Mangroves 4: Mangrove as Resource

MANGROVES 4: Mangrove as Resource

Casting net for fish, Ludmilla Creek (Bo)

The mangrove habitat is a refuge for many types of marine life during various stages of their development. The tangled growth of the Rhizophora roots offer a haven from predators and the warm nutrient laden waters provide an ideal environment for young organisms. As an example of the efficiency of natural ecosystems, mangroves are worthy of our interest and attention. However, there is a much more convincing argument for regarding the mangroves as being of some value. They are a habitat for some species of prawns in the early stages of growth and earnings from prawns in the NT were about $67 million in 1999 (latest available data). The value of the annual catch is fairly variable and seems to be in part determined by the rainfall in the wet season.

Life cycle of a penaeid prawn, showing dependence on mangroves during the cycle.

Besides prawns, the mangrove and freshwater wetland habitats are home to other forms of marine life of economic importance. The mangroves and wetlands play an essential role in the life cycle of Barramundi (Lates calcarifer), with the larval forms living and feeding in the coastal wetlands. Commercially, in 1999 the barramundi fishery in the NT was worth about $4.4 million, and more if the value of the recreational fishery was included. The Threadfin Salmon () fishery netted $0.5 million the same year. Mud Crabs (Scylla serrata) also use the mangroves during their life cycle and the value of this industry was $9.6 million in 1999. 

Saltwater Crocodiles (Crocodylus porosus) are other animals which depend on the wetlands for breeding, and move between fresh and salt water environments and include the brackish mangrove habitats. Females lay their eggs in the wet season on the edge of the freshwater floodplains. Numerous farms have been set up to raise crocodiles in captivity, now a multi-million dollar industry. The farms depend on eggs taken from the wild as a supply of young crocodiles; the eggs are incubated and this results in much higher survival rates than in wild populations.

It would therefore seem essential that the social and financial benefits of any development projects, involving the loss of even the smallest area of mangroves should be weighed against the continued monetary value of the mangroves as a natural resource.