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Marine Biology

, Volume 143, Issue 4, pp 669–677 | Cite as

Coexistence and reproductive isolation of the sympatric echinoids Diadema savignyi Michelin and Diadema setosum (Leske) on Kenyan coral reefs

  • N. A. MuthigaEmail author
Article

Abstract

The sympatric echinoids Diadema savignyi and D. setosum coexist in shallow reef lagoons throughout East Africa. The reproductive strategies of these echinoids were studied to investigate reproductive isolation as a possible mechanism for maintaining the coexistence of these closely related species. The annual reproductive cycle and lunar periodicity were determined by gonad index measurements, histological examination of gametogenesis, and induction of spawning with injections of KCl. The peak reproductive period of D. savignyi coincided with the north-east monsoon period (when light and temperatures are high) as gonad indices were high (>8%) beginning in February and peaked at 9.7% in May. Gonad indices subsequently rapidly decreased (by 26%) in June at the beginning of the cooler south-east monsoon period. However, the presence of sperm and ova in most months of the year indicates continuous gametogenesis with reduced reproductive effort during the cooler months. The annual cycle for D. setosum showed less of a seasonal trend as gonad indices remained above 7% throughout much of the year but tended to be highest when temperatures were lower. This is the first confirmation of continuous reproduction in these two species at the equator. The reproductive patterns of both species remained consistent over 2 years of sampling. Both species exhibited a synchronized lunar spawning periodicity during the 3 months sampled, with D. setosum spawning on lunar days 8–10 and D. savignyi spawning after the full moon (lunar days 17–18). Whereas spawning in D. savignyi was very tightly synchronized, 20% of D. setosum individuals still spawned after the peak spawning period. The coexistence of these closely related species appears to be maintained by temporal reproductive isolation during the lunar spawning period reinforced by seasonal differences in reproductive effort.

Keywords

Full Moon Reproductive Pattern Gonad Index Large Oocyte Mature Gamete 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgements

My sincere thanks go to James Gonda for his field and laboratory assistance, and the Kenya Marine & Fisheries Research Institute and Coral Reef Conservation Project (CRCP) for logistical assistance. I am also grateful for the critical reviews of Dr. T.R. McClanahan and Prof. V. Jaccarini. This work was supported by a research grant from the East African Wildlife Society and the Wildlife Conservation Society through CRCP.

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Copyright information

© Springer-Verlag 2003

Authors and Affiliations

  1. 1.Kenya Wildlife ServiceMombasa Kenya

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