Little Bay and South Point ••••••••••• 50 - v -

FIGURE PAGE 14. Correlation between percentages of N. versicolor in spawning condition at Little Bay and South Point •••••••• 52 15. Correlation between percentages of N. tesselata in spawning condition at Little Bay and South Point •••••••• 53 16. Photographs and diagram of copulating Nerita ...... •.....•.• 54 17. Histograms showing percentages of animaIs in two stomach fullness classes froID Harrison's Lighthouse and Little Bay ••••••••••••••••••••••• 65 -vi-

LIST OF TABLES

TABLE PAGE 1. Coefficients of regression lines representing monthly growth rates for the three Nerita species at both Harrison's Lighthouse and Li ttle Bay ••••••••••••••••••••••••••••• 29 2. Chi-square values and levels of significance on high and low values of breeding graphs •••••••••••••• 47 Chi-square values and significance levels of sex ratios ••••••••••••••••••• 49 4. Chi-square values and levels of significance of intraspecific stomach fullness classes frolIt:the same stations...... 66 5. Chi-square values and levels of significance of intraspecific stomach fullness classes from different stations...... 67 - 1 - PREFACE The Nerita, fami1y , be10ngs to the group • Neritacea which is the most high1y developed group of the diotocardian gastropod mo11uscs. Nerita pe1oronta was first described by Linnaeus in 1758, and and Nerita tesselata by Gmelin in 1791. Warmke and Abbott (1961) have given brief morpho1ogical descriptions of these three species, with mentions of their range and habitat. Boume (1908) has provided detailed anatomical descriptions of several members of the Neritidae including some species of Nerita. The geographical distribution, according to Russell (1941), for N. peloronta and N. versicolor extends from south Florida and the Bahamas, through the West Indian archipelago and Central and South America, as far as Para, Brazil. N. tesse1ata is found only as far south as Trinidad. Several ecologica1 studies have been done on species of Nerita. Suzuki (1935), working with Nerita japonica, studied the effect of water leve1 on rheotaxis, geotaxis, and phototaxis. Russell (1941), as weIl as describing geographica1 distribution, also reported on the genera1 ecology of the recent Neritidae of the western Atlantic. Mattox (1949) also studied the effects of drying on N. peloronta, N. versicolor, and N. tesselata in

Puerto Rico. Zonation studies were performed on Nerit~ species by Stephenson and Stephenson (1950) in the Florida Keys, and by Voss and Voss (1960) in Bimini. Lewis (1960,) described the zonation of Nerita in Barbados. He a1so discussed the spawning - 2 -

activity and larval development of the three resident Nerita species. Lewis (1963) also measured environmental and tissue temperatures of N. tesselata in Barbados. Kolipinski (1964) reported on the growth, life history, and ecology of four

species of Nerita in south east Florida. Zhirmunskii ~dTs'u Li-Ts'ung (1964) measured the heat resistance of sympatric species of Nerita. McLean (1961) studied the erosive activity of intertidal , including Nerita, on beach rock in Barbados. The purpose of this study was to compare the growth, breeding, and feeding of the three species of Nerita endemic to Barbados, in contrasting locations. A study similar to this, as yet unpublished, has also been conducted in Jamaica, some thousand miles to the north-west of Barbados. Growth and feeding data were co11ected from the Little Bay and Harrison's Lighthouse stations, and breeding data from Little Bay and South Point. Several environmental parameters were monitored from the three stations, and microclimate data were recorded from Little Bay and Harrison's Lighthouse. These are discussed more fully in a later section. This project is part of a more comprehensive long_duration study of the ecology of intertidal communities throughout the West Indies. - 3 -

1- FIELD STATIONS Three stations were chosen for this study: Little Bay, Harrison's Lighthouse, and South Point (Fig. 1). AlI stations were surveyed using a standard surveyor's staff and a Zeiss surveyor's level, from which the maps and profiles of Figs. 2, 3, and 4 were drawn. Little Bay: The Little Bay station was similar to the station described by Axelsen (1968), and the River Bay station described by Lewis (1960 ). This station wes exposed to the prevailing north-easterly and easterly winds, and wes subjected to heavy wave action particularly during the winter months (Sailing Directions for the West Indies 1949). The .area used in this study wes approximately 200 meters along the shore. It consisted of a seaward platfor.m, approximately at mean sea level, var,ying in width from 5 to over 10 meters. The platform rose to meet the landward limestone cliffs by a series of more or less , sudden elevations. There were boulders and debris along the base of the cliffs as a result of slippage. The whole area was covered by depressions and crevices, affording protection from wave action and increased area for browsing. The vertical profile clearly exhibited the six zones described by Lewis (1960.). Harrison's Lighthouse: The Harrison's Lighthouse station, on the north west of the island, was largely protected from the prevailing winds by the northern tip of the island. As a result, rough wave cOllditions occurred infrequently and usually as a result of storm conditions - 4 -

N

HARRISON'S LITTLE BAY L1GHT ""'- BARBADOS W.I.

10 o, 1 k.m.

13°---t-----lf------~--

SOUTH PO"INT Fig. 1. Map of Barbados showing annual wind direction and location of field stations. Wind rose based on 50 year means ( Sailing "'directions for the West !ndies, 1949 ). - 5 - far from land. This station~s similar to that at Little Bay except that it was on a much smaller scale. The area under study here a1so extended for about 200 meters along the shore. The mean sea level plat form varied in wid th from less than a meter to a maximum of three meters. The limestone cliff, landward of the platform, reached a maximum height of four meters. From the top of the cliff, the land sloped upwards to the lighthouse level. There were also many depressions and crevices here to afford protection to the .

The zonation here was of the sarne type as tb~t at Little Bay, but due to generally reduced wave action, was vertically compressed. South Point: The station at South Point received even less wave action than Harrison's Lighthouse, as the wind blew from the south for only short and intermittent periods. Also, there was a fringing reef (Bowbell's Reef) Which dissipated most of the energy of the rollers. The land sloped gently to the sea with a maximum height of 1.5 meters at the seaward escarpment, the average height being closer to 0.5 meters. The land vegetation came to within an average distance of 4 to 5 meters of the water's edge. This area was greatly eroded and wes covered by crevices and deep holes, providing retreat locations for the snails. The typical zonation previously mentioned was unrecognizable for the most part due to the absence or narrow.ness of some of tue zones. - 6 """

~-...... -.. -... -, .-"'"-.~

'A

Fig. 2. (A) Photograph. of a 't1pical platform and cliff area at Little Bay. Ses conditions are average.

'/ (B OVERLEAF) Scale contour map of a typical area

used in the study at Little Bay. , , ! Î (0 OVERLEAF) Profiie of (B) drawn to scale ~lopg , " i the line A - A • 1

1 1

j i t I~' !'~

1 f ! ....

6

/ \

A

:;'io:. 2. (A) :E'hot00;r;:i oh of él typical pla tform and cliff

area at Little B3Y. S8~ conditions are average.

contour map of 8. typical ~rea

used in the study at Little Bay •

.,. t 11 e lin e ,fi.. - A • 7 B

A 4" , LITTLE BAY

1 A

c

"" KEY LITTLE BAY: PROFILE. ''-CONlOUIS , -.. 1ft ...... ' ... Cliff CIIISf "" ". ""''''JII'''~• ·sOiIMc. _ • ~...... , 4fT A___ A __ LN - 8 -

A

Fig. 3. (A) Photograph of t,ypical sloping shore at South Point. Sea conditions are average. (B OVERLEAF) Scale contour map of a typical area used in the study. (C OVERLEAF) Profile of ,(B) drawn to scale along the line A - A • 8 -

A

,li 1 j ()-:-r""," "0"'\,:: " t

... ' \ . ~ -t- ~ 1 J'H,

(",r"". J LI (: (j" 1: ",-' : ":i , , c~ l

,-. ~) ( ~ 'Y' L'" , ,\ '\"l(', : l , , \ "r"" • --.. ï 1

l' ; l ." {': .. - 9 -

B ·...... --.....·"""'-CDInOUII ...... _In ." ...... ••••••••• ..- Of ..... VlMWION ......

c - 10 -

A

Fig. 4. (A) Photograph of typical shore line at Harrison's Lighthouse. (B OVERLEAF) Scale contour map of a typical area used in this study. (0 OVERLEAF) Profiles, of (B) drawn, to sesle; along the lines A - A and B - B •

, !. - 10 -

(

A

l' ,1 ~ .' f

Fi~. 4. (A) rhotoeraph of typicRl shore line at l :~nrri8 on' s I,i;'rh thouse. ~ " . (\ (~ OV~:rr~A~) Scale contour map of a tynical ~rea

u~)ed in thi8 :::;tud;y. (c OV~ll';;AF) :r'rofi18s, of (B) dra'im, to scale ~Ü011g the lines A - A and B - B • . - 11 - B

ID ...... HARRISONS LlGHT .....,....cu,..=·"_. ,u. 'u, -....._~.;'~:=-~I'\A'~ ..... a,....-'; ....LlU. '- • .- ---

" HARRISONS LIGHT: PROF"ILES.

B

l'IV! fŒT

c - 12 -

11- ENVIRONMENTAL OBSERVATIONS MicroclimateData: Microclimate data were eollected in the following manner. Observations were made during days of differing weather conditions, for example: hot dry days, and cool wet days.

Recordin~ were taken every hour from 0600 hours to 1800 hours at both Harrison's Lighthouse and Little Bay during the days ehosen. Hourly temperature readings of the rock surface at different levels; in crevices, tide pools, and the sea, were taken using a thermocouple. Temperatures from wet and dry thermometers were taken using a sling psychrometer. Hourly mean values of these temperatures and of relative humidity were plotted. (Fig. 5) Weather Station Data: Tw6 weather stations were maintained, one at North Point adjacent to Little Bay, the other at Harrison's Lighthouse. Meteorological data for the station at South Point wes obtained from the Government Meteorologieal Office at Seawell Airport. Each weather station eontained the following instruments: a rain gauge ealibrated in inehes, an anemometer measuring total m.p.h./day, and a Stevenson Sereen eontaining maximum and miRimum thermometers, and wet and dry thermometers. Continuous weekly reeording thermohydrographs were also installed in the sereens, but these instruments were not designed for use under 'sueh corrosive conditions and were continually malfunctioning. They were eventually removed. - 13 -

Temperature, rainfal1, ànd wind speed readings were taken dai1y at 0800 hours from both these two stations. The mean values from September 1967 to August 1968 were ca1culated and plotted according1y (Fig. 6). -

./ ./ "...... ' ,... ,...... ,' " .0 ,...' ,,' •• .JIP • -,' . ~ ,,' ",. ,...',' .- /-,' .... ' • ,.,j- ,,' ...... "".~ ' " '. '. .... "l...t" LU e. 1-,- C'.-' >- -.. ,1 "' . 012: .... ,o~. . 1 ...e/) Ll- , . . a: CI , '01. c:: ' 0 ~ en== :E " ... e/) :t.:: ::t:== #', 1'· ~ Co:» " • ·0 ~ CI LU CC a: LU > "1,~ '.. c.,) ,...... -. ::J:: a: ....- -...... La.I > .....

