Key environmental pressures
Overall, environmental pressures affecting inshore seagrass meadows were low to negligible in 2020-21.
There was limited cyclone impact on the inshore areas of Reef, and rainfall and river discharge were close to the long-term average. Inshore seagrass sites were exposed to visually ‘brown’ or ‘green’ waters during many weeks of the wet season (December-April) but at a lower frequency than in recent years.
How did inshore seagrass meadows respond?
- Inshore seagrass meadows findings:
- Inshore seagrass meadow condition improved slightly in 2020-21 from the previous year, with the condition grade increasing from poor to moderate. However, trends were not uniform across the Reef.
- Condition improved to a moderate grade in the northern regions (Cape York, Wet Tropics, and Burdekin), while conditions in the southern regions (Mackay-Whitsundays, Fitzroy, and Burnett-Mary) remained poor.
- Substantial decrease in seagrass abundance was observed in the Mackay-Whitsundays and Fitzroy regions, where meadow extent remains low and highly fragmented. This condition is likely a legacy of recent impacts such as Tropical cyclone Debbie in 2017 and localised disturbances.
- Resilience improved, and critical thresholds were exceeded in the majority of sites surveyed. Specifically, most sites showed reproductive structures or recent history (less than three years) of reproduction.
- Signs of recovery were observed such as: (1) decreasing or stable proportion of colonising species in favour of foundational species, (2) increasing or stable meadow extent in most sites, culminating in the greatest meadow extent in the last three years, (3) increasing seed banks at coastal habitats, and (4) reduced epiphyte cover across all habitats.
What is monitored and where?
Inshore seagrass meadows are monitored in four types of habitats: estuarine, coastal intertidal and subtidal, and reef intertidal.
- Two main indicators are assessed:
- seagrass abundance (per cent cover)
- resilience (resistance and recovery potential – full details of the resilience metric can be found in the Resilience in practice report)
- In addition to these indicators, seagrass species, the size and patchiness of the seagrass meadows, and the density of seeds in the seed bank are also assessed. Factors that can affect seagrass condition are recorded, which include within-canopy seawater temperature, the amount of light reaching the plants, the sediment characteristics, and the abundance of macroalgae and epiphytes.
Six regions are included in the sampling design: Cape York, Wet Tropics, Burdekin, Mackay-Whitsundays, Fitzroy, and Burnett-Mary.