| Bernadette Bezy |
| Masters Student Biology, University of Costa Rica |
| Coral Reproduction: The Hope for Future Generations! Reproduction Research on and Conservation of the Reef-building Coral, Pavona clavua, in Culebra Bay, Costa Rica |
| Location: Pavona Reef, Culebra Bay, Gulf of Papagayo, Costa Rica |
| Species: Reef-building coral (Pavona clavua) |
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| Abstract: This project will study coral reef reproduction (regeneration) and recruitment (successful larval settlement) to quantify the natural recovery potential of the damaged Pacific reefs of Culebra Bay. Specifically, it will define the reproductive characteristics of the Agariciid reef building coral, Pavona clavus and produce science-based recommendations for the conservation and restoration of this and similar reefs in a region where there is a desire to balance the delicate reef ecology with a surge of tourism development. The project results will provide resource managers with information to delineate marine reserves as centers for larval export, and define appropriate restoration methods for degraded sites, thus protecting coral larvae and future generations of reefs! |
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| P. clavus larvae | P. clavus larvae and cilliates |
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| Coral recruit (juvenile) | P. clavus juvenile |
Project Update: May 2005
Monthly field and lab work supported by local fishermen and undergraduate biology students continues to shed light on the reproductive regime of the reef-building coral species, Pavona clavus, in the tourist region of Culebra Bay, Costa Rica. To date, the biggest news regarding this project continues to be the Pavona clavus spawning observed in late 2004. This was the first-ever documented spawning event for this species and one of a handful of coral spawning events ever documented in the tropical eastern Pacific. Despite continued evening and night dives during the full moon week each month, no additional spawning events have been documented since September. To corroborate our in situ spawning data, using a stereoscope and microscope, we completed the analysis of the contents of larvae traps placed on corals during each full moon week since March 2004. The larvae traps are large, 1-2 meter diameter, plastic bags each with a removable plastic jar top. They are placed over 6-8 corals on the day of each full moon. The contents floating in the plastic top are collected each morning for 5-7 days. The purpose of the trap is to collect the floating gametes in the event of an evening, late night, or sunrise spawn. The contents of 12 months of larvae traps show that the peak spawning events were in August and September. These are non-upwelling months when the sea water temperature is stable and high (29.08 °C). Small amounts of eggs were found in larvae traps from other stable water temperature months, but never in the high quantities found during the August and September 2004 full moons. Therefore, during two of the last twelve months P. clavus spawning was documented in situ and in coral larvae traps. These observations, new to science for this species, demonstrate seasonal reproductive capabilities of this species. Despite documented spawning, recruitment (or successful larvae settlement) appears extremely limited in Culebra Bay; Pavona does not appear to be sexually self-replenishing at high rates. Each month during systematic SCUBA searches of permanent 1-m2 and 10-m2 plots "visible" coral recruit health and sizes are documented. As monthly data mounts size class patterns are starting to become evident, especially when Pavona clavus (the dominant reef building coral) recruitment survival is compared with that of its congener, Pavona gigantea. Survival rates seem to vary among species and size classes. This could be a "refuge in size" effect for P. gigantea, where zero new recruits survived, and no mid-size recruits were found; yet, juveniles experienced 100% month over month survival (during the last 4 months). By contrast, 97% P. clavus new recruits, 100% mid-size recruits, and 100% of juveniles survived. Our abstract describing these recruitment data has been accepted and will be presented orally at the Society for Conservation Biology Meetings in Brazil this July, 2005. Preliminary spawning and recruitment data seem to indicate limited reproductive capabilities (2 months/ year of peak spawning) and low recruitment. The reproductive regime of Pavona clavus perhaps is based on slow sexual regeneration augmented by asexual reproduction. Experiments were initiated early this year to study the survival rates of a sexual "recruits" or fragments. In addition, currently preparations are underway to conduct the histological analysis of coral tissues collected bi-monthly since March 2004. During 6-8 days each month 5 small coral samples are collected. In the marine laboratory (CIMAR) at the University of Costa Rica we have now decalcified all 450 coral samples. The samples are being dried in a succession of increasing % alcohol in preparation for tissue slicing, dying, and histological analysis. Such analysis will enable us to define the fecundity and exact lunar and seasonal reproductive periodicity of Pavona clavus. |
