Lesson 1

What are coastal ecosystems?

Lesson goals

Understand the ecological role and value of coastal ecosystems

Lesson description

Students investigate the variety of plant communities which form the coastal ecosystems of Minnamurra. Key environmental factors, such as tides and water salinity are introduced, and their role on patterns of zonation explained. Finally, students explore the ecological role coastal ecosystems play in the functioning and health of coastal environments.

Estimated time

40 minutes

Supporting materials

Lesson 1 worksheet - coastal ecosystems

Outcomes

Working Scientifically - Questioning and Predicting

Develops and evaluates questions and hypotheses for scientific investigation
Develop and evaluate inquiry questions and hypotheses to identify a concept that can be investigated scientifically, involving primary and secondary data

Module 3: Biological Diversity

Predict the effects of selection pressures on organisms in ecosystems, including biotic and abiotic factors

Module 4 - Ecosystem Dynamics

Investigate and determine relationships between biotic and abiotic factors in an ecosystem, including the ecological niches occupied by species

Worksheet access

Click on the image below to access the Lesson 1 worksheet. Once opened, save to your personal google drive or download your own copy.

Once saved, use your current knowledge and resources below to complete the document.

Lesson 1 worksheet

What are coastal ecosystems?

Coastal ecosystems occur wherever the land meets the sea. There are a wide variety of such ecosystems, including dunes, rock platforms and intertidal estuaries. The coastal ecosystems along the Minnamurra River are intertidal estuaries, consisting of seagrass, mangrove, saltmarsh and sheoak.

Coastal dunes

Dunes serve as natural buffers, protecting the land from tides, waves and wind. Communities of plants that grow on beaches and dunes are known as dune vegetation. There are usually three main zones of dune vegetation that are arranged roughly parallel to the coastline, each increasing in size and diversity. This vegetation provides stabilisation for the sediment and significant habitat for animals.

Rock platforms

Rocky shore ecosystems form where coastal shores are made from solid rock. The conditions are ever changing, yet a huge number of animals and algae can thrive. Rocky shore ecosystems are governed by abiotic factors like the tidal movement of water and wave action, which lead to biotic changes such as the distinct distribution of different species across the intertidal zone, from above high tide to the sub-tidal zone

Intertidal estuaries

Intertidal estuaries form in sheltered bays or rivers where fresh waters from inland rivers and streams mix with ocean water. As a result, estuaries are home to some of the most dynamic and diverse environments in Australia. Many different habitats are found in and around estuaries, including marshes, swamps, mudflats, oyster reefs, mangrove forests and seagrass beds. The vegetation and plant life that live underwater and on the fringes of estuaries provide unique habitats that sustain significant aquatic and terrestrial life.

Minnamurra River study site

Minnamurra River flows from Booderee National Park, high on the Illawarra Escarpment and west of Jamberoo, to the ocean just north of Kiama. As it flows as a freshwater stream, the surrounding ecosystems change from highland heath and swamps, temperate rainforest, moving through dairy farms before transitioning to a tidal estuary close to the coastline.

This coastal estuary is dominated by tidal flows, which bring salty ocean water upstream from the rivermouth, determining the suite of plants and animals which can survive in this coastal part of the river. The coastal intertidal estuary which subsequently forms is an excellent example of an ecosystem common on the east coast of Australia with a mix of natural vegetation and human development existing side by side.

Unfortunately, these ecosystems are highly susceptible to the impacts of climate change and sea level rise, and their long term future may be coming under threat. This study aims to identify the species and communities present within intertidal estuaries, determine their current range and abundance and attempt to identify and mitigate future threats to the ecosystem.

Minnamurra's coastal ecosystem

The 360 images below show typical low tide and high tide plant communities of Minnamurra's coastal ecosystems.

Ecosystem overview

Seagrass

Seagrasses are flowering plants (not algae or seaweed) which grow in shallow water. The most common species within the Minnamurra estuary is Eelgrass. In order to survive, they need to be deep enough to be covered by water at low tide, while still remaining shallow enough to receive large amounts of sunlight at high tide

Mangrove

Mangroves grow between the low and high tide mark (the intertidal zone). Many species are found in Australia, however only two are found at Minnamurra, the Grey and River mangroves They thrive with regular short term inundations, however, cannot survive if roots are covered by water for more than several days.

Saltmarsh

Saltmarsh plants grow above the high tide mark. The community consists of a diverse range of shrubby, herbaceous plant species. They are salt tolerant, however can only survive occasional water inundation, such as an annual spring tide or flood event.

Sheoak

Sheoaks are a tall species of Casurina which grow above the high tide mark, forming dense forests.

They are salt tolerant, however can only survive occasional inundation by water, such as an annual spring tide or flood event.

Zonation along Minnamurra River

The plant communities along the Minnamurra River grow within independent 'niches', where the biotic and abiotic characteristics are most suitable for their survival. They depict the following pattern of zonation from the river landward:

Seagrass - present in the shallow regions of the river bed towards the low tide mark.

Mangroves - mangrove trees dominate the intertidal zone, where water inundates the area twice daily during high tide.

Saltmarsh - saltmarsh species such as samphire and saltbush occur above the high tide mark, where inundation of tidal water is rare.

Sheoak - sheoak trees are only found in the raised areas above the high tide mark, as they are less tolerant to brackish water.

Figure 1: Zonation of plant communities along the Minnamurra River showing water levels between tides and highest astronomical tide (HAT)

Key abiotic influences driving zonation

Tides

Salinity

The value of coastal ecosystems

Each ecosystem present along Minnamurra River performs numerous functions. Click on the pictures below which link to articles describing the role and value of the ecosystem.

Then complete the following multiple choice quiz.

Seagrass

Mangrove

Saltmarsh

Sheoak

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