Reefscapers Monthly

A total of 27 new coral frames were deployed into the waters around Kuda Huraa during June. These were largely planted on the deeper House Reef site because of the seasonal temperature fluctuations and to provide greater resilience to future elevated temperatures. Two flat frames were placed in the Green Lagoon following some mortality during the past few months. The use of flat frames at these propagation sites keeps the coral fragments at increased depth and within a more stable temperature range. Re-transplantation and coral frame maintenance is well under way in the Channel, Green Lagoon, Spa and Turtle sites.

30 new frames were transplanted in June at Landaa Giraavaru, and a total of 389 frames were monitored (maintained and photographed) at the Al Barakat and Blu sites. The coral frames at Al Barakat are mostly very healthy, although several are being affected by sand brought by the prevailing currents. Some of the old coral frames (e.g. LG0729 and LG0730 from 2010) are now completely covered with corals.

Several frames were found to be affected by sand accretion (e.g. LG0427) and even fish predation (e.g. LG0413).

Coral frames (A: LG0729) (B: LG0730)

Coral frames (A: LG0729), (B: LG0730)

Coral frames - sand accretion (A: LG0427) and fish predation (B: LG0413)

Coral frames (A: LG0427), (B: LG0413)

Coral Bleaching

The 2015 coral bleaching event has been followed by a rapid drop in sea temperatures, and increased wave damage at the change in monsoon season has caused some mortality. This year has not been classified globally as a “mass bleaching event” (IUCN definition) as not all coral species have been affected. But certainly a large bleaching event has been seen in the Maldives, mostly affecting the Acropora species of corals.

Coral Bleaching - Acropora

Coral Bleaching Acropora

Coral Bleaching - some Acropora

Coral Bleaching Acropora

Coral Bleaching - mainly Acropora humilis

Coral bleaching closeup

During a swim over of the worst affected sites, estimations were made of: number of frames with mortalities, percentage of mortalities within frames, and percentage of mortalities between Acropora and non-Acropora species. The following results were recorded:

  • Frames with 100% mortality
  • Frames with greater than 50% mortality
  • Frames with 100% Acropora mortality

Coral Bleaching - mortality statistics

Coral Bleaching – mortality statistics

The shallower areas seemed most badly affected, in particular the Spa and Green Lagoon sites, which also have slow water currents with water pooling in the lagoon and subsequently heating up. The Water Bungalows, Turtle and parts of the Channel sites are also shallow but with much stronger currents flowing over them, and as such the bleaching was observed to be much less at these sites.

We have stationed temperature loggers at various sites around Landaa Giraavaru, and you can see a graph of the readings below. Between mid-March and mid-May 2015, the ocean temperatures were the highest we have seen for several years, peaking at 30.5 °C.

Temperature Logger data (2013-2015)

Temperatures (degrees C) from one of our oceanic temperature loggers in Landaa’s lagoon (data from 2013-2015)

Our new marine biology Intern, Sebastian Szereday, is currently recording the bleaching event data and analysing the impact on the coral frames. The selected site for the study is the Water Villas Arc, which is well representative of the affected sites. For this study, we count the number of live fragments versus the number of dead fragments on each frame, to obtain a mortality rate. We then classify the frames by age, and we have noticed that the younger frames (<2 years) are far more affected by mortality than the older frames (>2 years). These results are displayed in the graph, clearly showing the 6-month frames with 80% mortality, compared to the 2 year frames which largely recovered.

Coral Mortality Rates

Coral Mortality Rates – by age/maturity of frame

As an extension to this project, we plan to take extra monitoring photographs in the chosen area (Water Villa 400 site). Historically, we already have a full set of healthy frame photographs taken twice-yearly, so the next set of photos will be taken to show the extent of the coral bleaching. We will then take follow-up photos after the necessary maintenance and re-transplantation is complete, to produce 3 photo sets:

Before the bleaching event – After the bleaching event – After re-transplantation

Our new marine biology intern, Sebastian Szereday (University of Vienna), is based at Landaa for 11 weeks, and will be assisting with our coral bleaching research. As part of his busy schedule, he will also be studying coral fluorescence and continuing with our coral frame biomass project.

Coral Black band disease

Black band disease is still very apparent on some wild reef colonies of Pavona coral species, in between the House Reef and the Turtle sites. However this has not transferred onto the frames (there is one single frame in the Channel area showing symptoms).

Coral Black band disease in wild Pavona

Coral Black band disease …

Coral Black band disease in wild Pavona

… in wild Pavona

Coral Black band disease in wild Pavona