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Aquatic Plants Report Card

Aquatic Plants

Macroinvertebrates

Black Bream

Waterbirds

Fish Kills

Water Quality

Aquatic plants are critical to the Vasse Wonnerup wetlands providing food and habitat, oxygenating the water, using nutrients, and stabilising sediments. Aquatic plants include macrophytes (seagrasses and submerged plants), charophytes (plant-like algae) and macroalgae (seaweeds and filamentous algae). Macrophyte dominant communities indicate a healthy system, while high densities of macroalgae can inhibit the growth of key species and may indicate a poor ecological state.

Aquatic plant monitoring occurs across four regions in the wetlands in spring when maximum biomass and diversity is present. Percentage Volume Inhabited (PVI; the percentage of water volume occupied by plant material) of key species and the ratio of macrophytes to macroalgae were used to develop indicators for each region following methodology developed by Murdoch University.

2024 Aquatic Plants Grades and PVI Across Regions

Upper Vasse Estuary

A

Lower Vasse Estuary

B

Upper Wonnerup Estuary

A

Lower Wonnerup Estuary

B

MACROPHYTES

Ruppia megacarpa
Ruppia polycarpa
Stuckenia pectinata
Althenia cylindrocarpa

CHAROPHYTES

Lamprothamnium macropogon

MACROALGAE

Ulva
Rhizoclonium
Cladophora

1 Plant = 1-10% Mean PVI; small plant <5%

PVI = percent volume inhabited, which is a measure of the percentage of water volume occupied by plant material

Key Findings 2024

Very healthy aquatic plant communities were observed across the Vasse Wonnerup wetlands. The system shows strong signs of resilience, with consistent dominance of macrophytes and charophytes across all ecological regions.
Characteristic species were found in all regions, with high density in the lower regions of both estuaries, and very high density in the upper regions.
Macrophytes Ruppia spp. and Stuckenia pectinata dominated in the Upper and Lower Vasse regions respectively, with Althenia cylindrocarpa and charophyte Lamprothamnium macropogon also recording high densities in the Upper Vasse.

Macroalgal density was low for the system, indicating good ecosystem health and was lower than in 2023 throughout all regions, although it remained at moderate levels in the Lower Vasse. Ulva spp. was the only taxa of macroalgae found in all regions in 2024.
The charophyte L. macropogon remained dominant throughout the Wonnerup Estuary. Although the density was lower in the Upper region than in 2023, this was likely due to increased water depth. The Lower region returned to dominance by Ruppia megacarpa, suggesting a shift back to a more typical community structure following the unusual dominance of L. macropogon observed in 2023.