Our New Drone: Useful Tool or Frivolous Toy?

We recently purchased a DJI Mavic 2 Pro drone to take images of our local environment. This is a small folding drone that has a 20 megapixel 1” sensor camera with a 28mm lens. It is remarkably capable and has a flight time of about 30 minutes on a full charge. I initially wondered whether it would be useful in our work and after 6 months of regular flying in our local Whitsunday region I’ve decided that it is actually quite a useful tool for marine surveys. Looking at aerial views of reefs gives a unique overview that can help with site selection for surveys. The drone can also be used to fly transects searching for megafauna such as manta rays, dolphins, dugongs and turtles. The long flight time means I can fly two 2000 x 50m transects on a charge, recording a video from a height of 50m that can be searched for target species. With three batteries I was able to record six 2 kilometre long megafauna transects in just a few hours. I’ve seen lots of turtles and one dugong so far! The drone can also be used to take aerials of the reef flat to count numbers of holothurians or to measure the extent of corals such as Porites micro-atolls.

So I’d have to conclude that this drone can be a useful tool for marine biological surveys as well as providing lots of fun!

More Bad News on Cyclone Debbie Recovery

We recently dived in the bay on the north side of Rattray Island. This was previously another of our favoured dive sites but was badly damaged by Cyclone Debbie (see post from March 2018). Although it is now two years since the cyclone this reef is still devastated; some of the corals have suffered further mortality since the cyclone, succumbing to cyclone inflicted damage. This island is about 15km offshore with underwater visibility of between 5 and 15m but during our recent visit vis was less than 2m and there was lots of fine silt lying all over the bottom. We are at a loss to explain why there is so much silt here now and why the water was so dirty. Conditions were so bad that I couldn’t find the huge Porites bommie that had been turned on its side during the cyclone so I’m unable to report whether this has survived! Hopefully I’ll have better news on coral survival and recovery when next we visit this island.

Our boat is anchored in the bay on the north side of Rattray Island where the reef has not recovered at all from Cyclone Debbie damage

Our boat is anchored in the bay on the north side of Rattray Island where the reef has not recovered at all from Cyclone Debbie damage

I have been amazed, both by the speed of recovery at some reef sites and by the slow recovery at others. So far I have not been able to figure out what is the major determinant of recovery time for badly damaged reefs where more than 90% of the corals have been destroyed.

An Amazing Reef: Fringing Reef Super-Site

We often dive on Saddleback Island, only a few kilometres from our home here in Hydeaway Bay, but have only once briefly visited the reef on the south side of the spit. Last week I did two long dives on this reef and was amazed at the healthy state of the fringing reef. It looks like the reef was only slightly damaged by Cyclone Debbie along the shallow reef edge and the reef slope coral is lush and healthy.

A drones-eye view of Saddleback Island fringing reefs showing South Spit Reef and the amazing super-site

A drones-eye view of Saddleback Island fringing reefs showing South Spit Reef and the amazing super-site

On the shallow slope were huge stands of staghorn Acropora corals but the deeper slope, from about three down to eight metres depth, was dominated by continuous, undulating colonies of Goniopora. There were at least five different species of Goniopora but all mixed together into what looked like a single colony over 100 metres along the reef and 20-30 metres across. There were a mixture of other corals along the upper edge of the Goniopora stand and some soft corals but most of the slope was dominated by this single genus of coral. I have often seen large colonies of Goniopora on fringing reefs but this was much bigger than I have seen before and I didn’t explore it’s full extent. It always amazes me what we find when exploring coral reefs especially on fringing reefs that are often very turbid. The reefs on Saddleback Island often have less than two metres underwater visibility and only reach ten metres visibility very occasionally and yet they support wonderful coral reefs.

It is hard to convey the size of the coral colonies when the water vis is only about four metres but I’ve attached a few pictures here to give you some idea of this amazing fringing reef super-site.

