~ OJ- ~ P.S.Z.N. I: Marine Ecology, 12 (2): 105-121 (1991) Accepted: September 24, 1990 @ 1991 Paul Parey Scientific Publishers, Berlin and Hamburg JtJ ISSN0173-9565 '1:,

Life Histories and Breeding Patterns of Three Intertidal Sand Beach Isopods

AN M.C. DE RUYCK, THEODORE E. DONN, JR. & ANTON McLACHLAN

Zoology Department, Coastal Research Institute, University of Port Elizabeth, Box 1600, Port Elizabeth 6000, South Africa.

With 10 figures and 3 tables

Key words: Intertidal isopods, life history, breeding patterns.

Abstract. Three-weekly transects were done over a 14-month period at Sundays River Beach, a high energy beach in Algoa Bay, South Africa, to determine the life histories, breeding patterns, and fecundities of three intertidal cirolanid isopods, Eurydice longicornis, Pontogeloides latipes, and natalensis. E. longicornis exhibits an annual, multivoltine life history with a more extended breeding period than the other two species. P. latipes and E. natalensis both have biennial, univoltine life histories with lower fecundities than E. longicornis.

Problem

The life history and reproductive patterns of Eurydice pulchra and Eurydice affinis have been well studied, both in warm temperate (SALVAT,1966) and cold temperate climatic regimes (FISH, 1970; JONES, 1970). Differences in life his- tories and reproductive patterns in the same species in different climates have been ascribed to temperature differences (SALVAT,1966; FISH, 1970) and were also noted by DONN & CROKER(1986) in haustoriid amphipods. KLAPOW described ovoviviparity (1970) and a fortnightly cycle of reproduction (1972) in , and DEXTER(1977) studied the reproductive patterns of Excirolana braziliensis in Panama. Despite the widespread occurrence of E. longicornis, E. natalensis, and P.latipes in southern Africa (McLACHLAN,1977b, c; BALLY,1981; McLACHLAN et al., 1981; WENDT& McLACHLAN,1985; DONN, 1988 a, b; DONN & COCKROFT, 1989), no detailed work has been undertaken on their population structure or reproduction. The life histories and breeding patterns of these isopods were studied to better understand their ecology and their observed distribution and activity patterns.

U. S. Copyright Clearance Center Code Statement: 0173-9565/91/1202-0105$02.50/0 106 DE RUYCK, DONN & McLACHLAN Material and Methods

1. Study Area

Sundays River Beach (33° 43'S, 25° 53'E) in Algoa Bay, South Africa lies east of the Sundays River estuary and stretches without interruption for 40km. On McLACHLAN'S (1980) 20 point exposure rating system it rates 15.0, which classifies it as exposed to very exposed. Although the beach is occasionally dissipative, its modal morphodynamic state is high energy intermediate (see SHORT& WRIGHT,1983 and McLACHLAN& BATE, 1984 for description of beach morphology). The surf zone is approximately 150-250m wide. Water temperature in the surf zone has an annual range of 14-23°C (McLACHLAN, 1977 a). The sand consists of well sorted medium quartz particles with diameters of 225-335 11m,with a CaC03 content of 29-47% (WENDT& McLACHLAN, 1985). Two sites, 5!l<:mand 25 km from the Sundays River estuary were chosen. The mean intertidal slope varied between Yt9and ~2. No significant difference in sand particle size between the two sites has been found (McMuRRAY, 1985; DONN, 1987), but the intertidal slope tends to be slightly steeper and the wave height greater at 25km (pers. obs.; W.K. ILLENBERGERand M.M.B. TALBOT,pers. comm.).

2. Sampling and data analysis

The intertidal isopod populations at Sundays River Beach were sampled at three-weekly intervals from December 1987 to January 1989 at both sites. The transects extended from above the drift line downshore as far as isopods were still obtained. Along each transect, five replicate 0.1 m2 quadrats of sand were taken to a depth of 25 cm at 3 m intervals across the beach, in a modified stratified random design (PIELOU, 1974). The sand was sieved through 1 mm mesh and all isopods retained were preserved in 10 % formalin in seawater. The first two collections in December 1987 were sieved through a 1.5 mm mesh. However, small Eurydice juveniles were observed to crawl through this and subsequently a 1mm mesh size was used; this retained most individuals larger than 2mm length. Due to practical sicving problems, a smaller mesh size could not be used. In the laboratory the isopods were identified, counted, sexed, and measured to 0.1 mm length with a stereomicroscope fitted with an ocular micrometer. Isopod length was defined as the distance along the median axis from the front of the cephal on to the posterior border of the telson. Four sex classes were distinguished: 1) males: stylets present on the second pair of pleopods. 2) ovigerous females: with mature or immature eggs or embryos present in the brood pouch. The terms 'breeding' or 'reproductive' refer to ovigerous females with only mature ova or embryos. 3) females: no characteristics in non-ovigerous females, apart from absence of stylets, made sexing possible; oostegites become discernible only at sexual maturity. The smallest E.longicornis male was 3.1 mm and 80 % of all males caught over 14 months exceeded 3.4mm. Thus, all individuals ;;, 3.4mm and lacking a stylet were classified as females. Similarly, the smallest P.latipes and E. natalensis males sampled were 4.6mm and 7.2mm, respectively, and 80% of P.latipes males exceeded 5.5mm and 8.0mm for E. natalensis. Thus all P.latipes and E. natalensis individuals ;;, 5.5 mm and;;, 8.0 mm, respectively, and lacking stylets were regarded as females. 4) unsexables: all individuals';;; 3.3 mm for E. longicornis, .;;;5.4 mm for P. latipes, and';;; 7.9 mm for E. natalensis and lacking stylets. This group consisted mainly of juvenile females, late maturing males, and newly released individuals. The term 'juveniles' was used to describe all individuals, including males, smaller than or equal to 3.3 mm, 5.4 mm, and 7.9 mm, respectively, for E. longicor- nis, P. latipes, and E. natalensis and thus included the unsexables. The number of eggs or embryos in the brood pouches of ovigerous females was determined.

