THE RESPONSE OF GRAY MANGROVE (AVICENNIA-MARINA (FORSK) VIERH) SEEDLINGS TO SPILLS OF CRUDE-OIL

The effects of crude oil on grey mangrove seedlings were examined in glasshouse and field experiments. In a glasshouse experiment, fresh oil was found to cause greater leaf loss than aged oil. Fresh oil, which does not resemble oil washed into mangroves, should, therefore, not be used as a treatment in oil spill studies since it may exagerate effects. A field experiment examined the effects of weathered Bass Strait crude oil (11/m2) on seedling survival. The results were unequivocal: 96.4% of seedlings treated with weathered Bass Strait oil died within 14 days, while all untreated seedlings survived. A further field experiment also examined the effects of light, canopy gaps and Bass Strait crude oil in the sediment on propagule establishment and survival. Establishment and survival were not enhanced by light and canopy effects but crude oil in the sediment inhibited establishment and decreased the number of seedling surviving for several years. We predict the population response of a stand of Avicennia marina (Walp.) Moldenke to a series of oil spills from previous studies of population dynamics and the results of our experiments.