Seven species of seagrass occur in the south-east Queensland region. Extensive meadows are found in the Noosa River, Pumicestone Passage, Moreton Bay and the Gold Coast Broadwater.
Seagrass Depth Range (SDR)
Since the inception of the Ecosystem Health Monitoring Program (EHMP), the Seagrass Depth Range (SDR) of the most common species, Zostera muelleri, has been measured twice yearly at 17 sites throughout the region. SDR is a measure of the difference in height between the shallow and the deep distributional limit of Zostera muelleri. The method is based on the assumption that the shallow distributional limit is determined by the tolerance of the seagrass to desiccation at low tide, and the deep distributional limit is determined by water clarity and therefore light availability.
The SDR surveys have been an integral component of the EHMP for some time and this has provided temporal and spatial information on the changes in seagrass abundance, diversity and distribution in south-east Queensland.
Seagrass meadows in western Moreton Bay grow to shallower depths (0.5–2 m) compared to the cleaner eastern areas of the bay (2–3 m). As was the case in previous years, the seagrass meadow at Crab Island in the Eastern Bay had the deepest depth range of 3.2 m in 2006–07. This is due to the excellent water clarity in the region, resulting from low water residence times and excellent flushing with clean oceanic water.
In contrast, the depth ranges of meadows in southern Moreton Bay are variable ranging from an average of 0.7 m at Long Island and 1.5 m at Pannikin Island to 0.3 m at the mouth of Behm’s Creek. This is testimony to the fluctuating water quality conditions in the complex channels that flush that part of the bay.
Waterloo Bay, in central Moreton Bay adjacent to Manly, has four sites with a substantial variation in depth ranges that corresponds with variations observed in water clarity and water quality. The northern part of Waterloo Bay tends to catch the strong summer south-easterly winds that resuspend the sediments in the shallow waters. Additionally, northern Waterloo Bay is flushed with poor quality Brisbane River water that flows out of the Boat Passage. In response, the depth range of the meadow at Fisherman Island in the boat passage was 0.7 m in 2006–07. In contrast, the depth ranges at meadows near Wynnum and Birkdale, to the south of Waterloo Bay, have depth ranges of 1.8 m and 1.5 m respectively.
Seagrass-Watch is the largest scientific, non-destructive, seagrass assessment and monitoring program in the world. Since its genesis in Australia in 1998, Seagrass-Watch has now expanded internationally to 18 countries. Monitoring is currently occurring at over 205 sites, numerous sites exist along Queensland’s coastline.
Seagrass-Watch raises awareness on the condition and trend of near shore seagrass ecosystems and provides an early warning of major coastal environment changes. Seagrass-Watch monitoring efforts are vital to assist with tracking global patterns in seagrass health, and assessing the human impacts with potential to destroy or degrade these coastal ecosystems. Responsive management based on adequate information will help to prevent any further significant areas and species being lost. All relevant agencies must work together to protect the valuable seagrass meadows along Queensland’s coast.
Seagrass-Watch sites exist at numerous places along Queensland’s coastline.