'L, Embryos were defined as the second to fourth stages of development of the ova in the marsupium, as described by JONES (1970) for Eurydice pulchra. The system described by KLAPOW(1970) for Excirolana chiltoni was applied to Pontogeloides latipes and Excirolana natalensis, since the development stages looked morphologically similar except for size differences. Abundance was calculated per meter wide strip of beach, from above the drift line down to the low water mark. This makes allowance for uneven distribution of fauna that exhibit vertical zonation

~ DE RUYCK, DONN & McLACHLAN Intertidal sand beach isopod life histories 107

across the beach and for the dynamic morphology of sandy beaches with changing profiles (McLACHLAN,1983). LOglO(x + 1) transformation was done prior to analysis in order to normalize the data (patchy isopod distribution). Due to the low numbers of E.longicornis and P.latipes collected at the 25 km vs. 5 km site, population structure and cohort analyses were done only on the data from the latter site. The low abundance of E. natalensis at both 5 km and 25 km made it Igoa Bay, South Africa lies east of the Sundays necessary to combine data from the two sites to facilitate cohort and life history analyses. This was .n. fo~ 40km. On McLACHLAN'S (1980) 20 point considered justifiable because there was no significant difference in abundance between the two fles It as .expose~ to. very exposed. Although the sites. Length frequency separation by means of the probability paper method (CASSIE, 1954) was hodynamlc state IS high energy intermediate (see used to determine the number of cohorts present. , 1984 for des~ription of beach morphology). The ~emperature In the surf zone has an annual range SIStS of well sorted medium quartz particles with of.29-47% (WENDT & McLACHLAN, 1985). Results River e~tuary were chosen. The mean intertidal erence.In sa~d particle size between the two sites 1. Eurydice longicornis ut the IntertIdal slope tends to be slightly steeper W. K. ILLENBERGERand M. M. B. TALBOT, pers. The abundance of E. longicornis and the percentage of juveniles at 5 km is presented in Fig. 1. Two of the four peaks in abundance coincided with increases in juveniles, i. e., the peaks between March and the end of May (autumn) and between October and December. However, the main peak from July to August was not associated with an increase in juveniles. r Beach were sampled at three-weekly intervals The female: male ratio in individuals larger than 3.4 mm fluctuated markedly, The transects extended from above the drift line long each transect, five replicate 0.1 m2 quadrats ranging from 0.5-15.5 females per male. Females outnumbered males through- ervals across the beach, in a modified stratified out the year except on two occasions. Breeding females were present through- ed through 1mm mesh and all isopods retained out the year except in early May and June. Only two females in the 7-8 mm size class (1.2 % ofthe population; 2 % offemales) were found breeding in late May. s.ieved through a 1.5mm mesh. However, small his and subsequently a 1mm mesh size was used' The smallest female bearing immature ova was 3.4mm and the smallest size at tho Due to practical sieving problems, a smalle; which males could be distinguished was 3.1 mm. The largest individual sampled was a 10.5 mm male. ounted, sexed, and measured to 0.1 mm length eter. Isopod length was defined as the distance to the posterior border of the telson. Four sex E. longicornis TOTAL ABUNDANCE 1200 'pods. FEMALES BREEDING s or embry?s present in the brood pouch. The -- 100 .,~ females with only mature ova or embryos. . ... 1000 r...* - -- JUVENILES les, apart. from absence of stylets, made sexing \ ual matunty. The smallest E. longicornis male : ~ 80 ~ :: 800 z onths exceeded 3.4mm. Thus all individuals c: .:;:: emales. Si~iIarly, the smalles~ P.latipes and

t9 108 DE RUYCK, DONN & McLACHLAN The percentage of breeding females as a percentage of all females at 5 km followed a bimodal pattern (Fig. 1). The first peak, between July and October, produced a sharp, relatively low peak of juveniles in November (the spring brood); the second, from December to February, produced an extended, relatively high peak of juveniles from late December to May (the autumn brood). In early July, 83 % of the ovigerous females had immature ova; most ova had matured by late July, suggesting a maturation period of approximately 3 weeks. In addition, this indicates that egg development continues in winter. The maximum percentage of females that were breeding at any particular time was 87 % (late July, Fig. 1). At the start of peak breeding season (early July to August) most of the ovigerous females occurred in the 4-5 mm size class. Only from September onwards did significant numbers of ovigerous females measure 5-6 mm. Fecundity was estimated by regressing number of ova and embryos versus female body length (Fig. 2). The two equations were compared using analysis of covariance (KLEINBAUMet al., 1988) and were found to be significantly different (P < 0.01). Therefore, data for females carrying ova and embryos could not be pooled to yield a single equation. The mean length of females bearing ova and embryos was 5.3 mm and 5.1 mm, respectively, with each female producing on average 26 ova and 20 embryos. This discrepancy constituted an average loss of 11-14 % of ova during the incubation period for 3.5 to 9.4 mm long females, as calculated from the regression equations (Fig. 2). Two groups of breeding females are evident, one at 3.5-5 mm and the other at 8-9.5 mm (Fig. 2). This suggests two breeding cohorts or females breeding twice in a life cycle. The mean cohort length, based on length frequency separation, for E. lon- gicornis from December 1987 to January 1989 is shown in Fig. 3. Three cohorts were present in the population at any 'one time. Despite the undersampling of individuals less than 2 mm, juveniles appeared to be recruited at 3.5-4 month intervals, resulting in approximately three cohorts produced per year. The

E. longicornis Fig. 2. Regression of numbers of ova (0) 80 and embryos (E) versus E. longicornis female body length. The equations are: 0 11.5 (Length) = - 35.6 (n = 36; r2 = gj 60 0 90%) and E >- = 9.9 (Length) - 30.4 (n = 53; r2 = [!)a: 86%). ::> UJ 40 0~ ll.. 0 a: w 20 :J~ . OVA Z 0 EMBRYOS r 5 6 7 8 9 LENGTH (mm)

\' DE RUYCK, DONN & McLACHLAN Intertidal sand beach isopod life histories 109 tIes as a percentage of all females at 5 km ,The first peak, between July and October E. longicornis ~ak of juveniles in November (the sprin~ ,er to February, produced an extended 10 :om late December to May (the autum~ c 8 0 s fem~les had immature ova; most ova had E IturatlOn period of approximately 3 weeks. -5 : development continues in winter. The were breeding at any particular time was E of peak b~eeding season (early July to .s~ occurred III the 4-5 mm size class. Only lnt numbers of ovigerous females measure 2

