Temporal and Spatial Patterns of Harmful Algae Affecting Scottish Shellfish Aquaculture

Abstract

Consistent patterns of Harmful Algal Bloom (HAB) events are not evident across the scientific literature, suggesting that local or regional variability is likely to be important in modulating any overall trend. This study summarizes Scotland-wide temporal and spatial patterns in a robust 15-year high temporal frequency time series (2006–2020) of the incidence of HABs and shellfish biotoxins in blue Mussels (Mytilus edulis), collected as part of the Food Standards Scotland (FSS) regulatory monitoring program. The relationship between the countrywide annual incidence of HAB events and biotoxins with environmental variables was also explored. Temporal patterns exhibited interannual variability, with no year-on-year increase, nor any correlation between annual occurrences. Within years, there was a summer increase in bloom frequency, peaking in July for Dinophysis spp. and Pseudo-nitzschia spp., and a plateau from May to July for Alexandrium spp. Temporal-spatial patterns were analyzed with multivariate statistics on data from monitoring sites aggregated monthly into 50-km grid cells, using Principal Component Analysis (PCA) and cluster K-means analysis. PCA analyses showed correlation between areas with similar temporal dynamics, identifying seasonality as one of the main elements of HAB variability with temporal-spatial patterns being explained by the first and second principal components. Similar patterns among regions in timing and magnitude of blooms were evaluated using K-means clusters. The analysis confirmed that the highest risk from HABs generally occurred during summer, but demonstrated that areas that respond in a similar manner (high or low risk) are not always geographically close. For example, the occurrence of the most prevalent HAB genus, Dinophysis spp., is similar countrywide, but there is a regional trend in risk level with “very-high” and “high” clusters located primarily on the southwest coast, the islands of the central and northern west coast and the Shetland Islands. “Early” and “late” blooms were also associated with certain areas and level of risk. Overall, high risk areas mainly face in a southwest direction, whilst low risk locations face a south or southeast direction. We found relatively few countrywide relationships between environmental variables and HABs, confirming the need for regional analysis to support HAB early warning.

Variability patterns and phenology of harmful phytoplankton blooms off southern Portugal: Looking for region-specific environmental drivers and predictors

“…This study, based on a 6-year time series of the abundances of key toxigenic phytoplankton groups, revealed variable intra-annual and phenological patterns in the heterogeneous domain off southern Portugal (e.g., Krug et al, 2017Krug et al, , 2018a, depending on HAB-groups and coastal production areas. This variability is consistent with other studies and reinforces the need and value of region-and group-specific HAB studies (e.g., Gianella et al, 2021;Hallegraeff et al, 2021b). Our data on bloom phenology metrics will expand the limited information (Gobler et al, 2017;Wells et al, 2020;Glibert, 2020;Boivin-Rioux et al, 2021.…”

“…However, a recent meta-analysis showed no empirical support for a global increase in HABs and, instead, related this widespread perception with increased monitoring effort, in tandem with emerging HAB socio-economic impacts (see Hallegraeff et al, 2021a). Recent system-specific inter-annual analysis have indeed reported variable HAB trends, depending on species and their functional traits, sites, regions, study periods, and concurrent environmental forcing (Anderson et al, 2021;Belin et al, 2021;Gianella et al, 2021;Hallegraeff et al, 2021aHallegraeff et al, , 2021bMcKenzie et al, 2021;Pitcher and Louw, 2021). Thus, a comprehensive understanding of HAB spatial-temporal variability patterns, bloom phenology, and underlying environmental determinants at the regional level (Gianella et al, 2021;Hallegraeff et al, 2021a), integrated into predictive models, is fundamental for forecasting, mitigating, and effectively managing HABs in coastal waters (see reviews by Franks, 2018, Ralston andMoore, 2020).…”

Quantifying Spatio-temporal risk of Harmful Algal Blooms and their impacts on bivalve shellfish mariculture using a data-driven modelling approach

“…; these areas have also been shown to undergo rapid sea surface warming and prolonged thermal stratification during the summer (Pingree et al, 1975;1983;Brown et al 2022). In contrast, shellfish sites in sea lochs with a southwest facing aspect along the Western coast of Scotland appear to be at greatest risk, due to the potential advection of Dinophysis HABs from offshore (Gianella et al, 2021).…”

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

“…While many of these issues are due to market dysfunction and outside the power of an individual farmer to change, the environment also has its own impact on shellfish production. For the shellfish industry, a major worry is the need to implement a product recall or close an active harvesting site due to contamination of the farmed shellfish by one or more marine toxins [ 4 ]. These toxins are produced by a few of the thousands of species of microscopic algae—microplankton—that are ubiquitous in the marine environment, often reaching cell densities in excess of a million cells per litre.…”

“…Several different genera of microplankton produce toxins: Alexandrium , a dinoflagellate that produces saxitoxins, is responsible for the syndrome paralytic shellfish poisoning (PSP) [ 6 , 7 ]; Dinophysis, a dinoflagellate that produces okadaic acid (OA) group toxins, causes diarrhetic shellfish poisoning (DSP) [ 8 ]; and Pseudo-nitzschia (see Figure 1 ), one of the few diatom genera to produce a neurotoxin—in this case, domoic acid—is the cause of amnesic shellfish poisoning (ASP) [ 9 , 10 ]. These three genera are frequently observed in Scottish coastal waters [ 11 , 12 , 13 , 14 ] and responsible for most of the site closures [ 4 ], including scallop fisheries [ 15 ], and occasional incidences of human intoxication [ 16 , 17 , 18 ].…”