One inshore reef (Havannah Island) was surveyed using manta tows. No COTS were observed on this reef. The fringing reef on Havannah Island was severely affected by the 1998 bleaching event which reduced reef-wide live coral cover from a high level (40-50%) recorded in 1997 to a low level (0-5%) in 1999. Reef-wide live coral cover on this reef remains low in 2002.

Manta tows were not possible at Pandora Reef but no COTS were seen in SCUBA searches

Sixteen mid-shelf reefs were surveyed using manta tows. Active Outbreak levels of COTS were detected on four of these: Reef 18-026, John Brewer, Kelso and Rib. Incipient Outbreaks of COTS were detected on another two reefs: Little Kelso and Lodestone. COTS were observed on a further six reefs, but below outbreak levels. With the exception of Rib Reef (which has been an Active Outbreak since 1999), COTS on Outbreaking reefs were generally small and cryptic. This made them hard to spot during manta tows and would suggest that true numbers of starfish were probably much higher on some reefs. This was particularly true of Little Kelso, Lodestone and Hopkinson Reef where COTS were detected below Active Outbreak levels though scars from COTS feeding activity were very common. Spot checks on these reefs revealed high densities of cryptic COTS (many less than 25cm in diameter).

Reef-wide live coral cover (henceforth "coral cover") is low (0-10%) on all reefs that have Active Outbreaks. Coral cover on Reef 18-026 is similar to levels seen at the last survey of this reef in 1988 when it was classified as Recovering from prior COTS activity. Coral cover on Kelso Reef was also close to the value that was recorded when it was last surveyed in 1990. It too was classified then as Recovering from a previous outbreak that ended in 1986. Coral cover on John Brewer Reef has declined since 2000 when cover was moderate (20-30%). John Brewer Reef was classified at the time as Recovering from a previous outbreak that ended in 1986. Coral cover on Rib Reef has declined from a peak of 40-50% in 1998 (a year before the current outbreak and when it was classified as Recovering from an outbreak ending in 1987).

There are many feeding scars on the two reefs that currently have Incipient Outbreaks, and manta tow surveys may not adequately reflect the true numbers of COTS on these reefs. Thus we expect coral cover on these reefs to decline. Coral cover is currently moderate (10-20%) on both Little Kelso and Lodestone reefs an increase from the last survey of these reefs in 1990. At that time coral cover was low (0-10%) and they were classified as Recovering from prior COTS activity.

Eight of the ten remaining reefs surveyed in this region are classified as Recovering from prior COTS outbreaks. No COTS were observed on reef 18-099 which had an Active Outbreak up until 1991 when coral cover was low (5-10%). Coral cover is currently moderate (10-20%) on this reef. One COTS was seen on Davies Reef, which had an Active Outbreak from 1988 to 1992. Coral cover on Davies Reef is currently moderate (20-30%) and similar to levels seen since 1986 despite Active Outbreak levels of COTS from 1988 to 1992. One COTS was seen on Grub Reef. This reef was classified as Active Outbreak from 1986 to 1989, by which time coral cover was low (5-10%). Surveys in 2002 show coral cover was only moderate (10-20%) on this reef. Five COTS were seen on Hopkinson Reef. The abundant feeding scars and the large numbers of small cryptic COTS seen during spot-checks suggest that starfish numbers were greater on this reef than the survey results indicate . Hopkinson Reef was previously surveyed in 1990 when it was classified as Recovering from an Active Outbreak. Coral cover on this reef has recovered from a low level (5-10%) recorded in 1990 to a current moderate level (20-30%) in 2002. One COTS was seen on Keeper Reef. Keeper Reef was classified as an Active Outbreak up until 1987 when coral cover was low (5-10%). Surveys in 2002 found moderate coral cover (20-30%). Six COTS were seen on Slashers #2 Reef that had an Active Outbreak in 1987. Coral cover has shown only limited recovery since, from a low level (5-10%) in 1990, to a moderate level (10-20%) in 2002. No COTS were seen on Wheeler Reef that was last classified as an Active Outbreak in 1989. Coral cover has recovered well on this reef from a low level (5-10%) in 1990 to be high (30-40%) in 2002. No COTS were observed on Yankee Reef, which was last classified as an Active Outbreak in 1988. Recovery of coral cover on this reef has been poor with a low coral cover recorded in 2002 (5-10%) showing no improvement from the low cover recorded in 1988. This contrasts with the high coral cover (30-40%) when this reef was first surveyed in 1986.

The remaining two reefs surveyed in this region, Reef 18-025 and Centipede are classified as No Outbreak. Coral cover on Reef 18-025 was low (5-10%) and similar to levels recorded when it was last surveyed in 1989. Small numbers of COTS were seen on Reef 18-025 during surveys in 2002 but in numbers that were too low to affect coral cover. Given the low coral cover on this reef it is quite possible that it is recovering from recent outbreak levels of COTS. This reef is adjacent to reefs that have supported outbreak levels of COTS in recent years. On Centipede Reef coral cover was moderate (10-20%) and a level similar to when it was last surveyed in 1992.

