If someone were to mention ecosystems in the Whitsundays most people's minds would instantly go to the Great Barrier Reef, one of the most diverse and incredible ecosystems in the world. Stretching for 2,300 km and covering an area of 348,000km2 along the east coast of Australia, the Great Barrier Reef takes the title of the largest coral reef system on the planet and its current form has been growing for over 8,000 years, continually adapting and changing.
Its size is not the only thing that makes this world heritage listed ecosystem so special. The reef contains an array of different habitats from the shallow water reefs near the coast to open waters past the continental shelf at depths over 2,000m. These waters are home to a staggering number of marine animals, including over 1,500 species of fish, 400 species of coral and 4,000 species of mollusc. The 400 different species of coral act as a base for complex food webs involving invertebrates, crustaceans, fish, marine reptiles and mammals . From the smallest crustacean to the largest marine mammal, all the animals depend on the reef and in turn play a vital role in maintaining balance and health within the ecosystem. In turn a functioning and balanced reef system, especially one as large as the Great Barrier Reef is a major player in keeping the world's oceans healthy. They maintain overall biodiversity, contribute to water quality and clarity and play a major role in the nutrient cycle which is essential for continued growth and productivity.
Most people are unaware that corals are actually animals and not plants which they can so closely resemble. Individual coral animals are called polyps and are closely related to jellyfish and sea anemones. Single polyps join others of the same species and form colonies with a calcium carbonate “skeleton”. As polyps die new ones grow using the skeleton as a base. This death and regeneration cycle is how coral reefs form and grow.
Here in the Whitsunday islands our coral reefs are what are known as fringing reefs. These are reefs which form around the coastlines of land masses and are separated from the shore by shallow lagoons. The waters in the Whitsunday region carry a high sediment load which soft coral species thrive in and beautiful, colourful and diverse soft corals are what the Whitsundays are known for.
The longevity and biodiversity of the Great Barrier Reef cannot be credited to the reef itself alone however, its interconnectivity with other ecosystems in close proximity have ensured its endurance and success. These ecosystems include intertidal zones, mangroves, seagrass meadows and estuaries.
Estuaries are an area where freshwater streams and rivers meet the sea creating brackish waters. Estuaries are also highly variable and dynamic environments which are extremely tide effected. Conditions such as temperature, salinity, depth and water flow all change daily due to changes in tidal movement. This unique environment is home to an array of animals from birds to fish which have specialised adaptations to deal with such variability.
The high species diversity of estuaries can be attributed to the range of different habitats and ecosystems within the estuary itself. These can include mangrove swamps and seagrass beds, both common sites in the whitsunday region.
They also provide calm and protected waters for recreational activities such as fishing, boating and swimming and are also often at the centre of many major cities across the world. This makes estuaries extremely important both ecologically and economically.
The best known estuary in the Whitsunday region is the mouth of the Proserpine river, which is great for fishing and spotting local wildlife. Perhaps the most well known and probably feared animal that calls this estuary home is the estuarine crocodile, also known as the saltwater crocodile or salty. At low tide these giant reptiles can often be seen sunning themselves in the cool mud around the mangroves that line the shores of the estuary.
Mangroves are an intertidal ecosystem consisting largely, as the name suggests, of mangrove trees. In the Whitsundays mangroves can be found in the intertidal zones along the coastline of most islands and the mainland especially in areas where there is freshwater discharge. The high levels of salinity and waterlogged, anoxic (no oxygen) soil/mud of intertidal zones are not usually prime conditions for vegetation to thrive. However mangroves have developed specialised adaptations to do just that. One of these adaptations is their roots. Many species of mangroves, such as those found in the Whitsundays, have aerial roots. These roots stick up vertically out of the mud which allows them to extract oxygen directly from the air. Their roots can also filter out salt from the water to reduce the amount delivered to the plant.
Mangroves are incredibly important and perform vital functions for marine and coastal ecosystems. On the surface they provide prime habitat and food for a host of birds and marine animals such as crustaceans and fish. The mangroves also act as a nursery for many marine species including the lemon shark, juveniles of which can be frequently seen in Hill inlet at high tide as they leave the protection of the mangroves further up the inlet in search of a tasty fish meal.
Mangroves also help to maintain water quality by filtering out pollutants and stabilising otherwise vulnerable soil and coastlines. This also means that they are extremely important in the prevention of erosion due to waves, tidal movement and storm surges.
Another important ecosystem in the Whitsundays which is also dominated by vegetation are seagrass meadows. Although they are often overlooked, seagrass meadows are some of the most productive and biodiverse marine ecosystems on the planet.
Just like corals they are an important foundation in the marine environment, providing food and also vital habitat for a number of marine organisms such as crustaceans, molluscs, fish and even large marine animals like turtles and dugongs.
In the Whitsundays seagrass beds can be found in numerous bays in the islands such as Tongue bay and also on the mainland in places like Pioneer bay and Turtle bay, making these locations great places to go and spot sea turtles and the extremely shy dugongs.
Similar to mangrove ecosystems seagrass beds also improve water quality by stabilising the substrate and filtering out runoff from the surrounding land. They also protect coastlines from erosion.
As primary producers the seagrass species are significant contributors to the nutrient cycle in the marine environment. It is also important to note that although seagrasses appear quite similar to seaweeds, the two are actually quite different. Seagrasses are a plant related to things like palm trees and terrestrial grasses and have root systems where seaweeds are a type of algae which lack a root system. Being plants means that the seagrasses use carbon dioxide that has been dissolved into the ocean, and water to produce sugars and oxygen. In one day these plants can produce a whopping 10L of oxygen per 1m2 of biomass. This means that they are not only important to the marine environment but also to us humans as they contribute to the oxygen that we breath and help to remove carbon dioxide from the atmosphere. Seagrasses also provide a significant economic benefit to humans in that they act as important nursery areas for commercial and recreational fish stocks including prawns and barramundi and are vital to the survival of these fishing industries world wide.