Ising .number of ova and embryos versus 0 ~quatlOnswere compared using analysis of 0 F M A M J J A s 0 N 0 J lIdwere found to be significantly different 1987 1988 1989 ~scarrying ova and embryos could not be MONTH Fig. 3. Mean lengths of E.longicornis cohorts from December 1987 to January 1989. ing ova and embryos was 5.3 mm and \ Ie producing on average 26 ova and 20 an average loss of 11-14 % of ova during 1m long females, as calculated from the recruitments in late February and June coincided with the peaks in juvenile lIpSof.breeding females are evident, one abundance shown in Fig. 1, but the recruitment in October was out of phase with the November peak in juvenile abundance. The mean length of the early 1~ (FIg. 2). This suggests two breeding hfe cycle. October cohort was 2.6mm; it may not have been sampled efficiently (small length f~equency separation, for E. lon- size) and may have been retained in the sieves only in November. The average growth rate of cohorts D, E, and F in the first three weeks after ry 19~9 ISshown in Fig. 3. Three cohorts pne time. Despite the undersampling of they appeared in the samples was 0.5 mm per month. If the same growth rate is ppeared to be recruited at 3.5-4 month assumed for juveniles after emerging from the brood pouch at the mean size of three cohorts produced per year. The 1.7mm (pers. obs.), they would reach 2.2mm and thus become available for sampling only 3 to 4 weeks after release from the brood pouch. Hence it can be assumed that cohorts D, E, and F were released 3-4 weeks earlier than is Fig. 2. Regression of numbers of ova (0) indicated in Fig. 3. Based on this assumption and the recruitment of juveniles at 3.5-4 month intervals, it appears that cohort C was released from the brood and embryos (E) versus E. longicornis female body length. The equations are: pouch in mid October 1987 and would be retained in the sieves only from mid 0 = 11.5 (Length) - 35.6 (n r2 November 1987, approximately four months prior to the appearance of cohort = 36' - W%)ud ' D in late February. Cohort C disappeared from the samples in mid August, E = 9.9 (Length) - 30.4 (n .,3 r 2 86%). = 5 ' - approximately 10 months after release from the brood pouch. From this a life span of 10 to 12 months can be deduced for E. longicornis at Sundays River Beach, with continuous reproduction and possibly two breeding cycles per female.

2. Pontogeloides latipes

The abundance and composition of the P. latipes population at 5 km is presented in Fig. 4. The maximum abundance during February-March coincided with recruitment of juveniles into the population. The increase in abundance in 110 DE RUYCK, DONN & McLACHLAN P. latlpes 100 """. TOTAL ABUNDANCE 700 .,"1. . 0° e--. FEMALES 80 BREEDING '" -"" : e- - -e JUVENILES : """,". w I -8- -8, z fl."",. \ /~ -8, 500 f ~ 60 : I ...~, !II : \ m z I :lJ """ '. \ ()w f I \ . I ~: m"0 a: : I '., .. :lJ ~ 40 e..: .' ". s:: \ 'e, .fI" m "" '- 300 ': "t..o' ,... m-i """.e.. !/ \ :lJ 20 ..l' """ ."" :,'.. I ~...""'''''' \'. I 0° \ I' "''''' \ I -"'''.' \ 0 , A M A S 0 " 0 J

MONTH Fig. 4. Total abundance, percentage juveniles, and percentage 5 km site. breeding females for P. latipes at the

September, after a minimum in winter, did not correspond with an increase in juveniles. The percentage of juveniles followed a unimodal pattern, with a peak in late summer and a steady decline during the fOllowing continued. During winter they represented 50-73 % of the population.months as growth The female: male ratio ranged from 0.4-2.3 females per male during the study period but did not differ significantly from unity, except on one occasion. Females bearing mature ova and embryos were present from October to March. The minimum size at which females became sexually mature (immature ova observed in the internal marsupium) was 8.3 mm and the minimum length for females with mature ova was 9.1 mm. The smallest size at which males could be distinguished was 4.6 mm and the largest individual sampled was a 14 mm male. The majority of breeding females were in the 10-11 mm size class. The percentage of breeding females (Fig. 4) followed a unimodal pattern, with a peak in December-January, approximately two months later, in February-March.followed by a peak in juvenile abundance tion period of approximately 2 months for P. tatipes. TheThis unimodalsuggests anpatternincuba-in both breeding females and juveniles indicates the production of one generation per year. The maximum percentage of females breeding at anyone time was 56 % (January 1988, Fig. 4). As in Eurydice tongicornis, a small percentage with immature ova were found throughout the year; only during winter did they constitute a significant part of the ovigerous females. Analysis of covariance showed a difference (P of numbers of ova and numbers of embryos versus< 0.01)femalebetweenbody lengththe equations(Fig. 5). The difference constituted a loss of 15-22 % of ova per female in the 9.5-13 mm size range during the incubation period. The mean length of females bearing ova and embryos was 11.3mm and 11.6mm, respectively, with each female produc- i'

\J DE RUYCK, DONN & McLACHLAN Intertidal sand beach isopod life histories 111 P. latipes ~. latipes Fig. 5. Regression of numbers of ova (0) and embryos (E) versus P. latipes female 33 700 . TOTAL ABUNDANCE body length. The equations arc: 35; r2 29 0 = 4.5 (length) - 33.7 (n = = (fJ 8-- FEMALES BREEDING 57.1 %) and 0 >- 8- - -8 JUVENILES E = 4.0 (length) - 31.08 (n = 34; r2 = z ::;:ffi 25 0 500 ~ 50%). w t -8 ro ;' \ m ~ \ JJ . \ 6 21 . . \ m"U u.. JJ 0 '., ..1,'''. "0 ;: 17 "8, ". '- 300 m ffi ." --i (!J "(' ' m ::;: """ JJ ;:) :.." \ :,: z 13 . OVA ....4. \ -"" 0 0 "°. Ie '. " 000 0 EMBRYOS \. . . .1 ."" \ \ 9 . \ , 10 11 12 13 LENGTH (mm) A S 0 " rH ing on average 17 ova and 15 embryos. The breeding females belonged to one , and percentage breeding females for P. latipes at the size group, indicating a single breeding cycle per female. Two P. talipes cohorts were present for most of the year except in February (Fig. 6), when three cohorts were present (recruitment of juveniles). The ~r, did not correspond with an increase in recruitment of cohort C coincided with the peak of juvenile abundance shown in foll~wed a unimodal pattern, with a peak Fig. 4. Cohort A died off in February, the same time that cohort C appeared, .~ dunng the following months as growth suggesting that most females reproduce once and die shortly thereafter. ented 50-73 % of the population. Since cohorts Band C required approximately 12 months to grow from 8 mm >m 0.4-2.3 females per male during the to 12 mm and from 4 mm to 8 mm, respectively, P. talipes may reach the average antIy from unity, except on one occasion breeding size of 11.3 mm within 16-22 months after release from the brood yos were present from October to March' pouch. It thus follows that P. talipes has a life span of 1.5-2 years, incorporating Ibecame sexually mature (immature ov~ a single breeding cycle per female. The population breeds once a year. Was 8.3 mm a~d the minimum length for rh~ s~~llest SIze at which males could be rS~mdIvIdual sampled was a 14 mm male. ~ m the 10-11 mm size class P. latipes !s (Fig.4) followed a unim~dal pattern ~lowed by a peak in juvenile abundanc~ tbruarY-M~rch. This suggests an incuba- .for P. taupes. The unimodal pattern in ~' Icates the production of one generation C eS bre~ding. at anyone time was 56 % tonglcornlS, a small percentage with the year; only during winter did the y rous females. 5 rence (P < 0.01) between the equations y~s versus female body length (Fig. 5). 3 D F M A M J J A S 0 N D J Yoof ova per female in the 9.5-13 mm 1987 1988 1989 he me~n length of females bearing ova MONTH respectIvely, with each female produc- Fig.6. Mean lengths of P.latipes cohorts from December 1987 to January 1989. 112 DE RUYCK, DONN & McLACHLAN 3. Excirolana natalensis