Cyclone Debbie Recovery: the Good News and the Bad News

Over the past week we have dived on five local reefs to check out cyclone Debbie recovery. Most reefs in this northern Whitsunday region were badly damaged during the slow passage of Cyclone Debbie almost two years ago. Reefs on the South face of Gumbrell Island and on the north side of Saddleback Island previously had very high coral cover but had been devastated by the cyclone (see previous news item on March 2018). These reefs are only recovering very slowly, especially in shallow water where corals have been completely stripped off by the cyclone. These areas were covered in algae with only the occasional small coral colony appearing two years after the cyclone. North spit reef was still mostly devastated in deeper water as well, although there were a few corals starting to regrow in patches and a few new coral recruits. The deeper parts of Gumbrell Island, on the other hand, had started to recover, with many of the larger corals repairing themselves and surviving Acropora and Montipora coral fragments starting to grow rapidly.

The reef off the northern side of the Saddleback Island spit had been turned into a rubble bank by Cyclone Debbie and coral recovery has been very slow after two years.

The reef off the northern side of the Saddleback Island spit had been turned into a rubble bank by Cyclone Debbie and coral recovery has been very slow after two years.

Coral recovery on other reefs that were not completely devastated by Cyclone Debbie has been much more rapid. I’ve already reported that the reef in Bommie Bay on Saddleback has recovered rapidly and we confirmed that on this recent trip. It is now hard to tell that there has been a cyclone on this reef! Recovery has also been very rapid on Middle Reef, an isolated, long, narrow reef that is about 1,300 metres off Hydeaway Bay. This reef now has lush cover of Acropora staghorn corals and whorl-forming Montipora corals that have all regrown from fragments within two years. It appears that the reef on the south side of the Saddleback Island spit had only light cyclone damage on the shallow sections of the reef and this has almost completely recovered (I’ll be making another post on the condition of this amazing reef).

Camp Island Again

We revisited Camp Island in November. This inshore island is just north of the Abbott Point coal terminal. The water was dirty around Bowen and around the coal terminal but just before we reached the island we got into blue water and vis was around 10m again. The reefs were very similar to when we surveyed them 6 months ago except that lots of Sargassum algae were tangled amongst the stag horn corals at one of the sites. These reefs are very shallow and waves often break or turn over corals even in ordinary rough weather.

One thrill during this visit was seeing a huge shovelnose ray. We don’t often encounter these unusual fishes, especially one about 2.5m long!

Return to Holbourne Island

We re-surveyed the reefs on Holbourne Island offshore from Bowen and the Abbott Point Coral Terminal recently. Cyclone Debbie had devastated the reefs around much of this island and we were looking forward to see how recovery was going. It had been 20 months since the cyclone tore these reefs apart and some of the broken and damaged corals were recovering well, especially the branching Millepora fire corals. There were also still some good corals on the deeper parts of the reef at about 10 metres depth and a few hardy corals in shallow water that had miraculously survived the cyclone. However, we were surprised to see that parts of the reef that had been stripped bare by the force of the cyclone waves did not yet have any new coral recruits on them. Normally we would expect to see many new recruits on such bare reef substratum within a year or so of the cyclone but nothing was visible.

The work was lightened by visits from several groups of large manta rays. One group of three mantas swimming nose to tail made about four visits over about 15 minutes, swooping close around us before going off about their business. It is always such a huge thrill to see manta rays when we are diving. As usual there were a few beautiful nudibranchs that temporarily distracted us from our work!

