Osmotrophy of dissolved organic compounds by coccolithophore populations: Fixation into particulate organic and inorganic carbon.

Coccolithophores are typically thought of as photoautotrophs, yet a few genera inhabit sub-euphotic environments with insufficient light for photosynthesis, suggesting that other carbon acquisition strategies are likely. Field experiments were performed in the northwest Atlantic (a region with potentially abundant coccolithophores). Phytoplankton populations were incubated with 14C-labeled dissolved organic carbon (DOC) compounds, acetate, mannitol, and glycerol. Coccolithophores were sorted from these populations 24 hours later using flow cytometry, and DOC uptake was measured. DOC uptake rates were as high as 10-15 moles cell-1 day-1, slow relative to photosynthesis rates (10-12 moles cell-1 day-1). Growth rates on the organic compounds were low, suggesting that osmotrophy plays more of a survival strategy in low-light situations. Assimilated DOC was found in both particulate organic carbon and calcite coccoliths (particulate inorganic carbon), suggesting that osmotrophic uptake of DOC into coccolithophore calcite is a small but notable part of the biological carbon pump and alkalinity pump paradigms.

Dihydrodinophysistoxin-1 Produced by Dinophysis norvegica in the Gulf of Maine, USA and Its Accumulation in Shellfish.

Dihydrodinophysistoxin-1 (dihydro-DTX1, (M-H)-m/z 819.5), described previously from a marine sponge but never identified as to its biological source or described in shellfish, was detected in multiple species of commercial shellfish collected from the central coast of the Gulf of Maine, USA in 2016 and in 2018 during blooms of the dinoflagellate Dinophysis norvegica. Toxin screening by protein phosphatase inhibition (PPIA) first detected the presence of diarrhetic shellfish poisoning-like bioactivity; however, confirmatory analysis using liquid chromatography-tandem mass spectrometry (LC-MS/MS) failed to detect okadaic acid (OA, (M-H)-m/z 803.5), dinophysistoxin-1 (DTX1, (M-H)-m/z 817.5), or dinophysistoxin-2 (DTX2, (M-H)-m/z 803.5) in samples collected during the bloom. Bioactivity-guided fractionation followed by liquid chromatography-high resolution mass spectrometry (LC-HRMS) tentatively identified dihydro-DTX1 in the PPIA active fraction. LC-MS/MS measurements showed an absence of OA, DTX1, and DTX2, but confirmed the presence of dihydro-DTX1 in shellfish during blooms of D. norvegica in both years, with results correlating well with PPIA testing. Two laboratory cultures of D. norvegica isolated from the 2018 bloom were found to produce dihydro-DTX1 as the sole DSP toxin, confirming the source of this compound in shellfish. Estimated concentrations of dihydro-DTX1 were >0.16 ppm in multiple shellfish species (max. 1.1 ppm) during the blooms in 2016 and 2018. Assuming an equivalent potency and molar response to DTX1, the authority initiated precautionary shellfish harvesting closures in both years. To date, no illnesses have been associated with the presence of dihydro-DTX1 in shellfish in the Gulf of Maine region and studies are underway to determine the potency of this new toxin relative to the currently regulated DSP toxins in order to develop appropriate management guidance.

Non-dioxin like polychlorinated biphenyl indicator congeners in Northwest Atlantic spiny dogfish (Squalus acanthias).

In the Northwest Atlantic Ocean (NWAO), spiny dogfish (Squalus acanthias) is a promising commercial species following of collapse of traditional groundfish stocks. There are little available data assessing polychlorinated biphenyls (PCBs) in NWAO spiny dogfish. Here, six non-dioxin like PCB indicator congeners used in European Union regulations (EU NDL-PCB) were quantified via gas chromatography/mass spectrometry in 50 mature male spiny dogfish landed in southern New England. The average total concentration of EU NDL-PCBs was 58±43ng/g (mean±1 standard deviation). PCB values (corrected for co-elution) were below the 200ng/g EU regulatory limit. Results provide first recent regional insight into the PCB content of spiny dogfish in the NWAO. However, our study offers only a snapshot of one particular dogfish population, and might not be representative for the whole NWAO. This study underscores the need for further testing in this species.

The role of a PSP-producing Alexandrium bloom in an unprecedented diamondback terrapin (Malaclemys terrapin) mortality event in Flanders Bay, New York, USA.

Diamondback terrapins (Malaclemys terrapin) are a threatened or endangered species in much of their range along the U.S. Atlantic and Gulf coasts. Over an approximately three-week period from late April to mid-May 2015, hundreds of adult diamondback terrapins were found dead on the shores of Flanders Bay, Long Island, New York, USA. Concurrent with the mortality event, elevated densities of the paralytic shellfish toxin (PST)-producing dinoflagellate, Alexandrium fundyense (>104 cells L-1) and high levels of PST in bivalves (maximal levels = 540 µg STX eq. 100 g-1 shellfish tissue) were observed in the Flanders Bay region, resulting in shellfish bed closures in regional tributaries. Gross and histologic postmortem examinations of terrapins revealed no physical trauma to individuals or a common, underlying disease process to explain the deaths. PST compounds (0.2-12.5 µg STX eq. 100 g-1) were present in various M. terrapin tissues collected over the duration of the mortality event. High-throughput sequencing revealed that the ribbed mussel (Geukensia demissa, a PST vector) was present in the gastrointestinal tracks of all terrapin samples tested. While the potential of PST to cause mortality in chelonians has not been well-characterized, in the absence of other significant findings from necropsies and pathological analyses, we provide evidence that PST in shellfish was likely high enough to cause or contribute to the mortality in these small (<2.0 kg) animals.