Late elkhorn coral spawning at Curacao 2015
After diving for 19 exhausting nights since early August and checking for coral spawning activity, the Curacao team eventually witnessed the long-awaited mass spawning of the critically endangered elkhorn coral, Acropora palmata. Our team consists of long-term partners Dr. Mark Vermeij, Science Director of CARMABI Research Station, Valerie Chamberland, PhD Candidate (SECORE/CARMABI/University of Amsterdam), and Skylar Snowden (SECORE/Pittsburgh Zoo and PPG Aquarium) senior aquarist and indispensable helping hand. The team was completed by CARMABI students, who joined the diving as well as the spawning work. Everybody was relieved when the spawning finally happened, as other elkhorn corals throughout the Caribbean had already spawned in August (e.g. at Mexico). “We are dancing right now,” announced Skylar on the big spawning night. And Valerie shared her lesson learned: “we might not always be as good at predicting coral spawning, but it does eventually happen!” The waiting was worth it: approximately 30000 larvae were reared from the collected gametes and about 25% successfully settled―that are ~7300 growing coral colonies! They are currently outplanted to a reef where a healthy A. palmata population once thrived before this species dramatically declined starting from the late 70s.
Why did elkhorn corals at Curacao spawn so late this year? “We believe that both abnormal seawater temperatures in combination with this year’s lunar cycle could have caused a different timing of A. palmata spawning compared to the previous years. But this species has always been slightly unpredictable,” Valerie explains. “In early August this year, the temperature of the seawater was much lower than usual due to what we think was an upwelling event whereby deep cold water comes to the surface and A. palmata might have not experienced the usual temperature cue to spawn. Additionally, the respective full moon occurred really early on July 31st, which sometimes leads to so-called split spawns, whereby part of a population will spawn during the first month, and the other part during the next. Seawater temperature on Curacao increased quickly during August and on August 30th, the dive team noticed that there was more activity on the reef than last month in terms of fish schools, shrimps, etc. We therefore had good hopes that we would get spawn this month.” And hopes were fulfilled.
“We were not really surprised that the elkhorn coral spawned in September, but what really surprised us was that spawning occurred almost a week after the predicted date in September,” admits Dirk Petersen. “Thanks to a very dedicated team, which kept on diving every night, we managed to document this very unusual event. We will see in the coming years if this has been an exception or if there is a shift in spawning time. We also managed to produce enough coral settlers from this year’s spawn to continue our restoration work for this endangered species, so it may return to Curacao's reef again.”
Valerie Chamberland is a PhD candidate, who has evolved to an expert in coral reproduction and restoration during her project work. Over the last few years, she has reared thousands of coral offspring from over five different coral species and reintroduced them to several coral reefs on Curaçao. “I track the survival, growth and health of these sexually propagated corals over months to years in order to generate long-term data sets on the effectiveness of coral restoration efforts,” Valerie explains. “While the critically endangered elkhorn coral is at the center of SECORE’s restoration research, we are also working on expanding the range of species that can be reared for restoration purposes.”
Certain coral species thrive in areas affected by heavy anthropogenic disturbances. That means, in areas that are too disturbed to bring back historically dominating species such as the elkhorn coral. “These new candidate species might not form the reef communities as we used to know them, or would like to see them, but are at least preferred over algae dominated reef systems and likely still provide most of the ecosystem services that traditional Caribbean reefs once performed such as coastal protection and habitat provisioning for ecologically and commercially important fish species,” tells us Mark. “But bringing artificially settled corals back to the reef is not enough to restore or regrow an entire reef community. When waters remain polluted and overfished, reintroducing coral recruits will not simply lead to the recovery of reefs. It is important that all such management interventions―like restricting fishing and treating sewage―are conducted simultaneously where possible as part of one holistic approach for reef restoration.”
This is SECORE's strategy and Valerie’s research results confirm that approach: “simply reintroducing will not restore a reef by itself. It is essential that the major causes of degradation are minimized at the restoration site prior to outplanting,” she points out. Otherwise all efforts are likely doomed―you cannot plant a forest in the desert. “It is also crucial to base coral restoration programs on comprehensive knowledge of the targeted species’ early life-history traits,” stresses Valerie. You have to know your corals, especially when you work with sexually derived recruits. These kinds of restoration efforts―working with sexually derived recruits, rather than with fragmented clones―may have taken a while to evolve, but its sustainability, its close to nature manner and its growing success, both in effectiveness as well as in its extent, prove those efforts right!
Dirk gives us an outlook on the upcoming coral reproduction and restoration workshop in October, at Curacao: “more spawn is to come and we will also work with new species, document their spawning times and try to rear and settle their larvae for the first time. It will be an exciting two weeks, which will hopefully allow us to incorporate a few new species to our restoration program.”
Special thanks go to the team on-site―without their support, such efforts would not have been possible!