The abundance of E. natalensis and the percentage of juveniles at 5 km is shown in Fig. 7. Similar to Eurydice longicornis, the E. natalensis population showed marked fluctuations unrelated to season or peaks in juvenile abundance. Maximum abundance was reached during June with secondary peaks in April, September-October, and January. A high percentage of juveniles was present throughout the year and 60-85 % of the population The female: male ratio ranged from 0.3-8 females overwinteredper male duringas juveniles.the study period. It did not differ significantly from unity during the breeding season (October to early May) but changed during winter (late May to September) to approximately 2 females per male. Marked fluctu1:ltions occurred in the percentage of breeding females (Fig. 7), even within the breeding season (October to April). The maximum percentage breeding at any particular time was 67 % (January 1988). The sharp increase in juveniles approximately 9-12 weeks later suggests an incubation period of approximately 2.5-3 months. Females bearing mature ova and embryos were present from October to April. Ovigerous females with immature ova were present in small numbers throughout the year but constituted a significant proportion of females only during winter. The smallest female with immature ova measured 11.5 mm, the smallest male 7. 2mm, and the largest individual sampled was a 17.5 mm male. The regression equations of ova and embryos against female body length were not significantly different (ANACOV A, P > 0.05), indicating no loss of ova; thus the data were pooled (Fig. 8). The mean length of females with ova or embryos was 13.8mm, with each female producing an average of 19.5 offspring.

E. nata/ensis TOTAL ABUNDANCE 300

100 FEMALES BREEDING 250 e- -. JUVENILES BO-

C)w 200 ~ « ;:: I- 60 CD Z /\. m W :JJ U / \ cr: 150 W \ m Q. \ :JJ" 40 ,.. ;:: .\. m .\. 100 m-i : \ :JJ \ 20 !

0 D M J A J ('G MONTH Fig. 7. Total abundance, percentage juveniles, and percentage breeding females for E. natalensis at the 5 km site.

r

~ DE RUYCK, DONN & McLACHLAN Intertidal sand beach isopod life histories 113 ,.;«..."".-- ~is Fig. 8. Regression of numbers of ova or em- E. natalensis 26 bryos combined (OE) versus E. natalensis . :he ~ercentage of juveniles at 5 km is shown female length. The equation is: OE = 2.8 (length) 22; r2 orms, the E. natalensis population showed - 19.3 (n = = 52.5%). CfJ 0 23 se~son or peaks in juvenile abundance ex:>- CD tun?g June with secondary peaks in April' ::;: w ~ hIgh perce?tage of juveniles was presen; ;: 20 > the populatIon 0 overwintered as juveniles. l.L. m 0.3-8 fe~ales per male during the study 0 17 0 ex: y w fr?m U?Ity during the breeding season CD ::;: dunng wmter (late May to September) to ::> z . e OVA e percentag~ of breeding females (Fig. 7), a EMBRYOS ~~er to Apnl). The maximum percentage 12 13 14 15 Yo(January 1988). The sharp increase in LENGTH (mm) later suggests an incubation period of embryos were present from October to E. nata/ensis tur: o:~ were present in small numbers 15 a s~gllIfIcant proportion of females only A ~h I?I~ature ova measured 11.5 mm the IndIVIdual sampled was a 17. 5 mm ~ale 13 Id embryos against female body length B

COY A, P > 0.05), indicating no loss of 11 The me~n length of females with ova or ~ ~ produCIng an average of 19.5 offspring. E 9 .§ :r: C e)f0- I/ensls Z 7 W e TOTAL ABUNDANCE 300 -I

1: --- FEMALES BREEDING 5 I.i: 250 \ : -8 JUVENILES 3 : \ D F M A M J J A S 0 N D J . 200 Z :/e--e, .""- c: 1987 1988 1989 iI /: -- ~ MONTH r~ :. . /8, m~ " :JJ : , / \ 150 Fig. 9. Mean lengths of E. natalensis cohorts from December 1987 to January 1989. : ..e' / \ ;Jj /",.e... y 100 \ \C .i ' , The observation that breeding females belong to one size group supports the " hypothesis of one breeding cycle per female. / \./... .. The population consisted of two cohorts for most of the year (Fig. 9) except from late February to April, when a third cohort (C) was discernible, The A recruitment of cohort C coincided with a late February peak in juvenile abundance (Fig. 7). Cohort A disappeared approximately six weeks after the appearance of cohort C, suggesting that females reproduce once and die shortly ercentage breeding females for E. natalensis at thereafter. This is also reflected in the sudden absence of ovigerous females after April (Fig. 7). 114 DE RUYCK, DONN & McLACHLAN Cohort C took 12 months to grow from 4.2 mm (at release from brood pouch) to 8mm. Cohort B grew from 8mm in early February to the average breeding size of 13.8 mm in 6 months. E. natalensis at Sundays River Beach thus appar- ently reaches sexual maturity at about 18 months, has a life span of 1.5-2 years, and breeds once in a life time. As in P.latipes, the population breeds once a year.

Discussion 1. Abundance

Eurydice longicornis was the most abundant cirolanid isopod on Sundays River Beach during the study period, Excirolana natalensis the least abundant (Figs. 1, 4, and 7). The abundance of E. longicornis at 5 km showed marked non-seasonal fluctuations (Fig. 1) which can partly be explained by the production of multiple broods during the year. The low number of E. longicornis in June is unexpected, since cohort C appeared in the population at that time (Fig.3) and the population three weeks later showed a marked increase. Three possible reasons can be forwarded. The weather conditions during June sampling were most unfavourable (strong south-westerly winds, wave height 3-4m). The isopods may have been washed from the sand by the waves or have actively migrated offshore. Offshore migrations of Eurydice pulchra during stormy winter condi- tions have been described by JONES& NAYLOR(1970) and HASTINGS& NAYLOR (1980). LEBER(1982) reported that the bivalve Donax parvula in North Carolina migrated offshore during winter to a subtidal habitat, while ANSELLet al. (1972) found that Donax incarnatus disappeared from beaches in south-west India during the monsoon and reappeared afterwards. Secondly, with the recruitment of cohort C at this time, much of the population would be expected to consist of individuals smaller than 2 mm (already 37 % of the population during June measured 2-3.4mm; Fig. 1); since the sieves retained only isopods larger than 2 mm, a significant proportion of the population may not have been sampled. These newly released juveniles could grow large enough within three weeks to be retained by the 1mm mesh, hence the increase in numbers by early July. A third reason for the low June abundance could be mortality in cohort B (Fig. 3). Pontogeloides latipes showed the clearest seasonal fluctuation in abundance, with a gradual change from a late-summer maximum to a winter minimum (Fig. 4). After the February peak, numbers decreased (disappearance of cohort A) and reached a minimum in July. However, the September increase, unre- lated to recruitment, does not reflect undersampling of juveniles (as in E. lon- gicornis), since juveniles were retained by 1mm mesh from the time of release c) from the brood pouch. E. natalensis abundance showed marked non-seasonal fluctuations (Fig. 9), although to a lesser extent than in the E.longicornis population. A sharp decrease in numbers occurred in early May due to the mortality of cohort A (Fig. 9), but other peaks and troughs cannot be accounted for. E. longicornis showed greater fluctuations in abundance than P. latipes and E. natalensis. This variability can be partially explained by the production of

