How much crude oil can zooplankton ingest? Estimating the quantity of dispersed crude oil defecated by planktonic copepods. (January 2016) - Almeda, Rodrigo
Abstract: We investigated and quantified defecation rates of crude oil by 3 species of marine planktonic copepods ( Temora turbinata, Acartia tonsa, and Parvocalanus crassirostris ) and a natural copepod assemblage after exposure to mechanically or chemically dispersed crude oil. Between 88 and 100% of the analyzed fecal pellets from three species of copepods and a natural copepod assemblage exposed for 48 h to physically or chemically dispersed light crude oil contained crude oil droplets. Crude oil droplets inside fecal pellets were smaller (median diameter: 2.4–3.5 μm) than droplets in the physically and chemically dispersed oil emulsions (median diameter: 6.6 and 8.0 μm, respectively). This suggests that copepods can reject large crude oil droplets or that crude oil droplets are broken into smaller oil droplets before or during ingestion. Depending on the species and experimental treatments, crude oil defecation rates ranged from 5.3 to 245 ng-oil copepod −1 d −1, which represent a mean weight-specific defecation rate of 0.026 μg-oil μg-Ccopepod 1 d −1 . Considering a dispersed crude oil concentration commonly found in the water column after oil spills (1 μl L −1 ) and copepod abundances in high productive coastal areas, copepods may defecate ∼1.3–2.6 mg-oil m −3 d −1, which would represent ∼0.15%–0.30% of the total dispersed oil per day. Our results indicate that ingestion and subsequent defecation of crude oil by planktonic copepods has a small influence on the overall mass of oil spills in the short term, but may be quantitatively important in the flux of oil from surface water to sediments and in the transfer of low-solubility, toxic petroleum hydrocarbons into food webs after crude oil spills in the sea. Graphical abstract: Highlights: Copepods exposed to dispersed crude oil produced fecal pellets contained numerous small oil droplets (2.4 to 3.5 µm). Copepods could reject large oil droplets or oil droplets are broken into smaller droplets before or during ingestion. Ingestion and defecation of oil by copepods has a small influence on the overall mass of oil spills in the short term oil-containing fecal pellets may be a major vector in the vertical flux of petroleum pollution. Abstract : Fecal pellets of copepods exposed to dispersed crude oil contained numerous oil droplets, which represented oil defecation rates ranged from 5.3 to 245 ng-oil copepod −1 d −1 .