The brooding cycle of - Springer Link

Polar Biol (1991) 11:283-292

c Springer-Verlag 1991

The brooding cycle of Abatus cordatus (Echinodermata: Spatangoida) at Kerguelen Islands P. Schatt and J.-P. F~ral Universit6 Pierre et Marie Curie (Paris VI), Observatoire Oc6anologique de Banyuls, Laboratoire Arago, URA CNRS 117, F-66650 Banyuls-sur-Mer, France Received 10 July 1990; accepted 14 April 1991

Summary. The Schizasteridae includes a high p r o p o r t i o n of brooding species. The brooding cycle of Abatus cordatus (a species endemic to Kerguelen) at an intertidal site in the "Golfe du M o r b i h a n " is annual and lasts 8.5 months, from the end of M a r c h until the beginning of December. This cycle is reproducible a m o n g years, It is synchronous inside the Golfe between two intertidal sites. A displacement of a b o u t six m o n t h s occurs at a deeper site ( - 5 0 m). The delay of the cycle and depth does not seem to be related because an open-sea intertidal site has a similar displacement of the brooding cycle. It depends on the gonadal cycle which itself depends on the availability of trophic resources. On this basis and samples taken in J a n u a r y annual brooding cycles are hypothetized to occur in 3 Antarctic species of Schizasteridae from Terre-Ad61ie in relation to the annual sea ice cover and restricted s u m m e r period of p r i m a r y production.

Introduction As for other marine invertebrate groups, over 50% of the south polar regular and irregular echinoid species b r o o d their young (Arnaud 1974). We calculated from Fischer (1966) that 77% a m o n g the irregular echinoids do it. Most belong to the family Schizasteridae which includes 16 genera, 4 endemic to the subantarctic and antarctic zones (36~ to 75~ from Patagonia coast and subantarctic islands to Antarctica coast, see Table 4 in "Appendix"). An annual gonadal cycle has been established for Abatus (Magniez 1980a, b, 1983; Schatt 1985a, b, 1988, A. cordatus; McClintock and Pearse 1986, 1988, A. nimrodi, A schackletoni). Pearse and McClintock (1990) suggested for the two same species that they reproduce troughout most or all of the year in spite of observation of only partial cycles. The aim of the present study is to answer the following questions: (1) Is the b r o o d cycle of a species like A. cordatus repeatable each year? (2) are variations due to

Offprint requests to. J.-P. Feral

depth or fluctuations of variables such as temperature or food availability? Considering that the reproductive biology of A. cordatus is relatively well k n o w n (Pearse and McClintock 1990) we propose to use this species as a model for other Antarctic species of Schizasteridae which should have c o m p a r a b l e life history. We quote the scattered data from species sampled in Terre-Ad61ie as an example.

Materials and methods Study sites and collection of adults Adults were randomly collected either by hand at low tide or by diving up to 30m depth, or by dredging at different sites in Kerguelen Islands (Fig. 1 and Table 1). Females were kept in aquaria with running sea water in the laboratory before analysis within one or two days. High densities of Abatus cordatus (Verrill, 1876) occur in muddy sand (up to 170 adults/m 2, Magniez 1980b). Abatus nimrodi (Koehler, 1911), Abatus cavernosus (Philippi, 1845) and Amphipneustes rostratus (Koehler, 1926) were collected on muddy bottom around the Pointe G6ologie Archipelago (Terre-Ad61ie, see Fig. 2). The main characteristics of the sites are given in Table 1.

Collection and sorting of embryos and juveniles Brooded young were collected from each pouch of the female Abatus cordatus and sorted under binocular lens into six groups corresponding to six developmental stages: fertilized eggs, segmentation (segmented eggs and blastula), gastrulation (gastrula), embryo, juvenile 1 and juvenile 2 (as stated by Schatt 1985b). The total number of each group was ascertained almost every 15 days for individuals of the main sampling site (Halage des Swains) during one year (1982 1983). The collections for the other dates and sites were more scattered (Tables 1 and 2). For the 3 species from Terre-Ad61ie, brooded youngs were sorted only into two groups: "embryos" including the first stages of the development and "juveniles" including both juvenile stages 1 and 2.

