Seed predation by insects in mangrove forests in north Queensland

Field surveys of insect damage to mangrove seeds or propagules were carried out at 12 locations in north Queensland. Mangrove forests at the Escape River, Wenlock River, Claudie River, Lockhart River, McIvor River, Endeavour River, Daintree River, Missionary Bay (Hinchinbrook Island), Ross River, Alligator Creek and Haughton River were surveyed.

Data were collected on the seeds or propagules of Avicennia marina, Bruguiera exaristata, Bruguiera gymnorhiza, Bruguiera parviflora, Bruguiera sexangula, Ceriops australis, Ceriops tagal, Heritiera littoralis, Rhizophora apiculata, Rhizophora stylosa, Xylocarpus australasicus and Xylocarpus granatum. Not all species were available for sampling at every location. Sampling was carried out during the peak periods of seed or propagule fall for each species.

Random samples of between 54 and 1000 fallen seeds or propagules of available species were collected from the floor of each forest. Additional collections of seeds or propagules still attached to the parent tree were made from Ceriops tagal, Heritiera littoralis and Rhizophora stylosa.

Seeds or propagules were then assigned to one of the following damage categories: no damage; insect damage (borer holes or feeding tracks); crab damage; insect + crab damage; and other damage. The amount of damage was not recorded. Subsamples of insect damaged and undamaged seeds or propagules were collected for shadehouse experiments and to capture insects for identification.

In the shadehouse, replicate groups of damaged and undamaged seeds or propagules were grown until seedlings began to lose their first leaves. The number of surviving seedlings and height of seedlings from the soil surface were recorded. Seedlings were cleaned of sediment and the component parts (leaves, stems and roots) were separated and dried for 4 days at 80°C and weighed.