-~ . '.' _..... l' m' r·:"':"l'.. ;ri~'f"7·\~:rW ../Wâ-ffi§m;ITf::- «y';:''''

,.... \.. \ . ·· .. \ .. \ --...-':- ...... -. -"'- ... t.-...... -.... _..... \ ...... :... --...... '\. -, --.:,~ ----...... -- ~ -.---...... -...... -...... -... -...... ' .. < · ...... :...... , ...... '.. \, . '. '. . , 1

-~ 3 3~tn!VH3dW3! o

o ...... 1 ... - 1 1...... ! ...... ·····.~l~ ..... ~ ..... ~

-~ 3 3~tn!VH3dW3! o o . . 1 ...... -.• ...

/ ..

1 \ .. \.. ... 1 ...... , . 1 ... - 1 ..... 1...... 1. ~ ...... \

..... ~ \ - ..... ~~. . -----... ____ ~~~··~·.~.~:l~~~::~::~~,...... ~ ... ~ ...~ ... ~~-~ ... :i~ .....~ ... ::== -......

-~ 3~tn!VH3dW3! • \ .. \ .. \ .• , ..• \, 81 \ ....,...... -. \ \ \ fi \ 29 .. r>-- t 80 ::/ "\ .. ,/ \, '/ l -79 r . l 1 ,/ •'1. 28 • l '78 ·· ,l " ,,1 ". .. _.. - .. ~., " .. - .. .M.' - •• .. '[, ,, 27 ,, ,,1 ,, ,,1 ,, ,, 74 26 ,, ,, ,) 73 ," " 25 72

71

24 ~ r 70 6 1 8 9 10 4 6 liME - DAYLIGHl HOURS Fig. 5. Microclimate data graphs from Harrison's Light­ house and Little Bay. Hourly Uleans plotted. . · ... · . , . , ... , , .. \.... "" . ~.,. , <' . \ , .. ,, ··. . . ""'" ...... > ' ...",0 :'" · ...... "\, ...... · ,, .. a:. .. ,, Ci! •...... , ::E ...... ==~ . .- . , ~ ~ 1- .. , 1- .. :-...... , .. ---.., . \ ...... , :lE .-. .- ...... == . , ~ :e= . ::E •• • .. .. >< •• :z .. 0 • .. ~ ••• ". .. :e }. :e .. .. ,, . >- .. ~ , ...... :::c ,, :::c I- , l- . U"\ , .. . ,.; Z , .. z Q ,, ... Q 1 ::E , .. ~ Z \ .. z < ,.. 0< I.A.I I.C ~ ::E ,: =: ...... •••••• 1 ...... ·· .

i i r-. c:::» a') ca ..... ca .... ~ Ln ..., co.... ~ ~ r-. r-. co.... r-. - ~ co.... r-. r-. -r-. c-..... """ :1 !l 0 0 ...... \." \ \. \ ... \ \ ~ \ .\ \ . \ \ \ 1 \ \ ""'" \ ...... > ,J .. . . " " .. . " .. . . .,'.. ' " ...... -...... ::1: ...... ­ 1- ::: ...... Z ...... -.., ...... o .-. .- ...... =: "'\ ...... \ ....1 .. .. \ 0. \ ....1 .. 0 • \ .. \ ~ .. .. \ Z . 1 .. , 0< . 1 CI: 1 •• .. ,1 ~ •• 1 0< .. \ Cl .. \ .. \ Z .:. < ...... ," L&.I ...... " == ...... l'"~ .. \ .. \ . \ .. \ .· ,,\ · ,, . 1 . ,1

i i i -.- Ln ~ co.... C) Ln c::::t Ln C) Ln c:::» Ln co.... co.... C''I c::::; co.... C"':t co.... C) - """ c:" • • co:"" ":' "':" • !l :S N,I 0 35 n' ... " .... .,,, ... , .'n •••• "~"I nIVI., JI ' 1

'3D o , 1\ '25 1 \ 1 \

en 1 \ 1' \ \ 1 \ .z·20 1 \ ...... 1 \ ...... 1 \ \ ",, __ ...... ,1 ,.,...... ·r,~ ~-•.. ' r\ '15 1 ...' 1 .. .. 1 .. 1 l, ·10 1...... '05 . .. ..'.

MEAN MONTHLY RELATIVE HUMIDITY 10 " ..... I sm " ...... ""."., ___ c.------:C ...... ------,' , ...... - ...... -...... 1...... ,. ___ .. - =90 ---_ ;:Je. 80 ...... •...... •..• ...... ' ...... ' ...... , . .. .' 10

MEAN DAILY M.P.H / MONTH 13

:c 12 1 ~ :Ë 11 6 ::c~ ,.... 1 TH .. . . · .. . . . · .. . . i .. . ," 1 ·. ,."" 1 ·. .. - ..- "" ·•. .. " ·· ..-• ,,'*"*" · · · · .. . :> ·•. . .. . t- · ...... e ··· ...... :lE- · .. ::» · e •• ,> ...... X · ,"- .. .. L&.I 1 · " e •• .. > 1, · , e •• t­ \ · .. .. ::: \ · • rz:t \ .... \ ::c L&.I \ 1- ...... cr: \ · Z 1 · o .. · \ ~ 1, · :E .. - ::c · ~ .·1,," t­ •1 · •• 1 Z x .. \ » · a:. .. 1 LI.. o 1 .· 1 :le ; .· :Ë 1 1 1 1 .· · z 1 .· · 1 ~ ~ · 1 L&.I · -

MEAN DAILY M.P.H / MONTH

1

6 ..- ...... ••• fi • •• • ..... -.. V ._... ,"', ..••• ••••• _. ..,", a •• ...... --- - .,' \ . 9 ••• - _------...... •• ..-,' \·0. ... .,..---- -. ',.,' '\ -.. •• _•• ,fil' " -.'._.. ~(' " \ \_.0 • .. " -. .. , " \-. 8 o· ,,' -.. •• ~ ',. .. , . .. \ --...... ::,..,. ,"" -.- \ \ 1 •. ..•.. \ h SON DJ FM s ----NORTH POINT (N.P)

·················SOUTH POINT (S·P)

------HARRISON'S LlGHTHOUSE (H.U

Fig. 6. Maximttm and minimum temperatures, mean daily rainfall,

mean mon thly rela tive hl'unidi ty, a~d mean daily wind speed fol.' North Point, South Point, and Harrtson's Lie;hthouse. - 16 -

111- GRO'NTH CJ INTRODUCTION Several reports on the growth rates of members of the Neritidae have been documented. Woodward (1892) described the mode of growth and the structure of the shell of Vela tes conoideus (Lam.) and ether Neritidae. Andrews ( 1935) studied shel1 repair in Neritinia. Kolipinski (1964) deseribed the life history, growth, and ecology of four Nerita species. Recently, Axelsen (1968) studied the growth rates of the three Barbados species of Nerita at one east coast station. In other species of mollusca, a great deal of information exists on growth rates and factors affecting them. Wilbur and Owen (1964) bave reviewed the various methods of measuring growth rates and growth relationships of a variety of molluscs investigated in many reports. Many factors are known to affect growth rates of mol1uscs. Gonad maturation, age, temperature, food supply, environmental and biotic factors have been shown to alter growth rates (Russell 1909, Orton 1914 and 1928, Allee 1930, Moore 1938 e, Thompson 1942, Fox and Coe 1943, Carter 1951, Quayle 1951, Dehnel 1955, Orton et al 1956, Williams 1964 a,b, Frank 1965,a.) The typical reduction in growth rate during gonad maturation is understandable, because the energy required to elaborate gonads and sex products may reduce energy available for growth. Lawrence, Lawrence, and Giese (1965) worked with and found there was an inverse relation between the growth of the () digestive gland and gonade They suggested that nutritive - 17 -

demands of gonadal growth might be a factor in the reduction o in size of the digestive gland. It was not possible to say whether gonad growth was due to direct transfer of stored material from the digestive gland. These workers did, however, comment on the very close association between the gonad and the digestive gland in molluscs; also that the digestive gland is an organ of energy storage. Preliminary microscopical studies on Clione limacina by C.M. Lalli (personal communication) have indicated that there may be direct tissue connections between the gonad and digestive gland, with a resultant direct transfer of energy. Orton (1920) and Moore (1958) have suggested continuous breeding is appropria te in the tropicsG The resultant fluctuation of growth rates, as a result of the seasonal gonad maturation, would probably be insignificant. In some instances, even though there are definite pronounced breeding seasons, there appears to be no reduction in growth rate (Loosanoff and Nomejko 1949, Quayle 1952, Leighton and Boolootian 1963, Williams 1964 b). The effect of temperature on growth rates of molluscs has been reported on by several researchers (Russell 1909, Quayle 1951, Taylor 1959 and 1960, Williams 1964 a and 1964 b, Kolipinski 1964). In most cases, the growth rates increased with increasing temperatures. It has also been found, however,

that excessively hig~ temperatures have deleterious effects on the animaIs' metabolism, and if prolonged, cause death. Mayer (1914) stated that the effect of increased temperature - 18 -

is felt to a greater extent in tropical animaIs than in C) temperate or arctic forms. This, he stated, was probably due 0 0 to the fact that tropical animaIs live within 10 - 15 C. of their upper death temperatures. Thorson (1936) and Dehnel (1955) have found, however, that larval growth of arctic molluscs is very much faster than forms of more southerly latitudes. This appears to be an

adaptation of these pelagie ani~~ls so that they can take full advantage of the short productive season in the arctic. It has been universally recognized that with increasing age, growth rates decrease (Carter 1951). In sorne cases, growth has been known to cease after sexual maturity has been re.ached. Moore (1938 a) found this to be the case in

Purpurea lapillus. This cessation o~ growth after attainment of sexual maturity was not found to occur in the three Nerita species studied. The data did show, however, a reduction in growth rate with size (and hence age) increase. Food supply and its effect on growth rate has been investigated by Fox and Coe (1942 and 1943), Leighton and Boolootian (1963), and Frank (1965a).It was found that abundant food supplies, efficiency in foraging, an increase in time available for fe'eding, and food of high nutritive value, produced increases in growth ràte. The factors which probably affect growth rates in the most complex fashion are environmental factors. The difficulties in elucidating their separate effects is due to the fact that () there are subtle interactions between the factors. - 19 -

Severa1 authors (Colman 1933, Doty 1946, North 1954, Moore 1958, Meyer and O'Gower 1963, Lewis J.R. 1964, and others) have recognized the great influence of wave action on distribution and zonation of organisms in the intertida1 habitat. Changes in she1i shape and size accompanying increasing exposure, have been noted by severa1 researchers . (Russell 1909, Orton 1914, Abe 1931, Moore 1934, Segal 1956,

Wara and Wright 1964, Williams 1964 a, Frank 1965à~.The majority of authors have inferred that the higher intertida1 animaIs developed thicker she11s and exibited slower growth rates. Biotic factors, such as competition and crowding, have

been suggested (Allee 1930, Conne11 1961, Frank 1965~,Forster 1967) as causative in decreasing growth rates. - 20 -

