Abstract:
We used photosynthetic activity (measured as chlorophyll ɑ fluorescence) and photosynthetic pigment concentrations to assess
the effect of pulsed exposures of aged crude oil (Champion Crude), dispersant (VDC) and an oil + dispersant mixture on the seagrass
Zostera capricorni Aschers in laboratory and field experiments, using custom-made chambers. Samples were exposed for 10 h to
0.25% and 0.1% concentrations of aged crude oil and dispersant as well as mixtures of 0.25% oil + 0.05% dispersant and 0.1%
oil + 0.02% dispersant. During this time and for the subsequent four day recovery period, the maximum and effective quantum yields
of photosystem II (Fν/Fm and ΔF/Fm' respectively) were measured. In the laboratory experiments, both values declined in response
to oil exposure and remained low during the recovery period. Dispersant exposure caused a decline in both values during the recovery
period, while the mixture of aged crude oil + dispersant had little impact on both quantum yields. In situ samples were less
sensitive than laboratory samples, showing no photosynthetic impact due to dispersant and oil + dispersant mixture. Despite an
initial decline in ΔF/Fm', in situ oil-exposed samples recovered by the end of the experiment. Chlorophyll pigment analysis showed
only limited ongoing impact in both laboratory and field situations. This study suggests that laboratory experiments may overestimate
the ongoing impact of petrochemicals on seagrass whilst the dispersant VDC can reduce the impact of oil on seagrass
photosynthesis.
