The green tide causative-species Ulva prolifera responding to exposure to oil and dispersant

In order to study the role of oil spills in the occurrence of green tide in the Yellow Sea, the physiological characteristics and photosynthetic activities of green tide causative-species Ulva prolifera was monitored under different conditions including two oil water-accommodated fractions (WAFs) of diesel oil and crude oil, dispersed water-accommodated fractions (DWAFs) and dispersant GM-2. The results showed that, the physiological parameters of U. prolifera including the growth, pigment, carbohydrate and protein contents decreased with the increased diesel oil WAF (WAFDO) concentration, while crude oil WAF (WAFCO) showed low concentration induction and high concentration inhibition effect. In addition, with the increase of WAFs concentration, two antioxidant activities were activated. However, compared with WAFDO alone and WAFCO alone, the mixture of oil and dispersant enhanced the toxicity on the above physiological characteristics of U. prolifera. On the other hand, the photosynthetic efficiency of U. prolifera showed a similar trend. Two WAFs showed significant concentration effects on the chlorophyll-a fluorescence transients and JIP-test. The addition of dispersant further blocked the electron flow beyond QA and from plastoquinone (PQ) to PSI acceptor side, damaged the active OEC centers at the PSII donor side, suppressed the pool size and the reduction rate of PSI acceptor side, and reduced the energy transfer efficiency between PSII functional units. These results implied that the crude oil spills may induce the formation of U. prolifera green tide, and the oil dispersant GM-2 used after the oil spills is unlikely to further stimulate the scale of bloom, while the diesel oil spills is always not conducive to the outbreak of green tide of U. prolifera.