• Coral Monitoring: Start date 21st April 2015; Duration: 8.4 weeks
  • Dredging: Start date 29th April 2015; Duration: 7.3 weeks
  • Dredging Locations: Northern end of Tegako
  • Coral bleaching is below trigger levels (50% bleaching C1-C5 averaged over all corals) and no action is required.

Results this week

The coral watch results for the past 1.5 weeks (8-17th June) are shown in the latest 3 bars in Figure 1 below. Levels of bleaching at the impact sites, 1 North End and 2 Tegako Jetty, remained low during these past 2 weeks, though there are some signs of minor increases. Bleaching remains higher (an average of 14% of colony surfaces showing some form of bleaching) at Site 3 Catalina Patch (a current Control). This is about the same level observed at that site since 22 May. Bleaching observed at Site 4 South End (Control) remains at normal background levels. Overall the level of bleaching is low in terms of the overall coral population at all sites, with about twice as much bleaching at control sites (far from the dredge) compared with the impact sites (adjacent to the dredge).

On 17th June a few coral colonies were showing quite high levels of bleaching in terms of the percentage of their surfaces affected, however, this affected only a small number of colonies. At the Control sites (3 and 4) nearly all corals were either unbleached or only very slightly bleached. The higher average bleaching recorded at Site 3 Catalina Patch was mostly driven by a couple of corals that are almost completely bleached. At the impact sites, there was a bit more spread in the levels of bleaching (Figure 2), but overall it remained low.

In terms of species (Figure 3) the pattern previously observed at Site 3 Catalina Patch (Control site) for Acropora florida  worsened this week. The level of bleaching is also increasing at the two impact sites for all species except Acropora hyacinthus (plating coral). These will be monitored carefully, but for now they remain under the 50% trigger point.

Figure 1: Average percentage of all coral surfaces in each level of bleaching (C1-5) and unbleached (C6) at each of the 4 sites. At this time Site 1 North End and  Site 2 Tegako Jetty are close to the dredging and considered impact sites. Site 3 and 4 are considered controls.


Figure 2: Shows the occurrence of bleaching among the tagged colonies being monitored on 17th June 2015. The colour scale grades from GREEN  (Good, little of the coral’s surface is bleached) to RED (91-100% of the colony is bleached to some extent). This graph does not distinguish between the levels of bleaching – all categories C1-C5 are included as bleached. Unbleached corals appear here in dark green, with 0% of their colony showing bleaching of any kind.


Figure 3: Levels of bleaching by species and site this week (12 and 17th June surveys).

Coral Monitoring species