r DE RUYCK, DONN & McLACHLAN Intertidal sand beach isopod life histories 115 Vf~om 4.2mm (at release from brood pouch) multiple broods (Fig.3), whereas P.latipes and E. natalensis produced one n III e~rly February to the average breeding brood per year (Figs.6 and 9) and showed more stable populations. The talensls at Sundays River Beach thus appar- fluctuations, unrelated to recruitment of juveniles or mortality of cohorts, could )~t 18 JPo,nths, has a life span of 1.5-2 years, also be due to longshore patchiness in isopod distribution, which introduces III P. latlpes, the population breeds once a variability into the abundance estimates. Patchiness in the distribution of E. longicornis, P. latipes, and E. natalensis on sandy beaches on the west coast of South Africa was also described by BALLY(1981). Alternatively, the fluctuating numbers and the absence of males in E. longicornis and E. natalensis during certain periods of the year could be explained by offshore movement of parts of the population, i. e., males, similar to intraspecific zonation in the mysid shrimp, Gastrosaccus psammodytes, where males and juveniles are found furthest offshore and females move progressively inshore as the broods develop (W OOL- bundant cirolanid isopod on Sundays Rive DRIDGE,1981). 'olan~ natalensis the least abundant (Figs. 1~ cormsat km showed marked non-seasonal ~ be explallled ?y th~ ~roduction of multiple 2. Breeding season lber of l!. longlcormS IIIJune is unexpected, )opulatton at that time (Fig.3) and the The peak breeding season for E.longicornis stretched from July to March a ~arked Illcrease.. Three possible reasons (Fig. 1), although low numbers of breeding females were present in April and IldI~IOnsduring June sampling were most May, suggesting some breeding throughout the year. The breeding period for wlllds, wave height 3-4m). The isopods Eurydice pulchra was 7 months in France (SALVAT,1966), 5 months in South Id ?y the waves or have actively migrated Wales (JONES, 1970), and 3 months in the Dovey Estuary, Britain (FISH, 1970). ydlce pulchra during stormy winter condi- Similarly, the breeding period for Eurydice affinis was 7 months in France 1L~AYLOR (1970) and HASTINGS & NAYLOR (SALVAT,1966) and 3 months in South Wales (JONES, 1970). This demonstrates e bI~alve Donax parvula in North Carolina that the breeding season for the same species is prolonged in locations with :ubttdal habitat, while ANSELLet al. (1972) higher temperatures (SALVAT,1966; JONES, 1970). The temperature of the sea leared from beaches in south-west India water in Algoa Bay seldom drops below 15°C (CHRISTENSEN,1980), and then Lfterwa~ds. Secondly, with the recruitment only for a few days when occasional summer upwelling occurs due to easterly )opulatton would be expected to consist of winds (BECKLEY,1988; SCHUMANNet al., 1988). Hence the seasonal temperature ~d~ 37 % of. the population during June variation (14-23°C; McLACHLAN,1977 a) in Algoa Bay is minimal. SIeves ~etallled only isopods larger than - The breeding season for the other two species was more limited: October- ,populatIOn may not have been sampled. March for P. latipes (Fig. 4) and October-April for E. natalensis (Fig. 7). DEX- ~row large enough within three weeks to TER(1977) reported that Excirolana braziliensis at Naos Island, Panama, repro- [the increase in numbers by early July. A duced throughout the year but that the percentage of reproductive females was ~e could be mortality in cohort B (Fig. 3). lowest during the dry season. During the peak breeding season, reproductive rarest seaso~al fluctuation in abundance, E. natalensis females constituted up to 40 % of the population, a high proportion ~mmer maXImum to a winter minimum compared to 1.5 % throughout the year for E. chiltoni (KLAPOW, 1972) and bers decreased (disappearance of cohort 2.4-4.5 % and 0.13-0.94 % during the wet and dry season, respectively, for owever, t~e September increase, unre- E. braziliensis (DEXTER,1977). ndersamphng of juveniles (as in E.lon- by 1mm mesh from the time of release 3. Incubation period rked non-seasonal fluctuations (Fig. 9), he E.longicornis population. A sharp The incubation period is approximately 2 months for E. longicornis (Fig. 1) and May due to the mortality of cohort A P.latipes (Fig. 4), and approximately 3 months for E. natalensis (Fig.7) as nnot be accounted for. estimated from the time between peaks in abundance of gravid females and ti~ns in abundance than P. latipes and juveniles. JONES (1970) and FISH (1970) recorded an incubation period of 8 rtmlly explained by the production of weeks for Eurydice pulchra, and JONES (1970) found a 37 day period for 116

DE RUYCK, Eurydice affinis, a smaller species. DONN & McLACHLAN tion period at La Jolla (KLAPOW,Excirolana chiltoni had a 2-3 month incuba- isopod slightly larger than Excirolana1971), and Cirolana harfordi, a cirolanid terey Bay, natalensis, a 3-4 month period at Mon- California (JOHNSON, observed here in P. latipes vs. E. natalensis1976). Thecould1 monthpossiblyshorterbe attributedbreeding to the shorter season incubation period of P. latipes.

