ARE THERE CUMULATIVE EFFECTS IN RED MANGROVES FROM OIL SPILLS DURING SEEDLING AND SAPLING STAGES?

Studies of the effects of oil on coastal species seldom address multiple oilings, even though contamination of systems by more than one spill event is not uncommon. We report the results of two experiments in which first red mangrove ( Rhizophora mangle L.) seedling propagules were oiled with No. 6 fuel oil, and 34 mo later the surviving saplings were randomly assigned to new treatments and reoiled with south Louisiana crude oil in a 2 × 2 factorial design (main effects: crude oil and prior history of oiling with No. 6 oil). In Experiment 1 (No. 6 oil), there were no significant effects on seedling growth or survival at 10 mo. At 32 mo, the low‐oil group (<50% of propagule surface area covered) produced less lateral stem growth, fewer numbers of lateral stems, and fewer leaves than the control group. There were no significant effects of the high‐oil treatment (defined as >50% of surface area covered), although there was a tendency toward reduced survival. In Experiment 2 (crude × No. 6 oil), sapling survival, total stem growth, numbers of lateral stems produced, numbers of live leaves on plants, and leaf production were significantly reduced by application to the soil of 16.0 L/m 2 crude oil (the high‐crude treatment), but not by the low‐crude treatment of 1.6 L/m 2 . History of prior oiling with No. 6 fuel oil as seedlings had no effects, nor were there significant No. 6 oil × crude oil interactions. Total leaf production, maximum leaf size, numbers of yellow and brown leaves, stem diameter, and extent of main stem lignification in saplings were not significantly affected by the oil treatments. For these life history stages, oil types, and modes of oiling, there was no evidence of cumulative or synergistic effects of two oiling events on R. mangle.