MATERIALS AND METRODS Monthly increments of shell growth of tagged animals were measured to the nearest 0.1 m.m. by. micrometer gauge along the longest shell axis (Fig. 7). The tags used were small (3 m.m. x 7 m.m.) plastic fish tags supplied by Howitt Plastics of Molalla, Oregon. They were numbered from 001-999 and were of various colours. After the shells were superficially scraped and dried, the tags were cemented to the shell using an epoxy type cement manufactured by Lepage and Co. (Fig. 7). The adhesion in the majority of cases was good, and approximately only 1% of losses were attributed to tag dislodgement. At Little Bay, sorne of the specimens marked by Axelsen (1968) were used, as weIl as the animals marked by myself. In total, the numbers of marked animaIs a t Little Bay were:. 300 N. peloronta, 300 N. versicolor, and 250 N. tesselata. The marked population at Harrison's Lighthouse consisted of 450 N. peloronta, 400 N. versicolor, and 400 !. tesselata. These specimens were collected from the east coast, near

Little Bay, and transplanted to Rarrison's Lightho~se. This was done because the resident population at Harrison's Lighthouse was too small to supply enough animals. The pe·rcentage recovery varied between the two sites. At Little Bay, recoveries were relatively high and constant, and reached as high as 95% in li. tesselata. At Harrison's Lighthouse, there were heavy losses particularly with N. tesselata, which fell as low as 2% in sorne months. These losses were probably 21 -

----

Fig~ 7. Photograph of a tagged specimen of

il li. pe1oronta showing axis along which growth measurements we+e taken •

• / ',' 1

, i

1 \1 ,:. '1:' ",j' - 22 - due mainly to the lack of extensive platform areas, which this species inhabited, at Harrison's Lighthouse. There was also a variation in recovery during the year. It was found that at times of heavy surf (during the winter months) recoveries were low. This was due to the animaIs' ability to retreat into deep recesses and crevices during these times of intense wave action, and hence became impossible to find. Environmental parameters were measured from both these stations in order to try to relate differences in response to the environment to differences in these parameters. Unfortunately, in the case of wave action, only an indirect measure, wind speed, was attempted; thus actual wave effect was not really measured. Temperature and humidity differences existed between the two stations used in the growth study, and differences in the growth rates have been compared on this basis. Analysis of Tagging Data: The method of analysis of this growth data was that used by Manzer and Taylor (1947). A discussion of this and other graphical methods of representing growth data was prepared by Hancock (1965).

The time intel~als between initial and final measurements of shell growth, and hence the increase in shell length over these periods, were used in the graphical representation of growth rates for these time periods. In N. peloronta and li. versicolor it was possible to present Manzer and Taylor 23 - plots for growth rates of a year's duration, but in N. tesselata, due to the heavy losses at Harrison's Lighthouse, the plots represented growth rates for a six mon th periode These yearly and half yearly groWth periods were used to compare the growth rates of the three species between the two stations. Time intervals of one month between initial and final measurements were also used to represent growth rates during each month. These monthly data were plotted separately producing twelve individual Manzer and Taylor plots for each species at both locations. This provided an indication of whether or not there were variations in growth rates throughout the year (Fig. Il). The regression lines were fitted to the points on the graphs by the method of least squares, and tests of significance weré applied. The regression equation was of the form: y = y + b(X - X) where X was the length of the shell at the initial measurement (length at.time t), and Y was the length of the shell at the final measurement (length at time t + 1); b was the regression coefficient of Y on X. Y and X were means. Growth rates of!. tesselata were represented for the period Januar.y 1968 to July 1968, for N. versicolor the period was May 1967 to May 1968, and for N. peloronta, it wes August 1967 to August 1968. - 24 -

RESULTS The regression lines for the yearly growth rates for !. peloronta and N. versicolor are shown in figures 8 and 9. The regression lines for the growth rate of!. tesselata over a six month period are shown in figure 10. Growth rates of aIl species were found to be significantly greater at Harrison's Lighthouse than at Little Bay. In !. versicolor, however, animaIs below approximately 17.4 m.m. in length grew faster at Little Bay than at Harrison's Lighthouse. The regression line for!. peloronta at Little Bay had a regression coefficient of 0.6064, and for Harrison's Lighthouse, the coefficient was 0.7620. There wes a significant difference between these at less than the 0.01 level. The linear regression equation for M. peloronta at Little Bay was Y = 25.14 + 0.6064(X - 20.72) and the equation for Harrison's Lighthouse wes Y = 24.06 + O.7620(X - 16.05). The regression line for N. versicolor at Little Bay had a regression coefficient of 0.3074 and for Harrison's Lighthouse the coefficient was 0.5687. Again the difference was significant at less than the 0.01 level. The linear regression equation for N. versicolor at Little Bay was: y = 19.47 + 0.3074(X - 15.24) and for Harrison's Lighthouse was y = 17.72 + 0.5687(X - 12.96). In the case of !. tesselata, despite having had to use a six month growth period, the regression coefficients of the equations for Little Bay and Harrison's Lighthouse were significantly - 25 -

different at the 0.02 level. The linear regression equations o for Little Bay and Harrison's Lighthouse were: y = 15.56 + 0.5544(X - 14.30) and Y = 14.77 + 0.6093(X - Il.76) respectively. It was also found that aIl the coefficients differed significantly from a zero value at less than the 0.01 level. The regression lines for the monthly growth rates (Fig. Il) were found not to be significantly different, and thus there appeared to be no fluctuations of the growth rates throughout the year. Table 1 gives the regression coefficients for aIl regression lines representing monthly growth rates. There were also interspecific differences in growth rates. At both stations, the data showed li. peloronta ta have the most rapid rate of growth, followed by N. versicalor with N. tesselata the slawest of the three species (Figs. 8,9,10). '. '.,

...... ', '-' ......

' ..; 1 . ! 1 1

!;

....-..+ E .';: .' 't;; . .- ... a ';'JtoIN.. (I-2.n) J2- • • • • : . Little BaV Î. 24.... :lIIICI~lf1I) .; ~...... Hamsoo's .; ; ~ ,.

'. - 27 -

N.versicolor

, ,'" . • ..•• ftIII"" • .' .~.,,: . .. .; • • e. /.'. ..~ ~ ••.. • i(//IIIJ~ - .• •• ': ° .~, x,y) .....,' ~-- . . .00," 0 o •• ,' '.1',41 1-1114 (X-I5'II) .. ""'~.. ° 0., ° Little Bay . -'" . '=IHZo"5111(x-n'lI) " " . -~~..;- Harrison's , "

10 .15 20 25 lenglh al lime T Fig.9. Manzer and Taylor .plot for N.varsicolor. Regression lines represent growth rates for the period May 1967-May 1968. The length is measured in m.m. along the longest shell axis. The equations for both sites are shown. , - 28- • N.tesselata

•

-+ '-15-51+'·5544(1-14·.) ~ a:I • • • E • • c Little Bay 0';: '-14·n+ '.III3(X -lHI) -~~~- Harrisoo's

10 1 21 leogth at time T

Fig.10.Manzer and Taylor plot for N.tesselata. Regression lines represent growth rates for the period Jan.1968-Jul.1968. The length 1s messured in m.m. slong the longest shell axis. The equations for both sites are shown. - 29 -

HARRISON'S LITTLE . LIGHTHOUSE BAY Regression coefficient Regression coefficient 0.89 0.93 0.89 0.92 0.99 0.96 0.88 0.96 0.97 0.94 N. peloronta 0.94 0.97 0.98 0.97 0.96 0.97 0.94 0.96 0.97 0.97 0.96 0.95 0.98 0.96 0.97 0.89 0.94 0.91 0.92 0.99 0.97 0.98 0.99 0.93 0.98 0.94 N. versicolor 0.93 0.92 0.9,6 0.96 0.98 0.99 0.96 0.97 0.97 0.92 0.99 0.95

0.96 0.92 0.89 .0.89 0.96 0.93 0.94 0.99 0.97 0.97 0.89 0.97 N. tesselata 0.89 0.96 0.89 0.99 0.94 0.93 0.95 0.99 0.91 0.98 0.88 0.88

Table 1. Coefficients for regression lines representing monthly growth rates from May 1967 - May 1968. - 30 • Lit1;le Bay Harris, on."s

N.peloronta z

Il 1. ZI 1. 12 ,. Il 1. ZI 2.

+ E-t- :i -aCP N.versicolor -1d .cl -tIC -CP=

Il U U Il

N .. tesselata'i n

Il

Il Il

length at tiDl.e T

Fig 0 110 Manzer and Tay10r p10ts for No pe1oronta, ~. versico1or, and N. tesse1ata at Litt1e Bay and Harrison's Lighthouse. Regression 1ines represent growth rates for month1y periods. The 1engthis measured in m.m. a10ng the 1ongest.· she11 a:Jd.s. - 31 -

DISCUSSION The more rapid growth rates obtained at Harrison's Lighthouse were unexpected. The habitat at Little Bay was more extensive, and appeared to offer more forage area. Axelsen (1968) reported, however, that population densi4Y " of all three species was greater at Little Bay than at Norse's Bay, adjacent to Harrison's Lighthouse. ,The higher population densi ty may have had adverse ; 'ffec ts on growth ra tes a t Li ttlè Bay. The interspecific growth rates, though, agreed with those reported by both Kolipinski (1964) and Axelsen (1968). Quayle (1951), working with Venerupis pullastra (Montague) found that animals from higher intertidal levels grew faster than those at lower levels. In contrast to this was the work of Hayes (1927 b) who found that the opposite was the case with Littorina littorea.He suggested that immersion was important for more rapid growth. Also Orton (1914) reported that mid-tide-level grew faster than those at other higher levels. He accounted for this by the more stable conditions which existed at mid-tide-level. On the other hand, Mattox (1949) and Zhirmunskii and Li-Ts'ung (1964) discovered that certain species of Nerita showed adaptations allowing these animaIs to withstand exsiccation and high temperatures; further, that the ability to resist these factors was directly correlated to their intertidal stratification. Hewatt (1937), Broekhuysen (1940), and Southward (1958) also mentioned the correlation between - 32 -

intertidal height and resistance to high temperatures and

,~; de's1ccation:'. Fraenkel (1968) concurred wi th these findings, and also found that graduaI acclimation to high temperatures led to increases of heat resistance of 1_20 C. in some Neritidae. Lewis (1963) showed that in Nerita in Barbados, significant temperature differences existed between the animaIs' tissues and the air. He went further and suggested that the mechanism involved was evaporative cooling. Adaptations such as these allow Nerita, living at high intertidallevels (in the spray zone), to continue vital functions thus permitting maintenance of growth rates. Andrews (1940) investigated the Neritinia virginia (Lam.) in a salt pond in Jamaica, and found that larger animaIs were found in areas of greater salinity. Also from Pelseneer's (1920) evidence, it appeared that in some molluscs smaller animaIs were found in waters of higher salinity, but in many, larger animaIs seemed to prefer higher salinities. Salinity data was not collected from Little Bay or Harrison's Lighthouse, but the salinity of the upper intertidal zone varied from heavy encrustations of salt due to spray, to almost fresh water conditions during heavy rains. Discrepancies in growth rates may be partially explained on this basis in future investigations. Several authors (Russell 1909, Quayle 1951, Taylor 1959 and 1960, Williams 1964 a and 1964 b, Kolipinski 1964) showed that there was a tendency for an increase in growth rate to occur at times of increasing temperature. The temperatures obtained from microclimate data showed that rock surface 33 .... temperatures at the hottest period of the day were some 2.50 C. higher at Harrison's Lighthou~e than at Little Bay, and on an annual basis the maximum temperature of Harrison's Lighthouse was greater than that of Little Bay in aIl months except November (Figs. 5 & 6). These generally higher temperatures may have had an influence on growth rate. Monthly relative humidity values were similar from both Harrison's Lighthouse and Little Bay. However, the pattern of relative humidity during the day was qui te different between these stations. At Harrison's Lighthouse the relative humidity declined rapidly to relatively low values at 9:00 A.M. and remained low until about 4:00 P.M. when a sharp increase was noticed. At Little Bay there were no long periods where relative humidity wes at a low level. There was considërable fluctuation in the morning with a typical reduction at 2:00 PeM., the hottest part of the day. These differences are logically explained by the fact that at Little Bay, due to greater wave action, there was much more spray vmich would have tended to produce higher relative humidity values.

