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PLANTHOUSE
TRIALS ON SEEDLINGS |
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.
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There was significant mortality of
seedlings with levels of mortality dependent on oil type
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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.
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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: Ceriops spp. <
Rhizophora stylosa < Avicennia marina < Aegiceras corniculatum.
Sediment types were ranked by increasing vulnerability for damage to
Rhizophora stylosa seedlings as mud < sand. By contrast, sediment type
was less important for Avicennia marina than for Rhizophora
stylosa.
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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, including
Avicennia marina, Rhizophora stylosa, Ceriops tagal and Aegiceras
corniculatum.
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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.
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B. Individual seedlings were planted
in pots.
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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.
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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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