Analysis of data (Abatus cordatus) During a brooding cycle, we consider that for a given female (> 3 cm long) a given developmental stage is reached when the first individual

284

INDIAN OCEAN

GOLFE DES BALEINIERS

~:

;.'~J COURBET

ouwEox

'ILE HAUTE

Norvegienne

GOLFE DU MORBIHAN

~

o~

~-...~.~

'~=.~'~

PO~.

.~

I ~

~

ILE SUHM

"~'.',". -~

..P,~

P ....

Royale

Fig. 1. Map of Kerguelen Islands (Austral Indian Ocean). Abatus cordatus was sampled in intertidal sites at Port Jeanne d'Arc, Ile Haute and Port Couvreux, and in two deepest sites off Ile Suhm. (stars: collecting sites)

'".~ BI

~e du hal I~JEANNE D"ARC des swa,av . . . . . . . . . . . .

~.--

"':~ C. 10 km

Table 1. Collecting sites (abbreviation in brackets). Z: depth (m), M: mud, MS: muddy sand Geographical zone

Collecting site

lies Kerguelen 49~30'S, 7 0 E

Golfe du Morbihan Halage des Swains (HS) lie Haute (H) (Anse aux Rennes) Ile Suhm (S)

Terre-Ad61ie 66~'40'S, 140c01'E

Golfe des Baleiniers Port Couvreux (PC) Baie des Empereurs (BE) Cap Prudhomme (CP)

Z (m)

Bottom

Method

Date

Temperature

0

MS

MS

30 60

M

Dredging

15 25

M

Dredging

02/1982 to 01/1983, 01/1986, 12/1988 to 11/1989 01/1986, 11/1988 01, 03 & 07/1982, 01/83, 01/1986 12/1988, 09/1989

2.5 ~ 9.5C 6C

4

Picking at low tide Diving

4 15 18 25 30

MS M M

Diving Diving Diving

12/1988 01/1987 01/1987

at this stage is present even in only one marsupium (Females are not completely synchronous). The rest period of the brooding cycle begins with the opening of the protective spines covering the pouches and the "birth" of juveniles (sediment enters also the marsupia at this time). It ends when the forthcoming generation takes place (further spawning) and when the protective spines close again the brood chambers. The rest period takes about 2 to 3 months; it is characterized by the total absence of brooded youngs or by the presence of a very few number of brooded youngs in the pouches. They are all juveniles, mainly at stage 2 (see Tables 2 and 3). A brooding factor (FB) was calculated which is the ratio of the total number of brooded youngs of each stage to the total number of

7.5 C

5.2'C

- 1.6 'C - 1.6:C

females, analyzed fortnightly. Six FB values, corresponding to the six developmental stages, were calculated every 15 days period, over a one year period in the case of the specimens collected at the Halage des Swains in 1982 1983 (HS 82 83). The higher F B value gave the stage reached by most of brooded young. Other FB values allowed an evaluation of the actual progress of the brooding during each fortnight. Correspondence analysis (CA) was done to test the reproducibility of the brooding cycle among years and to describe this cycle and its variations at the different sites (see Picard 1982). Analyses were performed using the FB brooding factor. The cycle was defined for the Halage des Swains during 1982 83. Other values were

285 140~ o

_~asteur oo 0

E)La Selle

~o

i 66"39

D MER DUMONT D'URVILLE

(~

0~ 66 ~

k.

o I. Cuvier

%

C6e

Bake du Large

.,ooL >m,

~ i n t e du Rat

#

# #

O

o

c)

4 .

