Ž .
2
Ž .
GI . Watson’s U -test was used for the polar transformed values of MI Zar, 1996 . The factor we defined as ‘‘temperature’’ is in fact the combined effect of temperature
Ž .
and rearing structure. Indeed, the number of structures available four did not permit replicates. Thus, although the structures were identical and the seawater was the same,
the effect of temperature cannot be technically dissociated from a possible effect of the structures.
3. Results
Ž Observations of several cohorts of P. liÕidus specimens in culture i.e., follow-up of
. gonad growth and MIs, unpublished data led us to the conclusion that gametogenesis
Ž was continuous. In addition, the lack of variation in the external parameters i.e.,
. absence of seasonality causes the growth phase to be by-passed as shown in Fig. 1.
Consequently, the gonads are poor in stored nutrients. Finally, the individuals are not sexually synchronized.
Statistical analyses of the results are presented in Tables 1 and 2. The quantity of Ž
food ingested during the experiment was homogeneous for the higher temperatures Fig. .
2 . Only at the 128C treatments did the animals show significantly lower feeding. For the Ž
. 128C treatments, individuals exposed to the SD treatment winter photoperiod ate less
Ž .
Ž .
than those exposed to LD summer photoperiod . For higher temperatures over 128C , ingestion was similar for all treatments.
Fig. 2. P. liÕidus. Food ingestion vs. temperature and photoperiod. Bold horizontal lines at the same level mean no significant difference.
The results of somatic and gonadal growth are reported in Fig. 3. Somatic growth was Ž
. very low at 128C and increased significantly with temperature Fig. 3a . The somatic
growth was also affected by photoperiod: SD condition at 168C and at 248C gave a better growth than the LD condition. Likewise, the growth of gonads was positively
related to temperature: gonadal growth was significantly lower at 128C and significantly
Ž . Ž .
Fig. 3. P. liÕidus. Mean values of the a somatic production and b gonadal production vs. temperature and photoperiod. Bold horizontal lines at the same level mean no significant difference.
Fig. 4. P. liÕidus. Mean values of GI calculated in fresh and dry weight vs. temperature and photoperiod. Bold horizontal lines at the same level mean no significant difference.
Ž .
higher at 248C with no difference between 168C and 208C Fig. 3b . Difference between photoperiod regimes was significant only at 248C: gonadal production was more
Ž important for the SD treatment. Fig. 4 presents final values of GI dry weight GI-DW
. and fresh weight GI-FW . The GI was significantly lower at 128C and higher at 248C,
while 168C and 208C were equivalent for both fresh and dry weight measurements. For the SD-248C treatment, the GI-DW was unexpectedly superior to the GI-FW. This result
Ž .
led us to assess the mean water content of the gonads expressed in percent and allowed us to note an effective change in that parameter depending upon treatments. The data are
reported in Table 3. Water content and temperature were inversely related: water content was low when temperature was high. The initial group, measured after the starving and
Table 3 P. liÕidus. Mean values of MI and water content of the gonad in percent, all shown with the confidence
interval value at 95 Ž
. Ž .
Photoperiod Temperature 8C
MI Water content
Initial values 1.40.2
75.12.1 LD
12 3.20.6
74.71.4 LD
16 4.41.2
73.20.9 LD
20 4.91.0
72.71.3 LD
24 3.91.1
65.62.6 SD
12 3.00.6
75.20.3 SD
16 3.80.8
71.91.1 SD
20 4.91.3
70.70.8 SD
24 4.01.5
62.61.2
before the experiment, had about 75 2 water which was significantly higher than the Ž
. values obtained after treatment except 128C . Although some relationship must exist
between the maturity stage and the water content of the gonads, this does not explain the unusual low moisture percentage obtained at 248C. This was much lower than the range
obtained for wild individuals with all maturity stages pooled.
Ž .
Ž .
Concerning sexual maturity, no stage 6 fully mature or stage 8 post-spawned were observed, suggesting the individuals did not reach full maturation during the experiment.
Ž
2
. All treatments were significantly different from the initial one Watson U , U s 0.225 ,
Ž .
meaning that every batch had gone forward in the reproductive process Fig. 5 . This Ž .
difference was marked by 1 gonads filled with reserve material, represented by a heavy Ž .
network of nutritive phagocytes; and 2 the presence of some or many sexual cells. Ž
Basically, all sea urchins had reached a maturity stage, going from 3 to 5 recovering .
stage, growing stage and premature stage, according to Spirlet et al., 1998a , all of which are good for marketing. The echinoids were relatively in phase among the
batches: synchronicity in maturation is represented by the length of the vectors in Fig. 5 Ž
. i.e., homogeneity of the examined batch . Individuals matured faster as temperature
become higher except for the 248C treatment, where maturation speed was equivalent to
Fig. 5. P. liÕidus. Circular representation of the MI after polar transformation of the data. The vector Ž
. Ž
. characteristics represent the mean value of the MI direction and the homogeneity of the values length . LD
and SD are long and short day, respectively. The numbers 12, 16, 20 and 24 are 8C temperature. Lines 1 to 8 Ž
. are the phases of soma and gonad development see Fig. 1 .
Ž
2
. that observed at 168C Watson U -test, U s 0.225 . There was no significant difference
between SD and LD photoperiod treatments, although maturation was faster at 128C and 168C for the LD treatment.
4. Discussion