It must be i:'borne~ in mind, however, that these relative humidity observations were taken in the open. In aIl probability the relative humidity existing in crevices, where the snails retreated during the hot part of the day, would have been similar at both stations. The effect of low daily relative humidity did not appear to have a slowing effect on growth rates, however, possibly due to the reason stated above. - 34 -

Crowding has been found by Frank (1965à),working with an in tertidal snail population, to r.educe ·s1gn1f1c.antly.: growth

rates~ Also.Allee (1930) concluded that under certain conditions, crowding will retard growth. Forster (1967) found growth rates in intertidal populations of Ha1iotis greater than sub1ittoral population growth rates. He suggested that the main reasons for this were decreased competition and more abundant food supplies in the intertidal habitat. The density of the population was considerab1y less at Harrison's Lighthouse than at Little Bay. Probab1y one of the reasons for this is the current system: around Barbados. There are current vortices produced from the northern and southern tips of the island by the easterly currents reaching Barbados. These vortices would tend to remove neritic pelagie larvae, lessening spat settlement on leeward coasts (Emery 1964). Therefore crowding, and possibly competition, were reduced at Harrison's Lighthouse; which possibly contributed to increased growth rates there. The availability and abundance of food also affects the growth rate, increased food supplies tending to increase growth rates (Fox and Coe 1942, Leighton and Boolootian 1963).

Frank (1965~)also suggested that the time available for feeding in different areas was likely to influence growth rates. In this study, however, no data was collected on the availability, abundance or nutritive value of food. In the feeding studies, it was found that the animaIs apparently • started feeding at an earlier hour at Harrison's Lighthouse - 35 -

than at Little Bay. This would have had the resulting effect of 1engthening the feeding period at Harrison's Lighthouse.The faster rate of growth there may be partia11y exp1ained on this basis. It has long been considered by many authors (Colman 1933, DotY 1946, Stephenson and Stephenson 1950, North 1954, Moore 1958, Meyer and O'Gower 1963, Lewis J.R. 1964) that wave action is one of the fundamenta1 factors affecting intertida1 organisms. A comparison can be made between Harrison's . Lighthouse and Little Bay in this respect. The wind speed, and hence wave action, was less at Harrison's Lighthouse than at Little Bay (Fig. 6). Part of the explanation for the faster growth rates at Harrison's Lighthouse may be that more intense wave action at Little Bay reduced the time avai1ab1e for feeding. The snai1s tend to stop browsing, retreat into crevices, and remain stationary at high tides and during rough conditions. The apparent absence of significant monthly changes in growth rate during the year is puzzling, particularly since both Kolipinski (1964) and Axelsen (1968) showed these seasonal variations. Kolipinski's (1964) growth rate variations were direct1y re1ated to the fluctuations in air and sea surface temperatures, which were considerable in Florida. It seems 1ike1y, however, that the decreases in growth rates in September 1966, particular1y in N. tesselata, were due to unusua1, severe drying out of the intertida1 zone during that period ofAxe1sen's (1968) study. - 36 -

It has been reported by many workers (Russell 1909, Orton 1914 aIld 1928, Quayle 1951, Orton et al 1956, Moore 1958, Orton and Southward 1961, and Williams 1964 a) that there was commonly a reduction in growth rate during gonad maturation. On the other hand, Loosanoff and Nomejko (1949), Quayle (1952), Leighton and Boolootian (1963), and Williams (1964 b) have reported that spawning and gonad maturation appeared to have no inhibitor,y effect on growth rates. Orton (1920) suggested that temperature is of paramount importance in controlling breeding, and that if the breeding temperature for any species was attained and maintained, breeding will start and continue. Also, he stated, there is good evidence to support the theor,y that in stenother.mal conditions, such as the tropics, breeding (and in all probabil1ty growth) continued all year. Moore (1958) also suggested that growth and breeding occur simultaneouslyall year in the tropics.

In agreemen~ with these arguments was Randall's (1964) work on the West Indian topshell Cittarium pica L., where she did not report any seasonal changes in growth rate, even though there was marked recruitment of juveniles in January. She also mentioned that small animals were common all year, suggesting a generally constant breeding level with occasions! peaks. - 37 -

IV- BREEDING INTRODUCTION Several authors have found that animaIs living in stenothermal conditions, such as the tropics, commonly breed continuously aIl year (Moore 1938 a, Randall 1964, Frank 1965a,Struhsaker 1966). Giese (1959) stated that the most extended breeding periodswere to be found in the tropics, and that these extended breeding periods were a result of asynchronous breeding. This, he suggested, resulted from the fact that animaIs in the breeding population were not aIl in the same physiological breeding condition. Giese (1959) also suggested that two kinds of events induced the breeding condition; endogenous factors which built up inside the organism, and exogenous factors of the environment such as temperature, light, salinity, etc. He suggested that the combination of these two factors best explained the course of events in a reproductive cycle. These exogenous factors have been investigated by several researchers. Temperature, the most intensively studied, has been investigated by Orton (1920), Ingle (1951), Ansell (1961), Orton and Southward (1961), and Caddy (1967). Rainfall has been found to be correlated with breeding activity by Lenderking (1954) and Diaz-Piferrer (1962). Lenderking (1954) found that spawning in Littorina angulifera (Lam.) showed bilunar periodicity throughout a ten month period in the year. Caddy (1967) observed spawnings of Macoma balthica L. at full moon and new moon neaps. Marshall and Stephenson (1933) observed a lunar rhythm in - 38 - the release of planulae by the coral Pocillopora bulbosa. Spawning may also be influenced by wave action. Orton, Southward, and Dodd (1956) suggested that spawning of

~. vulgata was correlated with rough seas. Giese (1959) also reported a cessation of spawning by chitons in tide pools disturbed by waves. Orton and Southward (1961) stated that spawning in~. depressa might have been stimulated by mechanical effects of rough seas, and the voiding of gametes occurred over a short space of time. Struhsaker (1966) reported that increased wave action restricted copulation in Hawiian species of Littorina. She also found that the degree of viviparity and "oviviviparity was not correlated with the distance the animaIs lived from mean tide level. Ansell (1961) and Leighton and Boolootian (1963) found that food supply affected the proliferation of gonadal tissue. They both found that increase in gonad size coincided with increases in the food supply of the organisms they investigated. Giese (1959) mentioned that the endogenous factors have been investigated to a much lesser degree~ H owever, Ingle (1951) found that low glycogen content of did not appear to reduce the production of spat. Also Lawrence, Lawrence and Giese (1965) investigated the growth relationship between the gonad and digestive gland of chitons. They found that increases in gonad volume at approaching breeding seasons were accompanied by decreases in the size of the digestive gland. These size changes were not due to changes in water content of either of the organs. The workers were not able to say whether - 39 - there was a direct transfer of energy from the digestive gland to the gonad, or whether gonad size increase was due to increased synthesis and uptake from biood precursors. They did mention, however, the very close association of digestive gland and gonad in the mollusca. - 40 -

MATERTALS AND METRons By using line transects, random monthly collections of approximately sixtY animals were made from Little Bay and South Point. Harrison's Lighthouse was omitted in this study as there was a limited number of specimens available there.

The samples were colle~ted from the sarne general area each month in an effort to represent the breeding population at that location. The animals were then taken to the laboratory and were sexed using the cephalic penis (Boume 1908) as the definitive character. The greatest shell length was measured to the nearest 0.1 m.m., and the gonad was examined for colour, size, and texture. The method of defining the stages of gonad development was similar to that of Orton, Southward and Dodd (1956). Tt was found from microscopie examination of the female gonads that two colour stages represented two developmental stages. The two colour stages were pale yellow and chrome yellow. The latter stage was full of mature ova of uniform size, loose in texture, and a deep chrome yellow colour, and was the spawning female gonade The pale yellow gonad was small, "tight", and contained few mature ova, and was the unripe female gonade Immature and developing stages were not distinguishable by colour differences in the female, and microscopie examination was necessary to distinguish these stages. The male gonad was similarly examined and displayed three distinct colour stages, each representing a developmental -u-

stage. The three stages were referred to as sepia, orange, and red-brown. The red-brown condition proved to be the spawning male gonade At this stage, it was large, the lobules were loose, and contained many active mature sperme The orange stage was an intermediate developing stage, and the sepia gonad was immature. In about 1% of the animaIs from South Point and 0.5% of the animaIs from Little Bay there were specimens with brilliant orange gonads. Smears of these gonads, both male and female, under the microscope showed heavy infestation by cercariae. Identification of this larval fluke stage was not done and was considered outside the scope of this study. Analysis of Breeding Data: The number of animaIs in breeding condition in each month was. calculated as a percentage of the breeding population and plotted against time. This was done for each species at both

locations (Fig. 12 and Table 2). Chi-squar~ contingency tests were done by computer to determine whether the variations of the graphs were significantly different. In order to determine the influence of the environmental conditions on spawning activity, multiple lihear regressions were done using a programme written for the McGill Fortran IV G level computer on a 360/50 system. This programme allowed a multiple linear regression to be performed using the percentages of animaIs in breeding condition as the Y variable, and maximum temperature, rainfall, relative humidity, minimum tempe rature , and wind speed as the five X variables. The computer was programmed to provide the multiple linear regression - 42 - equations for each species for both sites, also the percentage contribution of any one X variable to the variation in Y was obtained. The typical multiple linear regression equation was in the form Y a + bl(X - Xl) + b (X - ) + ••• b (X - ) where = l 2 2 I 2 5 5 X5 y is the percentage of animals in breeding .condition, Xl to X5 are the five environmental variables, b to b are the l 5 regression coefficients of Y an each of the X variables, and a = Y which is the mean of Y and Xl to 15 are the means of the particular X variable. A correlation of the spawning activity between the two sites was performed for each of the three species. The percentage of animaIs in breeding condition for each month, at both sites, and for each species was plotted. South Point was on the ordinate and Little Bayon the abscissa. The correlation and regression coefficients were calculated for each of the plots and significance tests were performed on each (Figs. 13,14,and 15). Sex ratios were also determined for the three species at both stations, and also a combined sex ratio which was the sum of observations from both locations. Chi-square tests were applied, and the existe.nce of a 1:1 ratio vres postulated as the null hypothesis (Table 3). Copulation was observed and photographed. The process, to the best of the author's knowledge, has not been previously describBd. Also, gametes ot both sexes, from aIl three species, were microscopically examined and measured. - 43 -

