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The Presence of Pseudo-nitzschia australis in North Atlantic Aquaculture Sites, Implications for Monitoring Amnesic Shellfish Toxins - PubMed

  • ️Sun Jan 01 2023

The Presence of Pseudo-nitzschia australis in North Atlantic Aquaculture Sites, Implications for Monitoring Amnesic Shellfish Toxins

Callum Whyte et al. Toxins (Basel). 2023.

Abstract

The farming of shellfish plays an important role in providing sustainable economic growth in coastal, rural communities in Scotland and acts as an anchor industry, supporting a range of ancillary jobs in the processing, distribution and exporting industries. The Scottish Government is encouraging shellfish farmers to double their economic contribution by 2030. These farmers face numerous challenges to reach this goal, among which is the problem caused by toxin-producing microplankton that can contaminate their shellfish, leading to harvesting site closure and the recall of product. Food Standards Scotland, a non-ministerial department of the Scottish Government, carries out a monitoring programme for both the toxin-producing microplankton and the toxins in shellfish flesh, with farms being closed when official thresholds for any toxin are breached. The farm remains closed until testing for the problematic toxin alone, often diarrhetic shellfish toxin (DST), shows the site to have dropped below the regulatory threshold. While this programme has proved to be robust, questions remain regarding the other toxins that may be present at a closed site. In this study, we tested archival material collected during site closures but only tested for DSTs as part of the official control monitoring. We found the presence of amnesic shellfish toxin (AST) in low concentrations in the majority of sites tested. In one case, the level of AST breached the official threshold. This finding has implications for AST monitoring programmes around Europe.

Keywords: Dinophysis; North Atlantic; Pseudo-nitzschia australis; aquaculture; microplankton; monitoring; shellfish; toxins.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Figures

Figure 1
Figure 1

Exemplar images of P. seriata complex (A) and P. delicatissima complex (B) and an image of the two complexes side by side to give an idea of their relative sizes (C).

Figure 2
Figure 2

The location of the sites in Shetland discussed in this study.

Figure 3
Figure 3

Mean cell density of the P. delicatissima complex (dashed line) and P. seriata complex (solid line) and mean AST concentrations (grey columns), all with standard error bars, along with maximum AST concentrations (black columns), in Basta Voe Cove, Scarvar Ayre, Busta Voe Lee, Parkgate, East of Linga, Braewick Voe, Slyde, Seggi Bight, Sandsound Voe, Stream Sound, North Flotta and Burra Holm during the study period. The horizontal dashed line represents the regulatory limit for AST in shellfish flesh; i.e., 20 mg/kg.

Figure 4
Figure 4

Official control (grey columns) and additional AST testing (black columns) during the study period plotted against the Pseudo-nitzschia delicatissima complex (dashed line) and the Pseudo-nitzschia seriata complex (solid line) in Basta Voe Cove (A), Scarvar Ayre (B), Busta Voe Lee (C) and Parkgate (D).

Figure 5
Figure 5

Official control (grey columns) and additional AST testing (black columns) during the study period plotted against the Pseudo-nitzschia delicatissima complex (dashed line) and the Pseudo-nitzschia seriata complex (solid line) in East of Linga (A), Braewick Voe (B), Slyde (C) and Seggi Bight (D).

Figure 6
Figure 6

Official control (grey columns) and additional AST testing (black columns) during the study period plotted against the Pseudo-nitzschia delicatissima complex (dashed line) and the Pseudo-nitzschia seriata complex (solid line) in Sandsound Voe (A), Stream Sound (B), North Flotta (C) and Burra Holm (D).

Figure 7
Figure 7

(A) Concentration of DSTs below the regulatory limit during the study period (white columns) alongside the concentration of DSTs above the regulatory limit (grey columns) overplotted with the concentration of ASTs from both official control and additional testing (black columns) in Bunya Sand. (B) Official control (grey columns) and additional AST testing (black columns) during the study period plotted against the Pseudo-nitzschia delicatissima complex (dashed line) and the Pseudo-nitzschia seriata complex (solid line) in Bunya Sand. (C,D) Some of the scanning electron microscope (SEM) images used to identify the majority of the cells sampled from Bunya Sand. The images shown come from the same cell.

Figure 8
Figure 8

The concentrations of DSTs below the regulatory limit during the study period are indicated by the white columns in the plots. The concentrations of DSTs above the regulatory limit are shown by the grey columns. The grey columns have been overplotted with the concentrations of ASTs from both official control and additional testing, and these are shown by the black columns for Basta Voe Cove (A), Scarvar Ayre (B), Busta Voe Lee (C) and Parkgate (D).

Figure 9
Figure 9

The concentrations of DSTs below the regulatory limit during the study period are indicated by the white columns in the plots. The concentrations of DSTs above the regulatory limit are shown by the grey columns. The grey columns have been overplotted with the concentrations of ASTs from both official control and additional testing, and these are shown by the black columns for East of Linga (A), Braewick Voe (B), Slyde (C) and Seggi Bight (D).

Figure 10
Figure 10

The concentrations of DSTs below the regulatory limit during the study period are indicated by the white columns in the plots. The concentrations of DSTs above the regulatory limit are shown by the grey columns. The grey columns have been overplotted with the concentrations of ASTs from both official control and additional testing, and these are shown by the black columns for Sandsound Voe (A), Stream Sound (B), North Flotta (C) and Burra Holm (D).

Figure 11
Figure 11

Phylogenetic tree illustrating the relationships between the Pseudo-nitzschia species observed in Bunya Sand, Braewick Voe and Basta Voe Cove during the period of highest AST concentration.

Figure 12
Figure 12

Heat maps illustrating the distribution of the P. delicatissima complex (A), AST concentration (B) and the P. seriata complex (C) at each of the sites studied between weeks 24 and 45. High numbers of Pseudo-nitzschia and high concentrations of ASTs are represented by warm colours. Blue indicates that no samples were taken. From these maps, it is evident that the P. delicatissima group was prevalent around Shetland between weeks 27 and 29, while the P. seriata group appeared around week 33 and persisted for several weeks. The “hot spot” in (B) shows that the high concentration of ASTs occurred when the P. seriata group was prevalent, although (A) shows that there was also an increase in P. delicatissima at this site during the same week.

Figure 13
Figure 13

Maps (courtesy of JPL–NASA, 1 km MUR-SST) showing the progression of sea surface temperatures in degrees C (SST) around Shetland for the 4th of August (A), the 10th of August (B), the 18th of August (C), the 25th of August (D), the 2nd of September (E) and the 9th of September (F). Each map corresponds to the OCM sampling date for that week and illustrates the development of a warm water plume that engulfed Shetland in August. Panel (C) shows the SSTs coinciding with the toxic event in Bunya Sand.

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University of the Highlands and Islands Aquaculture Industry Engagement Fund (AIEF), with additional funding from the UK BBSRC/NERC project Off-Aqua (Evaluating the Environmental Conditions Required for the Development of Offshore Aquaculture)—BB/S004246/1 and the Interreg Atlantic Area Programme Project PRIMROSE (grant no. EAPA_182/2016). Sequencing of cultures was performed using funding and methods derived from the UK Seafood Innovation Fund, project: RD011 Shellfish Food Safety and Animal Health—A unified strategy for detecting multiple biological threats on a single platform.

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