Unpack Habitat – Seagrasses

As part of the Growing River Stewardship program OzFish, supported by the NSW Government’s Environmental Trust, is unpacking habitat in an eight-part series in which we explore key fish habitat. This week we’re looking into the hot topic of seagrasses.

 

What is seagrass?

Seagrasses are unique marine plants that have evolved over time from land plants. Seagrasses look similar to land grass however they prefer life under the water.

Seagrasses are vascular plants with stems, leaves, flowers and roots which grow down into the ocean floor so they can extract nutrients from the ground.

Seagrasses should not be confused with seaweed, which actually is a type of algae. Seaweed is multicellular algae which anchors itself to objects like rocks or wooden structures instead of putting down roots and extracts nutrients from the water around it.

Generally speaking, you’ll find seagrass in bays, estuaries and shallow coastal waters. They photosynthesize to produce energy which means that you won’t find them growing in areas of deep water where the sunlight can’t penetrate.

Seagrasses are found along both tropical and temperate coastlines of Australia, predominantly in estuaries and sheltered embayments.

Seagrass and its importance to fish

Seagrass meadows are highly diverse and productive habitats that directly and indirectly support many coastal fisheries.

Loads of our favourite fish species rely on seagrasses for at least some part of their life cycle including luderick, bream, snapper, sea mullet and leatherjackets.

They are important nursery grounds for juvenile fish, providing them with shelter from predators and strong ocean currents. Lots of invertebrates and other small fish also like to call seagrass meadows home, you’ll find plenty of crabs and calamari in and around seagrass also. In the north you’ll find seagrass homes for turtles and stingrays. Dugong’s are reliant on seagrass for food and can eat up to 40kg a day.

Seagrass meadows play an essential role in the marine food web, providing substrate for algae to grow on, detritus for marine organisms to eat, and homes for small critters to hide that larger fish like to eat.

Not only do they provide food and habitat for marine species, but seagrass meadows also deliver a wealth of other key ecosystem services that benefit fisheries and humans.

Other Seagrass benefits

Commonly referred to as Blue Carbon, seagrass meadows are more efficient per hectare at sequestering carbon than terrestrial forests, saltmarshes, grasslands and mangroves.  Only frozen tundra is more efficient.  Seagrass meadows also stabilise sand and sediment which both reduces turbidity and helps to protects our shorelines from erosion and storms. The role that seagrass has to promote general biodiversity and protect against pests and diseases is profound.  A recent study found that seagrass meadows can also remove plastics from the ocean! What’s not to love about this prime ecosystem engineer?

Fishing tips for fishing in seagrass

King George whiting commonly known as KGs are a rec species targeted on the south coast of Australia. Fleshy kind of bait often attracts the attention of KGs, ultimately cockles are your best bet. Fish for them around the edges of the white sandy holes in amongst the seagrass, often called the ‘broken bottom’.

Squid is another favourite to target, especially for beginners and young kids. Look for them on the edge of seagrass meadows because that’s where they tend to school, ready to ambush their prey.

To ensure you are leaving the seagrass in top shape and you have the best chance of a great catch, drift fish across the seagrass – never anchor in it. Around seagrass meadows it’s best to drift over the bed with a jig set up, preferably towards the back end of the boat, you want the jig to hit the bottom of the bed before starting the jigging motion. Use light sinkers with the bottom hook situated well above the sinker to keep it off the bottom, avoiding snagging in the seagrass.

What is causing seagrass decline?

Seagrasses are a fragile habitat that can be easily destroyed. Unfortunately, in parts of Australia like Western Australia we have seen a large decline in seagrass meadows since European settlement. Loss of up to 85% has been documented in Cockburn Sound, WA. This area and many other meadows have been destroyed by multiple factors, many through human impact including dredging for mining purposes, high levels of run off, some fishing practices, propellor damage from driving through meadows at low tide, algal blooms, man-made structures like jetties and pontoons that do not let enough sunlight into the meadows, and poor water quality that can create turbidity which also blocks out sunlight.

How can fishers help to take care of seagrasses?

Seagrass meadows are very delicate areas, and it is essential that we try not to disturb the habitat if we can help it. Avoid anchoring and mooring boats over the seagrass meadows and avoid driving over them at low tide, try not to walk on; take away; or dig bait up from the beds.

In some areas of Australia recently surveyed, over 85% of seagrass habitat has been lost, which is devastating for fish populations. OzFish are aiming to change things one seagrass seed at a time by undertaking vital seagrass restoration work, protecting the seagrass that remains, riparian planting in coastal areas to reduce nutrient run-off and promoting sustainable fishing habits.

More information on these projects can be found here:

Seeds for Snapper WA

Seeds for Snapper SA

Mourilyan Harbour QLD Seagrass Trial

 

 

Author – Demara Gates

Demara is currently studying at Southern Cross University completing her Marine Science and Land Management degree. She has been privileged to be accepted as an intern with OzFish. She enjoys fishing, snorkelling and getting out on her boat with family and friends around Northern Rivers in NSW.