RESULTS The results obtained from the breeding data suggested that there was continuous breeding aIl year, with significant increases and decreases in the number of spawning animaIs during the year. Table 2 shows the months which were significantly different in the numbers of breeding animaIs. Figure 12 shows a graphical comparison of the three species from South Point and Little Bay. It was also shown, by multiple linear regression, that rainfall and relative humidity were significant factors in influencing the breeding activity. The computer results on the multiple linear regression with five environmental parameters as X variables, produced one equation at South Point for !. ~loronta, and two equations for Little Bay, one for!. peloronta and on~ for!. tesselata. The equation for South Point!. peloronta is: y = 22.61 + 3.51 (X4 - 76.38), the X4 variable being relative humidity and the percentage contribution of X4 to variation in y is 35.48%. Similarly the equation for N. Eeloronta at Little

Bay· is Y = 57.41 + 153.48 (X3 - 0.13), the X3 variable being rainfall, and the percentage contribution of X to variation 3 in Y is 50.57%. In the case of N. tesselata at Little Bay: y = 70.33 + 73.32 (X3 - 0.13) is the equation, the variable X3 is rainfall, and the percentage contribution of X to variation 3 in Y is 11.49%. In aIl the other cases, namely !. versicolor, !. tesselata at South Point and N. versicolor at Little Bay, there were no - 44 -

multiple linear regression-equations generated by the computer. The .correlation of spawning activity between South Point and Little Bay for the three species, was shown to be not significantly different from zero. The correlation and regression coefficients respectively were: for N. peloronta

0.012 and 0.0056, for N. versicolo~ 0.00015 and -0.0003, aud for li. tesselata". Q.OOl and 0.00009. In aIl three species, with Il degrees of freedom, the probabilities obtained from t tables was greater than 0.50; thùs the correlation coefficients were fOlllld to be not significantly greater than zero (Figs.13.,14,15.). The sex ratios of the three species at Little Bay were not significantly different from a 1:1 ratio, the same was found for N. peloronta and N. versicolor at Sou.th Point. However, the N. tesselata sex ratio at South Point was found to d1ffèrfrom' a 1:1 ratio. The combined sex ratios for N. peloronta and N. versico1or from both stations did not differ significant1y from a 1:1 ratio; again, however, N. tesse1ata showed a significant difference to the 1:1 ratio. Table 3 shows the Chi-square values and probabi1ities. The three species were found to achieve sexual maturity at the fol1owing she11 1engths: N. peloronta between 18-21 m.m., N. versicolor between 16-19 m.m., and N. tesse1ata between 14-17 m.m. There were size differences in the ripe ovoid ova as . fo11ows: N. pe1oronta and Ji. versicolor produced ova approximate1y

2501( x 300A{ and Ji. tesse1ata ova were approximate1y 200,1( x 275~ • • The éperm of the three species were of approximately the same 45 size and of the normal eupyren~ type common in the

Diotocardia (Frazen 1956). The pointed hea~ of the mature sperm measured approximately 8.5J{ in length, and the tail varied in length fram 25.5..1( - 34.0.1.(. Copulation in Nerita occurred as follows. The male app'eared to locate the female by trial and error, as two males have often been observed in the copulatory position. The male climbed onto the shell of the female, andaligned the growing edges of the shells such that the superior had a slight bias to the right. After a few minutes, the male "extended the cephalic penis over the of the female's shell up to·the right side ,o.f the mantle. Shortly after this, a gelatinous 'copulation tube' was extruded fram the tip of the cephalic penis up into the mantle cavity, presumably coming to rest

~lose to or at the female genital aperture (Fig. 16). Immediately following the formation of this tube, spermatophores were seen to move rapidly through this tube and to disappear into the mantle cavity. After severai spermatophores had been transferred, the male moved off, eventually breaking the copulation tube. This 'copulation tube'was undoubtedly a tubular structure as it maintained its fom and shape yet allowed the passage of spermatophores through it.

The female had a spermatophore sac which, in virtual~y all mature animals, contained spermatophores at all times. The

situation in the male was peculiar in that in no case ha~ there been found a spermatophore in a male animal. This agreed with Bournets (1908) findings. This may be due to the fact that the spermatophores are produced immediately prior to release. - 46 -

In addition, at no time during the gonad examinations was a specimen found to be in a transition stage between male and female, indicating that a sex reversaI does not occur. Boume (1908) stated that the sexual apparatus': of Neri ta is too elaborate and hence sex reversaI would necessitate structural changes which would be too extensive. e e

N.pe1oronta P Oct-Nov Nov-Jan Jan-Mar Mar-May May-Jul Jul-Sep Table 2. Chi-square 0.05 DS DS DNS DNS DS DS values and significance South Point 0.01 DNS DS DNS DNS DNS DNS 1eve1s (0.01 and 0.05) )(2 5.0031 18.4046 0.6405 3.5660 6.3273 4.4436 of peaks and troughs Oct-Nov Nov-Mar Mar-May ~~y-Jul Jul-Aug Aug-Sep of breeding cycles. 0.05 DS DS DS DNS DNS DNS (DS)-Definiet1y signif- Little Bay 0.01 DNS DS DNS DNS DNS DNS icant. )G 2 5.8781 31.1074 5.8128 1.3260 2.8371 0.2295 (DNS)-Definitely not si~nificant. N.versico1or P Sep-Oct Oct-Nov Nov-Dec Dec-Jan Jan-Feb Feb-Apr Apr-Jun Jun-Aug AUg-Sep 0.05 DNS DS DNS DS DNS DS DNS DNS DS ~ 1 South Point 0.01 .DNS DNS DNS DS DNS DS DNS DNS DS . ?<:2 1.6015 6.5366 .2.0860 7.8526 2.7880 8.3806 1.2825 1.6736 18.0765 Oct-Nov Nov-Dec Dec-Feb Feb-Mar Mar-Apr Apr-May ~-Jun Jun-Jul Jul-Sep 0.05 DNS DNS DS DS DNS DS DNS DNS DNS Little Bay 0.01 DNS DNS DS DS DNS DNS DNS DNS DNS ~ 2 0.0957 0.0491 12.0469 10.8986 1.5615 4.1235 3.7984 0.9995 1.2599

N.tesse1ata .P Sep-Oct Oct-Nov Nov-Dec Dec-Feb Feb-Mar Mar-Jun Mar-Jul Jun-Jul Jul-Sep 0.05 DNS DNS DS DNS DS DS DS DS . DB South Point 0.01 .DNS DNS DNS DNS DNS DS DS DNS DNS )(2 2.7408 0.6747 3.8624 1.6612 5.4130 8.1311 24.3036 5.8139 5.9437 Sep-Oct Oct-Dec Dec-Feb Feb-Mar Mar-Apr Apr-Jun Jun-Jul Jul-Aug Aug-Sep 0.05 DNS DNS DS DNS DNS DS DS DS DS Little Bay 0.01 DNS DNS DS DNB DNS DS DS DS DNS )(2 1.2599 0.2196 7.1676 1.0325 0.0667 6.6533 12.7439 8.2087 5.9362 48- • N.peloroD.U

CD OCas =0 N.versicolor bD CD St J.t ...c:a ~ Ec g. s:a.. L.B .....bD OC= CD CD li = -ml as -.a.... =as • ct-. 0 ~ N.tesselata

®

s D A M J A CD OCas 0 N.versicolor =bD CD St J.t 80 ...c:a ~ Ec g. s:a...... bD OC= CD CD ~ = -ml -as .a.... =as • ca ~ 1 N.tesselata

®

s D1.onths Fig. 12. Breeding cyc1es for the three species of Nerita at Litt1e Bay (L.B.) and South Point (S.P.). The asterisks indicate the points Which differ significant1y at the 0.05 1eve1. - 49 -

SOUTH POINT LITTLE BAY 2 e X P -X2 P N. Eeloronta 1.3714 0.30-0.20 0.0433 0.90-0.80 N. versicolor 0.7902 0.50-0.30 0.2333 0.70-0.50 N. tesselata 21.9428 (0.001 1.0293 0.50-0.30

COMBINED

X2 P N. Eeloronta 0.7200 0.50-0.30 N. versicolor 0.8192 0.50-0.30 N. tesselata 12.6313 (0.001

Table 3: Chi-square on sex ratios from South Point and Little Bay. The combined chi-square is the sum of observations from both stations. (p) is the probability that the variation can be expIained on the basis of sampling error. - 50 -

c::t -c::t

-c::t • • • ..-CD • ~ CCI 1>- Il ~ c:::t 1)( CD w C CD "., • -' -0 c:::I ...... c::t c:::t .... 0 - c::. 'i • -' Il)( Il)( • . - >- • z ~-= c::t ".,

l'i:l -c:x: • p::J ~ c::t f; • - 0

~tQ

--• c::t t<\ C"".I ri • • bD 'rI • 1%1

CD c::t c::t c::t c::t c::t c:::t CD CD ~ - C"".I - - - INIOd HlnOS - 51 -

Fig. 13. Scatter diagram for N. pe1oronta showing the correlation between monthly percentages of snails in spawning condition at South Point and Little

Bay. The months Sept. 1967 - Sep~. 1968 are p1otted. The correlation coefficient Cr) and the regression coefficient Co) are shown. - 52 -

N . versicolor 10 r = 0·00015 yx . • b =fO~OO03 10 yx • • • 60

Fig.14,Scatter diagram for N.versicolor showing the correlation between monthly percentages of snails in spawning condition at South Point and Little Bay. The months Sept.1967-Sept.1968 are plotted. The correlation coefficient (r) and the regression coefficient (b) are shown. - 53 -

90 N . tesselata r =0·001 - • yx b =0-00009 80 yx

40 •

30~~----T-----~T------r------~-----' • H U MU 'H LlT-TLE BAY

Fig.15.Scatter diagram for N.tesselata showing the correlation, between monthly percentages of snails in spawning condition at South Point and Little Bay. The months Sept.1967-Sept.1968 are plotted. The correlation coefficient (r) and the regression coefficient (b) are shown. , ...... " .• l,.: . .,

"' ..."

