Co-occurrence of marine and freshwater phycotoxins in oysters, and analysis of possible predictors for management

Abstract

Oysters (Crassostrea virginica) were screened for 12 phycotoxins over two years in nearshore waters to collect baseline phycotoxin data and to determine prevalence of phycotoxin co-occurrence in the commercially and ecologically-relevant species. Trace to low concentrations of azaspiracid-1 and -2 (AZA1, AZA2), domoic acid (DA), okadaic acid (OA), and dinophysistoxin-1 (DTX1) were detected, orders of magnitude below seafood safety action levels. Microcystins (MCs), MC-RR and MC-YR, were also found in oysters (maximum: 7.12 μg MC-RR/kg shellfish meat wet weight), warranting consideration of developing action levels for freshwater phycotoxins in marine shellfish. Oysters contained phycotoxins that impair shellfish health: karlotoxin1-1 and 1-3 (KmTx1-1, KmTx1-3), goniodomin A (GDA), and pectenotoxin-2 (PTX2). Co-occurrence of phycotoxins in oysters was common (54%, n = 81). AZAs and DA co-occurred most frequently of the phycotoxins investigated that are a concern for human health (n = 13) and PTX2 and KmTxs co-occurred most frequently amongst the phycotoxins of concern for shellfish health (n = 9). Various harmful algal bloom (HAB) monitoring methods and tools were assessed for their effectiveness at indicating levels of phycotoxins in oysters. These included co-deployed solid phase adsorption toxin tracking (SPATT) devices, toxin levels in particulate organic matter (POM, >1.5 μm) and whole water samples and cell concentrations from water samples as determined by microscopy and quantitative real-time PCR (qPCR). The dominant phycotoxin varied between SPATTs and all other phycotoxin sample types, and out of the 11 phycotoxins detected in oysters, only four and seven were detected in POM and whole water respectively, indicating phycotoxin profile mismatch between ecosystem compartments. Nevertheless, there were correlations between DA in oysters and whole water (simple linear regression [LR]: R² = 0.6, p < 0.0001, n = 40), and PTX2 in oysters and SPATTs (LR: R² = 0.3, p = 0.001, n = 36), providing additional monitoring tools for these phycotoxins, but oyster samples remain the best overall indicators of seafood safety.

Keywords: Azaspiracid; Domoic acid; Karlotoxin; Microcystin; Okadaic acid; Pectenotoxin.

Graphical abstract

Fig. 1

Locations of the five sampling stations in the lower Chesapeake Bay, Virginia, USA: station 2 Rappahannock, station 4 York River, station 6 Lynnhaven Inlet, station 9 Cherrystone Inlet, and station 10 Wise Point.

Fig. 2

Prevalence of each phycotoxin detected in oyster samples (n = 81); i.e., for each phycotoxin, the percentage of oyster samples that it was detected in, in an amount greater than the limit of detection (LOD) for that phycotoxin. Microcystin-LR was not detected in oysters. Extracts underwent alkaline hydrolysis, and therefore, okadaic acid (OA) and dinophysistoxin-1 (DTX1) concentrations represent esterified and free toxins combined. AZA1 = azaspiracid-1, AZA2 = azaspiracid-2, AZAs = azaspiracids, DA = domoic acid, MC-RR = microcystin-RR, MC-YR = microcystin-YR, MCs = microcystins, PTX2 = pectenotoxin-2, GDA = goniodomin A, KmTx1-1 = karlotoxin1-1, KmTx1-3 = karlotoxin1-3, KmTxs = karlotoxins.

Fig. 3

Oyster phycotoxin data (μg/kg shellfish meat [SM] w. w.) for azaspiracid-1 and -2 (AZA1 and AZA2, respectively) across five stations from January to June 2019 and from March to August 2020. Station 9 was only sampled in 2019 and station 10 was only sampled in 2020. Hollow circles are below the limit of quantitation (

Fig. 4

Oyster phycotoxin data (mg/kg shellfish meat [SM] w. w.) for domoic acid (DA) across five stations from January to June 2019 and from March to August 2020. Station 9 was only sampled in 2019 and station 10 was only sampled in 2020. Hollow circles are below the limit of quantitation (

Fig. 5

Oyster phycotoxin data (μg/kg shellfish meat [SM] w. w.) for microcystin-RR and -YR (MC-RR and MC-YR, respectively) across five stations from January to June 2019 and from March to August 2020. Microcystin-LR was not detected in oysters. Station 9 was only sampled in 2019 and station 10 was only sampled in 2020. Hollow circles are below the limit of quantitation (

Fig. 6

Oyster phycotoxin data (μg/kg shellfish meat [SM] w. w.) for diarrhetic shellfish toxins (DSTs) okadaic acid and dinophysistoxin-1 (OA and DTX1, respectively) as determined using alkaline hydrolysis, across five stations from January to June 2019 and from March to August 2020. Station 9 was only sampled in 2019 and station 10 was only sampled in 2020. Hollow circles are below the limit of quantitation (

Fig. 7

Oyster phycotoxin data (μg/kg shellfish meat [SM] w. w.) for pectenotoxin-2 (PTX2) across five stations from January to June 2019 and from March to August 2020. Station 9 was only sampled in 2019 and station 10 was only sampled in 2020. Hollow circles are below the limit of quantitation (

Fig. 8

Oyster phycotoxin data (mg/kg shellfish meat [SM] w. w.) for goniodomin A (GDA) across five stations from January to June 2019 and from March to August 2020. Station 9 was only sampled in 2019 and station 10 was only sampled in 2020. Hollow circles are below the limit of quantitation (

Fig. 9

Oyster phycotoxin presence/absence data for karlotoxin1-1 and -3 (KmTx1-1 and KmTx1-3, respectively) across five stations from January to June 2019 and from March to August 2020. Station 9 was only sampled in 2019 and station 10 was only sampled in 2020. Phycotoxin presence is denoted by hollow circles; phycotoxin absence is denoted by plus signs (+).

Fig. 10

Comparison of phycotoxin profiles within oyster, solid phase adsorption toxin tracking devices (SPATTs), particulate organic matter (POM, > 1.5 µm), and whole water across four stations for all 2019 sampling dates (n = 40-44). Proportions were calculated by summing the concentrations of a phycotoxin group across all 2019 samples and then dividing by the total concentration of all phycotoxins detected across all 2019 samples of that sample type. Karlotoxins (KmTxs) were not included as they were not quantified in this study, however, KmTxs were present in oysters and whole water samples, and absent from SPATTs and POM samples. AZAs = azaspiracids, DA = domoic acid, MCs = microcystins, DSTs = diarrhetic shellfish toxins (okadaic acid and dinophysistoxin-1), PTX2 = pectenotoxin-2, GDA = goniodomin A.