Reefscapers Diary November 2022

Coral Propagation – Monthly Progress

At Landaa this month, we transplanted 19 new coral frames, kindly sponsored by guests (eight), the Resort (eight), and online (three), using a total of 901 new coral fragments. In addition, we monitored 530 coral frames at various sites around Landaa Giraavaru.

At Kuda Huraa, we transplanted seven new guest coral frames, recycled (cleaned and retransplanted) two old frames, and monitored (cleaned, repaired, photographed) a total of 141 frames around the island.

Coral Spawning (see also: our indepth reporting)

This month, our Kuda Huraa team divided across two sites for 18 nights of spawning surveys around the time of the full moon. To further maximise our data collection, we also conducted morning surveys, to check for presence of gametes at unmonitored sites.

We successfully observed and documented a total of 52 coral colonies, spawning over eight nights in five locations, representing six different species: Acropora tenuis, A. plantaginea, A. humilis, A. retusa, A. secale, A. rosaria.

We collected gametes from five coral colonies of A. tenuis (from frames at the Blue hole and Water Villas sites), fertilised them, and observed successful settlement on substrate.

Gamete Monitoring

A total of nine species of wild, relocated, and local colonies (at six different sites around Kuda Huraa) were found to have gametes: Acropora monticulosa, A. gemmifera, A. humilis, A. plantaginea, A. millepora, A. tenuis, A. cf. tenuis, A. muricata, A. retusa.

Larval Development

• Acropora tenuis – larvae have continued to grow since settlement, but have not shown signs of symbiont (zooxanthellae) uptake.
• Acropora secale – due to water flow problems in our coral pool, most larvae became stressed and consequently lost their pigmentation. Microscopic analyses revealed that some of the larvae were starting to uptake symbionts. As the month progressed, the symbiont density within the larvae greatly increased (darker colouration).
• Algal removal – we trialled the addition of snails (Trochus species) to control algal growth, but this seemed to adversely affect the coral larvae. We have now resorted back to gently brushing the rubble substrate with toothbrushes, while continuing to research alternative methods.

References

• Omori, M., 2005. Success of mass culture of Acropora corals from egg to colony in open water. Coral Reefs, 24(4), pp.563-563.
• Humanes, A., Bythell, J., Beauchamp, E., Carl, M., Craggs, J., Edwards, A., Golbuu, Y., Lachs, L., Randle, J.L., Martinez, H. and Palmowski, P., 2021. A framework for selectively breeding corals for assisted evolution. bioRxiv.
• Villanueva, R.D. and Baria, M.V.B., 2013. Effects of grazing by herbivorous gastropod (Trochus niloticus) on the survivorship of cultured coral spat. Zoological Studies, 52(1), pp.1-7.
• Toh, T.C., Ng, C.S.L., Guest, J. and Chou, L.M., 2013. Grazers improve health of coral juveniles in ex situ mariculture. Aquaculture, 414, pp.288-293.