Integrative monitoring strategy for marine and freshwater harmful algal blooms and toxins across the freshwater-to-marine continuum

Microcystins in the benthic food-web of the Sacramento-San Joaquin Delta, California

Harmful cyanobacteria blooms are a growing threat in estuarine waters as upstream blooms are exported into coastal environments. Cyanobacteria can produce potent toxins, one of which-hepatotoxic microcystins (MCs)-can persist and accumulate within the food web. Filter-feeding invertebrates may biomagnify toxins up to 100× ambient concentrations. As such, bivalves can be used as an environmentally relevant and highly sensitive sentinel for MC monitoring. To date there has been little research on cyanotoxin bioaccumulation in estuaries. The Sacramento-San Joaquin Delta (Delta) aquatic food web has undergone a profound change in response to widespread colonization of aquatic invasive species such as Asian clams (Corbicula fluminea) in the freshwater portion of the Delta. These clams are prolific-blanketing areas of the Delta at densities up to 1000 clams/m2 and are directly implicated in the pelagic organism decline of threatened and endangered fishes. We hypothesized that Asian clams accumulate MCs which may act as an additional stressor to the food web and MCs would seasonally be in exceedance of public health advisory levels. MCs accumulation in Delta Asian clams and signal crayfish (Pacifastacus leniusculus) were studied over a two-year period. ELISA and LC-MS analytical methods were used to measure free and protein-bound MCs in clam and crayfish tissues. We describe an improved MC extraction method for use when analyzing these taxa by LC-MS. MCs were found to accumulate in Asian clams across all months and at all study sites, with seasonal maxima occurring during the summer. Although MC concentrations rarely exceeded public health advisory levels, the persistence of MCs year-round still poses a chronic risk to consumers. Crayfish at times also accumulated high concentrations of MCs. Our results highlight the utility of shellfish as sentinel organisms for monitoring in estuarine areas.

Does climate change increase the risk of marine toxins? Insights from changing seawater conditions

Marine toxins produced by marine organisms threaten human health and impose a heavy public health burden on coastal countries. Lately, there has been an emergence of marine toxins in regions that were previously unaffected, and it is believed that climate change may be a significant factor. This paper systematically summarizes the impact of climate change on the risk of marine toxins in terms of changes in seawater conditions. From our findings, climate change can cause ocean warming, acidification, stratification, and sea-level rise. These climatic events can alter the surface temperature, salinity, pH, and nutrient conditions of seawater, which may promote the growth of various algae and bacteria, facilitating the production of marine toxins. On the other hand, climate change may expand the living ranges of marine organisms (such as algae, bacteria, and fish), thereby exacerbating the production and spread of marine toxins. In addition, the sources, distribution, and toxicity of ciguatoxin, tetrodotoxin, cyclic imines, and microcystin were described to improve public awareness of these emerging marine toxins. Looking ahead, developing interdisciplinary cooperation, strengthening monitoring of emerging marine toxins, and exploring more novel approaches are essential to better address the risks of marine toxins posed by climate change. Altogether, the interrelationships between climate, marine ecology, and marine toxins were analyzed in this study, providing a theoretical basis for preventing and managing future health risks from marine toxins.

Understanding the risks of co-exposures in a changing world: a case study of dual monitoring of the biotoxin domoic acid and Vibrio spp. in Pacific oyster

