Disappeared reef wildlife of Port Phillip Bay

The loss of fish and rock lobsters from Port Phillip Bay is nothing short of catastrophic. If this loss isn’t addressed in the coming years, there will be nothing left to look after. The disappeared reef wildlife of Port Phillip Bay will Melbourne’s undoing.

The table (below) is adapted from the work by John Neville (2006). This might be the only anecdotal record of what the reefs used to be like.

Several species have declined to almost non-existence since the 1950s.

• Purple Wrasse
• Bluethroat Wrasse
• Rock Lobster
• All Leatherjackets

… were all abundant back then. All three feed on sea urchins. All are virtually extinct now. 

How did this happen?

Spearfishing started in the 1950s. At that time fish were abundant but their numbers were depleted rapidly. Many of these species are reef-dependent and don’t migrate. Once they are gone, they don’t return.

Hence, their populations have never bounced back. Today, the small amount of remaining fishing, is enough to stop any recovery. That will remain the case while their numbers are so small.

The consequence

Science doesn’t work

The number of fish left today is only a tiny fraction of what once existed. No-one can remember what it was like before, so we struggle to imagine what it should look like. Any scientific observations we make today bear no relevance to how the ecosystem should 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, as there is so much fish biomassThe weight of living organisms. Biomass can be measured in relation to the amount of carbon, the dry weight (with all moisture removed) or living weight. In general it can be used to describe the volume of energy that is contained inside systems, as the size of animals relates to their metabolism and therefore, how much energy they contain and More missing. We observe a broken, chaotic system, that cannot be described as it’s too changeable.

This leads to inherent bias in studies and mistakes, such as assuming that sea urchin removal will fix the problem, when it will actually make things worse.

Ecosystems are chaotic and less resilient

Reef systems are becoming dominated by herbivores. This is because there is too much algae, not too little. The system is being made less diverse by the proliferation of certain seaweed-eating species. Sea urchins are among these.

But removing sea urchins can’t be the solution. We’ve created this problem by removing the top part of the ecosystem structure, taking us from a 4-5 trophic levelDescribes the amount of energy contained within one step of the food chain. Animals in one trophic level utilise about 90% of the energy they absorb for living, emitting the rest as heat and waste. This means the next step up the trophic chain (e.g. the bigger animals that eat them) only have access to about 10% of the energy More system, to one that’s only 2-3. Removing sea urchins reduces this to a 1-2 step system. It makes absolutely no ecological sense to remove more biomass.

The consequence is an ever-decreasing destruction of 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 that the bay relies on for its economy and all livelihoods and past-times, including fishing. As long as we delay rebuilding wild fish populations, we can only make things worse.

If we do not rebuild the ecosystem structure soon, it will collapse altogether. We are already seeing the beginning of this. Our bay is dominated by algal growth, infestations of sea urchins and plagues of jellyfish.

The solution

The only solution is to remove fishing pressure until populations of fish and rock lobster have recovered to pre-1950s levels. This will mean reintroducing the animals and imposing strict controls to protect them.

The decision about protection of these reefs will have to be given to local custodians.