Marine macrophytes

Mangroves and seagrass are vital for the coastal ecosystems of NSW. However, the impact of flooding on many macrophytes was not well understood.

Aerial and satellite imagery was cross checked in the field to determine how recent floods affected mangroves and Zostera seagrass in NSW estuaries.

Mangrove dieback from the 2021 and 2022 floods was mapped across eight estuaries. About 106 ha (2.9%) of the 3,616 ha of mapped mangroves was damaged. Dieback mainly occurred in low-lying areas that experienced prolonged flooding. Grey Mangrove (Avicennia marina) experienced the most extensive dieback and showed little recovery.

Since the 2021 floods, Seagrass (Zostera muelleri) has declined in all 10 mapped estuaries. A total loss of 250 ha (41%) was recorded. In eight of the 10 estuaries, over half of the seagrass was lost. Losses ranged from a 20% reduction in the Shoalhaven River to 99% in the Richmond River. Despite its smaller percentage decline, the Shoalhaven River experienced the largest area loss at 74 ha.

As of 2026, recovery has not yet been detected. Seagrass seeds stored in the sediment were scarce across the estuaries, though a few were found in the Richmond River. This offers some hope that new plants could still establish. Further surveys and more time are needed to confirm seed numbers and to assess the potential for recovery in surveyed estuaries.