Determination of Domoic Acid in Plankton Net Samples from Golden Horn Estuary, Turkey, Using HPLC with Fluorescence Detection

Occurence and Variability of Domoic Acid in Mussel (Mytilus galloprovincialis) Samples from the Golden Horn Estuary, Sea of Marmara (Turkey)

The occurrence and variability of domoic acid (DA) levels in wild Mytilus galloprovincialis samples, compared with the Pseudo-nitzschia spp. abundance and particulate DA (pDA) concentrations in relation to the environmental changes in the Golden Horn Estuary, Turkey from October 2018 to September 2019. Biotoxin analysis were performed by high-performance liquid chromatography with diode-array detection (HPLC-DAD). DA concentrations in particulate matter (pDA) and mussel samples were found between 0.090-0.685 µg L^-1 and 0.905-2.413 µg g^-1, respectively. Accumulation of DA in wild mussel samples could be the result of the increasing tendency of P.nitzschia spp. abundances between April and May. Maximum DA levels were detected in particulate matter when the salinity was measured as the lowest in May. Thus, it can be said that the DA production was driven by the significant salinity decrease in the GHE. This is the first attempt regarding the presence of DA in M. galloprovincialis samples collected from Turkish coasts.

A Time Series of Water Column Distributions and Sinking Particle Flux of Pseudo-Nitzschia and Domoic Acid in the Santa Barbara Basin, California

Water column bulk Pseudo-nitzschia abundance and the dissolved and particulate domoic acid (DA) concentrations were measured in the Santa Barbara Basin (SBB), California from 2009–2013 and compared to bulk Pseudo-nitzschia cell abundance and DA concentrations and fluxes in sediment traps moored at 147 m and 509 m. Pseudo-nitzschia abundance throughout the study period was spatially and temporally heterogeneous (<200 cells L⁻¹ to 3.8 × 10⁶ cells L⁻¹, avg. 2 × 10⁵ ± 5 × 10⁵ cells L⁻¹) and did not correspond with upwelling conditions or the total DA (tDA) concentration, which was also spatially and temporally diverse (<1.3 ng L⁻¹ to 2.2 × 10⁵ ng L⁻¹, avg. 7.8 × 10³ ± 2.2 × 10⁴ ng L⁻¹). We hypothesize that the toxicity is likely driven in part by specific Pseudo-nitzschia species as well as bloom stage. Dissolved (dDA) and particulate (pDA) DA were significantly and positively correlated (p < 0.01) and both comprised major components of the total DA pool (pDA = 57 ± 35%, and dDA = 42 ± 35%) with substantial water column concentrations (>1000 cells L⁻¹ and tDA = 200 ng L⁻¹) measured as deep as 150 m. Our results highlight that dDA should not be ignored when examining bloom toxicity. Although water column abundance and pDA concentrations were poorly correlated with sediment trap Pseudo-nitzschia abundance and fluxes, DA toxicity is likely associated with senescent blooms that rapidly sink to the seafloor, adding another potential source of DA to benthic organisms.

Pseudo-nitzschia, Nitzschia, and domoic acid: New research since 2011

Some diatoms of the genera Pseudo-nitzschia and Nitzschia produce the neurotoxin domoic acid (DA), a compound that caused amnesic shellfish poisoning (ASP) in humans just over 30 years ago (December 1987) in eastern Canada. This review covers new information since two previous reviews in 2012. Nitzschia bizertensis was subsequently discovered to be toxigenic in Tunisian waters. The known distribution of N. navis-varingica has expanded from Vietnam to Malaysia, Indonesia, the Philippines and Australia. Furthermore, 15 new species (and one new variety) of Pseudo-nitzschia have been discovered, bringing the total to 52. Seven new species were found to produce DA, bringing the total of toxigenic species to 26. We list all Pseudo-nitzschia species, their ability to produce DA, and show their global distribution. A consequence of the extended distribution and increased number of toxigenic species worldwide is that DA is now found more pervasively in the food web, contaminating new marine organisms (especially marine mammals), affecting their physiology and disrupting ecosystems. Recent findings highlight how zooplankton grazers can induce DA production in Pseudo-nitzschia and how bacteria interact with Pseudo-nitzschia. Since 2012, new discoveries have been reported on physiological controls of Pseudo-nitzschia growth and DA production, its sexual reproduction, and infection by an oomycete parasitoid. Many advances are the result of applying molecular approaches to discovering new species, and to understanding the population genetic structure of Pseudo-nitzschia and mechanisms used to cope with iron limitation. The availability of genomes from three Pseudo-nitzschia species, coupled with a comparative transcriptomic approach, has allowed advances in our understanding of the sexual reproduction of Pseudo-nitzschia, its signaling pathways, its interactions with bacteria, and genes involved in iron and vitamin B₁₂ and B₇ metabolism. Although there have been no new confirmed cases of ASP since 1987 because of monitoring efforts, new blooms have occurred. A massive toxic Pseudo-nitzschia bloom affected the entire west coast of North America during 2015-2016, and was linked to a 'warm blob' of ocean water. Other smaller toxic blooms occurred in the Gulf of Mexico and east coast of North America. Knowledge gaps remain, including how and why DA and its isomers are produced, the world distribution of potentially toxigenic Nitzschia species, the prevalence of DA isomers, and molecular markers to discriminate between toxigenic and non-toxigenic species and to discover sexually reproducing populations in the field.