Throughout 2007, the project, with the assistance of community volunteers, undertook regular monitoring of seagrass diversity and density at three intertidal sites adjacent to the Broome town site. Project outcomes will help to identify sources of threats to the seagrass meadows and to inform key organizations and departments of management priorities.

A recent announcement by Envirofund, granting further funding, has confirmed that the project will continue in 2008/2009. This phase of the project has committed to ongoing monitoring and a number of educational talks, promoting community awareness and understanding.

Environs Kimberley thanks Coastwest, Envirofund, the Department of Environment and Conservation and Seagrass-Watch for their support.

The Broome community and associated industries are growing at an unprecedented rate. The impact of this growth on the world renowned, Ramsar listed Roebuck Bay is of considerable concern to Environs Kimberley.

Roebuck Bay supports a myriad of marine life, many of which are adapted to long periods of exposure in the region’s massive tidal range. Furthermore, innumerable wader and shore birds utilize the abundance of available food to ‘feed-up’ before and after migrating extraordinary distances. Threatened species including dugongs and green turtles also frequent the Bay.

To date, the northern section of Roebuck Bay has been the focus of seagrass research (much due to logistical reasons) however, it is hoped that the scope of research and monitoring will eventually encompass a much larger area of the Bay.

Nudibranch in Roebuck Bay, Broome.

Seagrass ecology
Seagrass is a marine plant that grows similarly to grass in that it requires sunlight for photosynthesis (the process by which a plant uses sunlight, water and carbon dioxide to produce energy for growth). Hence the growth of all species is limited by available light. Seagrass is most commonly found in shallow areas, such as coastal, reef and estuarine environments, where light is accessible. In some areas however, such as in the deep clear waters between mainland and coral reef, seagrass may be found to depths of up to 60 metres.

MORE : Seagrass Project poster (pdf 320kb)

Dugong Trail

A valuable resource
It is commonly acknowledged that seagrass is essential for maintaining healthy and productive marine ecosystems. With the exception of dugongs and green turtles, which feed almost exclusively on seagrass leaves and roots, few animals feed directly on the seagrass. However, the detritus formed during the breakdown of seagrass forms the basis of a complex food chain which starts with minute marine creatures and ends at the top of the food chain with large sharks. Seagrass leaves also support the growth of epiphytes (filamentous algae) which are fed upon by marine creatures, including juvenile fish species.

For many juvenile fish and crustaceans the seagrass is a nursery, providing food to sustain them and shelter from predators, currents and waves. The recreational and commercial fishing industries owe a lot to seagrass. In many instances seagrass is responsible for raising the next generation of commercially significant fish and crustacean species.

Seagrass is also beneficial to the structure of our coastline. It eases the impact of waves and currents, reducing erosion and the movement of sediment. Moreover, seagrass helps to filter nutrients entering the marine ecosystem.

MORE: An Essential Ecosystem poster (pdf 315kb)

TOP

Seed monitoring in Roebuck Bay.

Under pressure
Across the world, the impacts of urban and rural development on seagrass meadows has prompted investigation by numerous groups including the Queensland based, Seagrass-Watch (www.seagrasswatch.org). By adopting the monitoring protocols and objectives of Seagrass-Watch, the Broome community has joined over 200 other locations world-wide who have implemented Seagrass-Watch monitoring systems. The Project continues to receive support and guidance from Seagrass-Watch. This ensures consistency in our methods and produces data which is comparable and statistically robust.

During 2007, three locations in Roebuck Bay were monitored every two months. Data taken from strategically located monitoring quadrats included seagrass species, percentage cover, fauna presence and algal and epiphyte cover. This data will help us understand ecological trends in the seagrass meadows and therefore help us to recognize when this ecosystem is facing undue pressure. Seed monitoring was also initiated during 2007. Information about seed density is used to predict the capacity of seagrass to recover from acute impacts.

MORE : Seagrass Under Pressure poster (pdf 321kb)

Seagrass Broome November, 2007.

The primary threats facing the seagrass meadows in Roebuck Bay come from increased turbidity (suspended sediments) and excessive nutrients. Storm water run-off, land clearing, bushfires, urban run-off, ship groundings, boating, dredging and over grazing can all contribute to the excessive amounts of sediment entering the water ways. Unnaturally high levels of sediment obscure the light available to the seagrass.  Natural events such as storms and cyclones can also increase turbidity and damage seagrass meadows by smothering them or uprooting them. Predictions of more intensive tropical storms associated with global warming suggest that such impacts are likely to be more frequent and more severe.

Nutrient rich run-off from gardens, sewerage and industrial and agricultural areas prompt algal blooms which smother seagrass meadows. One algae species in particular, Lyngbya majuscula, has in recent years formed large dense mats which have impacted upon the health of local seagrass meadows. The Department of Environment and Conservation, in conjunction with the Seagrass Project, has been monitoring the seasonal spread of Lyngbya and have helped to coordinate research to understand what is prompting the seasonal outbreaks. 

Environs Kimberley is looking forward to commencing the next stage of the project. In addition to continuing regular monitoring, the project will expand to include sub-tidal monitoring and intensive community exposure with numerous educational talks planned. The project always welcomes new volunteers. Please call Environs Kimberley for more details.

TOP

© Environs Kimberley