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A very fine Port

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Situated in the middle of the tropical currents from the north and the cooler ones from the south, Sydney Harbour boasts many different habitats as well as regarded by many as the most beautiful harbour in the world.     
There are rocky reefs, kelp beds, sea grass beds, mangroves, saltmarshes and patches of mud and sand. Some of these are exposed and some protected so this wide range accommodates more fish species in Sydney Harbour than the entire coastline of New Zealand or Great Britain.
David Booth, Professor of Marine Ecology at the University of Technology Sydney, outlines some of the work from the Sydney Institute of Marine Sciences (SIMS), one of the few marine institutes situated on an urban harbour. 

This was the outcome after many years of looking for a suitable site in Sydney for a marine institute and SIMS was finally established in 2005 by four Sydney universities that run marine science courses, when together they rented some buildings at Chowder Bay, a Sydney Harbour Trust site which used to be a naval site. One large building on the water was converted into a state of the art aquarium. There are also offices, molecular labs, a boatshed and a dock. 
 Underwater off SIMS, Chowder Bay (image by Bill Gladstone)

The Sydney Harbour Research Program is based at SIMS and not only includes members from universities but also people from the Office of Environment and Heritage and Fisheries. This multidiscipline undertaking is unusual especially since collaboration between universities is difficult as they are all struggling for the tiny pieces of pie that are available. As part of SIMS the collaborators started the Sydney Harbour Research Program.

Before beginning the research it was decided to assess what was already known about Sydney Harbour in order to arrive at a baseline. Professor Booth looked at fishes, fisheries and climate change while others worked on areas like seaweed and contaminants.

UTS Fisheries Resources class about to immerse in Sydney Harbour (image from Fish Ecology Lab)

Two papers, which have just been published, centre on biodiversity and the problem of benthic (bottom) contaminants. Sydney Harbour is an estuary in a drowned river valley but there is still salt water as far up as Parramatta, evidenced by the mangroves. The estuary is very narrow at Parramatta and the mud is very fine and silty. This is good in one sense because it traps nutrients for the worms and other creatures but it also traps contaminants like heavy metals, sourced from industries in the upper harbour. Homebush Bay, with a history of industry including Union Carbide, still has a lot of contaminants so the site was capped and then planted above with mangroves. Drilling down (or dredging) would release some horrible contaminants so leaving them alone is partly why Sydney Harbour is in such good shape. Commercial fishing has been banned in Sydney Harbour because of the risk from dioxins getting into fish tissue. 

Another important issue is sewage run-off and storm water run-off entering the harbour and fresh water is a pollutant for salty habitats.
Some advanced councils net the canals that lead to the harbour to catch big things like plastics but a lot of contaminants (sediment, micro plastics) still get through.

Right: SIMS state of the art aquarium facility allows studies of the effects of climate change on vagrant tropical fishes

The harbour fish are quite mobile. Bream do move up and down the estuary searching for molluscs in the mud. The migratory tropical fish that come from the north every summer are found in the mouth of the harbour but numbers drop off westward so few are found near the Harbour Bridge. Other fish like the puffer fish and goby are more common upstream. Sea dragons (an Australian relative of sea horses but larger at some 50cm) like the edges of large kelp habitats in the outer harbour but other fish, like the tropical fish don’t like kelp, so that changes in the extent of the kelp beds are good for some creatures but not for others. 
Below right: Weedy Sea Dragons in Sydney Harbour (image from Fish Ecology Lab)

There is an ongoing contraction in kelp beds on the Australian coast. Some is due to increasing invasion by Sea Urchins, made possible by increasing coastal sea temperatures. Sea Urchins feed on kelp, leaving bare rocks with bands of algae in place of forests of kelp. The warmer waters have seen them spread south into Tasmania where they are decimating the marine ecosystems through overgrazing. 

The climate change signals in Sydney Harbour are getting quite strong, temperature being the main factor. As an indicator of a possible future, Tosa Bay in Japan, is at the same latitude as Sydney, and has largely turned into a coral reef instead of its usual kelp habitat over just a few decades. Such changes also affect other harbour services like fisheries. With climate change, there is also a change in the rainfall in estuaries, which means less fresh water flow so prawn catches can drop off. Less fresh water means that the sea-type habitats (which mangroves like) move further upstream, further changing the balance of species who will be able to find a suitable habitat. 

Warmer water means that cold water species have to move south and Australia’s coastline does not go very far south. Already performance cold water species like the Atlantic salmon that are farmed in Tasmania are an issue. 

However, it seems that at present, Sydney Harbour remains a very fine port. 

Professor Booth was interviewed for A Question of Balance by Ruby Vincent. Summary text by Victor Barry, April 2016.

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