,,"

J" o~o+-,,~

O ~r~i/Em2;Y:" o

66~

,, /

r %

! ImO

st-e Blanche 0

I. du

0

i

Navigat~_

/

/

/

/

Nunatak %%duB o n D o c t e u r # /

______66~

.//iS//'~ --. 66~

O Cap A ~, it Prudhomm ;]~

k I !,_g i t" ii

i X~,

139~

/~

/it

t

i

!

TERRE

ADELIE

Archipel de Pointe Geologie

i

0

//

~.t

/

~

=

i

0

lhm

1140~

Fig. 2. Map of Terre-Adelie, Antarctica. Abatus nimrodi was sampled between 15 m and 30 m depth offCap Prudhomme and in the Bake des Empereurs. Abatus ca~:ernosus a n d Amphipneustes rostratus were sampled between 25 m and 30 m depth offCap Prudhomme. (stars: collecting sites)

taken as supplementary elements which are not taken into account by the analysis. The first set of values (HS 82 83) may be considered as a model to which other values may be compared. S T A T - I T C F (1988) and BIOMECO (1988) program packages were used for analyses.

Results

Kerguelen Islands Halage des Swains. Brooding cycle of Abatus cordatus is annual (Table 2). Females do not brood during the austral summer from January to the middle of March (rest period, as defined above). Fertilized eggs (FB = 11.4) and the first segmented eggs (FB= 10.6) are found for ca. one month, between the end of March and the beginning of April. Segmentation occurs from the end of April to the beginning of May (about one month). Some brooded indi-

viduals have already reached the gastrula stage (F B= 11) which occurs at the end of May and at the beginning of June (F B= 12.9). Embryos are present over a period of 5 months, from the end of June until the first fortnight of November. Juveniles 1 differentiate from the end of July to December over a period of 5 months during which the first juveniles 2 appear (end of October, F B=2.6) reaching a maximum between the end of November and the beginning of December, FB=39.5 ). Juveniles 2 leave the pouches until the beginning of April as shown by the F~ values in the Table 2. In the factorial plan I/II (21 =0.689, ~ =38.5 and 22 =0.608, ~2=34.0) the points from 1982-83 follow an approximately circular route in the order of the fortnight collections. The stages occur in the same order along the same circle (Fig. 3). Cycles similar to the cycle of 1982-83 occurred in 1986 and in 1988-89. Juveniles 2 from the previous year were present from December to March. Nevertheless, in 1989,

01'86-2

11 "88-2

1298-1

H 1988

PC 1988

01/86-1 01/86-2

S 1986

H 1986

01/82-1 01/82-2 03/82-2 07/82-1 07/82-2 01/83-I

S 1982 - 1983

12/88-1

12/88-1 12/88-2 01/89-2 02/89-2 03/89-2 04/89-1 06/89-1 08/89-1 08/89-2 11/8%1

HS 1988 1989

09/89-1

01/86-1 02/86-1

HS 1986

S 1989

02/82-2 03/82-2 04/82-1 04/82-2 05/82-1 05/82-2 06/82-1 06/82-2 07/82-1 07/82-2 08/82-1 08/82-2 09/82-1 09/82-2 10/82-1 10/82-2 11/82-1 11/82-2 12/82-1 01/83-1

HS 1982 1983

S 1988

Month/Year fortnight

Station

8

11

11

5

9

I 5

3 2 4 2 ! 3

15 11 15 28 11 6 7 7 7 15

8 6

3 5 11 15 7 4 15 2 2 2 4 16 12 7 4 12 3 2 2 13

Total females

2

4

2

3

6

0 1

l 1 0 0 0 I

5 8 13 24 6 4 2 2 1 7

2 2

1 0 2 0 0 0 0 0 0 0 0 1 5 0 0 0 0 0 0 1

Females without young

0.0

0.0

0.0

0.0

0.0

0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0

0.0 11.4 7.6 3.9 2.7 5.3 1.2 1.0 0.0 0.0 0.0 0.0 0.0 0.0 0.8 0.0 0.0 0.0 0.0 0.0

FE

Fa

(0)

