| Abstrakt: |
In continental Portugal, high levels of diarrhetic shellfish poisoning toxins (DSTs) and paralytic shellfish poisoning toxins (PSTs) can be accumulated in bivalves. DSTs presented maxima during the dry summer season and were linearly related to precipitation accumulated over the previous months. Precipitation is highest on the northwest (NW) than on the southwest (SW) or south (S) coasts. An NW to S decreasing gradient in DSTs is commonly found. An NW to S decreasing gradient can also be found for some macronutrients (N, P and Si). Coastal fertilisation also favoured contamination with ASTs (amnesic shellfish poisoning toxins) and PSTs mainly on the NW coast, followed by the SW coast, with the lowest contaminations found on the S coast. Despite its marked autumnal seasonality, PSTs were unpredictable interannually. High PST’s contamination was coincidental with the last four solar minima periods of the 11-year sunspot cycle. On the opposite, ASTs increased slightly during maxima of geomagnetic activity (GMA). AST incidence in April and October was 2.7 times higher when GMA was above the monthly average (18.5 nT) in March and September, respectively. In the last two decades (2001–2020), average DST levels in June + July reduced after 2008, following a trend in the reduction of precipitation after 2003. Nevertheless, no trends were observed in the average percentage of samples exceeding annually the regulatory limit (PSEARL) for DSTs (18.4%) due to the high percentage of indicator-species analysed, which maintain DSTs for a prolonged time. Despite the low average PSEARL of 1.0% for ASTs during 2001–2013, it reduced to 0.4% in 2014–2020. This might have been coincidental with a global change in the northern hemisphere ocean temperature anomaly in 2014 or with weaker GMA stimulation during the weaker solar cycle 24. Due to the large interannual variability in PSTs associated with the solar cycle, no average PSEARL can be defined and no clear trends can be associated with global change. [ABSTRACT FROM AUTHOR] |
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