Further reading: To dredge or not to dredge? The Kingston Pier channel project
Last week’s post was about the proposed Kingston Pier channel deepening project, which aims to make boat access to the historic port of Kingston easier and safer. You can find that post, here: To dredge or not to dredge? The Kingston Pier channel project. This week, I thought I’d do some digging (pun intended) and follow up with some real-world examples of how dredging next to corals has panned out. So this post steps back and asks a very simple question:
When we’ve dredged near coral reefs elsewhere in the world, what actually happened?
I’ll begin with a few short summaries of some well-documented examples of larger projects that have taken place around the world and the impacts these have had. Then we’ll look at some that are more ‘to scale’ and comparable with what we may soon be experiencing here on Norfolk Island.
I’ve provided links to each example if you wish to dig deeper.
But before I do that, I will repeat my disclaimer with regards to the Kingston Pier channel widening project that is due to take place here on Norfolk Island in 2026. I am certainly not opposed to progress and improved infrastructure and I would prefer to leave a discussion on the necessity for this for others to debate. I am also not in a position to comment on the use of Kingston by our local fishing fleet and their requirements for entering and exiting the water safely. Will the dredging make a difference to their access, and will the prolonged closure of the pier to community members be worth the final outcome? I can’t help you on those matters. This post is merely to inform readers about the possible issues associated with dredging near coral reefs.
Video reproduced with permission, from New study finds over half a million corals killed during Port of Miami dredging, USF College of Marine Science, 29 May 2019
1. Port Miami, Florida – deepening the channel, burying the reef
In 2013–2015, the shipping channel into Miami was widened and deepened. It was all done under permits with conditions and monitoring – much like what is proposed for Kingston.
When scientists went back and looked closely at the reefs beside the channel, they found something ugly. Corals near the dredge site were coated in fine sediment, in some places millimetres to centimetres deep. Those colonies had much higher recent mortality and disease than corals at more distant reference sites. In other words, they were smothered first and finished off by disease later.
Further reading:
Miller M.W., Karazsia J., Groves C.E., Griffin S., Moore T., Wilber P., & Gregg K. 2016. Detecting sedimentation impacts to coral reefs resulting from dredging the Port of Miami, Florida USA. PeerJ 4:e2711 https://doi.org/10.7717/peerj.2711
2. Barrow Island, Western Australia – a real-world sediment ‘test’
Off Barrow Island, a big gas project needed a deep channel and turning basin. About 7.6 million cubic metres of sediment was dredged over roughly 18 months, right next to coral reefs. (image link https://www.sail-world.com/Australia/Dredging-link-to-WA-coral-disease/-125220 )
Researchers tagged more than 500 individual coral colonies at different distances from the dredge – from a few hundred metres out to 25 km (note these distances, and bear in mind that here on Norfolk Island we are talking from 20 metres through to a few hundred only!) – and photographed them every two weeks during the works. Where more sediment settled out of the plume, they saw exactly what you would expect:
more ‘snow-covered’ corals,
more partial smothering, and
more partial and whole-colony mortality.
They were able to calculate how much deposited sediment it took to push mortality through the roof. That work now underpins many of the ‘thresholds’ that regulators talk about.
Further reading:
Jones, R., Fisher, R., & Bessell-Browne, P. 2019. Sediment deposition and coral smothering. PLOS ONE 14(6): e0216248. https://doi.org/10.1371/journal.pone.0216248
3. Singapore – death by a thousand cuts
Singapore is a long-running experiment in what happens when you keep dredging and reclaiming land around reefs for decades.
Since the 1970s, huge areas of the coastline have been reshaped for ports, shipping and industry. A major review of dredging impacts notes that around 60% of Singapore’s original reef area has been lost, largely to land reclamation and associated sediment stress. Surviving reefs are now small, shallow, and chronically bathed in turbid water.
Some corals hang on – tough, turbid-water species – but the system is a shadow of what it was. Singapore shows how ‘managed’ dredging and reclamation can slowly squeeze reefs out of existence, even without a single dramatic accident.
Further reading:
Erftemeijer, P. L. A., Riegl, B., Hoeksema, B. W., & Todd, P. A. 2012. Environmental impacts of dredging and other sediment disturbances on corals: A review. Marine Pollution Bulletin 64(9): 1737–1765. https://doi.org/10.1016/j.marpolbul.2012.05.008
An aerial view of the man-made islands of Palm Jebel Ali, Palm Jumeirah, and the World Islands, Dubai. This image includes data from Google, Landsat / Copernicus, Data SIO, NOAA, U.S. Navy, NGA, GEBCO. Imagery from the dates:14/12/2015–01/01/2021.
4. Dubai and Jebel Ali – turning reefs into real estate
Dubai’s famous palm-shaped islands and extended coastline did not appear out of nowhere. They were built with massive dredging and sand fill right on top of shallow coral and seagrass habitats.
Assessments by UNEP and others report that reefs off Jebel Ali – once some of the most extensive along that coast – have been buried or badly degraded by reclamation works, sedimentation and altered currents. Coral cover and diversity have fallen, and the structure of the habitat has changed in ways that also affect fish and other reef life.
Here the ‘impact mechanism’ is very simple: where there were once living reefs, there is now rock armour, concrete and sand fill.
Further reading:
Erftemeijer et al. (2012) again summarise the Dubai / Jebel Ali situation within their broader review of dredging impacts.
5. Spratly Islands, South China Sea – gaining land, losing reefs
In the South China Sea, several countries – especially China – have been building artificial islands and airstrips on top of atolls in the Spratly group.
