Sydney Harbour What is biodiversity? Sydney Harbour habitats
Food chains and food webs Impacts to food webs Play the food chain game
 

Sydney Harbour

Sydney Harbour is the magic ingredient that makes Sydney one of the world's best cities. The harbour means many things to different people. It provides transport to get to work or school, it provides employment through its ports and tourism businesses, it is a place to relax for boaters, swimmers and walkers and a place to connect with nature in the heart of a busy city.

Sydney Harbour means many things to many people, but no matter what values someone places on the harbour most people agree with the need to protect its environment.

Prior to the arrival of Europeans the Sydney Harbour region was home to the Guringai people. Sydney Harbour and the land surrounding the harbour provided them with all the resources they needed. They developed a rich cultural life and had a very strong affiliation with their land.

Today Sydney Harbour is officially known as Port Jackson as named by Captain Cook when he sailed past the harbour heads in 1770. Cook originally recommended Botany Bay in Sydney's south as the best place for European settlement, but in 1788 the first European arrivals soon moved to Sydney Harbour, as it was a safer port for their ships.

Sydney Harbour begins at an imaginary line drawn between North Head and South Head and stretches 20km inland to the mouth of the Parramatta River. It has a surface area of over 52 square km and holds up to 562,000 mega litres of water.

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What is Biodiversity?

Biodiversity is the variety of all life including all plants and animals. There are three types of biodiversity:

Within Species
A difference between individuals of the same species is caused by differences in the make up of their genes. This is known as genetic diversity. Genes are pieces of chemical information that decide the characteristics of individuals. If we look at humans as an example although we are all one species (Homo sapiens) we are all different from each other such as hair colour, height and skin tone. These differences within our species are the result of differences in our genes.

Between Species
The number of different species in an area is known as species diversity. Some areas such as rainforests and coral reefs are home to many different types of plants and animals and so have a high diversity of species, while other areas such as the Antarctic or deserts have a low diversity of species.

Variety of ecosystems
The different areas in which living things interact with each other and their environment is known as ecosystem diversity. An ecosystem is the name for an area of land or water and all the things that live there. Ecosystems can be large areas like the Great Barrier Reef or small areas such as a pond. Sydney Harbour is an ecosystem but it can also be broken down into many smaller ecosystems such as rocky shores or sandy beaches and all the plants and animals that live there.

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Sydney Harbour habitats

Sydney Harbour contains many habitats like sponge gardens, salt marshes, rock platforms and sandy beaches. Rocky reefs and kelp forests are found around the outer harbour and mangroves and seagrass beds are found in the inner harbour and rivers.

These habitats provide homes to many plants and animals including more than 580 different species of fish. Some species are only found in one habitat, while others move between different habitats to look for food, a place to live or for a mate. Many young fish live in mangroves to hide from predators only moving to other habitats when they become adults.

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Food chains and food webs

One way that species interact is their dependence on each other for food. Some species eat plants and are known as herbivores. Other species eat other animals and are known as predators. Animals that eat both plants and animals are known as omnivores. Humans are omnivores.

The food relationships between species are shown in food chains and food webs. Most food chains begin with an autotrophs, which is a species that can make its own food. Plants are autotrophs as they use sunlight energy to turn water and carbon dioxide into food and oxygen.

A food chain shows the pathway of food consumption and looks like this (the arrows show the direction in which the food energy travels):


In this example the base of the food chain is a group of tiny rootless plants known as phytoplankton. The phytoplankton are eaten by tiny animals called zooplankton, which are eaten by small fish, which are themselves eaten by bigger fish. So you can see that plants at the start of the food chain turn sunlight energy into food and that this energy is passed along the food chain from species to species.

A food web is more complex and shows that there are many links between separate food chains. This is because most species eat more than one prey and are eaten by more than one predator.

Let’s look at these two food chains:
1.
2.

Simply they can be connected like this:

However, if we look at all the food relationships between these species they look like this:

When all the food chains in an ecosystem are linked together they become a food web. By looking at a food web we can see all the species that will be affected if one species is removed due to impacts on the food web.

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Impacts to food webs

If any species in a food web is disrupted it can have an impact on many other species. Food webs are often altered by human activities such as: 

Bringing a new species to an area:
Humans bring new species to an area in many ways. It can happen accidentally such as a mussel that attaches itself to a ship's hull and gets carried to a new area. Or people can mean to do it like a gardener who has plants in their garden from outside Australia or from other areas of Australia. These plants soon spread their seeds into natural areas. Introduced species can harm or kill local species by competing for food and habitat or through predation.

Changing habitats:
Habitats can be changed naturally due to floods, fires and earthquakes. But people also change habitats such as clearing mangroves to build houses. When habitats are dramatically changed many species will be affected and some may die out in the area. When this happens other species will fill the gap but this can totally change a food web leaving some other species with little to eat.

Over-harvesting
Human activities such as fishing can reduce the population size of a species if that species cannot reproduce quickly enough to replace its numbers. If a species is seriously reduced in numbers, or is killed off entirely, the impact will be felt by all species that are part of the same food web.

Example of how a food chain can be changed:

Food chain:

Action:
Humans catch big fish for their own consumption but take too many.

Effect:
Less big fish means that numbers of small fish numbers rise as they now have fewer predators. More small fish means more small crustaceans are eaten, which reduces their number. When small crustaceans become hard to find the numbers of small fish may decrease, and they will have to find something else to eat. Fewer big fish means less for humans to eat, which will lead them to start catching another species.

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Food Chain Game

See if you can work out who eats who by playing the HarbourKids Food Chain Game!

Stuck? then download these handy clue cards!
Click here to play the Food Chain Game