.r,

DORSAL, "

'" -­ ~ ..... -

VENTRAL , (-

,..---CEPHAUC PENIS

.-~-' COPULATION TUBE

--f-H---FOOT f-r---MANTLE EDGE

~*"=,F-F----OPÈRCULUM

X 1.5 Fig~6(a) and (b). Dorsal, and ventral photographs of!co~ulating Nerita, (c) diagram of copuJ.ating Nerita Viewtd rentra~l~. 1

/'t , ;l.. >a, 'i - 55 -

DISCUSSION The criterion of spawning activity in this study, as with many others, (Orton et al 1956, Ward 1965) was the condition of the gonad; ripe, mature gonads presumably being indicative of spawning. The assumption was made that upon maturation and ripening of the gonads spawning normally followed. The results ·obtained suggested that the three Nerita species investigated, spawned continuously throughout the year. Indeed, it was observed that egg capsules of all three species were present the year round at both Little Bay and Harrison's Lighthouse. Boolootian, Farmanfarmian, and Giese (1962) suggested that mol1uscs could be divided into three groups based on their spawning habits. Group (1) were those which breed all year, group (2) were winter breeders, spawning between the end of autumn and the beginning of spring, and group (3) summer breeders, spawning between the end of spring and the beginning . of autumn. Moore (1938 a), Randall (1964), and Frank (1965a)reported that the animals they studied were able to spam1 aIl year, with peak periods occurr~ng at certain times. Orton (1920) has stated that in tropical climates good evidence existed for year round breeding. Moore (1958) supported this view. Struhsaker (1966) a1so found that Littorina pintado and~. picta breed all year in Hawaii, and a1so that the primary and secondary characteristics did not degenerate at any time after sexua1 maturity had been reached. A similar situation was found to exist with the species - 56 - of Nerita in this study. The concept of temperature as a major controlling factor in the initiation of bre\9ding activi ty has found support with many researchers. Ingle (1951) found that a minimum temperature of 20° C. was necessary for gonad ripening in oysters. Ansell (1961) suggested that a rise in temperature may induce spawning in Venus striatula (da Costa). Orton and Southward (1961) also found that spawning in

Patella depressa (Pennant) coincided with maxim~ air temperatures. Caddy (1967) suggested a correlation between spawning in Macoma balthica (Linneaus) and rising ambient temperatures. Other environmental conditions have been found to influence spawning. Lenderking (1954) noticed a correlation between spawning and copulation and rainfall. Diaz-Piferrer (1962) reported a close correlation between reproductive activity and rainfall in a in Cuba. The multiple linear regression analysis showed that available moisture, either as vapour or rainfall, had significant: effects on breeding activity. These factors, though, are different enough in nature to require closer examination of their effect. Orton and Southward (1961) suggested that a spawning stimulus may be provided by wave action. Giese (1959) also reported that chitons ceased spawning in tide pools when the water was disturbed by wave action. Orton, Southward, and Dodd (1956), after studying (L.) in Britain, inferred that spawning did not appear to be related to temperature, tides, or moon phases, but did seem correlated with onshore winds and rough seas. They suggested that spawning may have been initiated - 57 - by physical shock, though experimental investigation of this phenomenon failed. Struhsaker (1966) discovered that~. pintado and~. picta were stimulated to spawn only during high tides, presumably because they 1ived at high intertida1 leve1s_. She also reported that the degree of viviparity and oviviviparity was not correlated with distance fram mean tide leve1. Wind speed, as an indicator of wave action, though, was not shown by the computer to exert any significant effect on breeding activity in this study. Giese (1959) and Leighton and Boolootian (1963) have reported that food is also an important exogenous factor in reproductive activity. Some authors (Lenderking 1954, and Caddy 1967) have suggested that spawning is influenced by moon phases. The breeding activity for Little Bay and South Point, as illustrated by figure 12, showed a relatively high annua1 percentage of animals in spawning condition. Randa1l (1964) found that in the West Indian topshell there was recruitment all year with a peak in Januar,y. Other researchers have reported variations in breeding activity. After a review of present literature, Williams (1964) stated that~. littorea appeared to be capable of breeding at different times of the year. Sim1larly Orton, Southward, and

Dodd (1956) reported that even though~. 1ittorea was, in

Eng1and, a winter breed~r, subsidiar,y spawning cou1d occur at any time between September and June. Further, they stated that the main spawning period varied in time of occurrence from year to year and place to place. The lack of correlation of - 58 - breeding cycles of the three Nerita species between Lit.tle Bay and South Point suggested that this variation in 'timing of spawning peaks occurred in Barbados. Giese (1959) suggested that extended breeding periods such as these were a result of asynchronous breeding in the population. . - 59 -

v- FEEDING INTRODUCTION • Graham (1955) reported that the Neritidae feed on algae, and they have a microphagous mode of feeding. Fretter and Graham (1962) have produced an elaborate classification and description of feeding methods. Southward (1964) found that the grazing of limpets had drastic effects on algae cover, and there was a rapid succession to a climax of fucoids after removal of aIl limpets. He also suggested that a cyclic relationship existed between the and algal population. The stabilization of the cycle was dependent on external factors, the most important being wave action. Best (1964) found that in Tegula funebralis (Adams), the preferred forage was microscopie algae and detrituso He also found that the feeding rates were unaffected· by sunlight, and that smaller animaIs fed faster. The species

of Nerita studied in this project showed a degree of negative phototropism and were never seen actively foraging during daylight. They were usually stationary with the lip of the shell pressed close to the sl''''stra tum. Several authors have found that feeding activity has important effects on growth rates. Moore (1938 b) found that the body volume of limpets was directly proportional to the areas they kept clean of algae. Moore (1938 a) suggested that the difference in growth rates of Purpura ... lapillus, from two locations, was probably due to the relative values of food

supply between older and younge~ stages. Fox and Coe (1942), • Leight6n and Boolootian (1963), and Forster (1967) reported the close correlation that existed between food supply and growth rate. Ansell (1961), working with Venus striatula, found that gonad proliferation coincided with phytoplankton increases, and concluded that food supply was more important

tha~ temperature in reproduction. Somewhat in contrast to the evidence presented above, Quayle (1951) noted an increase in growth rate of Venerupis pullastra in the late summer, which he was unable to correlate with any particular factor such as food supply. The feeding activity of herbivorous intertidal gastropods has been observed to co'ntributesignificantly to erosion (Ginsberg 1953 a, McLean 1967). North (1954) ca1culated the gross metabo1ic efficiency of two species of Littorina in Ca1ifornia, and also computed that the feeding of Littorina deepened tide pools 1 c.m. every 16 years. Southward (1964) a1so mentioned the contribution of 1impets to intertida1

e~osion. He cited the large percentage of ca1careous materia1 in faeca1 pellets and radular tooth marks on the limestone as evidence. Arnold (1959) and Newe11 (1962) investigated the effect of environmental factors on feeding activity. Arnold (1959) found that Patella vulgata responded to changes in sa1inity, particular1y calcium and chlorine ions. He suggested that these euryhaline 1impets can take advantage of high sa1inities, rain, and high humidity to prolong feeding times. Newel1 (1962)

reported that the typica1 periodic feeding activity in Peringia (=Hydrobia)ulvae (Pennant) was corre1ated with light intensity; - 61 - the floating response, a feeding activit,y, was invoked by an increase in light intensity. Frank (1965a)worked with an intertidal snail population and suggested, in agreement with Arno1d_(1959), that the

1ength of time available for feeding ~robably has important repercussions on such things as growth rate. Some authors have found relationships between feeding and various physiological phenomena. Spencer-Davies (1967) d~scovered that respiration rates of intertida1 populations of Patella were not only found to be a function of intertidal height, but also of abundance of algal food. Ingle (1951) reported that lowglycogen content of oysters did not appear to reduce spat production. - 62 -

MATERIALS AND METRODS Four random collections of approximately 30 snails each were made for purposes of the study of feeding. The three species were sampled and the specimens were immediately placed i~ neutral formalin to prevent digestion. At both Little Bay and Harrison's Lighthouse two collections were made at 0600 hours, and two at 2100 hours at low tide. More collections would have been made but there was a danger of depletion of the population at Harrison's Lighthouse. Stomach contents were first microscopically examined to determine the nature and quantity of food consumed. It was found, however, that identification of food organisms by this means was impossible. Instead, the gross stomach contents were considered and tabulated on a scale of fullness, viz: tfull, ifull, ~full, or full. At no time was an animal collected from the field observed to have an empty stomach. It was also observed that these animaIs were more active during the night at low tide than at any other time; during the day, movement was confined to retreating from the increased wave action at high tides. Assuming that the chief night time activity was grazing, the collections were made in an attempt to determine if feeding started earlier at one station than the other, and to find out' if one station provided more forage than the other. Analysis of Feeding Data: Histograms showing the percentage of animaIs against two classes of stomach fullness ( ifull + ifull, and ifull + full) 63 - were prepared ( Fig. 17). Chi-square tests of significance were applied to each of the classes for eacll species at the same collection time and the same station; for example, the ~full + !füll and the !full + full classes of N. peloronta were compared at 9:00 P.M. at Harrison's Lighthouse. This was done to determine if the difference was significant ( Table 4 ). Chi-square tests were also applied between the two classes for each species at the same collection time but at different stations; for example, the ~full + full classes for N. peloroilta at 9 :00 F.M. were compared between Little Bay and Harrison'·s Lighthouse. This was done to determine whether the numbers of animaIs in the same class weresignificantly different between stations ( Table 5 ). - 64 -

RESULTS At Harrison's Lighthouse the comparison between the two classes !full + tfull and ~full + full at 9:00 P.M. showed there were significantly greater numbers of animaIs with stomachs in the more full condition ( ~full + full) in aIl three specie~. At Little Bay for the 9:00 P.M. collections, however, the class differences in the three species were not significant (Table 4). At 6:00 A.M. for both stations, the reverse was the case.

That is, ther~ were significantly greater numbers of animaIs with stomachs in the less full condition, i~ull + tfull (Table 4). The results producedby applying the chi-square test between similar classes from the two stations did not show a continuous trend. For the 9:00 P.M. collections there were significantly less animaIs with stomachs !full + tfull in the Harrison's Lighthouse collections; also there were significantly more animaIs with stomachs ifull + full in the collections of N. versicolor and N. tesselata from Harrison's Lighthouse. There was no significant difference between the ifull + full classes on N. peloronta collections (Table 5). The only significant difference in the 6:00 A.M. collections occurred between the ~full + full classes of N. versicolor. AlI other differences were not significant. - 65.-

Harrison's 900 PM '. Little Bay

%

T SS P L e· '. stomach fullness '. i---·F1g:ii.,·p~rc~ntag~ -~f individÜals of N.~~i~~ënta'·{PËL)',·" ...... : . N.versicolor (VERS) and N.tesselata (~SS) trom Harrison's Light- : . house and' Little Bay at 9.00 p.m. and 6.00 a.m. against degree .: .' of stomachfullness (.25 t·,.5) and (.75 + F). . ;' c. 65 -

Harrison's 900 PM Little Bay

%

)

I"

1.1 1 j 1 1 Fig.17.Percentage of individuals of N.~eloronta (PEL), .1\ N.versicolor (VERS) and N.teaselata (T~SS) from Harrison's Light- .l house and Little Bay at 9.00 p.m. and 6.00 a.m. against degree '! of stomach fullness (.25 + .5) and (.75 + F). - 66 -