4. Fecundity I r We found a linear relationship c length of ovigerous between the number of ova or embryos and females for all three species. This is in agreement findings of many workers on with 1 NAYLOR,1970; KLAPOW,1970; JOHNSON,(SALVAT,1976; DONN1966;& CROKER,JONES, 1970;1986;JONESWOOL-& E DRIDGE,1986) with the exception of FISH (1970). The slope of the regression line is steepest for E. longicornis (Fig. 2), which has a higher fecundity than the other s two species (20-26 offspring per female versus 15-17 and 19.5 for P.latipes and E. natalensis, respectively). E produces In addition, of the three species, only E. longicornis multiple broods per year. to Breeding E. longicornis E the 3.5-4.5 mm size class presumablyfemales belong to 2 different cohorts (Fig. 2), those in pI the 8-9 mm size cJass producing their first brood and those in E brood to grow throughtheirserond. Rapid growth (Fig. 3) could enable the spring pI autumn brood at an agesummerof aboutand6reachmonths;sexualSALVATmaturity(1966)in time to produce the EI phenomenon P~ in Eurydice recorded a similar brood, tbey migbt produce pulchra.a secondIf broodE. longicornisafter a period of growth, at about EI females survived the first afj 8mm. JOHNSON(1976) found that females of Cirolana El prolonged breeding period like E. long;eornLt, harfordi, an isopod with a afj as 60 days after release of the first. produced a second brood as early Po FrsH (1970) also found tat, differences Eurydice pulchra (Table 1), between numbers of ova and embryos in Ex enon. The difference although she gave no explanation for this phenom- naz more than that for constitutes a loss of about 55-{j5 %, which is considerably Ex E.longicornis (11-14 %). In accordance with bre SALVAT(1966), FISH (1970), embryos in E. longicornis and JONES (1970) on E. pulchra,observationsall ova andby Ex, ever seen to degenerate. were in the same stage of development chi could be due to loss of ova fromThe differencethe brood pouch during high energyand none were Cir between ova and embryo har in the surf zone, as also described by WOOLDRrooE(1981) for the sand burrowingnumbers mysid, conditions Gastrosaccus psammodytes. unlikely. Ova loss due to handling in the laboratory is m2 E. natalensis females carried an average of 19.5 ova versus 30.7 ova in se, Excirolana chiltoni (KLAPOW,1970) and 4-17 in Excirolana twc () TER,1977), two smaller species. There was no significant Bri braziliensis (DEX- number of ova and embryos in ovigerous E. natalensis iml difference between the loss from the protected ges internal brood pouch of fuclrolanafemales.spp. This(KLAPOW,suggests no as compared to the external brood pouch in Eurydice, pre cirolanids. 1970) However, KLAPOW(1971) Pontogeloides foIl over the incubation recorded an embryo and other ( period in E. chiltoni. mortality rate of 19 % of an I spa

j' DE RUYCK, DONN & McLACHLAN Intertidal sand beach isopod life histories 117 'i:xcirolanachiltoni had a 2-3 month incuba- J971), and Cirolana harfordi a cirolanid 5. Life histories 1lanatalensis, a 3-4 month pe;iod at Mon- Eurydice longicornis starts reproducing at approximately 6 months of age and 76). ~he 1 month shorter breeding season talensls could possibly be attributed to the breeds a second time, after an interval of 3-4 months. Pontogeloides latipes breeds f'S. at 16-22 months and Excirolana natalensis at approximately 18 months (Fig. 10). E. longicornis at Sundays River Beach exhibits an annual life history and produces multiple generations per year (Fig. 3, Table 2). Its life history and reproductive strategies compare best with those of Eurydice pulchra as described by SALVAT(1966) in France. He found that E. pulchra could reach veen the n~mber of ova or embryos and Table 1. Fecundity: data for various cirolanid isopod species. Data for ova and embryos of t.hree specIes. This is in agreement with * 'Ida (SALVAT,1966; JONES, 1970; JONES& E. natalensis combined. .oN, 1976; DONN & CROKER,1986; WOOL- Species Oval or embryos2/female Source [S~(1970). T?e slope of the regression line Range x vhIch has a hIgher fecundity than the other Ie versus 15-17 and 19 5 for . Eurydice 5-901 26.01 present study . P. la lpes an n, of the three species, only E. longicornist d longicornis 3--632 20.42 Eurydice 30-451 JONES, 1970 pulchra )ng to 2.different cohorts (Fig. 2), those in Eurydice 22-541 FISH, 1970 pro dUCIngtheir first brood and th . ose In pulchra 12-352 lid grow th Ig. 3) could enable the spring (F ' Eurydice 21-632 SALVAI',1966 .ch sexual maturity in time to produce the pulchra lonths; ~ALVAT(1966) recorded a similar Eurydice 18-291 JONES, 1970 E. longlcornis females survived the first affinis )rood a~ter a period of growth, at about Eurydice 23-352 SALVAI',1966 ~eso~ Orolana harfordi, an isopod with a affinis :cornzs,produced a second brood as early Pontogeloides 9-311 17.01 present study latipes 4-252 15.42 letween numbers of ova a . Excirolana 13-25* 19.5* present study nd emb ryos In natalensis ~e gave no explanation for this phenom- Excirolana 4-171 DEXTER,1977 p! about 55-65 %, which is considerably braziliensis Yo).In accordance with observations by \ Excirolana 30.71 KLAPOW,1970 IES (1970) on E. pulchra, all ova and chiltoni ~e stage of development and none were Cirolana 18-681 JOHNSON,1976 ~ce between ova and embryo numbers harfordi pd pouch during high energy conditions pLDRIDGE(1981) for the sand burrowing maturity in 8 months, thus enabling juveniles hatched early in the breeding ~oss due to handling in the laboratory is season to reproduce by the end of that same breeding season, thereby making I rage two generations per year possible. However, JONES(1970) and FISH (1970) in o! 19.5 ova versus 30.7 ova in Britain found reproduction of the early brood in the same breeding season to be 4-17.In !i.xcirolana braziliensis (DEX- s no sIgmfIcant difference between the impossible, possibly due to different temperature regimes. JONES (1970) sug- E. natalensis females. This suggests no gested that the autumn brood was produced by the autumn brood of the previous year, which, after overwintering as juveniles, needed most of the ~h of Exc~rolana spp. (KLAPOW,1970) In Eurydice, Pontogeloides and other following spring and summer to reach sexual maturity. A review of life histories rded an embryo mortality rate of 19 % of other cirolanid isopods is given in Table 3 for comparison. Temperature has an effect not only on breeding season length, but also on the life history and life span of the same species in different locations (DONN & CROKER,1986). JONES 118 DE RUYCK, DONN & McLACHLAN

10 E. long/cornls Fig. 10. Summary of the life his- 8 tories of E. longicornis, P. latipes, and E. natalensis at 6 Sundays River Beach. Lines indi- 4 cate growth curves and boxes breeding periods. 2

0 2 4 12 14 16 18 20 22 24

14

12 P. lat/pes

10

8 E S 6 I C)I- 4 z w ...J 2

a 4 6 8 10 12 14 16 18 20 22 24

16

14 E. natalens/s

12

10

8

6

4

2

0 2 4 6 8 1 12 14 16 18 2 22 24

AGE (MONTHS)