(0)

(0)

(0)

(0)

(0) (0)

(0) (0) (0) (0) (0) (0)

(0) (0) (0) (0) (0) (0) (0) (0) (0) (0)

(0) (0)

(0) (57) (83) (59) (19) (21) (18) (2) (0) (0) (0) (0) (0) (0) (3) (0) (0) (0) (0) (0)

0.0

0.0

0.0

0,0

0.0

0.0 0.0

1.7 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0,0 0,0 2.0 5.0 0.0 0.0 0.0 0.0

0.0 0.0

0.0 10.6 1.1 15.5 25.6 4.0 5.9 0.0 2.0 1.5 2.3 2.7 1.3 0.0 0.5 0.0 0.0 0.0 0.0 0.0

SG

(0)

(0)

(0)

(0)

(0)

(0) (0)

(5) 10) (0) (0) (0) (0)

(0) (0) (0) (1) (22) (30) (0) (0) (0) (0)

(0) (0)

(0) (53) (12) (232) (179) (16) (89) (0) (4) (3) (9) (43) (16) (0) (2) (0) (0) (0) (0) (0)

25,9

0.0

0.0

3.8

0.0

18.0 0.2

9.0 0.0 0.0 0.0 0.0 10.3

0.0 0.0 0.0 0.0 0.0 0.0 40.4 0.7 0.0 0.0

0.0 0.0

0.0 0.0 0.0 0.0 11.0 8.8 12.9 0.0 2.0 8.5 4.8 2.1 0.4 1.4 0.0 0.3 0.3 0.0 0.0 0.2

GA

(207)

(0)

(0)

(19)

(0)

(18) (1)

(27) (0) (0) (0) (0) (31)

(0) (0) (0) (0) (0) (0) (283) (5) (0) (0)

(0) (0)

(0) (0) (0) (0) (77) (35) (193) (0) (4) (17) (19) (34) (5) (10) (0) (3) (1) (0) (0) (3)

2.4

9.7

1.3

0.0

3.6

26.0 5.4

0.0 13.0 2.5 1.5 0.0 0.3

0.3 0.0 0.0 0.0 0.0 0.0 0.3 4.9 37.7 7.3

1.6 0.0

3.7 0.0 0.0 0.0 0.6 0.0 7.5 29.0 33.0 17.0 9.5 16.4 3.9 18.7 4.3 10.9 23.3 0.5 0.5 0.8

EM

(19)

(107)

(14)

(0)

(32)

(26) (27)

(0) (26) (10) (3) (0) (I)

(4) (0) (0) (0) (0) (0) (2) (34) (264) (110)

(13) (0)

(ll) (0) (0) (0) (4) (0) (113) (58) (66) (34) (38) (262) (47) (131) (17) (131) (70) (1) (1) (10)

0.0

4.5

7.8

0.0

0.0

0.0 0.0

0.0 0.0 32.3 0.5 1.0 0.0

1.1 0.9 0.6 0.2 0.2 0.0 0.0 0.3 2.4 12.7

1.5 1.2

3.7 0.4 0.0 O.1 0.0 0.0 0.6 4.0 1.0 25.5 1.0 2.8 0.4 4.0 18.8 15.0 6.3 23.0 23.0 2.2

J1

(0)

(49)

(86)

(0}

(0)

(0) (0)

(0) (0) (129) (1) ( 1) (0)

(16) (10) (9) (5) (2) (0) (0) (2) (17) (190)

(12) (7)

(11) (2) (0) (1) (0) (0) (9) (8) (2) (51) (4) (45) (5) (28) (75) (180) (19) (46) (46) (29)

0.0

28.9

29.0

0.0

0.0

0.0 0.0

61.0 0.0

28.0

0.0 0.0 0.0

3.7 0.0 1.2 0.9 1.5 0.0 0.0 0.0 0.0 0.0

2.8

2.8

2.3 6.6 3.8 0.0 0.0 0.0 0.1 0.0 0.0 0.0 0.0 0.0 0.8 0.0 0.3 2.6 0.0 39.5 39.5 1.6

