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ScientificWorldJournal
2014 Jan 01;2014:918028. doi: 10.1155/2014/918028.
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Effects of delayed metamorphosis on larval survival, metamorphosis, and juvenile performance of four closely related species of tropical sea urchins (genus Echinometra).
Rahman MA
,
Yusoff FM
,
Arshad A
,
Uehara T
.
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We report here, the effects of extended competency on larval survival, metamorphosis, and postlarval juvenile growth of four closely related species of tropical sea urchins, Echinometra sp. A (Ea), E. mathaei (Em), Echinometra sp. C (Ec), and E. oblonga (Eo). Planktotrophic larvae of all four species fed on cultured phytoplankton (Chaetoceros gracilis) attained metamorphic competence within 22-24 days after fertilization. Competent larvae were forced to delay metamorphosis for up to 5 months by preventing them from settling in culture bottles with continuous stirring on a set of 10 rpm rotating rollers and larval survival per monthly intervals was recorded. Larval survival was highest at 24 days, when competence was attained (0 delayed period), and there were no significant differences among the four species. Larvae that had experienced a prolonged delay had reduced survival rate, metamorphosis success, and juvenile survival, but among older larvae, Em had the highest success followed by Ea, Eo, and Ec. Juveniles from larvae of all four species that metamorphosed soon after becoming competent tended to have higher growth rates (test diameter and length of spines) than juveniles from larvae that metamorphosed after a prolonged period of competence with progressively slower growth the longer the prolonged period. Despite the adverse effects of delaying metamorphosis on growth parameters, competent larvae of all four species were able to survive up to 5 months and after metamorphosis grew into 1-month-old juveniles in lab condition. Overall, delayed larvae of Em showed significantly higher larval survival, metamorphosis, and juvenile survival than Ea and Eo, while Ec showed the lowest values in these performances. Em has the most widespread distribution of these species ranging from Africa to Hawaii, while Ec probably has the most restricted distribution. Consequently, differences in distribution may be related to differences in the ability to delay metamorphosis.
Figure 1. Effects of delayed metamorphosis on larval survival (%) of Echinometra sp. A (Ea), E. mathaei (Em), Echinometra sp. C (Ec), and E. oblonga (Eo). Larvae attained metamorphic competence within 24 days after fertilization were on month 0 (control). Each value represents the mean ± SD of six replicate experiments from each species with 400 larvae per replicate for each delayed period. Results of one-way ANOVA (F value and P value) are presented above each set of bars. Columns with the same letter represent means that are not significantly different (Tukey's test, P > 0.05).
Figure 2. Effects of delayed period on larval competence to metamorphosis (%) of Echinometra sp. A (Ea), E. mathaei (Em), Echinometra sp. C (Ec), and E. oblonga (Eo) in response to coralline red algae. Larvae attained metamorphic competence within 24 days after fertilization were on month 0. Each value represents the mean ± SD of 12 replicate experiments from each species with 15 larvae per replicate for each delayed period. Results of one-way ANOVA (F value and P value) are presented above each set of bars. Columns with the same letter represent means that are not significantly different (Tukey's test, P > 0.05).
Figure 3. Effects of delayed metamorphosis on 1-month-old juvenile survival (%) of Echinometra sp. A (Ea), E. mathaei (Em), Echinometra sp. C (Ec), and E. oblonga (Eo). Larvae attained metamorphic competence within 24 days after fertilization were on month 0. The juveniles produced from the metamorphosis experiments were continued to rear on coralline algae for a period of 1 month. Each value represents the mean ± SD of 3 replicate experiments from each species for each delayed period. Results of one-way ANOVA (F value and P value) are presented above each set of bars. Columns with the same letter represent means that are not significantly different (Tukey's test, P > 0.05).
Figure 4. Effects of delayed metamorphosis on 1-month-old juvenile growth (test diameter in μm) of Echinometra sp. A (Ea), E. mathaei (Em), Echinometra sp. C (Ec), and E. oblonga (Eo). Larvae attained metamorphic competence within 24 days after fertilization were on month 0. The juveniles produced from the metamorphosis experiments were continued to rear on coralline algae for a period of 1 month. Each value represents the mean ± SD. A total of 15 juveniles were measured for test diameter from each species with 5 individuals per replicate for each delayed period. Results of one-way ANOVA (F value and P value) are presented above each set of bars. Columns with different letters represent means that are significantly different (Tukey's test, P < 0.05).
Figure 5. Effects of delayed metamorphosis on 1-month-old juvenile growth (spine length in μm) of Echinometra sp. A (Ea), E. mathaei (Em), Echinometra sp. C (Ec), and E. oblonga (Eo). Larvae attained metamorphic competence within 24 days after fertilization were on month 0. The juveniles produced from the metamorphosis experiments were continued to rear on coralline algae for a period of 1 month. Each value represents the mean ± SD. A total of 15 juveniles were measured for spine length from each species with 5 spines per individual for each delayed period. Results of one-way ANOVA (F value and P value) are presented above each set of bars. Columns with different letters represent means that are significantly different (Tukey's test, P < 0.05).
Figure 6. Distribution patterns of common Echinometra spp. on the Pacific reef (after Palumbi [49]). Species are designated according to the published documents [8, 49–58]: Ea, Echinometra sp. A; Em, E. mathaei; Ec, Echinometra sp. C; and Eo, E. oblonga. Localities are C, Isla del Coco, Costa Rica; H, Hawaiian Islands; G, Guam; O, Okinawa; B, Bali; GB, Great Barrier Reef; R, Rottnest Is.; F, Fiji; N, Niue; and T, Tahiti.
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