What is Gulf St Vincent to you?
A playground with great beaches, somewhere to go walking, swimming, crabbing, fishing or sailing?
A place of business, where ships ply the coast, where fishermen make their living, where salt is manufactured, where drinking water is produced?
A complex marine environment, with a diverse range of habitats for fish, invertebrates, birds, mammals, plants.
The receiving waters for runoff from roads, sewage plants, building sites, storm drains.
The gulf is all of these things, and its long-term health depends on our ability to manage the things that threaten water quality – the main factor affecting the gulf’s condition.
Biodiversity – life above and below the surface
Coastal ecosystems in SA are unique, with 3-5 times as many macroalga species as there are corals in the Great Barrier Reef. We have the highest biodiversity for a temperate region anywhere in the world, and 60-90% of our species aren‘t found anywhere else.
While our gulf is not as threatened as many other places in the world, it is quite vulnerable, due to the unique biota and environment. Our waters are very low in nutrients, with natural nutrient levels less than one tenth of other temperate systems. Those environments are better able to deal with nutrient influx, but ours are less able to cope. This is why we have experienced such devastating loss of seagrasses in the past 50-60 years.
But there are still relatively unique and untouched areas in the gulf, and many of these will be protected by the proposed South Australian marine park network.
Even along the metropolitan coast we can get a glimpse of the variety of marine plants and animals that live nearby. A walk on the beach following a storm can be a rich experience if you stop to look at what has been washed up!
Among the colourful array of creatures you might find are:
- bivalve and gastropod molluscs
- starfish, sea urchins and sea cucumbers
- crabs and other crustaceans
- lace corals
- sea squirts
Seagrasses grow in vast meadows in the shallow coastal waters of the gulf. They provide food and shelter for a large range of marine creatures, and they also stabilise sand on the sea floor, just as vegetation on land prevents erosion.
Increasing population and urbanisation, particularly on the Adelaide Plains, has resulted in the destruction of more than 4,000 hectares of seagrass – the most severe losses occurring in the 1960s – 70s. The main cause of the seagrass loss is excess nitrogen, and the biggest sources are sewage and industry.
Another factor in seagrass decline is turbidity – muddy water. Silt and other pollutants are washed into the gulf after heavy rains and reduce light penetration for days at a time. Eventually the silt settles quite close to shore, and is then stirred up again by prevailing winds.
When you see large piles of seagrass on the beach, it is probably a sign that recent storms have uprooted more seagrasses.