Reefscapers Diary July 2020

Some of our Reefscapers coral frames at the deep ‘Blue Hole’ site

QGIS-mapping

CoralWatch – Monitoring for Signs of Coral Bleaching

During July, we conducted a small assessment of the effects of the recent bleaching event on our frames. Depth is known to influence the structure of coral reef communities mainly due to light penetration, water temperature and resource availability. Additionally, exposed locations with greater water movement can reduce any increases in ambient temperature.

• 2 locations were selected, with contrasting environmental conditions.
• We examined the coral fragments depicted in our database of monitoring photographs taken during January and June 2020.
• At each site, we sampled 304 Acropora coral fragments (on 8 different frames) that had been transplanted back in June-July 2019.
• We recorded corals as ‘healthy’, ‘dead’ or ‘bleached’ (the latter including partial/complete bleaching and fluorescence).
• Mortality was slightly lower at Anchor Point for both months (with approximately equal mortality rates).
• No bleaching was seen in January (as expected); in June, bleaching was slightly lower at Anchor Point.

Initially, we had hypothesised that our frames at the Anchor Point site would be healthier due to the protective environmental conditions; this turned out to be true but only by an unexpectedly small margin.

Based on this snapshot of the 2020 bleaching event, the deeper outplant site only seems to provide a minimal benefit over the shallower site, although a severe bleaching event may have yielded a greater protective effect.

Coral Plates in Aquarium One (plates KH01, KH02, KH05) and Aquarium Two (plates KH03, KH04)

• KH01 – retransplanted with new fragments of Acropora digitifera and Acropora millepora. After some initial discoloration (normal), 90% of the fragments have now encrusted into the plate.
• KH02 – the Galaxea fascicularis fragments remain healthy, and any paled fragments have recovered.
• KH03 – cleaned of algal accumulation; fragments are regaining colour and the calcified areas are growing.
• KH04 – cleaned of algal accumulation; the two remaining fragments are recovering and growing slowly.
• KH05 – the two new fragments (transplanted in May) have regained their colouration and are healthily fusing. The older fragments continue to grow, and there is currently little competition between two colour morphs.

Coral Reproduction Spawning Experiment

In July, two of the smallest colonies died from competition with algae, and four colonies were observed merging (resulting in three colonies transitioning from polyp count to size measurement). Now the external ocean water has returned to normal lower temperatures, we have restarted the continuous water flow intake.

Time Lapse Experiment to Record Coral Bleaching

This month, we successfully recorded the bleaching process using our new time-lapse camera, however, the video footage was sub-optimal. The bleaching process took 5 weeks, and was eventually a result of poor water quality rather than elevated temperatures. We have adjusted our methodology and will be adding warm salt water twice daily to the closed system to elevate temperatures to accelerate the bleaching process.

‘Coral Core’ Experiment

Our in situ coral plug propagation trial has been running for over 4 months now. Some of the corals are under stress due to the recent elevated sea temperatures, and are exhibiting purple tissue surrounding both the extraction and outplant sites. Replicate-2 has seen both medium-sized fragments return to full health this month, whereas 2 of the fragments in Replicate-3 have declined in health.

Healthy Acropora microphthalma growing on a Reefscapers coral frame