- Hard coral cover has declined since 2017 to historically low values (0-10%)
- Some recent coral losses are likely due to the 2016 and 2017 bleaching events
- Outbreak densities of coral feeding crown-of-thorns starfish, Acanthaster cf. solaris* were observed on several reefs
Figure 1: Map showing location of reefs in the Innisfail sector. Click on figure to go to AIMS Spatial Maps for information on individual reefs.
Table 1: Overview of results obtained from manta tow surveys of reefs in the Innisfail sector
|Innisfail Sector||Summary||Trend since last survey|
|Median Coral Cover||Low (0-10%)||Decreased|
|COTS status:||3 Active Outbreaks, 0 Incipient Outbreaks||Increased|
As part of the Long Term Monitoring Program (LTMP), surveys of coral cover and abundance of the coral feeding crown-of-thorns starfish (COTS), Acanthaster cf. solaris* on seven reefs in the Innisfail sector of the Great Barrier Reef (GBR) were completed using manta tows. Preliminary results of the manta tow surveys are presented in Tables 1 and 2. In all cases median reef-wide live coral cover had fallen to low values (less than10%). The decrease in hard coral cover at McCulloch, Peart, Farquharson and Taylor Reefs was due to COTS activity in recent years and summer bleaching in 2015/16 and 2016/17. COTS remain active on Peart, Farquharson and Taylor Reefs which were classified as Active Outbreaks in 2018. Low numbers of COTS were also recorded on Feather Reef and Hedley Reef. Declines in coral cover on reefs that were not affected by recent COTS outbreaks appear due to summer bleaching in 2015/16 and 2016/17
Scuba surveys only recorded low levels of coral bleaching on Peart Reef, where it was limited to scattered individual colonies. There was widespread evidence of relatively recent coral mortality on all reefs surveyed, presumably from coral bleaching over the previous two summers (and COTS on affected reefs). There were cases of white syndrome coral disease on all reefs but these were generally within the range of previous observations. Incidences of three other coral diseases (black-band, brown-band and skeletal eroding band) were negligible. Numbers of the corallivorous snail, Drupella spp. were evident at most reefs and abundances were generally higher than recorded previously.
Details of the manta tow method can be found in the Standard Operational Procedure No. 9 [AIMS Research - Crown-of-thorns Starfish and Coral Surveys - Standard Operational Procedure 9]. Further details of the monitoring program design, sampling methods and a full explanation of the A. solaris outbreak terminology can be found on the AIMS website.
*Note: genetic studies show that there are at least four species of COTS. These are the North and South Indian Ocean species (A. planci and A. mauritiensis). a Red Sea species (not yet named) and a Pacific species. The range of the Pacific includes the Great Barrier Reef and it has been provisionally named Acanthaster solaris (Haszprunar et. al. 2017).
Table 2: Summary of manta tow surveys of reefs in the Innisfail sector. Arrows indicate the trend in live coral cover and A. solaris since last survey; ▲ = increase,▼ = decrease, “ ” = no change.
|Reef||Shelf Position||Tows||Previous survey year||A. solaris||A. solaris per tow||Median Live Coral Cover||Median Soft Coral Cover||Reef Status|
|FARQUHARSON||Mid||67||2016||554 ▲||8.27||5-10% ▼||0-5%||AO|
|FEATHER||Mid||44||2017||5 ▲||0.11||0-5% ▼||0-5%||NO|
|MCCULLOCH||Mid||93||2016||0 ▼||0||0-5% ▼||0-5%||RE|
|MOORE||Mid||75||2016||0 ▼||0||0-5% ▼||0-5% ▼||NO|
|PEART||Mid||46||2016||20 ▼||0.43||0-5% ▼||0-5% ▼||AO|
|HEDLEY||Outer||58||2016||1 ▼||0.02||0-5% ▼||0-5% ▼||NO|
Figure 3: Effects of marine park zoning. Comparisons of the median values of nine variables through time, based on surveys of fixed sites on matched pairs of reefs in this sector. One reef in each pair was rezoned so fishing was prohibited (Green zone) in 2004, the other reef in each pair remains open to fishing (Blue zone). Error bars are 95% credible intervals. Please click on each panel for an enlarged view.
Figure 2: - Sector-wide changes in coral cover and the numbers of A. solaris for survey reefs in the Innisfail sector of the GBR.
Image 1: Exceptionally high numbers of A. cf. solaris were recorded on two reefs in the Innisfail sector.
Image 2: Recent coral bleaching and outbreaks of A. cf. solaris have reduced coral cover to low levels throughout the Innisfail sector, although some patches of live coral remain.