Unfortunately, seagrasses are under threat and seagrass coverage is being lost globally at a rate of 1.5 percent per year or 2 football fields an hour. Seagrass loss occurs naturally due to storms and herbivore grazing, however much of the reduction is due to human activities.
The most widespread cause of seagrass decline is a reduction in available light through reduced water quality. Processes that reduce light penetration to seagrass include floods, enhanced suspended sediment loads, pollution and elevated nutrient concentrations. Phytoplankton and fast-growing macro algae are better competitors for light, and if their growth is accelerated by increased nutrients in the water their biomass can shade seagrass, resulting in progressive eutrophication.
In addition, coastal development reduces habitat area, anchoring and boat props and watercraft scar the seabed and uproot the seagrass (see image above), and over-fishing upsets the ecosystem balance, resulting in further seagrass decline. Pollution washed off the land may have toxic effects on seagrass species. These local and regional threats to seagrass all exist within a backdrop of global issues such as of climate change.
In recent decades there have been substantial changes in the distribution of seagrasses in SEQ. Since mapping started, there are about 2300 fewer hectares of seagrasses in the region. This is the size of over 300 Suncorp Stadiums!
Find out more here: https://ozcoasts.org.au/indicators/biophysical-indicators/changes_seagrass_area/
In some areas the distribution of seagrass meadows is highly variable from year to year, but the overall amount of seagrass remains stable. However, there are many areas where seagrasses have declined significantly, including the southern Broadwater on the Gold Coast. Please check our recent survey results here: http://watergum.org/seagrass/
Research indicates that if the amount of sediment entering South East Queensland waterways is not reduced, reduced water quality will continue to cause loss of seagrass habitat in large areas of Moreton Bay and the Broadwater. This will have a huge impact on the commercial ﬁsheries in the region and will also impact marine species, such as dugongs and sea turtles, which rely on seagrasses for their survival.