Reef watcher

Issue 1, number 4, November 1997

Dredging strategy - clear as mud

Since mid November, many divers have reported the extremely poor visibility along the entire metropolitan coast, from Gull's Rock at Maslin Beach through to Port Adelaide. In many areas the water has been a milky colour, with visibility reduced to less than half a metre.

The source of the problem has been the sand dredging operations at Port Stanvac. Sand is dredged from this site and pumped ashore at Seacliff and Brighton to replenish the rapidly eroding beaches in that area. This is one of many sand moving operations conducted each year to replenish the sand onAdelaide's beaches.

Such dredging operations are deemed necessary due to the effects of extensive development along the metropolitan coast. With the benefit of hindsight, we now know that inappropriate coastal development can cause huge environmental impacts. Beachfront housing construction has altered the delicate balance of sand exchange between dunes and beaches, while breakwaters at Glenelg, North Haven and the currently proposed facility at West Beach have blocked the natural northerly flow of sand. This commonly results in erosion of beaches on the northern side of the breakwaters, thus requiring ongoing and very costly sand management. Additional development on the metropolitan coast, particularly of breakwaters, can only add to the ongoing need to dredge sand.

Sand is currently sourced from the Port Stanvac area as it is deemed suitably coarse for use on beaches. According to the Coastal Management Branch, the dredge uncovered an ancient, submerged dune composed of extremely fine sands. After being disturbed, these sediments have remained in suspension, forming an enormous plume causing the extreme turbidity. Earlier studies into the dredging operation by the University of Adelaide indicated that considerable variation exists in the character of the sediments in the area. It is known that a layer of very fine clay underlies the sand.

As is often the case in the marine environment, impacts from one area are easily transported to other neighbouring areas. Many divers have reported on the conditions at their local reefs and hardest hit have been the reefs in the Brighton to Noarlunga area. The following observations were made by Mary-Anne Stacey, Senior Snorkelling Instructor at the Port Noarlunga Aquatic Centre.

Tuesday 18 November - noted milky colouring of water leeward of the reef.

Wednesday 19 November - turbid but calm conditions, with vision reduced to 1 - 2 metres. Fine sand and silt had settled on everything that didn't move, kelp, sponges, simple and compound ascidians and hard plate corals. Coralline algae beds, fibrous green algae beds and mussel beds choked with silt, gills just poking through, even starfish had silt settling on them. Standing on the rocks with students caused a mushroom cloud of silt. I have dived from October to June on a daily basis for 10 years and have never seen conditions like this before. The media and the Environment Protection Authority were notified.

Thursday 20 November - media coverage of damage to the Northern end of Port Noarlunga Reef appeared on the evening news.

Friday 21 November - a light plane was dispatched and aerial photos clearly showed the dredge as the source of the plume.

Tuesday 25 November - north of the jetty in the squid/scallop/razorfish ground between the shore and the reef a lack of starfish were noted and mussels were silted up.

Wednesday 26 November - at 4 - 5 metres single and compound ascidians were observed with up to 70% silt coverage both externally and internally. Sponges also had up to 70% coverage with some pore penetration.

Thursday 27 November - 10 - 15% of the corals on the northern end of the reef showed degradation on the periphery of each plate. Viewed from the cliff top (Whitton Bluff) it was noticed that the plumes would swirl with the currents both north and south, but not actually leave the reef area. Rather, they would continually eddie around.

Monday 1 December - visibility was 0.5 - 1m and a layer of fine silt covered mussel beds. A leatherjacket was caught by hand, perhaps weakened by a lack of food.

Tuesday 2 December - visibility on the leeward side of the northern reef was down to 25 - 50cm. Some degradation of hard corals was seen, sponges and bryozoans were coated with fine silt. Coralline algaes at the top of the reef where wave action is greatest appeared normal.

Sunday 7 December - it was discovered that during the storm the dredge had continued to operate and had swung around, damaging pipes, which had to be repaired by a dive team.

Tuesday 9 December - in the northern shallows of Port Noarlunga Jetty 10 dead nudibranchs (2 different species) were seen amongst disintegrated sponge material.

Wednesday 10 December - conditions on the leeward side of the northern reef were clearing. Single and compound ascidians seemed to have disappeared. Most of the devastation appears to be on the top and exposed sides of rocks. Inside the caverns the sponges, ascidians encrusting algaes and bryozoans appear to be surviving although many are heavily covered in silt.

Short lived sponges, ie the bright yellow and pink sponges seem to have disappeared without a trace. Many other sponges are in a state of degradation, beginning to rot and taking on a ghostly white slimy appearance. Some look like bruised fruit.

Most longer living sponges seem still alive, although discoloured. Most are really choked with silt. I have taken to dusting these sponges of as much silt as I can If these die I believe it will have a long term effect on the appearance of the reef and will take many many years to restore it The short lived sponges will probably return in 12 - 18 months.

Some hard corals have died and in doing so they appear to have a slimy outer covering as if they had just released their larvae into the water. Their appearance suggested they had died within the previous 48 hours.

