SECORE team collects larvae of Clubtip Finger Coral for the first time
This branching species is fast growing and can form large banks of complex structures on reefs. SECORE’s crucial first collection will now provide a basis for prediction to attempt further larval collection and restoration with this species.
Photo: A clubtip finger coral in the shallow marine waters of Fernandez Bay, offshore western San Salvador Island, eastern Bahamas. The blue-and-black fish are Chromis cyanea - blue chromis. (James St. John, Flickr, CC-BY 2.0)
The SECORE team in Curaçao has had their eyes on Porites porites as a potential species for larval restoration for some time because its large reef fields are home to an incredible diversity of marine life. There are a ton of fish and inverts living between their branches where they find a sheltered habitat. However, huge clubtip finger coral colonies are less and less common, enhancing the need for restoration. "The clubtip finger coral is a brooder and we expect brooded larvae to be more robust and have higher survivorship than the broadcast spawning species which are the focus of much of SECORE's work", says SECORE Research Director, Dr Margaret Miller.
The challenge was that there is very little literature regarding larval ecology and release of this species. SECORE Research Scientist, Dr Valerie Chamberland and Restoration Technician, Kelly Latijnhouwers began a quest to capture Porites porites larvae in November 2017, bringing several colonies back to the lab and isolating them each and every night to see if any larvae were released.
After months of not observing any larval release, a new collection of parental colonies from four different sites was made in early April and, starting at the new moon on April 15th, hundreds of larvae have been collected over several nights!
Photos: left) Swimming larvae of Porites porites. mid and right) Close-up of young Porites porites settlers (all photos taken by Dr. Valérie Chamberland)
Investigating the coral’s reproduction patterns
Now the team’s main priority is to determine the timing and patterns of reproduction of Porites porites populations over an entire year, so that in future years the scientists know exactly when to expect larval release. This information will hopefully allow SECORE to effectively use this species for restoration purposes. "This first observed Porites porites larval release coincided exactly with April's new moon, which means their reproductive timing likely is influenced by the lunar cycle. It is, however, too early to confirm this; we will need to monitor larval release over additional lunar cycles to verify lunar periodicity", says Valérie Chamberland.
It is also too early to say if there is a seasonality in their larval release. The only two articles published on the topic (Goreau et al. 1981, Tomascik and Sander 1987) mention larval release to be likeliest from November through April - mostly based on histological analysis. "While we have been monitoring Porites porites colonies since November, we did not witness any larval release before last week, when we collected new individuals from four reef sites", the research scientist states.
A list of challenges
Because the clubtip finger coral is a species with separate male and female colonies, there is an added challenge to identifying female colonies that can be used for brood stock. It is also further challenging as those female colonies continuously need be around male colonies with whom they can mate. At last, Porites porites is also known to heavily reproduce via fragmentation; colonies at one reef location are therefore likely to be clonal and therefore incompatible for sexual reproduction. "Thus, the fact that we have not observed larval release until now could have been due to the fact that the colonies we previously were monitoring were i) all males, ii) one clone, or iii) all females which had not been fertilized by male conspecifics before we collected them. It is a true puzzle", Valérie Chamberland reports.
New breeding program
To address these challenges, the SECORE team is currently developing a breeding program, where female colonies would be held in our aquarium system during larval release. In between periods of larval release however, they would be placed back on the reef around conspecifics so that their eggs can be fertilized by male colonies before they are brought back to the lab for larval collection. "We further think that by allowing our brood stock colonies to regularly spend time in natural conditions, they will remain healthier and thereby more fecund than if kept in aquarium system over long periods of time", Valerie Chamberland says.
As for the larval rearing work in the lab at CARMABI Marine Research Station, the team is currently documenting baseline information on the larvae’s biology and ecology, such as larval size, swimming behavior, settlement rates and survival rates. It is also running experiments to determine if they have specific settlement preferences by providing them with different substrates and water conditions. Valérie Chamberland: “Hopefully we will have enough settlers to outplant a batch on the reef and keep some more in controlled conditions for comparison. That would allow us to track their post-settlement growth, development as well as survival rates.”
Photo: A large field of Porites porites in the waters of Curaçao (Valérie Chamberland)