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 below this post.

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.

Coral Recovery Following Cyclone Debbie

As I've documented in a previous news item, Cyclone Debbie devastated coral reefs in the Whitsunday area where we live. Until now we have not found a site near us where coral still looks good. We recently spent a day exploring Saddleback Island again and found that the fringing reef in the southeast facing bay of this island is recovering quickly from the coral damage caused by this powerful cyclone. Most of the larger corals were healthy and the extensive shallow staghorn coral gardens were looking remarkably good again after being broken up by the cyclone waves. The many large soft corals on this reef were also healthy and happy. The signature huge Porites boulder coral on this reef was undamaged by either the 2017 coral bleaching event or the cyclone.

It was a different story on the devastated northern Saddleback reef. Here the newly formed rubble bank showed little evidence of coral recovery. Various seaweed species carpeted the dead coral rubble with only an occasional live fragment of coral surviving. It will be many years before coral recovers to its former richness on this reef.

Long-Term Changes in Coral Trout Numbers on the Far North GBR

We carried out coral trout counts on lots of reefs in the Far North Section of the Great Barrier Reef in 1984 for the Great Barrier Reef Marine Park Authority. This was before any zoning restrictions applied and the entire area was open slather for trawlers and fishers. We surveyed coral trout on some of these reefs again in November 2017 and have been able to compare present coral trout abundance on protected reefs and reefs open to fishing in the Far North with the numbers we recorded in 1984. We divided surveys into inner and outer reefs from both surveys because there are often large differences in fish abundance between these two groups of reefs.

It was intriguing that coral trout abundance in 1984 was equal to or higher on these reefs than in 2017 when the 'green' reefs had supposedly been protected from fishing for 30 years. There are several possible explanations for this. The Far North is a remote area and fishing levels may have been very low prior to marine park zoning and not having a measurable effect on coral trout numbers. This is unlikely to have been the case as at that time the reef fishery was based on filleted, frozen product and many commercial vessels operated in the Far North for at least part of the year. Alternatively, because of the remoteness of the area, present zoning may not be enforced regularly and fishing may presently occur on green reefs as well as on the blue reefs. I was surprised to see small outboard-powered vessels fishing on the outer barrier around Lagoon Reef during this trip and this suggests fishing pressure is relatively high in spite of the remoteness of the region.

It is extremely important that we have large areas of the Great Barrier Reef that are securely protected from fishing so that we can build up a pristine stock of large, reproductively active fishes that can seed fished areas with plenty of fish larvae. Studies have shown that a disproportionately large percentage of the fish larvae that settle on fished reefs have come from protected reefs.

 

 Blue reefs are open to fishing and green reefs are theoretically protected. All reefs open to fishing in 1984.

Blue reefs are open to fishing and green reefs are theoretically protected. All reefs open to fishing in 1984.

New Fish and Echinoderm Records

In November/December 2017 we took part in a fantastic trip with GBR Legacy to the Far-North section of the Great Barrier Reef. This includes the remote reefs up north of Princess Charlotte Bay that are rarely visited and poorly known. 

We have been fortunate enough to make extended trips to this area on two previous occasions but it was great to get back in the Far-North and explore some more reefs. During this trip a number of fishes were photographed that we had not seen before on the GBR. We also photographed a remarkable sea cucumber or holothurian that was not like any we'd seen before. 

After enquiring with the experts in these fields we have confirmed that several of these animals have never been recorded from Australia before. One fish was a new record for the GBR and two other fishes had only been seen on the GBR on one previous occasion!

The new records for Australia are the candycane sea cucumber Thelenota rubralineata and the spaghetti garden eel Gorgasia maculata. The ambon emperor Lethrinus amboinensis was a new record for the GBR. The goldback damselfish Pomacentrus nigromanus and the strange-looking squarenose unicornfish Naso mcdadei had both only been seen once before on the GBR. I've included some pictures of these animals below.

Cyclone Devastation of Reefs

Almost exactly a year ago Tropical Cyclone Debbie crossed over our house in the northern Whitsunday region. This huge category 4 storm was moving at a walking pace and we had destructive winds for about 24 hours. These winds destroyed our house, which has now been repaired and is stronger than before, but they also destroyed our local reefs.

Our favourite shallow fringing reefs around nearby islands have been completely devastated. Most of the more fragile Acropora and Montipora coral has been torn off, broken up and deposited in a huge rubble bank on the reef flat. Larger corals have been damaged and partially broken.  Huge boulder corals, some of them over eight metres across, have been dislodged and turned on their side. The power of the waves kicked up by the 300+ km/hr wind gusts packed by this cyclone was almost unbelievable. It will take many years for the reefs to recover.

On some reefs fast growing algae has seized the opportunity to grow and cover the bare bottom and this will probably slow down recovery. Although some corals have survived, especially in the deeper parts of the reef, all have suffered damage to varying degrees. 

We have before and after photographs of many of these reefs and I will post some here to show the scale of the reef devastation.

 

Mackay Fringing Reefs

During January we revisited the fringing reefs in the Mackay Region that we have been monitoring for over a decade. We were working for North Queensland Bulk Ports, who run the Ports of Mackay and Hay Point, via TropWater at JCU in Townsville. Although Mackay had missed most of the wet season rain we had storms around us during this work and got rained on regularly.

We were lucky with the water conditions and underwater visibility was about 5 metres which made the diving easy. The reefs were healing following the damage from Cyclone Debbie in March 2017 and most corals were healthy. There was no evidence of bleaching from the 2018 summer period. As usual we saw some amazing sights on these fringing reefs and I'll post a few pictures below.