Marine environment fact sheet | Field of Mars EEC

What are marine environments?

Marine environments are saltwater surroundings connected to seas and oceans. They include open ocean, shallow coastal waters, rocky shores, beaches, bays, reefs, seagrass meadows, kelp forests and estuary areas where freshwater mixes with salt water. An environment is wider than one habitat because it can include many habitats and ecosystems.

A marine ecosystem forms when living things and non-living features interact. For example, algae, seagrasses, fish, crabs, corals, bacteria, sunlight, salt water, waves, currents and the seafloor can all be part of a marine ecosystem. A habitat is a smaller place where one organism lives, feeds, shelters or breeds, such as a rock pool, seagrass bed, coral crevice or sandy seabed.

Field of Mars Reserve is not a marine environment, but it is connected to marine environments through water movement. Rainfall and stormwater can move through local creeks, the Lane Cove River catchment, Sydney Harbour and eventually the sea. This means caring for inland bushland and waterways can also help care for downstream estuary and marine environments.

A marine environment.

Marine environments in Jervis Bay Marine Park include ocean water, rocky shores, sheltered inlets, reefs and many habitats.

Where are marine environments found?

Marine environments are found around every coastline and across the world’s oceans. In Australia, they range from tropical coral reefs in the north to temperate rocky reefs, kelp forests, seagrass meadows, beaches, estuaries and deep ocean habitats in the south.

In NSW, coastal, estuarine and marine waters contain many habitat types and are influenced by subtropical and temperate currents. Around Sydney, marine environments include ocean beaches, rocky shores, nearshore reefs and estuary waters connected to Sydney Harbour and the Tasman Sea.

Sydney coastal environments include ocean water, rocky headlands, beaches and places shaped by waves and wind.

What living and non-living features make up marine environments?

Living features include producers, consumers and decomposers. Producers such as phytoplankton, seaweeds, seagrasses and some algae use sunlight to make food. Consumers include animals such as snails, crabs, sea stars, fish, turtles, seabirds, dolphins and whales. Decomposers and detritus feeders, including bacteria, fungi, worms and small crustaceans, help break down dead material and recycle nutrients.

Non-living features include salt water, sunlight, depth, tides, waves, currents, temperature, oxygen, nutrients, sand, mud, rock, coral structures and the shape of the seafloor. Light is strongest near the surface, so many producers grow in shallow water where sunlight can reach them. Deeper or darker places can still support animals and microorganisms that use different food sources.

Rocks, seaweeds and the seafloor create habitats for many marine organisms.

What plants and animals live in marine environments?

Marine environments support tiny and large living things. Phytoplankton are microscopic producers that float in sunlit water. Seaweeds and seagrasses grow in shallow water where light is available. Corals, sponges, shellfish, crabs, worms, sea stars and sea urchins live on reefs, rocks, sand, mud and other surfaces.

Fish may feed, hide or breed in reefs, seagrass beds, mangroves, salt marshes and open water. Seabirds feed at the surface or along shorelines. Marine reptiles and mammals, such as turtles, seals, dolphins and whales, move through marine environments for feeding, migration, resting or breeding. In Sydney estuaries, saltmarsh, mangrove and seagrass habitats provide important vegetated habitat for many fish and invertebrates.

Corals, algae, fish and many other organisms can interact in reef ecosystems.

How do living things depend on marine environments?

Marine food webs begin with producers such as phytoplankton, seaweed, seagrass and algae. These producers use sunlight, water, carbon dioxide and nutrients to grow. Small consumers, such as zooplankton, snails, worms, small fish and crustaceans, eat producers or tiny food particles. Larger consumers, such as bigger fish, seabirds, seals, dolphins and sharks, may eat smaller animals.

Dead plants, animal remains and waste do not disappear. Decomposers and detritus feeders break them down and return nutrients to the water and seafloor. These nutrients can then be used again by producers, helping energy and matter move through marine food chains and food webs.