(1970) for example recorded a univoltine life history and a life span of 15-20 months and FISH (1970) a life span of 24 months for E. pulchra in South Wales and the Dovey Estuary, respectively, whereas SALVAT(1966) found a bivoltine life history and a 1-year life span in the same species in the warmer waters of the Mediterranean. Higher temperatures result in a prolonged breeding season and more than one generation per year due to faster growth rates and earlier attainment of sexual maturity (SALVAT,1966; JONES, 1970). Growth and egg maturation in E. longicornis at Sundays River Beach apparently continued c) through winter. The small seasonal water temperature fluctuation provides a favourable environment for a prolonged breeding season and a multivoltine life history. JONES(1970) also recorded growth in Eurydice pulchra during winter in South Wales, where temperatures are generally lower than at Sundays River Beach. Both P. latipes and E. natalensis exhibit a biennial life history at Sundays River Beach, with a life span of 1.5-2 years, and produce one brood (Table 2;

/'

~ DE RUYCK, DONN & McLACHLAN Intertidal sand beach isopod life histories 119

Fig. 10. Summary of the life his- Table 2. Comparison of various reproductive characteristics of E.longicornis, P.latipes, and tories of E. longicornis, E. natalensis at Sundays River Beach. P. latipes, and E. natalensis at Sundays River Beach. Lines indi- Parameter E. longicornis P. latipes E. natalensis cate growth curves and boxes breeding periods. Breeding Jul.-Mar. Oct.-Mar. Oct.-Apr. season :t 9 months :t 6 months :t 7 months 18 2'0 2'2 2'4 Incubation 2 months 2 months 3 months period Life Multivoltine Univoltine Univoltine cycle ~ Life 1 year 1.5 to 1.5 to span 2 years 2 years

Table 3. Life histories of some cirolanid isopods from different locations around the world.

Species Location Life cycle Source

3 2~ 2'2 2'4 Eurydice France Bivoltine SALVAT, 1966 pulchra South Wales Univoltine JONES, 1970 Dovey Estuary Univoltine FISH, 1970 Eurydice Marseille Bivoltine ~::: inermis Ireland Bivoltine TULLY & O'CEIDIGH, 1986 Excirolana California Bivoltine KLAPOW, 1971 chiltoni Cirolana California Multivoltine JOHNSON, harfordi 1976

, I I I 20 22 24 Figs.6 and 9). This compares well with the 2 year life span described for Cirolana harfordi, a slightly larger, multivoltine cirolanid isopod in California (JOHNSON,1976), and for dilatata on the Cape Peninsula of South Africa Wne life history and a life span of 15-20 (Koop & FIELD, 1980). HARVEY(1968), in her work on Sphaerorna serraturn and 124 months for E. pulchra in South Wales Sphaerorna rugicauda in Britain, recorded a life span of 2-2.5 and 1-1.5 years iwhereas SALVAT(1966) found a bivoltine for these species, respectively, the former at the northern limit of its distribu- ~same species in the warmer waters of the tion. result in a prolonged breeding season and The bimodal pattern in breeding E. longicornis females is similar to the i due to faster growth rates and earlier findings of JONES(1970) and SALVAT(1966) in Eurydice pulchra. KLAPOW(1971) ~T, 196?; JONES, 1970). Growth and egg similarly describes a spring and autumn brood and two generations per year for pays RIver Beach apparently continued Excirolana chiltoni in California. ater temperature fluctuation provides a d breeding season and a multivoltine life wth in Eurydice pulchra during winter in Summary generally lower than at Sundays River Eurydice longicornis has a life history of about 1 year, an extended and possibly hibit a biennial life history at Sundays year-round breeding period, and produces multiple broods, while Excirolana years, and produce one brood (Table 2; natalensis and Pontogeloides latipes have life spans of 1.5-2 years, shorter 120 DE RUYCK, DONN & McLACHLAN breeding periods, and only one brood per year. This may explain the numerical In dominance of the former on this warm temperate, high energy beach. KI

K( Acknowledgements LE We thank students and staff at U. P. E. for invaluable help in the field. The first author was supported by I. C. R. and C. S. I. R. bursaries, without which this work would not have been M, possiblc.

References

ANSELL, A. D., P. SIVADA~,B. NARAYANA& A. TREVALLION,1972: The ecology of two sandy beaches in south-west India. III. Observations on the population of Donax incarnatus and D. spiculum. Mar. BioI., 17: 318-332. BALLY, R., 1981: The ecology of three sandy beaches on the west coast of South Africa. Ph. D. thesis, University of Cape Town, Cape Town; 404 pp. BECKLEY,L. E., 1988: Spatial and temporal variability in sea temperature in Algoa Bay. S. Afr. J. Sci., 84: 67-68. M( CASSIE,R. M., 1954: Some uses of probability in the analysis of size frequency Mar. Freshwater Res., 5: 513-522. distribution. Austr. J. CHRISTENSEN,M. S., 1980: Sea-surface temperature charts for southern Africa, south of 26 oS. S. Afr. J. Sci., 76: 541-546. Pn DEXTER,D. M., 1977: Natural history of the Pan-American sand beach isopod Excirolana brazilien- sis (Crustacea: ). J. Zool., Lond., 183: 103-109. SA] DONN, T. E., JR., 1987: Longshore distribution of Donax serra in two log-spiral bays in the eastern Cape, South Africa. Mar. Ecol. Prog. Ser., 35: 217-222. - -, 1988 a: Intertidal macrofaunal community structure. In: T. H. WOOLDRIDGE(Ed.), Proposed SCI marina development in the southwest sector of Plettenberg Bay University of Port Elizabeth, Institute for Coastal Research, Report No. 18: 9-19. - an ecological assessment. SHI - -, 1988 b: Macrobenthos - intertidal. In: L. MCGWYNNE(Ed.), Sandy beaches of Maputaland ecology, conservation and management. Tv Research, Report No. 16: 39--46. University of Port Elizabeth, Institute for Coastal- - - & A. C. COCKROFT,1989: Macrofaunal community structure and zonation of two sandy beaches on the Central Namib coast, S. W. A. /Namibia. Madoqua, 16 (2): WE - - & R: A. CROKER,1986: Life-history patterns of Haustorius canadensis129-135.(Crustacea: Amphipoda) in northern New England. Can. J. Zool., 64: 99-104. We FISH, S., 1970: The biology of Eurydice pulchra (Crustacea: ). J. Mar. BioI. Assoc. U. K., 50: 753-768. HARVEY,C. E., 1968: Breeding and distribution of Sphaeroma Anim. Ecol., 38: 399--406. (Crustacea: Isopoda) in Britain. J. HASTINGS,M. H. & E. NAYLOR,1980: The ontogeny of an endogenous rhythm in Eurydice pulchra. J. Exp. Mar. BioI. Ecol., 46: 137-145. JOHNSON,W. S., 1976: Biology and population dynamics of the intertidal isopod, Cirolana harfordi. Mar. BioI., 36: 343-350. JONES,D. A., 1970: Population densities and breeding in Eurydice pulchra and E. affinis in Britain. J. Mar. BioI. Assoc. U. K., 50: 635-655. - - & E. NAYLOR,1970: The swimming rhythm of the sand beach isopod, Eurydice pulchra. J. Exp. Mar. BioI. Ecol., 4: 188-199. KLAPOW, L.A., 1970: Ovoviviparity in the genus Excirolana (Crustacea: Isopoda). J. Zool., London, 162: 359-369. - -, 1971: The ecology and behaviour of a sand beach isopod, abundance and temporal patterns in molting, Excirolana chiltoni: Distribution, thesis, University of California, San Diego, California;reproduction231 pp.and swimming activity. Ph. D. - -, 1972: Fortnightly molting and reproductive cycles in the sand beach isopod Excirolana chiltoni. BioI. BuU. (Woods Hole, Mass.), 143: 568-591.

