|dc.description.abstract||The effects of bunker fuel oil on the growth of A. marina, B. gymnorrhiza and R.
mucronata were investigated in glasshouse and field experiments. The effects of oil on
community structure in micro-organisms were also investigated in microcosm
glasshouse experiments. The differences in oil tolerance of the three mangroves were
compared in propagule and sediment oiled treatments and growth monitored for 13
months under glasshouse conditions. In propagule oiled treatments, various portions of
the propagule were coated with oil. In the sediment oiled treatments, 50ml oil were
added to the sediment in each pot. In oiled treatments, plant height, number of leaves
and chlorophyll content were significantly reduced in all species compared to the
control. In A. marina and R. mucronata, oiling resulted in growth malformations such as
abnormal phyllotaxy and deformity of leaves and stems.
The effects of oil on root growth were investigated in rhizotrons for 245 and 409 days
respectively. In oiled treatments, root growth rate, length and volume were significantly
reduced in all species. In A. marina and B. gymnorrhiza oil increased root diameter.
In another series of experiments, PAH accumulation in roots and leaves of the three
species were determined in one year old seedlings subjected to oiling for 21 days. The
concentrations of 15 PAHs in roots and leaves were determined by gas
chromatography / mass spectrometry. The highest total concentration of PAHs was
accumulated in oiled roots of A. marina (44,045.9μg/kg), followed by B. gymnorrhiza
(10,280.4μg/kg) and R. mucronata (6,979.1μg/kg). In oiled treatments, the most
common PAHs in roots of all species were fluorene and acenaphthene (two rings),
phenanthrene and anthracene (three rings), pyrene and chrysene (four rings) and
benzo[a]pyrene (five rings). In the leaves of all species in oiled treatments, the common
PAHs were naphthalene and acenapthene (two rings) and phenanthrene (three rings).
To test for living and dead root tip cells and to compare the effects of oil on cell
ultrastructure in roots and leaves of the three species, one year old seedlings were
subjected to a control and sediment oiled treatments for seven days. Control root tips,
stained with fluorescein diacetate, exhibited green fluorescence in living cells of the
meristematic and conducting tissue in all species. Oiled root tips, stained with
propidium iodide, exhibited red fluorescence, indicating cell death or dead cells.
Transmission electron micrographs revealed that oil damaged cell ultrastructure in root
tips and leaves in all species. Anatomical changes induced by oil included,
disorganization of cells in the root cap, epidermis and meristem. Oil also induced loss
of cell contents and destruction of organelles in root tissue. Oil damaged chloroplasts
and cell organelles in spongy mesophyll and palisade cells of leaves.
To compare the effects of oil on the ability of the three species to tolerate salinity,
healthy one year old seedlings were subjected to 10% and 50% seawater in control
and sediment oiled treatments for 12 months. In the oiled treatments, 200ml oil were
added to the soil in each pot. Oil significantly reduced growth in the 50% seawater
treatment in all species. Results suggested that oil reduces salt tolerance in the three
The effects of oil on salt secretion in A. marina were investigated by subjecting one
year old seedlings to sediment oiling treatments at 0%, 10% and 50% seawater for
three weeks. Sodium accumulated in the leaves of oiled seedlings at 10% and 50%
seawater. The effects of oil on salt secretion in A. marina in the light and dark were
compared in one year old seedlings subjected to oiling treatments for seven days.
Sodium accumulated in the leaves of oiled seedlings in the light and dark within 11
hours. Oil reduced secretion rates of Na⁺, K⁺, Ca²⁺ and Mg²⁺ in all treatments.
The effects of oil on species abundance, richness and community structure of soil
micro-organisms were determined by subjecting microcosms to oiling treatments with
or without fertiliser for four weeks. In the oiled treatments, 15ml oil and 5ml/L fertiliser
were added to 200g soil. Fertiliser consisted of 4% N, 2% P and 5% K. Nematodes
were extracted after the experimental period and identified to genus or species level.
Oil significantly reduced species abundance and richness. Oil also eliminated sensitive
species and altered the abundance of dominant species thereby altering the free living
nematode community structure. Addition of fertiliser increased richness and dominant
species in oiled treatments.
The effects of oil coating on leaves and internodes on growth of the three mangroves
were investigated in field experiments for 48 weeks. Oiling of the leaves resulted in leaf
abscission and decreased leaf production in all species. The effects of sediment oiling
(at a dose of 5Lmˉ²) on the three species were also investigated in a field study for 53
weeks. In A. marina, oil caused adventitious roots to develop on the stem, about 10-15
cm above the soil surface after 38 weeks of treatment. In oiled treatments, plant
mortality occurred after 53 weeks in all three species.
The ability of B. gymnorrhiza and R. mucronata to exclude PAHs from sensitive root
tissues probably accounted for the higher oil tolerance than A. marina. The capacity of
the species to adapt to residual oil contamination by increasing root diameter (A.
marina and B. gymnorrhiza), producing adventitious roots (A. marina), increasing
root/shoot ratio (R. mucronata) and abscising oiled leaves (all species) probably
contributed to oil tolerance.||en_US