A crested tern carries a fish at Boat Harbour, NSW, showing a predator-prey link in a coastal marine food web.

How are marine environments connected to Aboriginal Peoples and Country?

For Aboriginal Peoples of coastal NSW, Sea Country can include saltwater places, shorelines, estuaries, plants, animals, stories, responsibilities, cultural practices and family connections. Sea Country is important for cultural connection, food, identity, family, community and wellbeing.

Aboriginal Peoples have cared for and used marine environments for thousands of years. Knowledge of tides, seasons, winds, currents, fish, shellfish, sea plants and coastal places helps people understand and care for Sea Country. Caring for marine environments should include respect for Aboriginal Peoples, cultural knowledge and ongoing responsibilities to Sea Country.

Arakwal National Park is a coastal NSW place co-managed by the Bundjalung of Byron Bay People (Arakwal) and NSW National Parks and Wildlife Service.

Why are marine environments important?

Marine environments provide habitat for many living things. NSW coastal, estuarine and marine waters help maintain water quality, protect coasts and seabeds from erosion, provide critical habitat for fish and other marine life, and support recreation, visual amenity and food production.

Marine environments also help people learn about interdependence, water cycles, Earth systems and human impacts. Healthy marine environments support biodiversity, fisheries, tourism, cultural values and wellbeing. Marine parks help conserve habitats and species while still allowing people to enjoy activities such as wildlife watching, diving, boating, snorkelling and fishing where permitted.

Large reef systems can include many smaller reefs, channels and habitats.

What threatens marine environments?

Marine environments can be affected by pollution, poor water quality, sediment, runoff from land, plastics, coastal development, invasive species, overuse, fishing pressure, vessel activity and disturbance to habitats. Land-based pollution can travel through gutters, drains, creeks and rivers before reaching estuaries and the sea.

Climate change is a major pressure because warmer waters, marine heatwaves, changing currents, sea level rise and ocean acidification can affect reefs, kelp forests, seagrasses, mangroves, animals and food webs. National reporting says parts of Australia’s marine environment are already being affected by climate change, pollution and cumulative pressures.

Bleached coral beside healthy-looking coral at the Keppel Islands, Great Barrier Reef, showing how heat stress can affect marine ecosystems.

How can you help protect marine environments?

You can help by keeping rubbish, soil, pet waste, oil, paint, chemicals and fertiliser out of gutters, drains, creeks and rivers. At school and home, use bins correctly, reduce single-use plastics, pick up litter safely with adult guidance and choose waterway-safe habits when visiting coasts.

At the beach or near waterways, stay on tracks, do not collect living things from rock pools, leave shells and seaweed where they are unless local rules allow collecting, keep dogs under control where permitted, follow fishing rules and respect signs, cultural places and marine park zones. Learning about catchments, water quality and food webs can help students make careful choices.

Volunteers use reusable bags during a beach clean-up, showing how people can remove litter before it reaches the ocean.

Related fact sheets

Environments and ecosystems

• Ecosystems and environments fact sheet⁠ – Compare environments, ecosystems, producers, consumers, decomposers and food webs.
• Beach, dune and rocky shore environment fact sheet⁠ – Explore coastal places shaped by waves, tides, wind, sand and rock.
• Mangrove forest ecosystem fact sheet⁠ – Learn about tidal forests where mud, salt water, crabs, fish and birds interact.
• Coastal salt marsh ecosystem fact sheet⁠ – Discover low coastal wetlands connected to estuaries and shorebirds.
• River and creek environment fact sheet⁠ – Follow freshwater through catchments towards estuaries and the sea.
• Freshwater wetland ecosystem fact sheet⁠ – Compare freshwater wetlands with saltwater and estuary environments.

Habitats and ecological relationships

• Water habitats fact sheet⁠ – Learn how water provides food, shelter, movement and breeding places.
• Habitat fact sheet⁠ – Learn how organisms use specific places to live, feed and breed.

Learn with us