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) 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 volume of water taken up by plants) of key species and the ratio of macrophytes to macroalgae were used to develop indicators for each region following methodology developed by Murdoch University.

2023 Aquatic Plants Grades and PVI Across Regions

Upper Vasse Estuary

B

49%

21%

Lower Vasse Estuary

C

35%

17%

Lower Wonnerup

C

23%

60%

Upper Wonnerup

A

62%

MACROPHYTES

Ruppia megacarpa
Ruppia polycarpa
Stuckenia pectinata
Althenia cylindrocarpa

CHAROPHYTES

Lamprothamnium macropogon

MACROALGAE

Ulva
Rhizoclonium
Cladophora

1 Plant = 1-10% Mean PVI

Key Findings

Healthy aquatic plant communities were observed across the Vasse Wonnerup wetlands. Characteristic species were present in each region and were growing well.
Macroalgae had moderate growth across the system. The key macrophyte species grew well despite this.
Macrophyte Althenia cylindrocarpa grew in extensive meadows in the upper Vasse Estuary, with the highest PVI on record. After being uncommon since 2019, this is a great result and demonstrates resilience of the species.

The density of key aquatic plant species increased in the upper regions of both estuaries, but declined in the Lower Vasse, compared with 2022.
The charophyte Lamprothamnium macropogon grew extensively in the system in 2023, with the highest PVI on record found in the upper Vasse Estuary and throughout the Wonnerup Estuary. This species is characteristic of the Wonnerup Estuary, but usually not so common in the Vasse Estuary.