Fate and effects of oil and dispersed oil
on mangrove ecosystems in Australia


In planthouse studies, five oils and their dispersed mixtures, using four dispersants, were applied to four species of mangrove seedlings grown in specially constructed tidal tanks.

There was significant mortality of seedlings with levels of mortality dependent on oil type The response of seedlings was monitored for around five months. During this time, there was significant mortality of seedlings with levels of mortality dependent on oil type, dispersed oil, species, and sediment type. Oils were ranked by increasing toxicity: Bunker C fuel oil < Arabian Light crude < Gippsland Light crude < Thevenard crude < Woodside condensate.
Dispersed-oils caused slight to significant reduction in seedling mortality compared with un-dispersed oil treatments. Dispersants, used with selected oils, were ranked by their increasing effect on mortality: Corexit 9580 > Corexit 9527 > Shell VDC > BP-AB. Species were ranked by increased sensitivity to oils:Ceriopsspp. <Rhizophora stylosa < Avicennia marina < Aegiceras corniculatum.Sediment types were ranked by increasing vulnerability for damage toRhizophora stylosaseedlings as mud < sand. By contrast, sediment type was less important forAvicennia marinathan forRhizophora stylosa.
Plate 4a, b, c, d.Planthouse studies were used to determine short term effects of oiling on potted mangrove seedlings. Propagules were collected from four species of mangrove species commonly found in Australia, includingAvicennia marina, Rhizophora stylosa, Ceriops tagalandAegiceras corniculatum.

A. Two sediment types were used in these experiments, including sand and mangrove mud. Mud was collected from local mangrove areas and kept moist until placed into pots.

B.Individual seedlings were planted in pots.
C.Around 60 potted seedlings of different species and sediment types were placed into troughs which were flooded over pots but below foliage for about two hours each day and be drained between times.
D.Twenty-one independent tidal systems were housed in a planthouse under 70% ambient light conditions. Each tidal system had similar salinity and nutrient conditions, and tank water was refreshed each three months during the 18 months of study.

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April 7, 2010