Outer-shelf Reefs

Eight outer-shelf reefs were surveyed using manta tows. No COTS were recorded on any of these. Five reefs (Reef 18-023, Dip, Faraday, Knife and Needle) are classified as Recovering from prior COTS outbreaks. Chicken, Coil and Myrmidon are classified as No Outbreak with few COTS observed on these reefs since surveys began in 1986. On the Recovering reefs the highest coral cover was moderate (20-30%) on Faraday and Knife Reef. Faraday Reef had an Active Outbreak in 1986 when coral cover was high (30-40%). Subsequent surveys in 1989 showed coral cover on this reef declined to a low level (1-10%). Since this time there has been some recovery in coral cover but it is still well below that recorded during initial surveys in 1986. Coral cover on Knife Reef is as high as it was when initially surveyed in 1986, though outbreak levels of COTS were also present on the reef at that time. Coral cover on Dip and Needle is also currently moderate (10-20%). Dip Reef was last classified as an Active Outbreak in 1986 when it had a high (30-40%) coral cover. Extensive surveys since this time reveal little improvement in coral cover over the intervening period and it is currently well below that recorded in initial surveys. Initial surveys of Needle Reef in 1986 showed an Active Outbreak and a low (5-10%) coral cover.

 While coral cover on Needle Reef has increased since this time, the presence of COTS during initial surveys makes it difficult to judge levels of coral cover on this reef historically. Coral cover on Reef 18-023 is currently low (0-5%). This reef has been surveyed since 1992 when it was classified as No Outbreak. Surveys in 1997 indicated a high (30-40%) coral cover on this reef. The next survey in 2000 recorded the highest densities of COTS on a single reef during the history of manta tow surveys. Thus it is not surprising that this reef currently has a low coral cover. Reef 18-023 is currently classified as Recovering.

On the No Outbreak reefs coral cover was the best on Coil reef (30-40%). This reef has been surveyed five times since 1984 and this level of coral cover is similar to previous surveys. Similarly for both Chicken and Myrmidon the moderate (10-20%) coral cover recorded in 2002 is similar to previous surveys which have, in both instances, an extensive history dating back to 1986.

Table 1. Summary of manta tow survey results for the Townsville sector.

Image 1. Crown-of-thorns starfish feeding on tabulate Acropora coral on Reef 18-026. In this case four COTS are crowded in to a small area. Competition for food between COTS will often occur during outbreaks particularly on a reef where coral cover is low.
Image 2. Crown-of-thorns starfish in the open, on sand, on the back of Reef 18-026. As mentioned in image 1, coral cover on this reef was low forcing the COTS to compete for food. In situations such as these some COTS will venture large distances off the reef and into barren sandy areas in the search for food. In some cases large numbers of COTS can be seen spread out on the sand.

Table 2. Summary of manta tow survey results for the Cape Upstart sector.

Coral Bleaching

Sampling for this field trip occurred out at a time when reefs in the sector were experiencing elevated water temperatures (due to the combined affect of clear skies, calm sea and maximum summer solar irradiation). Bleaching threat maps supplied by NOAA indicated that the area off Townsville was under serious risk of wide-scale bleaching. Observations of bleaching are part of our survey program; these are summarised below. These observations were taken while bleaching was developing; we cannot say how the phenomena will subsequently evolve from the time of survey. To a large extent this will depend on the length and intensity of the warm seawater event and the ability of the corals to persist and recover in the face of this environmental perturbation.

Inshore Reefs

Individual bleached coral colonies were found around the entire perimeter of Havannah Is reef during manta tows. Coral cover is very low on this reef (0-5%) as a result of a previous bleaching event in 1998. Pandora Reef was surveyed using SCUBA. Bleaching estimates on fixed survey sites on the NE face of Pandora Reef ranged from 0% to 5-10% of total live hard coral cover (median category of 1-5%). However survey sites on this reef are generally below 6m. Corals in the shallow areas above the survey site are more likely to have been affected by raised temperatures, so these results may underestimate the true level of coral bleaching on Pandora Reef as a whole.

Mid-shelf and outer-shelf Reefs.

The proportion of bleached coral colonies within reef zones (ie back reef, reef front and flanks) was generally low on all mid and outer-shelf reefs. Median percentage of total hard coral cover that was bleached was no greater than 7.5% and was generally 2.5% or less. The zone with the highest bleaching was the back of mid-shelf reefs. At the time of survey mid-shelf reefs were more affected by coral bleaching than were outer-shelf reefs. Limited zones on inner and outer-shelf reefs also had relatively high levels of bleaching. Bleaching on outer-shelf reefs tended to be higher on the reef front than on other parts of reefs. This contrasts with the pattern on mid-shelf reefs. Many colonies, while not bleached white, were showing clear signs of stress and had the lurid or pale (image 4) appearance of corals that are in the process of bleaching. Given the high stress levels of many corals the low level of bleaching reported here may well underestimate the final extent of bleaching.

The areas of reef within zones (i.e. reef flat, reef crest, slope above 10m and slope below 10m) that were affected by coral bleaching varied with shelf position. On mid-shelf reefs a similar proportion of reefs had bleaching present on the reef flat, the crest and the slope to 10m. There was no bleaching recorded below ten metres on mid-shelf reefs. This contrasts with outer-shelf reefs where bleaching occurred more often on the reef slope, down to 10m, and less often on the flat and the crest. In a number of instances bleaching was present below 10m, but only on the reef front.

Image 3. Bleached sub-massive Acropora coral in the foreground of this photo taken on the flank of Grub Reef. The bright white colour of the colony is in direct contrast to a colony of the same species, in the immediate left background, which has not been bleached.
Image 4. Partially bleached Acropora corals dominate this photo taken on Keeper Reef. Tabulate Acropora with the typical lurid appearance that is a precursor to bleaching occupies the foreground. In the center of the photo a pale Acropora colony is also rapidly reaching the point of bleaching. Scenes such as these, dominated by partially bleached corals, were typical on the mid-shelf reefs.
Image 5. Bleaching events do not restrict themselves to hard corals. Other organisms that have symbiotic zooxanthallae in their body tissues (e.g. soft corals, clams, and sponges) are also susceptible to bleaching events. In this particular instance it is an anemone that has become bleached.