Abstract
Phytoplankton play a central role in our ecosystems, they are responsible for nearly 50 percent of the global primary productivity and major drivers of macro-elemental cycles in the ocean. Phytoplankton are constantly subjected to stressors, some natural such as nutrient limitation and some manmade such as oil spills. With increasing oil exploration activities in coastal zones in the Gulf of Mexico and elsewhere, an oil spill during nutrient-limited conditions for phytoplankton growth is highly likely. We performed a multifactorial study exposing the diatom Phaeodactylum tricornutum (UTEX 646) to oil and/or dispersants under nitrogen and silica limitation as well as co-limitation of both nutrients. Our study found that treatments with nitrogen limitation (-N and-N-Si) showed overall lower growth and chlorophyll a, lower photosynthetic antennae size, lower maximum photosynthetic efficiency, lower protein in exopolymeric substance (EPS), but higher connectivity between photosystems compared to non-nitrogen limited treatments (-Si and +N+Si) in almost all the conditions with oil and/or dispersants. However, certain combinations of nutrient limitation and oil and/or dispersant differed from this trend indicating strong interactive effects. When analyzed for significant interactive effects, the-N treatment impact on cellular growth in oil and oil plus dispersant conditions; and oil and oil plus dispersant conditions on cellular growth in-N-Si and-N treatments were found to be significant. Overall, we demonstrate that nitrogen limitation can affect the oil resistant trait of P. tricornutum, and oil with and without dispersants can have interactive effects with nutrient limitation on this diatom.
Highlights
Phytoplankton, the driver of elemental cycles in the ocean (Carbon, Nitrogen, Phosphorus, Sulphur, Silica etc.), are integral to our ecosystems [1,2,3]
Treatments 9–12 include P. tricornutum grown into Si limitation combined with treatments 1–4, these treatments are termed as–Si, water accommodated fraction of oil (WAF)-Si, chemically enhanced water accommodated fraction of oil (CEWAF)-Si, and DCEWAF-Si
The growth response of P. tricornutum was determined for all the treatments (–N,Si, -N-Si, and +N+Si) in all the conditions (Control, WAF, DCEWAF and CEWAF) by calculating the percentage relative increase in cell density on Day 4 and 7 compared to Day 1 (Fig 1A and 1B respectively)
Summary
One of the objectives of this study is to understand the effects of combinations of N limitation, oil and dispersant exposure. The second objective of this study is to test this hypothesis by using a combination of oil and dispersant exposure with Si limitation. The third objective of this study is to test whether there is a synergy of negative effects between oil and/or dispersant exposure with N and/or Si limitation
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