HARRISON'S LITTLE LIGHTHOUSE ~ at 2100 hours • 2 2 X -p -X -P N. Ee1oronta 13.12- (0.001 0.308 0.70 - 0.50 N. versico1or 23.12 (0.001 0.080 0.80 - 0.70 N. tesse1ata 18.00 (O.OO:L 0.320 0.70 - 0.50

at 0600 ho urs X2 -P X2 -P N. Ee1oronta 3.920 0.05 - 0.02 3.920 0.05 - 0.02 N. versico1or 6.480 0.02 - 0.01 28.88 (0.001 N. tesse1ata 33.62 (0.001 40.50 (0.001

Table 4: Chi-square v'alues between the classes iful1 + tful1 and iful1 + full for animaIs co11ected at 2100 hours and 0600 hours from Harrison's Lighthouse and Little Bay •. The probabi1ity (p) that the differences occurred by chance is shown. - 67 -

N. peloronta 9:00 P.M. ~ ifull + ifull 5.882 0.02 - 0.01 ifull + full 3.031 0.10 - 0.05 6:00 A.M. -P tfull + ifull IDENTICAL VALUES IN EACH CLASS ~full + full

N. versicolor 9:00 P.M. !2 -P tfull + ifull 19.05 (0.001 !full + full 9.819 0.01 - 0.001 6:00 A.M. 2 -X -P ifull + ifull 2.564 0.20 - 0.10 :full + full 8.884 0.01 - 0.001

N. tesselata 9:00 P.M. -X2 P ifull + tfull 7.811 0.01 - 0.001 if'ull + full 4.587_ 0.05 - 0.02 6:00 A.M. X2 -P tfull + tfull 0.096 0.80 - 0.70 ifull + full 0.7499 0.50 - 0.30

Table 5: Chi-square values for the same classes, for the sarne species and the sgme collection times; but between different stations (Harrison's Lighthouse and Little Bay). The probability (p) that the dif'ferences occurred by chance 1s shown. - 68 -

DISCUSSION The results obtained from the collections at 9:00 P.M. suggested that the animaIs at Harrison's Lighthouse were able to begin feeding activity sooner than those at Little Bay" The significantly greater number of animals with stomachs in the !full + full classes st Harrison's Lighthouse, and the non­ significant differences between classes at Little Bay supported this conclusion. Also in all three species there were significantly greater numbers of animaIs with stomachs ifull

+ ifull at Little Bay~than at Harrison's Lighthouse. The collections of N. versicolor and li. tesselata also showed

significantly greater numbers of animals with stomachs ~full + full at Harrison's Lighthouse than at Little Bay. Results obtained from the 6:00 A.M. collections showed that there were significantly more animaIs with stomachs in theless full condition ( Î"full + tfull ). The resul ts also

s~gested that the animals ceased feeding at approximately the same time. The absence of significant differences between the ifull + tfull.classes ( except for N. versicolor ) from both locations tended -to support this conclusion. The resulting effect of these observations caused a general lengthening of the time period available for feeding at Harrison's Lighthouse. Frank (1965$)stated that the available feeding time may have significant effects on growth rates. Also the availability of more food has been found to have generally ameliorating consequences (Fox and Coe 1942, Ansell 1961, Leighton and Boolootian 1963, Forster 1967) • . e The reasons for this apparent increase of feeding time at - 69 -

Harrison's Lighthouse have not been compietely explained by investigations in this study. The relationship of light to browsing, as has already been mentioned, seemed to be inverse; increasing intensity caused withdrawal of the foot and cessation of moveme~~. Since Harrison t s Ligh thouse W8.S on the north west of the island, it seemed reasonable that animaIs at that station would have begun feeding after those at Little Bay. Wave action, however, which also caused withdrawal reactions, probably had an overriding effect on light intensity. It is probable that the larger waves at Little Bay took longer to subside after the typical reduction of wind velocity at night, hence the animaIs there had to wait longer bèfore beginning to browse. - 7:0 -

Vl- SUMrv1ARY· 1. Interspecific growth rates were different; !. peloronta grew fastest, with !. versicolor next, and !. tesselata the slowest. 2. Growth rates for all three species were greater at r Harrison's Lighthouse than at Little Bay. 3. There were no monthly variations in growth rates throughout the year at either station. 4. Breeding occurred all year with significant increases and decreases occurring throughout the year. 5. Sexual maturity waS attained at the f0110wing size ranges: N. pe1oronta 18 - 21 m.m., N. versico1or 16 - 19 m.m., N. tesse1ata 14 - 17 m.m. 6. There was no seasona1 degeneration of gonads after sexua1 maturi ty was attained. . . 7. There was no similarlty between breeding cycles at Little Bay and South Point in any of the species. 8. Sex ratios were shown to be of the normal 1:1 type except· for!. tesse1ata at South Point. 9. Ova of !. pe1oronta and N. versico1or were approximately

25~x 300~, and N. tesselata ova were approximately

200.1( x 275~.

10. Sperm ~~r~ of the eupyrene type and were of the same size for the three spec1es. The sperm had pointed heads

approximate1y 8.5~long with tails from 25.5.t(- 34.0-t(long. 11. Copulation consisted of the formation of a 'copulation tube' from under the cephalic penis of the male, and the transference of spermatophores through this tube. - 71 -

12. There appeared to be m~e t~e available for feeding at Harrison's Lighthouse than at Little Bay, and this may be the chief factor producing faster growth rates at Harrison's Lighthouse. 13. There is no sex reversa1-in any of the species studied. - 72-

B:œLIOGBAPHY Abe, B. 1931. Eoologioal observations on Aomaea"dortuoea Gould." Sc~. Rep. Tohom Sv. Sera i'! Biol" 6(4): 403-428. ' " - Allee," W, c. 1930. Animal aggregations~ llniTersit7 ot Chicago Press, Chicago, 431pp. Andrews; E. A. 1935. Shell repair"bythe snail B'èrit1Dia. J. Exp. Zool• .:m(l): 75-107. " 1940. The snail, Neritinia Tirginia (Lam.), iD a ohanging satî pond. Eco1087, .n(3): 335';'346. Ansell, "A. D. 1961. Reproduction, growth, and mortalit7 ot Venus striatula (da Costa) in" Kames Bq, nllport. J .. "I4ar. Biol. Ass. U. K• .!!(l}: 191-216. " Arnoldi ',D. C. ' " 195~. The reactio11S ot the limpet, Patella Peata L., to certain ot the ionic constituents 0 "sea': water. J. Mar. Biol. Ass.'U~ K.2§: 569-580. Axelsen; :&'. J.' 1965. Growth rate study ot some tropical ~e inTertebrateè. K.Sc. thesis, McGill . UniT., l3Spp.·

Best, B~ A. 1964. :&'eeding acti~ties ot ~ funebralis (A~ Adams, 1854). Velige~suppl.):42-45. - - .. Boume, -G. C. 1908. Oontributions to the morpho1ogr ot the group Beritacea ot the aspidobranch'gastropods~ Part 1. The Beritidae." Proo. Zool. Soc. London, §.g(2): 810-887. - 73 -

Bro ekhuys en , C. J. 1940. A pre1iminary investigation of the importance of 4esiècai:ioa-. temperature, and.sa1inity as factors contro11ing the vertical distribution of certain marine gastropods. in Fa1se Bay, South Africa. Trans. Roy. Soc. S. Afr., 28: 255-292. Caddy, J. F. 1967. Maturation of gametes and spawning in Macoma ba1thica L. Can. J. Zool. Part Il, Ottawa, !2(6): 955-966. Carter, G. S. _ 1951. A genera1 zoology of the invertebrates. Sidgwick and Jackson Ltd.; London, 421pp. Colman, J., 1933. The nature of intertida1' zonation of plants and animaIs. J. Mar. Biol. Ass. U. K. 18: 435-476. Conne11, J. H. 1961. The influence of interspecific competition and other factors on the distribution of the barnac1e, Chthgma1us stellatus. Eco10gy, ±g(4): 710-723. Dehne1, 'P. A. 1955. - Rates of growth of gastropods as a function of latitude. Physi~l. Zool. ~(2): 115-138. Diaz-Piferrer, M. 1962. Reproduction of Po1yMita muscarum (Lea) Cuban tree snai1. Caribbean J. Sci. 2(2): 59-61. DotY , M. S. 1946. Critica1 tide factors that arecorre1ated with the vertical distribution of marine a1gae and other organisms a10ng the Pacifie coast. Eco10gy, 27(4): 315-328. Emery, A. R. 1964. The ecological effects of current patterns around is1ands with special reference to Barbados. McGill Univ. thesis, 145pp. Forster; G. R. 1967. The growth of Ha1iotis tuberculala. Results of tagging experiments in Guernsey. 1963-65. J. Mar. Biol. Ass. U. K. ~: 287-300 • • - 74- " ~-,

Fox, D.'· L., end"~B. Coe 1942. B1010Qof the Oal1fornia seamussel, ' m11US cal1forn1anus L., 1D:t1uence of êiperature,food BUPP17, sex aiidage on the rate' of growth. J. Exp. Zo01. 2Q: 1-30. '

1943. B1010gr of the Cal1'tornia sea mas~ë1, m11US californianusL., 11 J'utrit1'on, . meabo118l11., grOW'th, and o$iUll deposition. ~. Exp. Z 001. fi: 205-249. ' Fraenkel, G. 1968. !rhe heat resistuee of intertidal sna1ls' at·' BimiD1, Bahamas; Ocean SpriDgà, Mississippi; and Woods Hole, Massachusetts. !h7siol. Zo01. ~(l).-

Fra:nk1 p~ W. 19b5a. !rhe biodemograp~ of an intertidal snail population. Ecology, J§(6). ]!Irazen, ' A. 1956. On spermatogenésis, morphology of the sper.matozoon and' b1010gy of'fertil1zation among invertebrates.Zool. Bidrag. . Uppsala. l!: 355-482. l'retter, V., and .l. Graham ' , 1962. British prosobranch mo:J,.1uecs. Itq Soeiet7, London, 755pp. G1ese, .l. C. 1959. Comparative pbysioloS7: Annual:reprodUétive' c7cles of marine invertebrates. Annu. Bev. P~sio1. ~: 547-576. Ginsberg; R. !le 1953a. Inte~idal erosion o~ the Florida KeTs. Bull. Mar. Sei. Gulf and Caribbean, 55-58pp. Graham, 'A. 1955. Molluscan diets. 'Ma1aco1. Soc. London Proc. J!: 144-159. Haneock; D. .A.. 1965. Graphiea1 estimation of growth parameters. J. Cons. Cons.'Per.ma. Int. Exp10r. Mer. ~(3): 340-351. ... 75 -

