Quality news, views and analysis of issues that affect and inform us in the Douglas Shire.

PERSPECTIVES / Daintree Interdependence

The Daintree Coast contains some iconic and familiar landscapes, from the wet tropical rainforests to the Great Barrier Reef, and the complicated labyrinth of mangrove systems in between. What most people don't know is that these various systems are intricately interdependent. In reality they are not separate systems at all, but three parts of a fantastically complex whole.

PAUL O’DOWD

The Daintree Coast contains some iconic and familiar landscapes, from the wet tropical rainforests to the Great Barrier Reef, and the complicated labyrinth of mangrove systems in between. What most people don’t know is that these various systems are intricately interdependent. In reality they are not separate systems at all, but three parts of a fantastically complex whole. 


This region is ranked amongst the most bio-diverse regions on the planet, The Reef is World Heritage listed and the economic backbone of numerous communities, it is also threatened with imminent destruction on multiple fronts. 

Adjacent the Reef and also Heritage listed, the Daintree Rainforest is widely considered to be the most ancient rainforest on the planet. Also ranked amongst the most bio-diverse ecosystems known, the Wet Tropical rainforests of this region are the last fragments of the ancient Gondwanan rainforests from which Earth’s great modern rainforests are considered to have have evolved. 

Between the rainforest and the reef, growing along the rivers and estuaries in the region, resides the most bio-diverse mangrove system on the planet, with more than two thirds of the total diversity of mangrove plants known to man.

What most people are seldom aware of, is that these three systems are intimately and inseparably interdependent.

Events within one system affect the others in ways that we are only now starting to appreciate. In fact, the interdependence we observe in this living laboratory is just a vivid local example of some shocking ideas that are forcing us to revise what we think we know about how our world works.

We sit here surrounded by this awesome story, so it’s worth having in mind as we commute between the hills and beaches, as we go about our lives here in this truly incredible place…

So how does it work?

Allow me to explain…

The Great Barrier Reef requires certain nutrients that originate on the land. They start out in the coastal forests in the form of organic debris which gets flushed out of the forests when it rains. But if lots of leaf litter made it all the way out to the reef, the reef would end up blanketed by a fibrous sludge of rotting vegetation.

This would be a problem.

Apart from the obvious impact of being buried by the debris, the tons of detritus decomposing in the ocean would release a rich organic chemistry over the reef. This would have a direct, chemical impact on the reef and could also fuel algal blooms which would seriously reduce the amount of light getting to the coral. So the reef does not need direct rainforest run-off. It needs filtered rainforest nutrients.

This is where the mangroves come in. 


The mangroves are the filter. Their dense, semi-submerged, bank-side vegetation acts as a very efficient filter, trapping the floating detritus and keeping it there as it breaks down in the rivers, swamps and estuaries. By the time the river empties out to sea, it contains exactly the right balance of nutrients to meet the reef’s requirements. 

There is another, less obvious way in which the mangroves manage the reef’s diet.

A great number of creatures from the reef begin life in the well-protected and nutrient-rich environment of the mangroves. They are the perfect nursery. In fact the fishing industry refers to mangroves as nurseries.

Many of the creatures from the reef, and from either side of the reef, start their lives in the coastal mangrove forests. Upon maturity, these young sea creatures migrate out to sea, carrying with them the rainforest nutrients from which they built their bodies during the mangrove phase of their lives.

In this sense, the mangroves are a factory; tasked with the conversion of rainforest detritus into self-guided, reef-bound nutrient packages called sea-life.

Of course, it goes a lot further than that.

As much as the reef relies on these coastal forest ecosystems, without the reef there could be no mangroves or rainforest on the Daintree coast. 

Mangroves can’t establish in crashing surf, and rainforest needs to keep very tight control over the internal climatic conditions below the canopy. The conditions needed by both systems would be impossible to maintain in the face of dynamic oceanic conditions.