Assessing the co-occurrence of multiple health risk factors in coastal ecosystems is challenging due to the complexity of multi-factor interactions and limited availability of simultaneously collected data. Understanding co-occurrence is particularly important for risk factors that may be associated with, or occur in similar environmental conditions. In marine ecosystems, the co-occurrence of harmful algal bloom toxins and bacterial pathogens within the genus Vibrio may impact both ecosystem and human health. This study examined the co-occurrence of Vibrio spp. and domoic acid (DA) produced by the harmful algae Pseudo-nitzschia by (1) analyzing existing California Department of Public Health monitoring data for V. parahaemolyticus and DA in oysters; and (2) conducting a 1-year seasonal monitoring of these risk factors across two Southern California embayments. Existing public health monitoring efforts in the state were robust for individual risk factors; however, it was difficult to evaluate the co-occurrence of these risk factors in oysters due to low number of co-monitoring instances between 2015 and 2020. Seasonal co-monitoring of DA and Vibrio spp. (V. vulnificus or V. parahaemolyticus) at two embayments revealed the co-occurrence of these health risk factors in 35% of sampled oysters in most seasons. Interestingly, both the overall detection frequency and co-occurrence of these risk factors were considerably less frequent in water samples. These findings may in part suggest the slow depuration of Vibrio spp. and DA in oysters as residual levels may be retained. This study expanded our understanding of the simultaneous presence of DA and Vibrio spp. in bivalves and demonstrates the feasibility of co-monitoring different risk factors from the same sample. Individual programs monitoring for different risk factors from the same sample matrix may consider combining efforts to reduce cost, streamline the process, and better understand the prevalence of co-occurring health risk factors.

Prediction of hydrological and water quality data based on granular-ball rough set and k-nearest neighbor analysis

Hydrological and water quality datasets usually encompass a large number of characteristic variables, but not all of these significantly influence analytical outcomes. Therefore, by wisely selecting feature variables with rich information content and removing redundant features, it not only can the analysis efficiency be improved, but the model complexity can also be simplified. This paper considers introducing the granular-ball rough set algorithm for feature variable selection and combining it with the k-nearest neighbor method and back propagation network to analyze hydrological and water quality data, thus promoting overall and fused inspection. The results of hydrological water quality data analysis show that the proposed method produces better results compared to using a standalone k-nearest neighbor regressor.

Extraction and analysis by liquid chromatography - tandem mass spectrometry of intra- and extracellular microcystins and nodularin to study the fate of cyanobacteria and cyanotoxins across the freshwater-marine continuum

The presence of microcystins (MCs) is increasingly being reported in coastal areas worldwide. To provide reliable data regarding this emerging concern, reproducible and accurate methods are required to quantify MCs in salt-containing samples. Herein, we characterized methods of extraction and analysis by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) for nine MCs and one nodularin (NOD) variants in both cyanobacteria (intracellular) and dissolved forms (extracellular). Different approaches have been used to cope with salinity for the extraction of dissolved MCs but none assessed solid phase extraction (SPE) so far. It was found that salt had negligible effect on the SPE recovery of dissolved MCs using the C18 cartridge while an overestimation up to 67% was noted for some variants with a polymeric sorbent. The limits of detection (LOD) and quantification (LOQ) were 1.0-22 and 5.5-124 pg on column for the intracellular toxins, while 0.05-0.81 and 0.13-2.4 ng/mL were obtained for dissolved toxins. Extraction recoveries were excellent for intracellular (89-121%) and good to excellent for extracellular cyanotoxins (73-102%) while matrix effects were considered neglectable (<12% for 16/20 toxin-matrix combinations), except for the two MC-RR variants. The strategy based on the application of a corrective factor to compensate for losses proved useful as the accuracy was satisfactory (73-117% for intra- and 81-139% for extracellular cyanotoxins, bias <10% for 46/60 conditions, with a few exceptions), with acceptable precisions (intra- and inter-days variabilities <11%). We then applied this method on natural colonies of Microcystis spp. subjected to a salt shock, mimicking their estuarine transfer, in order to assess their survival and to quantify their toxins. The colonies of Microcystis spp. had both their growth and photosynthetic activity impaired at salinities from 10, while toxins remained mainly intracellular (>76%) even at salinity 20, suggesting a potential health risk and contamination of estuarine organisms.