Hayes, F. R. 1927b. The effect of environmental factors on the development and growth of Littorina littorea. Trans. Nova Scotia Inst. Sci. 17: 6-13. Hewatt, W. G. 1937. Ecological studies on selected marine intertidal communities of Monterey Bay, California. Amer. Midland Natur. 18: 161-206. Ingle, R. M.' 1951. Spawning andsettling of oysters in relation to seasonal environmental.changes. Bull. Mar. Sci. Gulf and Caribbean,. l( 2). Kolipinski, M. C. 1964. Life history, growth, and ecology of four intertiàal gastropOds ( Genus Nerita, ) of south east Florida. Ph.D. the sis, Univ. of Miami, 131pp. 'Lawrence, A. L., J. M. Lawrence, and A. C. Giese 1965. Cyclic variations in the digestive gland and glandular oviduct of chitons (Mollusca). Science, 147: 508-510. ' Leighton, D., and R. A. Boolootian 1963. Diet and growth in the black , . Ecology, 44: 227-237. Lenderking, R. E. 1954. Some recent observations on the biology of Littorina angulifera (Lam.) of Biscayne and Virginia Keys, Florida. Bull. Mar. Sci. Gulf and Caribbean, 2(4): 273-295. Lewis, J. R. 1964. The ecology of rocky shores. English University Press, London, 323pp. Lewis, J. B. 1960. The fauna of rockyshores of Barbados, W.I. Cano J. Zool • .2.§: _391-435~ Environmental and tissue temperatUres of sôme tropical intertidal marine animals. Biol. Bull. 124(3): 277-284. Loosanoff, V. L., and C. -A. Nomejko 1949. Growth of oysters, o. virginica, during different months. Biol. Bull. Woods Hole, XCVll, 82. - 76 -

Manzer,·J.I., and F. H. q~ Taylor 1947. The rate of growth of 1emon sole in the Strait of Georgia.'Fish. Res. Board Can. Progr. Rep. Pac. Coast Sta. #72, 24-27. Marshall, S. M., and T. A. Stephenson 1933. The breeding of reef anima1s. Part 1. The cora1s. Sei. Rep. Great Barrier Reef Exped. l(8): 219-245. Mattox,N .. T. 1949. Effects of ·dr.ying on certain marine snai1s from Puerto Rico. Ecology, 22(2): 242-244. Mayer, A. G. 1914. The effects.of temperature upon tropical marine animaIs. Carnegie Inst. Wash. Publ. 183(6): 1-24. McLean, R. F. 1967. Measurements of b"eachrock erosion by some tropical marine gastropods. Bull. ~~r. Sci. 11(3): 551-561. Meyer, G. R., and A. K. O'Gower 1963. The ecology of six species of littoral gastropods. 1. Associations between species and associations with wave action. Aus. J. Mar. Freshwater Res. 1!(2): 176-193. Moore, H. B. 1934. The relation of she11 growth to environment in Patella vulgata. Ma1acol. Soc. London Proc. gl: 217-222. 1937. The biology of Littorina 1ittorea. Part 1. Growth of the shell and tissues, spawning, length of 1ife and mortality. J. Mar. Biol. Ass. U. K. ~: 721-742.

1938a. The biology of Pur~ura 1apillus. Part 11. Growth. J. Mar.ioi. Ass. u. K. ~: 57-66. 1938b. Alga1 production and the food requirements of a limpet. Malacol. Soc. London Proc. ~: 117-118. 1958. Marine eco1ogy. John Wiley and Sons, Inc., New York, 493pp • • -77 -

Newell, R. 1962. Behavioural aspects of the ecology of Peringia ( = Hydrobia ) ulvae (Pennant) ( Gasteropoda, prosobranchia ). Proc •. Zool. Soc. London, 138: 49-75. North, W. J. 1954. Size distribution, erosive activities, and gross metabolic efficiency of the marine intertidal snails, Littorina ~lanaxis and ~. scutulata. Biol. Bûl1. 10 (2): 185-197. Orton, J. H. 1914. Observations on Patella vulgata. Part Il. Rate of growth of shell. J. Mar. Biol • . Ass. U. K. 12: 319. 1920. Sea temperature, breeding and distribution in marine animaIs. J. Mar. Biol. Ass. u. K. 12: 339-366. 1928. Observations on Patella vulgata •. · Part 1. Sex phenomena, breeding and shell growth. J. Mar. Biol. Ass. U. K. 12: 851-862. Orton, J. H., A. J. Southward, and J. M. Dodd 1956. Studies on the biology of limpets. Il. The breeding of Patella vulgata (L) in Britain. J. Mar. Biol. Ass. U. K. 35: 149-176. Orton, J. H., and A. J. Southward 1961. Stud~es on ~he biology of limpets IV. The breeding of Patella depressa (Pennant) on the north Cornish coast. J. Mar. Biol. Ass. U.K. 41: 653-662. Pelseneer, P. 1920. Les variationes et leur heredite chez les mollusques. Bruxelles. Rayez, Imprimeur de l'Academie Royale de Belgique. 826pp. Quayle, D. B. 1951. The rate of growth of veneruîis pullastra (Montague) at Millport, Scot and. Proc. Roy.Soc. Edinburgh, _S_~cj;~.B.'.Biol. 64 pt. IV (20) •. 1952. The seasonal growth of the Pacifie (Ostrea gigas) in Ladysmith Harbour. Rep. Brit. Columbia Dept. Fish. 1950, (85). ;'-.'.

~andall, Helen.A. 1964. A study of tne growth and other aspects . of biology of the West Indian topshell, Ci ttarium pica L. Bull. Mar. Sei. Gulf and Caribbean, 1&(3): 424-443. Russell, E. S. 1909. . The growth of the shell, Patella vulgata. Proe. 'Zool. Soc. London, 235-253pp.

Russe~l; H. ~ D. 1941. The recent molluscs of the family Neritidae of the west~rn Atlantic. Bull. Mus. Comp. Zool. Harvard Univ. 88(4): 347-404. . • - . Sailing Directions for the West Indies .. 1949. 11. "The Lesser Antilles and the coast of Venezuela. Publ. 129. U. S. Navy Hydrographie Office, Wash., D. C. Segal, E. 1956.. Microgeographic variation as thermal acclimation in an intertidal mollusc. Biol. Bull. 111: 129-152pp. Spencer-Davies, P. 1967. Physiological ecology of Patella.'ll. Effect of environmental aeclimation on the metabolic rate. J. Mar. Biol. Ass. U. K• .il: 61-74. Southward, A. J • . 1958. Note on the temperature toleranc~s of some intertidal animals in relation to environmental temperatures and geographical distribution. J. Mar. Biol. Ass. U. K. 21: 49-66 • . . 1964. Limpet grazing and the control of vegetation on rocky shores. In: Grazing in Terrestrial and Marine Environments.Ed. by D. J. Crisp, Blaekwell Scientific. Publ. Oxford, 265-273pp • Stephenson, T. A., and A. Stephenson 1950. Life between tide marks in North America 1. The Florida Keys. J. Ecol. 2§(2). Struhsaker, Jeannette W. 1966. Breeding, spawning, spawning periodicity and early development in the Hawaiian Littorina: L. pintado (Wood), ~.}icta (Phillipi), and ~. scabra (Linne • Malacol. Soc. London Proe. 21= 137-165. - 7,$ -

~andall, HelenA. 1964. A study of tne growth and other aspects . of biology of the West Indian topshell, Ci ttarium pica L. Bull. Mar. Sei. Gulf and Caribbean, 1i(3): 424-443. . Russell, E. S. 1909. . The growth of the shell, Patella vulgata. Proc. 'Zool. Soc. London, 235-253PP.

Rus se'j.l, H.' D. 1941. The recent molluscs of the family Neritidae of the western Atlantic. Bull. Mus. Comp. Zool. Harvard Univ • .§.ê(4): 347-404 • • Sailing Directions for the West Indies " 1949. 11. -The Lesser Antilles and the coast of Venezuela. Publ. 129. U. S. Navy Hydrographie Office, Wash., D. C. Segal, E. 1956.. Microgeographic variation as thermal acclimation in an intertidal mollusc. Biol. Bull. Ill: 129-152pp. Spencer-Davies,P. 1967. Physiological ecology of Patella.'ll. Effect of environmental acclimation on the metabolic rate. J. Mar. Biol. Ass. U. K• .li: 61-74" Southward, A. J • . 1958. Note on the temperature toleranc~s of some intertidal animals in relation to environmental temperatures and geographical distribution. J. Mar. Biol. Ass. U. K• .21: 49-66. . , . 1964. Limpet grazing and the control of vegetation on rocky shores. In: Grazing in Terrestrial and Marin€ Environments. Ed. by D. J. Crisp, Blackwell Scientific Publ. Oxford, 265-273pp. ~ Stephenson, T. A., and A. Stephenson 1950. Life between tide marks in North America 1. The Florida Keys. J. Ecol. 2§(2)c Struhsaker, Jeannette W. 1966. Breeding, spawning, spawning periodieity and early development in the Hawaiian Littorina: ~. pintado (Wood), ~.ricta (Phillipi), and L. seabra (Linne • Malacol. Soc. London Proc • .21= 137-165. - 7' - Suzuki, S. 1935. Notes on the behaviour o~ Nerita japonica (Dunker). Sci. Rep. Tohoku Univ. Sere lV Biol. ~: 297-314. Taylor, C. C. 1959. Température and growth - the Pacific razor . J. Cons. Cons. Perma. Int. Explor. Mer. ~(l): 93-101. 1960. Temperature, growth, aIlld mortality - the Pacific . J. Cons. Cons. Perma. Int. Explor. Mer. ~(l): 117-124. Thompson, D'A. W. 1942. On growth and forme Camb~dge Univ. Press, London, Vol. 1. Thors on , G. 1936. The larval development, growth and metabolism of arctic marine bottom invertebrates. Medd. Grpnland 100(6). Voss, G. L., and N. A. ·Voss 1960. An ecological survey on the marine invertebrates of Bimini, Bahamas, with a consideration of their zoogeographiçal : relationships. Bull. Mar. Sci. Gulf and Caribbean, 10(1): 96-116. Ward, J. 1965. Some aspects of the biology of Fissurella barbadensis (Gmelin). M. Sc. thesis, McGill Univ. 155pp. Walne, P. R. 1958. Growth o~ oysters (L.) J. Mar. Biol. Ass. U. K. 21(3): 591-602. Wara, W. M., and Benjamin B. Wright 1964. The distribution and movement of Tegula funebralis in the intertidal region, Monterey Bay, California. Veliger, 6 (suppl.): 30-37. Warmke,G. L., and R. T. Abbott 1961. Caribbean seashells. Livings ton Pub1ishing Company, Narberth, Penna. 346pp. Wilbur, K. M., and G. Owen 1964. In: Physiology of Mollusca. Vol. 1.· Ed. by K. M. Wilbur and C. M. Yonge. Academic Press, New York and London, 211-242pp. -80-

Williams, E. E. 1964a. The growth and distribution of Littorina littorea (L.) on a rocky shore in Wales. J. Anim. Ecol. 22.(3): 413-432. 1964b. The growth and distribution of Gibbula umbilicalis (da Costa) on a roc~ shore in Wales. J. Anim. Ecol. 22(3): 433-442. Woodward, B. B. 1892. On the mode of growth and the structure of the shell in conoideus (Lam.) and other Neritidae. Proc. Zool. Soc. London, 528-540pp. Zhirmunskii, A. V., and Ts'u Li-Ts'ung 1964. Prisoposoblenie tropicheskikh mol1yuskov Nerita y Donax k temperaturnyur usloviyaur obitauii. In: Mollyuski Voprosy teoreticheskoi i prikladuoi malakologii.. Moscow, Leningrad, Ref. Zh. Biol. 62-77pp.