The reef forms an obvious physical barrier against the Pacific swell, which makes this coast very bad for surfing but perfect for mangroves. 

As for the weather, although the reef is under water, it still has an enormous effect on the atmosphere above it. This happens in a couple of ways. 

The lagoon is the body of water which is trapped by the Reef, over a shallow, sandy shelf. This water sits in the tropical sun and warms up. The warm water evaporates, generating an enormous, permanent wall of hot wet air which sits just offshore and acts as a barrier against the violence of the weather coming in off the Pacific. This ‘weather-wall’ protects the coast but as it does so it is blown into the coast by the very weather it is protecting us from. As this warm wet air gets forced over the mountains, it is in fact detected by the plants of the rainforest. These then react by generating a complex mixture of hydrophilic particles that cause the gaseous H2O in the air to form droplets of liquid water.

The water dissolved in air, the saturation of which we call humidity, remains dissolved unless it encounters a surface of appropriate chemistry to settle on. Water-loving chemical surfaces of leaves, and on the microscopic airborne particles generated by the forest, strip the moisture from the very air itself, clawing it out of the sky and sending it down the eastern slopes and out to sea, instead of being blown over the hills and lost to the coastal forests, farms and communities.

You see this effect every time you look at the mountains and see the columns of mist reaching up from the gullies in the upper slopes of the range. This is not the forest “giving birth to clouds” as is often stated, it is the forest sending great gaseous tentacles into the atmosphere above it to grab this vital resource before it escapes on the trade winds carrying it westward.


This is not the only method by which the reef “waters” the rainforest and the farms and gardens of the North. It is now clear that coral reef systems are capable of creating clouds in the sky above themselves to protect the coral from the sun. You read correctly, research on the Great Barrier Reef has demonstrated the ability of coral reefs, as communities, to literally generate clouds in the sky above them using an ingenious chemical trick to dim the harmful rays of the mid-day sun during the hottest time of the year.

Here’s how it seems to work; Due to the emission of a gas by the coral’s algal symbionts, the air above a reef becomes rich in sulphurous airborne particles which have a strong attraction for water. The water in the air quickly forms droplets around these microscopic cloud-seeds. This process of condensation releases heat which warms the air, causing it to rise. The rising air carries the droplets upward and fresh air is sucked in to replace that which has just risen. The fresh air picks up more and more of this gas as it rapidly diffuses into the air from the water below. Soon, strong thermals begin lifting tonnes of water into the airspace above the reef. By late morning, these rising droplets form actual clouds and the reef is spared the worst of the mutagenic attention of the tropical summer sun. These are truly biogenic clouds; weather created directly and for selfish purposes by a biological process. This is not an isolated example of this kind of thing. This, and other examples of biogenic weather radically change the way we now think about weather. 

These clouds, in due course, float into the hills of the Great Dividing Range and make their contribution to the hydrological budget of the coastal rainforests. These processes lift unimaginable tonnages of water out of the Coral Sea and dump it onto the all systems that need it on the north east quarter of the continent. If you don’t get rain, you don’t get rainforest or agriculture, or gardens or reliable drinking water for your communities. 

Of terrifying note, when the water temperature hits just over 30 degrees celcius, this mechanism fails and the cloud forming ability of the reef is shut down, right when it’s needed most.

In reality, what we have here is not three different systems at all. Rather, what we have is three parts of one system. In fact, this is just a one example of what we now know to be a fundamental feature of the natural world. It applies to every living system regardless of scale, from the microscopic to the global. And at this ignominious point in the history of our species, it is worth remembering that we are not an exception.


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Ashley Holliday
8 months ago

Don’t forget the dirt and erosion, mud and dust that enters the inshore reefs north of Cape Tribulation. The Bloomfield Track is an open wound that continually erodes soil, it by passes the mangrove system as the creeks are short and fast flowing.

Paul o'Dowd
8 months ago

Agreed. The unpaved roads north of the river have been devestating to the inshore reefs and who knows the effects further out and in the longer term…