J2

(0)

(318)

(319)

(0)

(0)

(0) (0)

(0) (0) (0) (56) (61) (0)

(55) (0) (18) (24) (16) (0) (0) (0) (0) (0)

(22) (17)

(7) (33) (42) (0) (0) (0) (1) (0) (0) (0) (0) (0) (10) (0) (1) (31) (0) (79) (79) (21)

Table 2. Fu values (brooding factors) for Ahatus cordatus calculated fortnightly for each stage (highest value of every fortnight is bolded). Number of brooded young is in brackets. FE: Fertilized eggs; SG: Segmented eggs and blastulas; GA: Gastrulas; EM: Embryos; J 1 Juveniles 1; J2: Juveniles 2; HS: Halage des Swains; S: lie Suhm; H: Ile Haute; PC: Port Couvreux t~ Or

287 Table 3. FB values (brooding factors) calculated fortnightly for Abatus and Amphipneustes species (highest value of every fortnight is bolded).

Number of brooded young is in brackets. EMB: early stages of development; JUV: 2 stages ofjuveniles; BE: Baie des Empereurs (Terre-Adelie); CP: Cap Prudhomme (Terre-Ad61ie):HS: Halage des Swains (Kerguelen) Species

Station

Author of work Abatus nimrodi present work Abatus nimrodi present work Abatus cavernosus present work Amphipneustes rostratus present work Abatus cordatus Magniez 1980a, b

Month/Year

Total

Females

FB

-Fortnight

Females

without young

EMB

JUV

BE

01/87-2

6

6

0.0

(0)

o.o

Io)

CP

01/87-2

12

5

0.4

(5)

1.9

(23)

CP

01/87-2

8

2

0.3

t2)

6.9

(55)

CP

01/87-2

7

6

0.0

(0)

2.4

117)

HS

01/78-1 03/78-2 05/78-2 07/78-1 07/78-2 08/78-2 09/78- 1

23 29 33 10 30 36 10

23 12 0 0 0 0 0

0.0 1.7 18.2 31.7 21.6 27.8

to) (317)

o.o o.o o.o o.o

(o) lo) (o) (o)

10/78-1

30

10,/78-2 11/78-2 12/78-2 01/79-1

27 22 33 32

segmentation took place 15 days to one month earlier compared to 1982 (Table 2). In the CA the corresponding points are distributed on the cycle determined with the data of 1982-83 (Fig. 3). lie Suhm. Gastrulation took place at the beginning of January in 1982 and 1983. Embryos were found mainly at the end of January (F a = 13). Juveniles 1 were found mainly during the second fortnight of March (FR = 32.3). Refering to the F Bvalue, juveniles 2 occurred during July, mainly at the end of the month (FR=61). In 1986, the cycle was earlier by about 15 days (Table 3). In 1988 and 1989 embryos were found in December and gastrulas in September. The points on the factorial plan l/ll of the CA are clearly different from those from the Halage des Swains. A displacement of 6 months is evident in all cases for specimens collected at 3(~60 m depth. Note that the point of September (91 in a circle) correspond to females from 15-25 m depth (Fig. 3). The points of January 1982 (l l) and January 1983 (1'1) are in an adjoining position. Other sites. Females from the lie Haute althought containing embryos and juvenile 1 already brooded juveniles 2 in both January 1986 (F~=29) and November 1988 (Fn =28.9). In the Golfe des Baleiniers, at Port Couvreux, gastrulation occurred in December (FR = 25.9). The points of the CA representing the other littoral sites in the Golfe du Morbihan (Ile Haute) are distributed near their corresponding points on the cycle as found for the Halage des Swains (Fig. 3). The sample of Port Couvreux is not clearly in phase with the previous ones (Fig. 3).