~ DE RUYCK, DONN & McLACHLAN Intertidal sand beach isopod life histories 121 )od per year. This may explain the numerical farm temperate, high energy beach. KLEINBAUM,D. G., L. L. KUPPER& K. E. MULLER, 1988: Applied regression analysis and other multivariate methods. 2ndedition. PWS Kent Publishing Co., Boston; 736pp. Koop, K. & J. G. FIELD, 1980: The influence of food availability on population dynamics of a supralittoral isopod, Ligia dilatata BRANDT.J. Exp. Mar. BioI. Ecol., 48: 61-72. LEBER, K. M., 1982: Bivalves (Tellinacea: Donacidae) on a North Carolina Beach: contrasting population size structures and tidal migrations. Mar. Ecol. Prog. Ser., 7: 297-301. pr invaluable help in the field . McLACHLAN, A., 1977 a: Studies on the psammolittoral fauna of Algoa Bay, South Africa. 1. . . . Th e fIrst author was mes, wIthout which this work would not have been Physical and chemical evaluation of the beaches. Zool. Afr., 12: 15-32. - -, 1977 b: Studies on the psammolittoral fauna of Algoa Bay, South Africa. 2. The distribution, composition and biomass of the meiofauna and macrofauna. Zool. Afr., 12: 33---{)0. - -, 1977 c: Composition, distribution, abundance and biomass of the macrofauna and meiofauna of four sandy beaches. Zool. Afr., 12: 279-306. - -, 1980: The definition of sandy beaches in relation to exposure: a simple rating system. S. Afr. J. Sci., 76: 137-138. & ~. TREVALLION,1972: The ecology of two sandy - -, 1983: Sandy b,each ecology - a review. In: A. McLACHLAN & T. ERASMUS(Eds.), Sandy :rvatlOns on the population of Donax incarnatus and Beaches as Ecosystems. Junk Publishers, The Hague: 332-333. - - & G. BATE, 1984: Carbon budget for a high energy surf zone. Vie Milieu, 34 (2/3): 67-77. y beaches on the west coast of South Africa Ph D . . . - -, T. WOOLDRIDGE& A. H. DYE, 1981: The ecology of sandy beaches in southern Africa. S. Afr. Town; 404pp. J. Zool., 16 (4): 219-231. 'ariability in sea temperature in Algoa Bay. S. Afr. J. McMuRRAY, H., 1985: Gastrosaccus psammodytes (sandy beach mysid) distribution along an estuarine Cape beach. Is patchiness related to features such as beach slope, presence or in the analysis of size frequency distribution. Austr. J. absence of sandbars, troughs, phytoplankton accumulations? Unpublished B. Sc. Honours project, University of Port Elizabeth, South Africa; 33pp. ~rature charts for southern Africa, south of 26 oS. S. PIELOU, E. C., 1974: Population and Community Ecology: Principles and Methods. Gordon and Breach Science Publishers Inc., New York, NY; 432pp. . 'an-American sand beac h ISOpOd Exclrolana. brazitien- SALVAT,B., 1966: Eurydice pulchra (LEACH 1815), Eurydice affinis HANSEN 1905 (Isopodes Lond., 183: 103-109. ) - Taxonomie, ethologie, ecologie, repartition verticale, et cycle reproducteur. of ~onax serra in two log-spiral bays in the eastern Actes Soc. Linn. Bordeaux, 103 (Ser. AI): 1-77. ~ ir., 35.217-222. SCHUMANN,E. H., G. J. B. Ross & W. S. GOSCHEN,1988: Cold water events in Algoa Bay and along Y structure. In: T. H. WOOLDRIDGE (Ed .,) Proposed the south coast, S.A. in March/April 1987. S. Afr. J. Sci., 84: 579-584. jctor of PI ett enberg Bay - an ecological assessment . SHORT,A. D. & L. D. WRIGHT,1983: Physical variability of sandy beaches. In: A. McLACHLAN& r Coastal Research, Report No. 18: 9-19 T. E. ERASMUS(Eds.), Sandy Beaches as Ecosystems. Junk Publishers, The Hague: 133-144. MC?WY~NE (Ed.), Sandy beaches of M~putaland TULLY,O. & P. O'CEIDIGH, 1986: Density variations and population structure of Eurydice inermis - UmversIty of Port Elizabeth, Institute for Coastal and E. truncata (Isopoda: Cirolanidae) in the neuston of Galway Bay (Ireland). Cah. BioI. Mar., 27: 225-233. n~u~ity structure and zonation of two sandy beaches WENDT,G. E. & A. McLACHLAN,1985: Zonation and biomass of the intertidal macrofauna along a IJIUbIa.Madoqua, 16 (2): 129-135. South African beach. Cah. BioI. Mar., 26: 1-14. os of Haustorius canadensis (Crustacea: Am phipoda ) WOOLDRIDGE,T. H., 1981: Zonation and distribution of the beach mysid, Gastrosaccus psammody- ,64: 99-104. tes (Crustacea: Mysidacea). J. Zool., London, 193: 183-189. (Crustacea: Isopoda). J. Mar. BioI. Assoc. U. K., - -, 1986: Distribution, population dynamics and estimates of production for the estuarine mysid, F Rhopalopthalmus terranatatis. Estuarine Coastal Shelf Sci., 23: 205-223. h of Sphaeroma (Crustacea: Isopoda) in Britain. J. geny of an endogenous rhythm in Eurydice pulchra. rynamics of the intertidal isopod, Cirolana harfordi.

~eding in Eurydice pulchra and E. affinis in Britain. pftheI sand beach Isopod,. Eurydice pulchra. J. Exp. rnus Excirolana (Crustacea: Isopoda). J. Zool.,

beach isopo~, Excirolana chiltoni: Distribution ng, .repr~ductJon and swimming activity. Ph . D'. Cahforma; 231 pp. in the sand beach isopod Excirolana chittoni. y~~~S

'\