Microcystin Concentrations, Partitioning, and Structural Composition during Active Growth and Decline: A Laboratory Study

Microcystin can be present in variable concentrations, phases (dissolved and particulate), and structural forms (congeners), all which impact the toxicity and persistence of the algal metabolite. Conducting incubation experiments with six bloom assemblages collected from the Chowan River, North Carolina, we assessed microcystin dynamics during active growth and biomass degradation. Upon collection, average particulate and dissolved microcystin ranged between 0.2 and 993 µg L-1 and 0.5 and 3.6 µg L-1, respectively. The presence of congeners MC-LA, -LR, -RR, and -YR was confirmed with MC-RR and MC-LR being the most prevalent. Congener composition shifted over time and varied between dissolved and particulate phases. Particulate microcystin exponentially declined in five of six incubations with an average half-life of 10.2 ± 3.7 days, while dissolved microcystin remained detectable until the end of the incubation trials (up to 100 days). Our findings suggest that concerns about food-web transfer via intracellular toxins seem most warranted within the first few weeks of the bloom peak, while dissolved toxins linger for several months in the aftermath of the event. Also, it was indicated there were differences in congener profiles linked to the sampling method. We believe this study can inform monitoring strategies and aid microcystin-exposure risk assessments for cyanobacterial blooms.

What happens in the shadows - Influence of seasonal and non-seasonal dynamics on domoic acid monitoring in the Monterey Bay upwelling shadow

Domoic acid produced by toxigenic Pseudo-nitzschia species is the main toxin threat from harmful algal blooms in Monterey Bay and the larger California Current region on the West Coast of the United States. Toxin monitoring in Monterey Bay includes a long-running time series of weekly measurements of domoic acid from water samples, sentinel mussels, and solid phase adsorption toxin tracking (SPATT) at the Santa Cruz Municipal Wharf (SCW). The SCW sampling site is unusual because of its position in the Monterey Bay upwelling shadow in the north bay. The upwelling shadow circulation pattern has been previously characterized as a bloom incubator for dinoflagellates, but it has not yet been analyzed in the context of long-term monitoring methods. In data collected from the SCW from 2012 - 2020, domoic acid from water samples and sentinel mussels had a different temporal distribution than domoic acid from SPATT. Here we explore the discrepancy through a seasonal and non-seasonal analysis including physical oceanography of the region. Results show that domoic acid from water samples and sentinel mussels are related to seasonal upwelling and Pseudo-nitzschia blooms. Domoic acid monitored by SPATT, on the other hand, is correlated to anomalous upwelling and warmer than usual temperatures during the relaxation season. This work builds on previous analyses of the SCW time series and contributes to understanding of the circulation of dissolved toxin in the environment. Results lend rationale for the continuation of rigorous domoic acid monitoring in Monterey Bay and encourage stakeholders to consider local physical dynamics when interpreting toxin monitoring data.

Co-occurrence of freshwater and marine phycotoxins: A record of microcystins and domoic acid in Bogue Sound, North Carolina (2015 to 2020)

Harmful algal blooms (HABs) create issues both environmentally and economically in coastal regions, especially if algal growth is linked to the production of toxins which can affect ecosystems, wildlife, and humans. This study is the first to confirm near year-round presence and co-occurrence of microcystins (MCs) and domoic acid (DA) within the outskirts of the largest lagoonal US estuary, the Pamlico-Albemarle Sound System (PASS). Monthly sampling at a time-series location in Bogue Sound, located within the eastern part of the PASS, showed DA and MCs were commonly present and detected together 50% of the time based on an in situ toxin tracking approach over a 6-year time period (2015-2020). Particulate toxin concentrations based on monthly grab sampling remained well below regulatory thresholds for MCs and below DA concentrations associated with animal sickness and mortality elsewhere. Time-integrated levels for dissolved MCs and DA, however, indicated a continuous presence of both toxins within Bogue Sound where high flushing rates (∼2-day average residence time) presumably alleviate potential issues linked to nutrient inputs, subsequent algal growth, or toxin accumulation. Pseudo-nitzschia spp. contributed 0 to 19% to the resident microplankton community. Light microscopy analyses did not reveal the source of MCs production in the sound but suggested potential downstream transport and/or autochthonous production due to taxa not accounted for in this study (e.g., picocyanobacteria). Nitrate+nitrite (NO_x) concentrations, wind speed, and water temperature explained a third of the variations in accumulated dissolved MCs, but no relationship was seen for DA concentrations based on monthly sampling within this highly dynamic system. This study emphasizes the importance of continued algal toxin monitoring in systems like Bogue Sound which might experience decreases in water quality similar to adjacent, nutrient-impaired regions within the PASS.