Sandy Bottom Habitats Are Interesting As Well

A lot of the Great Barrier Reef region is not reef habitat. There are seagrass meadows, mangrove forests and a large area of sand or silt habitat. On several recent projects we have done some diving exploration of shallow sand and silt bottoms and we are always amazed at the variety of interesting animals and plants that live in these habitats. Feather stars sit on the sand bottom or cling to stones or dead shells, holothurians (beche de mer) suck up the rich sediment to digest the organic content, sea shells search for prey and a variety of sea pens, anemones and soft corals filter plankton from the passing water. There are even small free-living hard corals that are specialised soft bottom dwellers. Two very similar hard corals have adapted to sand living by teaming up with a sipunculid worm. The worm lives in a tunnel in the coral base and can move the tiny coral around when needed, even turning it over so it won’t get smothered if the coral gets turned upside down. Many sedentary animals have special bases that can bury in the sand to hold themselves up into the current so they can filter planktonic food from the passing water. Seagrasses and algae can send down roots or tendrils into the sand to maintain position in the shifting sands. A number of fish species are soft bottom specialists, either burrowing in the bottom like shrimp gobies, or lying camouflaged on the sand surface.

I’ve attached a gallery of typical soft bottom dwellers photographed during recent expeditions.

Healthy Reefs on Camp Island

On Saturday 7th July we carried out coral surveys on Camp Island for North Queensland Bulk Ports as part of the Port of Abbott Point ambient monitoring program. This small island is only a couple of kilometres off the mouth of the Elliot River, just to the south of Cape Upstart. it's about 17 kilometres north of the Abbott Point coal terminal and about 40 kilometres north of Bowen. The sea floor slopes very slowly in this area and the island is surrounded by water less than 10m deep. The fringing reefs are even shallower, falling to sand in less than three metres of water. We thought the water would be dirty and the reefs dominated by seaweed but that was not the case. Underwater visibility was around 10m, very good for inshore fringing reefs, and although patchy there were some very rich patches of coral. There were patches of reef dominated by Sargassum algae but much of the reef had moderate to good coral cover.

Corals were mostly fast growing Acropora and Montipora species and many were quite colourful. There were also some large coral colonies including Galaxea colonies over two metres across, Porites boulder corals of the same size and large Goniopora colonies. We were surprised to find many large colonies of the coral Pavona decussata, some of them five metres across. 

We were surprised that these shallow coral communities had not been badly damaged by Cyclone Debbie. Although there were some corals that had been turned over there was very little coral breakage apparent even though it is only 15 months since the cyclone. Coral cover in our four sites averaged about 25% but it was much higher in some adjacent parts of the reef.

Fish Biomass Assessment in Timor-Leste

In June 2018 we spent two weeks in Timor-Leste (East Timor) doing reef fish biomass assessments for the WorldFish NGO. This was a repeat of surveys we first carried out in December 2016. This project is designed to see whether fish biomass can be improved by encouraging local fishers to target more pelagic species by the use of FADs or Fish Attracting Devices. We made fish counts at three sites in each of four locations. No diving was possible at a fifth, south-coast, location because of rough weather and dirty water. 

The three locations around Atauro Island, 25 km offshore from Dili on the north coast of Timor, had clear water and good coral cover but the coral had been damaged by bleaching at Vemasse on the north coast of Timor itself. Most Acropora corals were dead at Vemasse although most other corals were still healthy. Fish populations were similar to those recorded in 2016 although a detailed comparison will have to wait until all the data is entered and analysed.

Coral reefs in Timor-Leste fall steeply into deep water. The 25 km wide channel between the mainland and Atauro Island is a staggering 5,000 metres deep! Strong currents sweep the reef and there is a rich growth of filter feeding invertebrates amongst the corals in the shallows and on the deep reef below about 25 metres depth. This is quite a contrast to the Great Barrier Reef where sponges, ascidians and other invertebrates are much less abundant.

Clear Water on Saddleback Island

We had another dive on Saddleback Island yesterday, the only local reef that still has good coral after Cyclone Debbie. The water was unusually clear with 5 to 8 metres underwater visibility and we were able to better document the surviving corals. There are many huge coral colonies in this bay including a Porites that is over 8 metres across and Galaxea corals over 5 metres across. It is always interesting exploring inshore fringing reefs on the Great Barrier Reef and you can never be sure what you will find. On this dive I came across a huge blotched fantail ray Taeniura mayeni that let me get very close before it moved away.