Aerial view of seagrasses show signs of hope
WE DON’T ever hear much about seagrass, a natural grass like aquatic growth which occurs in shallow waters up to a little more than 1 metre deep. Perhaps it’s best known as the food that Dugongs graze on as they swim along the sea floor.
The seagrass beds in the Noosa River estuary do not attract much attention by either locals or visitors, but they are critical food and shelter resources for the young fish and crabs that people get more excited about.
So it makes sense to monitor the health and extent of these complex ecological features of the waterway, because their decline would indicate our failure to maintain the health of the river and its catchment.
Conventional seagrass monitoring was conducted for several years by NICA volunteers as part of a national Seagrass Watch program conducted by SeagrassWatch, an organisation based in Townsville. Unfortunately funding for this activity was terminated in 2015 due to the dwindling number of volunteers qualified to undertake the work. At that time a very detailed and time consuming technique required staff to identify and count individual grasses growing in selected 1m x 1m patches, and then tally the results for a whole area.
In 2017 a grant from the Wettenhall Foundation enabled NICA to run a trial to see if drones could be used to monitor the health and extent of seagrass beds in the Noosa estuary. This work was carried out by Dr Javier Leon of Sunshine Coast University, who was able to obtain high-resolution images of local seagrass beds. He also produced a detailed manual for the procedures needed to produce accurate maps from the image data, and gave some NICA members basic lessons in drone operation.
At the end of the trial, it was felt that volunteers would be unlikely to achieve the skills in drone operation and image manipulation that were needed to produce maps like those assembled by Dr Leon. The technique, with some modifications, would, however have great potential for enabling efficient seagrass monitoring.
Applications of drones to field observation have been developing at a furious pace, and recently interest by a private drone operator has suggested that a simplified design of image analysis might enable seagrass monitoring in the Noosa estuary to continue in a modest but valuable way.
The photographs show images of Weyba Creek estuary taken by drone at an altitude of 50m. The most recent one on the left, taken on August 31 this year, can be compared with the one on the right which was taken on September 17, 2017.
There has been an obvious increase in extent of the seagrass bed margins in two years, as well as a densification of the growth, a very desirable outcome for fish life in the river.
NICA plans to seek funding to enable this research to be developed into a routine tool for monitoring of river quality, and welcomes any input and suggestions to assist such a program.