There is one large plate coral about 1m x 1.5m in size. As these are slow growing I believe they are very old - about 80 - 100 years for one of this size. I have observed this particular plate coral for 10 years. At this stage this specimen is hanging in there, but I am dusting it about 3 times a week.

Concerns

Will anything be done? Will I have to watch sections of my beloved reef partially die; will I hopefully watch it regenerate over the next 12 - 18 months. Will the authorities put this in the too hard basket? Or will they rethink the impact of the dredging operation on this Heritage area. After all, it is a Marine Reserve!

Mary - Anne Stacey
Senior Snorkelling Instructor
Dip T Grad Dip HC

Editors comment: Sedimentation and temperate reefs - not a good combination!

The effects of sedimentation on the benthic organisms of temperate reefs is known to have both immediate and long term effects. This is an important opportunity to begin monitoring the effects of this unfortunate occurance.

As some divers will be aware, many benthic (or bottom dwelling) reef organisms feed by filtering tiny particles of food from the water. It is important, therefore, that the apertures they use to draw water through their bodies are not blocked. Many of these organisms are sessile, meaning that they are attached to the reef surface and cannot simply move to a more appropriate position if they are threatened.

Considering that some reef areas, particularly the low-lying sheltered areas, are reported to have up to 2cm of silt deposited on them, it is likely that many of the smaller filter feeders have been smothered. This will include some ascidians (sea squirts), sponges and bi-valve molluscs (eg mussels). It seems likely that larger filter feeders and mobile biota will survive, although their larvae may not.

Impacts will be felt by reef flora too. In order to attach to the reef surface, many reef algaes have developed a 'holdfast', a strong anchor enabling them to cling to the rock surface and withstand the pounding of waves and currents. For successful reproduction, the microscopic spores released by reef algaes must be able to attach to a solid, clean reef surface. The current concern is that the spores will simply attach their tiny holdfasts to pieces of sediment, which will eventually become mobile, resulting in the loss of the juvenile plant. If this is the case, there may be little new growth on the metropolitan reefs this year.

Other, perhaps more obvious impacts on reef flora include the effects of impeding the penetration of sunlight. As with most land based plants, most reef flora require a good supply of light in order to photosynthesise, or generate energy. Should the suspended sediments prevail for an extended period, perhaps for two months or more, the ability of flora to photosynthesise may be impeded.

At this stage, it is not known how long the water off the metropolitan coast will remain turbid. Improvements one day seem to be counteracted by rough weather the next, which simply re-suspends much of the sediment again.

To gain an understanding of both the short and long term impacts of this event, it is important that we begin monitoring the effected areas immediately.

Reef Watch Diver Training

Training of divers has officially commenced with three groups now equipped to launch into reef monitoring over the summer season. Get in touch and join in on one of the upcoming sessions!

Training includes two sessions. The first involves an indoor 'dry run' in which we run through the Kit and training manual, and the various activities involved in the survey process. This is followed up with practical dives the following weekend at either Port Noarlunga or Hallet Cove, depending on the conditions. These sites have been chosen due to their accessibility for shore based dives.

Individual divers are welcome to attend, and if you have a regular buddy, it is a good idea for them to attend also. If you don't have a regular buddy, this may be a good way to meet one. The training evenings are very informal and the aim is to have a bit of fun too.

Throughout the summer period, training sessions will be run on a fortnightly basis. If you can attend any of the following sessions please call and reserve a space.

Dates~
Wednesday January 14 (indoor)
Saturday January 17 (practical )

Wednesday January 28 (indoor)
Saturday January 31 (practical)

Wednesday February 11 (indoor)
Saturday February 14 (practical)

Wednesday February 25 (indoor)
Saturday February 28 (practical)

Place~
All indoor sessions will be held at the Conservation Council SA, 120 Wakefield St, Adelaide. (Enter at the rear of the building)

Time~
7pm - 9pm

Phone~
(08) 8223 5155

Pt Noarlunga Steps

The Scuba Divers Federation of South Australia has worked hard to improve the safety of access for divers at Pt Noarlunga reef. The new Diver Access Steps were officially opened on Saturday December 6.

The steps seem very well designed and make access to the water easy and safe. No more struggling to climb that perilous vertical ladder at the end of the jetty! Thanks to the SDF for persisting with this issue.

Ocean Care Day / West Beach Dune Boogie

Sunday December 7 was Ocean Care Day. To mark the occasion the Henley and Grange Residents Association, in conjunction with the West Beach Lifesaving Club organised a free concert to protest construction of the proposed boat harbour at West Beach.

It was a beautiful day for the occasion and local residents turned out in force. About ten bands volunteered their efforts to keep the crowd entertained, and the afternoon included a number of speakers from community groups and marine and coastal conservation organisations.

The proposed West Beach boat harbour could add considerably to the erosion of beaches to the north, especially West Beach, Henley and Grange. It will require sand management in perpetuity which, as the opening article suggests, can have further impacts on other marine ecosystems such as reefs.

Residents are concerned over the mounting environmental and economic costs of this development, which many say would be more appropriately sited in the northern end of the Patawalonga basin.

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