Coral Reef Bleaching in Port Phillip Bay this year

Introduction

For coral bleaching to occur there needs to be a sustained increase in temperature of about 1.5 degrees celsius above average. However, the problem is exacerbated in the presence of excess nutrients and absence of reef fish*, both of which are factors in Port Phillip Bay. These are things we can address fast and see results quickly … if we took action to reduce pressures today we may see change in 5-7 years, and this might account for a third of the problem we are seeing. Climate change is a longer-term issue but acting now on these other factors buys us time.

Coral bleaching in Melbourne is a wake up call that things are not right. Now is the critical moment to begin working as a community and identify real change needed to protect our bay.

*Note, critical reef-resilience species such as Blue-throated Wrasse were exterminated from these areas 70 years ago and won’t come back without help. We know fish can recover fast and we need everyone on board to make this happen, or we might lose everything. We’re talking about stopping fishing … in actual fact, these efforts are likely to enhance fishing.

Why do we need coral reefs in Port Phillip Bay?

Most people don’t realise we have extensive coral reefs along our coastline near Melbourne. Or, that they are part of the natural sea defence that supports the functioning of our coastal 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, providing a wealth of economic value.

There were many fishers casting lines over the bleaching reef I photographed. They don’t know there is coral there but this isn’t simply about fishing … they fish because it makes them feel good (others swim, snorkel, dog-walk etc) and that contributes enormously to our economy. Without healthy reef, we can’t be healthy and neither can our economy. So the key to restoring our bay is to understand how our values connect with specific ecosystem features (including coral reef). These are essential values shared between us all. That is why we need you to sign up to Restore the Bay today.

The bleaching event that has happened is going unnoticed because:

• we do not value this environment;
• we do not understand how important it is to our current way of life; and
• the authorities that are set up to protect our Bay’s health, are busy doing things that are not addressing coastal 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 and don’t necessarily link to our economy.

Why and when does coral bleaching occur?

Coral is a symbiosis between an animal (polyp) and plant (algae). When temperatures get too high for too long, the algae vacates its polyp home and takes with it the ability to feed the coral, as well as the colour. Polyps are white without it. Polyps can recover quickly if temperatures fall within about six weeks.

How is Port Phillip Bay’s water temperature changing?

These are EPA temperature records recorded for January and February from 1985 to 2021 expressed as 2-month rolling averages. In other words, January is the average of Jan + Dec, Feb the average of Jan + Feb. Since the start of the millennium the temperature has climbed from about 20.5 degrees but that slowly increased to 22 degrees by 2017 before dropping again in 2019 – 2021 (no data was recorded for 2020).

As a word of caution, I don’t know how these temperature data are collected. If they are averaged sea surface temperatures, these tend to be lower than observed, especially in shallow water (coastal) areas. For instance, on 1 March my dive watch was recording over 23 degrees at 3m but the sea surface temperature according to the Port Phillip Bay temperature data was 21 degrees. It’s all rather academic though. While we procrastinate over temperature accuracies it merely delays doing something to rebuild reef resilience, while we can literally see the coral bleaching.

The average temperatures for January and February (1985 – 2007) expressed as averages within each month are as follows:

At what point does coral bleaching begin in Port Phillip Bay?

Perhaps we can assume that our Green Corals are evolved to withstand reported summer temperatures averaging about 20–22 degrees celsius on average – this was the variation before about 2007, when ocean temperatures began to rise significantly. However, it’s the duration of temperature that causes bleaching and that risk has been increasing also. Bleaching this year is clear evidence we are at or near the +1.5°C 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 that would see our coral reef systems collapse. Aside from reducing fossil fuel dependency, we need to reduce the other mounting pressures including nutrientEnergy 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 overload and rebuild our populations of resident reef fish, as they are key to the reefs’ resilience.

Here are before and after photos of a large coral bommie in Beaumaris. The first photo was taken on 26 May 2024 (15.0–15.4°C). The second was taken on 1 March 2025 (23.0–23.4°C). This bommie was fairing okay but showing significant signs of stress, indicated by the washed out ‘luminous’ colouration. Below are photos from 1 March 2025 showing other clearly bleached coral close up. I estimate that 50-60% of coral is bleached on this important area of reef.

These are data for 2025 showing a sustained period of 22-23 degrees between January and February 2025.

Already this year, we have seen temperatures above 22 °C since mid-January. They have remained that way for about 6-7 weeks. Only in the last week or so have we seen temperatures begin to subside, so hopefully the corals will recover. I will revisit the same spots in the coming weeks and let you know.

What can you do about it

Petitions aren’t going to solve this problem and there is no single point of blame. Our only hope is coming together as a community to identify where best to spend resources tackling the issues that can be resolved quickest – and then working with our elected officials to make this happen. This is why the Restore the Bay project is so important.

We have to be able to put our own value on how we connect with ecosystem features. This has never been done before … the Restore the Bay project is a first of its kind. Now is your chance to get involved and giving just 25 minutes of your time to answer some questions, may be one of the most important things you can do right now.