Heavy rainfall increases the risk of pollution, like last year, when sewage entered the bay. But these more obvious threats hide a greater problem … one that remarkably goes unnoticed. The fact is, freshwater can poison marine ecosystemsHow ecosystems function An ecosystem is a community of lifeforms that interact in such an optimal way that how ecosystems function best, is when all components (including humans and other animals) can persist and live alongside each other for the longest time possible. Ecosystems are fuelled by the energy created by plants (primary producers) that convert the Sun's heat energy More and saltwater can poison the land. In this blog I will discuss how freshwater is the greatest threat to Ricketts Point.
Overview
There are already indications that abalone and shellfish are beginning to suffer from freshwater intrusion. For instance, after recent storms, almost all the seastars, mussels and abalone died in front of the stormwater drain at fossil beach. Certain areas of Ricketts Point Marine Sanctuary at low tide now resemble saltmarsh. They are even attracting saltmarsh birds like Sharp-tailed Sandpipers and Grey Teal. It’s commonly known that they have lost their intertidal fauna over the last few decades.
As a result of a proliferation of stormwater drains rock lobsters can never be reintroduced. Rock lobsters were once abundant but are extremely intolerant of freshwater.
This destabilisation of ecological processes is leading to the gradual erosion of natural values. These are losses that groups like Marine Care Ricketts Point talk about. For example, there is a worry about the disappearance of intertidal animals from the reef flats. While this is often blamed on people rock-pooling, I very much doubt that’s the case. It is evident that we may have reached a tipping pointThe rapid move of an ecosystem from one steady state to another state. Ecosystems don’t rapidly move from one steady state to another steady state. Tipping points are typically reached when the amount of free energy is so significant, that there is total structural collapse and the new state, is simply one where most of the energy is contained at More in the last few years. Important parts of the park are turning into an estuary.
Unfortunately, no-one seems to be talking about this. Meanwhile, we are distracted with ideas like urchin culls. This is such an important oversight, I am choosing to write here, to raise awareness of this threat.
Competing influences and lack of adaptation
In our coastal ecosystem we have competing ecosystem processes. Engineered drains and sea defences compete with natural systems. This means our coastal habitatsWhat is habitat for animals and people? Habitat, hence the word "habitable" describes the natural surroundings in which any animal (or human) lives, that houses basic needs, such as food and shelter. Vegetation, for example, is habitat for animals. On its own, habitat is not necessarily stable or sustainable, which is why it differs from an ecosystem. Habitat in disrepair More are constantly under pressure, unable to establish themselves and reach a point of resilienceReferring to an ecosystem’s ability to maintain a steady stable-state. The need to build resilience is entirely anthropocentric and symptomatic of ecosystems that are damaged or declining, leading to loss of ecosystem services on which humans depend. More.
The result is a pincer action on the ecosystem. First, we have an increase in the frequency and intensity of storm events that move salt into freshwater areas, and freshwater into salt areas. Second, we engineer drains to move freshwater into the sea as fast as possible. All the while we build sea defences that exacerbate movement of salt onto the land. These events are becoming more extreme. The human-engineered hard interface between land and sea leaves no scope for natural adaption.
For anyone interested, I’m going to step through some of the indicators of these changes that are easy to see, along the coast from Black Rock to Beaumaris.
Inshore conversion to saltmarsh
When rivers meet the sea, ‘brackish’ systems (semi-saline) form. Saltmarsh tends to dominate along the edges of these.
There are clear signs of a marine-side shift from a saline to brackish between Sandringham and Beaumaris. This is most prominent in places like Quiet Corner but even more at the southern end of Ricketts Point car park, where a major storm water drain sits just south of Teahouse. Here, a large storm drain opens into a mini-estuary. The substrate has become silty, not sandy and the top of the reef is increasingly dominated by saltmarsh. The rock pools between used to contain more intertidal habitat. After each intensive storm, however, they are exposed to an excess of freshwater, nutrientsEnergy and nutrients are the same thing. Plants capture energy from the Sun and store it in chemicals, via the process of photosynthesis. The excess greenery and waste that plants create, contain chemicals that animals can eat, in order to build their own bodies and reproduce. When a chemical is used this way, we call it a nutrient. As we More and sediment.
Freshwater offshore
Freshwater floats on top of seawater, as it contains less salt and is therefore, less dense (see below). So, after heavy storms, you can see the effect of freshwater outflows. Mostly, these flow south along the coast. All the stormwater drains that emanate further north, push a significant amount of freshwater into the sanctuary. At the boundary of these fronts is transported sediment and nutrients. Nutrients are in excess and are extremely bad for the bay.
