Report on surveys of the Innisfail sector of the Great Barrier Reef

Summary

  • Seven reefs were surveyed in this sector, six mid-shelf and one outer-shelf reef.
  • Sector-wide hard coral cover was low (0-10%) and had declined since the last surveys in 2018.
  • Hard coral cover increased marginally on three reefs and declined on four reefs.
  • No crown-of-thorns starfish (COTS) were observed during manta tow surveys, however sub-adult and juveniles were detected on fixed site surveys at Farquharson Reef and Peart Reef.
  • Coral bleaching was observed at moderate levels on reef crest and reef flat habitats during manta tow surveys. Coral bleaching on reef slope habitats, assessed using scuba at fixed survey sites, was low.

Hard Coral Cover   0-10%  10-30%  30-50%  50-75%  75-100%

Figure 1: Map showing location of reefs in the Innisfail sector. Click the points for more information.


Table 1: Overview of results obtained from manta tow surveys of reefs in the Innisfail sector

As part of the Long-Term Monitoring Program (LTMP), manta tow surveys of hard coral cover and the abundance of the coral feeding crown-of-thorns starfish (COTS), Acanthaster cf. solaris were completed on seven reefs in the Innisfail sector of the Great Barrier Reef (GBR) (Fig 1).

Preliminary results of the manta tow surveys are presented in Tables 1 and 2. The overall median hard coral cover for the sector was low (7%) (Table 1) (Fig 2) and had declined marginally since the previous surveys in June 2018 (Fig 2). All seven reefs had low (0 to 10%) hard coral cover (Fig 1, Table 2).

Preliminary results of the manta tow surveys are presented in Tables 1 and 2. The overall median hard coral cover for the sector was low (0 to 10%) (Table 1) (Fig 2) and had decreased marginally since the previous surveys in June 2018 (Fig 2).

Among six reefs previously surveyed in June 2018, hard coral cover had increased at two reefs and decreased at four reefs (Table 2). At Feather Reef , previously surveyed in February 2019, hard coral cover had increased marginally. Low coral cover in this sector reflects the cumulative disturbances, such as COTS outbreaks and the 2016/2017 mass coral bleaching events, that have afflicted these reefs in recent years.

No COTS were recorded during manta tow surveys (Table 2), however, individuals in the sub-adult and juvenile size classes were detected on scuba during fixed site surveys at Farquharson Reef and Peart Reef. Three reefs were classified as ‘recovering’ from active outbreaks reported in 2018 (Table 1, Fig 2).

The majority of the GBR Marine Park was under a bleaching warning, issued by NOAA Coral Reef Watch on the 13th February, at the time of these surveys. Coral bleaching was recorded at moderate levels sector-wide during manta tow surveys, particularly on reef crest and reef flat habitats (Table 1). Bleaching was restricted to scattered, individual colonies on reef slope habitats, surveyed using scuba during fixed site surveys. Bleaching occurred on most transects and a wide variety of coral genera were affected, in particular colonies of Porites spp.

Abundance of coral diseases, including white syndrome, brown-band disease, skeletal eroding band disease and black-band disease, was rare in the Innisfail sector. The densities of the corallivorous snail, Drupella spp., varied between 27/ha to 87.5/ha and had declined at all reefs since previous surveys. More results on fish and benthic assemblages from fixed site surveys will be available soon.

 

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. Outbreak Status: NO no outbreak, PO potential outbreak >0.1 COTS per tow, IO incipient outbreak >.22 COTS per tow, RE recovering, AO = Active Outbreak>1 COTS per tow.

Figure 2: - Sector-wide changes in coral cover and the numbers of A. solaris for survey reefs in the Innisfail sector of the GBR. Orange trend line = Hard coral. Purple bars = Crown-of-thorns (COTS)

Figure 2: - Sector-wide changes in coral cover and the numbers of A. solaris for survey reefs in the Innisfail sector of the GBR. Orange trend line = Hard coral. Purple bars = Crown-of-thorns (COTS)

Image 1. A pair of Eastern Clown Anemonefish (Amphiprion percula) inhabit a magnificent sea anemone (Heteractis magnifica) that is starting to bleach at Peart Reef.  Image 1. A pair of Eastern Clown Anemonefish (Amphiprion percula) inhabit a magnificent sea anemone (Heteractis magnifica) that is starting to bleach at Peart Reef.
Image 2. Remnant live branching and plate corals on the crest of Farquharson reef that survived previous years of COTS outbreaks were bleaching. Image 2. Remnant live branching and plate corals on the crest of Farquharson reef that survived previous years of COTS outbreaks were bleaching.
Image 3.  Convict surgeonfish (Acanthurus triostegus) school above the reef crest of Feather Reef, scattered with small Acropora plates undergoing bleaching. Image 3. Convict surgeonfish (Acanthurus triostegus) school above the reef crest of Feather Reef, scattered with small Acropora plates undergoing bleaching.
Image 5. A view of the crest of Peart Reef, where hard coral cover remains low following recent COTS outbreaks. Image 5. A view of the crest of Peart Reef, where hard coral cover remains low following recent COTS outbreaks.