Responses of the mangroves Avicennia marina and Bruguiera gymnorrhiza to oil contamination

The effects of bunker fuel oil on morphological and physiological responses of Avicennia marina and Bruguiera gymnorrhiza were investigated in glasshouse and field experiments. In the glasshouse study, 15-month-old seedlings of A. marina were subjected to oiling or debarking treatments for 6 months. Oiling or debarking of a 5 cm ring of the basal portion of the stem, alone and in combination, reduced leaf CO₂ exchange by over 50% and resulted in the production of adventitious roots immediately above the debarked and/or oiled stem 8–12 weeks after the commencement of treatments. In the field study, sediment oiling at a single dose of 5 l m⁻² of A. marina and B. gymnorrhiza trees reduced electron transport rate (ETR) through Photosystem II (PSII) and PSII quantum yield. Oiling also reduced the photochemical efficiency of PSII (F_v/i_m) in B. gymnorrhiza, but not in A. marina. After 15 weeks of oiling, adventitious roots developed at the base of the stem in A. marina, but not in B. gymnorrhiza. Naturally occurring A. marina seedlings with adventitious roots exhibited lower leaf CO₂ exchange rates, photochemical efficiency of PSII and leaf chlorophyll content than similar seedlings without these roots. These results indicate that bunker fuel oil adversely affects photosynthetic performance of A. marina and B. gymnorrhiza mangroves. A. marina responds to oiling by producing adventitious roots at the base of the stem. Adventitious root production at the base of the stem may be a useful biological indicator of oil or other toxic pollutants in A. marina.