(50) (600) (648)

0.4

(13)

(lOOO)

0.5

(18)

(354)

oo

(o)

0

35.4 12.9

(387)

14.o

(419)

0 0 0 4

5.4 5.3 2.7 1.8

(145) (117) (89)

15.7 29.3 21.3

(424) (644) (703)

(57)

3.7

(118)

Terre-Adblie At the end of January 1987, six females of Abatus nimrodi at the Baie des Empereurs had no brooded young (F B= 0) while these (7 of 12) at Cap Prudhomme brooded mainly "juveniles" (F B= 1.9). Females of the 2 other species (Abatus cavernosus and Amphipneustes rostratus) at Cap Prudhomme also brooded mainly juveniles in January (F R= 6.9 and 2.4 respectively, Table 3). Discussion

Reproducibility of the brooding cycle

The brooding cycle in 1982 83 of Abatus cordatus at the Halage des Swains took about 8.5 months from the end of March until the beginning of December. In spite of about one fortnight of displacement, the brooding cycle was similar in 1988-89. Scattered data from 1986 as well as the results in 1978-79 (Magniez 1980a, b, see Table 3) confirm the stability of the brooding cycle of A. cordatus. In the case of the Abatus cordatus collected at 50 m depth (Ile Suhm) although data are available only from gastrulation to juvenile 2 stages, the brooding cycle is annual and lasts about 8.5 months. It should begin at the end of November and ends at the beginning of August (Fig. 3). As in the previous case, the good position of the data from other years led us to conclude that the cycle is reproducible. It must be pointed out that the data from 1988 and 1989 of individuals from between 15-25 m depth do not agree with the brooding cycle observed for individuals collected at deeper depth.

288

(38,5%J

[][q Segmentation [ ] Fertilized ~ 4~ 4>'4 ~ egg ..,~..~-t ~

[]

~

Gastrulation~[]

,

9

Juvenile~ Juvenile2

~_~) ~--~

~

HALAGE 019++

ILE$UHM

D 1988-19890 1988-1989

PORC TOUVREUX ~1988 ~1986 01986

Fig. 3. Correspondence analysis (factorial plan 1/I1): Projection of the brooding factor (FB) of Abatus cordatus from the localities studied and of the brooding stages. The digits in squares (Halage des Swains), in circles (Ile Suhm), in hexagones (Ile Haute) and in lozenge (Port-Couvreux) are the number of the month from January (l) to December (12). Subscripts 1, 2 indicate the first or the second fortnight of the considered month. The main brooding stages are represented by means of black stars. Arrows figurate the brooding cycle calculated for Abatus cordatus collected at the Halage des Swains during the year 1982 83. Other specimens from other years and sites were taken as supplementary elements. One can see the displacement of about 6 months between the brooding cycle of intertidal A. cordatus (Halage des Swains) and deepest ones (lle Suhm) collected in the Golfe du Morbihan

Factors influencing the gonadal and the brooding cycles

The displacement of the brooding cycle of Abatus cordatus between the 2 sites at the Halage des Swains (0 m) and at Ile Suhm (50 m) seems to be correlated with the depth. But a displacement of the same order of magnitude was found between the littoral stations (inside the Golfe du Morbihan, the Halage des Swains and the Ile Haute and outside the Golfe, Port Couvreux. Note that the Golfe des Baleiniers, where Port Couvreux is situated, is not separated from the open-sea by a sill like the Golfe du Morbihan is). Temperature could not be invoked directly, because its annual variation is similar at both depths. It is about 9.5 ~ in summer and 2.5 ~ in winter at the Halage des Swains (Schatt 1985b) and 6 ~ in summer and 2.5 ~ in winter at 50 m depth at Ile Suhm (Fiala, personal communication).