Satellite analyses show what that really means underwater. Between 2013 and 2015 alone, at least 15 square kilometres of shallow coral reef were converted to land, harbours and channels. The authors describe ‘considerable losses of, and perhaps irreversible damage to, unique coral reef ecosystems’ as entire reef flats are dredged, deepened and then buried under fill.
Coral reefs were turned into a runway.
Further reading:
Mora, C. et al. (2016). Dredging in the Spratly Islands: Gaining land but losing reefs. PLOS Biology 14(3): e1002422. https://doi.org/10.1371/journal.pbio.1002422
Now let’s take a look at some of those smaller projects. None of these are mega-ports. They’re harbours, channels and sand pits drawn on maps at the same scale as Kingston’s proposed dredge. In each case, the reef didn’t just ‘bounce back’ once the excavators left.
6. Heron Island boat harbour – and spoil dump (Great Barrier Reef)
Heron Island is a tiny sand cay with a fringing reef – not wildly different in scale to Kingston’s reef flat. In the late 1980s and early 1990s, dredging was used to maintain the small resort boat harbour, and the spoil was dumped on the reef flat nearby.
A detailed GBRMPA study later mapped the spoil mound and surrounding reef flat. It found that dredged material had changed how water and sediment moved across that part of the reef, created a persistent patch of altered habitat, and was prone to erosion and re-deposition during storms.
For a small harbour, the footprint was surprisingly stubborn – a reminder that even one localised spoil dump on a reef flat can leave a long-term scar immediately adjacent to ‘undisturbed’ reef.
Further reading:
Gourlay, M. R., & Jell, J. S. (1993). Heron Island spoil dump. GBRMPA Research Publication No. 28. https://elibrary.gbrmpa.gov.au/entities/publication/5b977ee4-3c8d-42f4-8c02-eee6eb9e269a
Heron Island, harbour. Image by Ciambue - https://www.flickr.com/photos/ciamabue/6106191035/, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=40691429
7. Coral sand dredging near Suva, Fiji – permanent changes to fringing reefs
Around Suva, Fiji, coral sand has been dredged for decades to supply local construction materials, creating shallow cuts in reef flats and nearshore areas rather than the massive port works mentioned above.
Nicholas Penn’s field studies and thesis in the early 1980s documented what this looked like on the ground: pits and channels dredged into the reef, local loss of live coral cover, more loose sand and rubble, and higher turbidity and siltation in affected areas compared with nearby undisturbed reefs. These ‘worked’ patches tended to remain sand-dominated with poor coral recruitment.
On a map, each site was small. Collectively, they added up to a network of permanently altered spots within what used to be continuous fringing reef.
Further reading:
Penn, N. (1983). The environmental consequences and management of coral sand dredging in the Suva Region, Fiji. PhD thesis, Swansea University. https://cronfa.swan.ac.uk/Record/cronfa42860/Description
8. A shallow channel in Kāneʻohe Bay (Hawaiʻi) – and an expensive restoration
In Kāneʻohe Bay, Oʻahu, a section of shallow reef flat near Coconut Island was dredged and deepened in the mid-20th century to create a seaplane runway and boat access – essentially a one-off channel and basin on a lagoonal reef.
Later work showed that those dredged patches remained deeper, sandier and less coral-rich than neighbouring undisturbed reefs. Researchers trialled coral transplantation to try to rebuild structure and cover in the modified area – an early recognition that the original coral framework had been stripped away and would not simply grow back by itself.
For Norfolk Island, the lesson from this example is simple: one small channel on a small reef can still mean a permanent hole in the coral landscape, unless you are prepared to invest heavily in active restoration.
Further reading:
Bahr, K. D. et al. (2015). The unnatural history of Kāneʻohe Bay: coral reef resilience in the face of centuries of anthropogenic impacts. PeerJ, 3, e950. https://peerj.com/articles/950/ Maragos, J. E. (1974). Coral transplantation: A method to create, preserve, and manage coral reefs. University of Hawaiʻi Sea Grant. https://repository.library.noaa.gov/view/noaa/46802
9. Village harbours and boat channels on atolls more widely
On low coral atolls, many islands have small village harbours and boat channels cut straight through the reef flat to let supply or fishing boats cross the crest.
A recent global analysis of atoll development found that these works – tiny by global standards – consistently cause local destruction of reef flat coral, disrupt longshore sediment transport, and reduce the reef’s natural wave-buffering capacity along that stretch of coast. On satellite images, the dredged basins and cuts show up clearly as geometric ‘bites’ out of the reef.
Individually, each harbour is only tens of metres across. But for the islands that depend on those narrow belts of reef for protection and fisheries, those small cuts can have outsized effects.
Further reading:
Duvat, V. K. E. (2019). Rapid human-driven undermining of atoll island capacity to adjust to ocean-climate related pressures. Scientific Reports, 9, 15129. https://pubmed.ncbi.nlm.nih.gov/31641143/
All these examples are very different, but the pattern is the same:
close to the works, corals are buried or physically removed
further out, they are stressed for weeks to months by extra sediment and low light
the longer this goes on, the more room there is for disease and other stressors to finish the job.
That does not mean every dredging project will automatically wipe out a reef. But it does mean that when someone says ‘don’t worry, it’s all under control’, it is worth remembering what ‘under control’ has looked like for coral reefs in other parts of the world.
It’s easy for agencies to say ‘this is only a small job’ – a modest channel, a boat harbour, a bit of sand extraction. Unfortunately, the track record from big and small projects that are close to coral reefs shows that these words are not exactly reassuring.