In spring, there is almost permanently a lens of freshwater that hangs over the beach at Ricketts Point. The boundary layer can often be seen while snorkelling, as it appears like a mirage, making it hard to see the seafloor. When you duck down below this, you can see more clearly.
The depth and intensity of this freshwater lens varies. Sometimes it washes towards the beach, when it dominates most of the shallow water column. At low tide and during offshore winds, it is pushed over the reef tops. At its boundary, in some years, it concentrates nutrients and we see enormous dense congregations of blooming lions mane jellyfish. Toxic bioluminescent algae also proliferate. These are all signs of excess nutrientA substance that contains the raw materials for life. At a chemical level, these are contained inside compounds that are absorbed into the body and essential energy-containing molecules are extracted, so that energy can be transformed into other chemical processes that use the energy for living. More, which leads to ecosystem collapse.
Salt burn off of coastal vegetation
After the recent heavy storms of August 2024, you may have noticed much of the bushland turning brown. This is salt poisoning. Several days of persistent inundation of the plants and soil with salt spray, has changed conditions.
The problem here is that native vegetation on the landward side of the sea wall mostly comprise freshwater-dependent species. Rainfall on the land side nourishes these for most of the year but the sea defence doesn’t attenuate wave force. The full energy of a storm strikes the wall head on and this lifts salt water onto the cliffs and dunes above.
As you can see today, the most resilient and surviving vegetation are the succulents such as pig face and bower spinach. Very little treed vegetation can survive this constant flip between fresh and saltwater. We will now expect a gradual change in the nearshore vegetation to more salt tolerant species such as pig face and bower spinach. Replanting the burned off vegetation would be a waste of money.
Increase in storm intensity and climate change
The threat from freshwater, meanwhile, is a greater problem, as its hidden from view.
It relates to two things. First, there is an increase in the frequency and intensity of storms. The annual frequency of potential severe thunderstorm days is predicted to rise by 22% for Melbourne. There are also stronger winds forecast, with wind speeds over oceans rising by at least 0.75 percent per year, leading to larger storm surges. According to the Insurance Council of Australia’s report, the economic costs of such events have tripled over the last three decades.
The engineered threat
The greater problem is the increase in intensity and frequency of freshwater reaching the bay.
Within the City of Port Phillip alone there are over 7,600 drainage pits which take stormwater from the street into drains. There are over 300 in the bay.
Melbourne Water are currently redirecting drains into a superdrain near Elwood. While this won’t, in theory, increase the total volume of water entering the Bay, it will increase the intensity of these events. The mouth of the new, larger, drain, is over a kilometre further south. The relatively larger volume reaching Ricketts, combined with increasing storm intensity, will pose a significant additional risk which has not been considered by planners.
What will happen is that freshwater events will occur more frequently (due to climate change) and with greater magnitude (due to engineering). While some freshwater is natural it is a common misconception that it is harmless.
Sadly, it is rare for ecosystem impacts to be considered at all. It takes a level of skill and knowledge about how ecosystems function(Of an ecosystem). A subset of ecosystem processes and structures, where the ecosystem does something that provides an ecosystem service of value to people. More and the processes at play, to plainly see this. Engineers and decision-makers have not considered impacts of freshwater on Ricketts Point Marine Park. Nor have the caretakers of the park itself, Parks Victoria’s scientists (who are not trained ecosystem specialists), related academic researchers or even Marine Care Ricketts Point.
What impact does this have on your lifestyle and livelihood?
Whether you’re a dog-walker, cyclist, paraglider, fisher or snorkeler; or if you just visit the bay to be with friends and family, this will affect you.
Ask yourself this. If you weren’t able to spend your time in a healthy bay, how much would this affect your work-life balance? How much less happy would you be? How much does a healthy bay contribute to making you a better, stronger and more productive person at work and at home? 20%? 40%? 80%? Chances are, you’ve just identified the huge economic impact that the bay has on all of us. When we ignore ecosystem processes, we ignore the largest component of our economy.
From what I can see, we may have reached a critical point where those interested in our sanctuary’s future need to step up and start looking more holistically at this as a key threat to the ecosystem.
The good news is, there is a way to act differently, and we are about to launch a community initiative to enable better decisions.
More on that in a later post ; )