Depth and temperature are not factors able to explain the cause and the variations of both the brooding and gonadic (Magniez 1983; Schatt 1985; Schatt, unpublished data for Suhm) cycles of Abatus cordatus. Similar conclusions were reached by Keats et al. (1984) in the case of the gonadal cycle of the regular echinoid Strongylocentrotus droebachiensis. They estimated that the differences in the gonads of individuals from different depths reflected the food conditions at those depths. Pearse and McClintock (1990) also pointed out relationships between food availability and reproductive cycle (size of eggs, embryos and juveniles) in Abatus nimrodi and A. shackletoni in spite of a small-sized sample. Abatus cordatus ingests sediment. Data on food sources are available only for the Golfe du Morbihan. This bay is located on the eastern side of the main island and is sheltered from the prevailing northwest wind. Communication with the open ocean is separated by a sill ( - 4 0 m). In late June, denser and nutrient-rich waters enter the gulf. This phenomenon is followed by an increase of phytoplankton correlated with a decrease of nitrates and a secondary enrichment of the sediment (Desbruy6res 1976; Delille 1977). At the Halage des Swains, the period of high organic sediment enrichment takes place from October to December (Bouvy and Soyer 1989; Delille and Bouvy 1989). This food availability corresponds to the period during which ovarian index and caloric contents rise (Magniez 1983). Thus variations observed over years may be related by the variation of the food availability depending on the entries of nutrient in the Golfe. These conclusions are summarized in Fig. 4. A comparable phenomenon is observed for Strongylocentrotus droebachiensis whose habitat differences in food availability affect the gonad weight and the reproductive cycle (Vadas 1977; Larson et al. 1980; Keats et al. 1984). At 30 m depth, in a station similar to Ile Suhm (Ile Charmer), 4 (or 5?) periods of availability of organic carbon at the level of the sediment have been defined by Delille and Bouvy (1989) as represented in Fig. 4, but they are much weaker (2 to 3 orders of magnitude) than at the littoral sites. We suggest that the periods of availability of organic carbon must be more or less continuous and definitely weak at 50m depth. The role of trophic ressources cannot be considered to be direct on the cycles. According to Emlet et al. (1987) it is more the quality of food than the quantity which should be investigated for planktotrophic and lecithotrophic species development but both aspects are likely important. As a result, brooding (and gonadal) cycles do exist in Abatus cordatus. They are not synchronous within the Golfe du Morbihan and in the open-sea. This endemic species may be differentiated into more or less isolated populations by (1) their reproductive mode (young dispersal) and (2) this asynchrony (timing of reproduction). Hypothesis on Antarctic brooding Schizasteridae

In the Antarctic, development of phytoplankton and organic enrichment of sediment occur just after the breaking out of sea ice (Vincent 1988). In our hypothesis that antarctic Schizasteridae have life cycles similar to that of

289 Om Halage des Snains time input : organi

(getille t~ ~Bou gonadal %tie

L i 84

ii)ii:iiiiiiiii:iiiii~

[Mctomzz t983) brooding cycle

....... 4

~ .......

presence @brooded young

F E SG

~A

in the pouches

~

~

EM

~ ~_.

-50 m Ile Suhm Kme inpul : 0r~anic rarn0n

(Odif~e k BouW 1989)

onad eyele ,

I

I

: ::

I:

I

(hypothetiz~d) brooding cycle

FE . . . . SG

(partm!!y h~othetized)

GA EM J1

_~_ _~

J2

KEY ~ ] go.ua~I,.(.st

Observed brood,l~g eyeh

U

gnnodul yrowlh

D

~oiifldol Nr

~

(presr of brooded young) (h(qhcst F v~l'uf) inerfas~,, 9f

Ol'([(,!l)~(' lit(Ill* ]

Ilypotheticed broolinl 9 ( ~,,~,'~ .

k:e floe

Fig. 4. Relationships between the gonadal and brooding cycles of Abatus cordatus and the periodic increases of organic material in the sediment hypothetized over a two years period at 0 m and - 5 0 m. Time is in months. FE Fertilized eggs; SG Segmentation; GA Gastrulation; EM Embryos; J1 Juveniles 1; J2 Juveniles 2

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