Mercury and methylmercury incidence and bioaccumulation in plankton from the central Pacific Ocean

Abstract

Open ocean samples of phytoplankton and zooplankton were collected from the central Pacific on board the R/V Kilo Moana in October of 2011. The cruise traveled from Hawaii to Samoa, progressing through a High Nutrient Low Chlorophyll (HNLC) zone, and an equatorial upwelling region. Phytoplankton samples were size fractioned into 0.2-5 μm, 5-20 μm, and N 20 μm samples. Methylmercury concentrations were 2.91 ± 2.58 pmol g −1 (wet weight) for the overall b200 μm size fractions, and highest around the HNLC region. Phytoplankton bioconcentration factors (logBCFs) averaged to 5.69 ± 0.98 and were higher than the values found for coastal regions. Both %MeHg ([MeHg]/[Hg]) and logBCF values indicated that the lowest size fraction had the largest fraction of the HgT as MeHg, signifying enhanced accumulation of MeHg into smaller organisms. Zooplankton vertical net tows were completed from depths of 200 m up to~10 m. Zooplankton samples were analyzed for carbon, nitrogen and sulfur in addition to Hg and MeHg at size fractionations of 0.2-0.5 mm, 0.5-1.0 mm, 1.0-2.0 mm and occasionally N 2.0 mm. Zooplankton abundance and MeHg concentrations both peaked at Stations 3 and 5 (upwelling region). The %MeHg in the organisms was highest in the N2.0 mm size class, displaying MeHg bioaccumulation for increasing zooplankton sizes. Separate day and night net tows were collected at Stations 3 and 5 in order to investigate differences due to diurnal migration of zooplankton. There were higher concentrations of MeHg for all sizes in night collections of zooplankton at Station 5, but no discrepancy for Station 3. These results represent some of the few measurements of Hg and MeHg at the base of the open ocean food chain, and are significant as they represent the instigation of bioconcentration into the base of marine food webs.

Effect of Mercury Transfer from Producer to Consumer in a Marine Environment

“…g -1 revealed 84% loss, indicating a poor transfer of Hg in the zooplankton. This agreed with earlier studies [25,[33][34].…”

“…Reasons may be attributed to the influence of the metabolic rate and the assimilation of Hg from phytoplankton by zooplankton during the summer. This agreed with earlier findings [2,9,33]. During the Table 2.…”

“…l -1 test dose from that of the Hg concentrations in the naturally collected phytoplankton. Thus, low assimilation of Hg concentrations in the phytoplankton was observed and possibly found in line with the earlier observations of [29,33]. Site-wise Hg concentrations in phytoplankton were in the sequence such as the observations of Hg levels in seawater.…”

“…g -1 ) concentrations as well, plus bioaccumulation studies (30 d) using the DMA-80 [31][32][33][34]. Quality control was assured following the use of blanks, controls, and standard reference materials from BCR, IAEA, NIST, and NRC (CRM-414 phytoplankton powder), (MA-A-1/ TM copepod), (SRM:1566b oyster tissue), and (CRM: DORM-2 dogfish muscle) [35][36].…”

Spatial and taxonomic variation of mercury concentration in low trophic level fauna from the Mediterranean Sea

“…Previous studies on zooplankton have often focused on size classes or bulk collections of zooplankton (e.g. Bargagli et al 1998; Cardoso et al 2013; Gosnell and Mason 2015; Hammerschmidt et al 2013), rather than individual taxa, which could mask important trophic transfer patterns for fish or birds with specific prey preferences. Studies that have looked at Hg bioaccumulation in particular species rather than size classes have been concentrated in polar regions, particularly the Arctic (Campbell et al 2005; Foster et al 2012; Pucko et al 2014).…”