Reproductive ecology of Stylophora pistillata
Currently, the focus species of my Ph.D. research is Stylophora pistillata. This species is one of the dominant reef-building corals on the Israeli coast of the Gulf of Aqaba. It is relatively well studied from Eilat and worldwide. Therefore, there is a strong baseline understanding of its physiology, ecology, and, progressively, its genetics. Like most corals, S. pistillata reproduces sexually with predictable timing. Unlike most corals, S. pistillata in the Gulf of Aqaba releases fully developed larvae, called planulae, quasi continuously, after sunset, between January and August each year.
Planulae released from the parent colony are positively buoyant causing them to float to the surface. This property facilitates their collection by covering the parent colonies with nets in the field. After a few days, lipid reserves decrease and the planulae begin to sink and search for an ideal place to settle. Chemical cues from crustose coralline algae, a common red encrusting algae, indicates that suitable reef conditions for coral growth are nearby. This location choice is crucial to a coral’s continued survival. Once settled, corals can not move again; they become sessile. This means that they must endure all the environmental and biotic pressures of their chosen place. Choose somewhere too exposed and they risk being predated on whilst they remain small. Choose somewhere too sheltered and they may not receive enough light for photosynthetically fuelled growth.
Fieldwork: planulae collection and husbandry
After completing in depth literature reviews and producing detailed experimental designs, I flew to Eilat in May 2015 to test some of my ideas for the first time. Knowing that the planulation season diminishes after June, I had lots to accomplish in a relatively short time.
Although I had by now gained a fair understanding of adult coral husbandry, I found collecting and raising coral planulae required learning a whole new set of skills.
Similar to human offspring, the early life stages of corals are the most fragile and sensitive. I quickly learnt that overzealous handling can easily cause lethal mechanical damage and forgetting to wash sun cream off ones hands before aquarium work can also have toxic effects. Various “housings” were testing to keep my planulae within the larger aquarium. I noted their obvious tendency to settle on rough and cryptic surfaces. Consequently, initial attempts to settle them in mesh-ended falcon tubes resulted in chimeric spat (name given to settled planulae). Planulae settled gregariously around the screw thread rather than on the (what I thought was an ideal) pre-conditioned surface.
Until next year…. take home findings
In summary, I optimisied many adult coral physiology protocols for use with planulae and successfully navigated a steep learning curve in larval rearing. I also learnt to utilise expert aquarists and engineers to assist in solving such problems which are outside of my experience. Now to assimilate all the aquired knowledge in preparation for next season!