Harmful algal blooms in the Eastern North Atlantic Ocean

Abstract

a Applying a mathematical model to the period 1982-2016 propose that ocean warming has expanded the niche for harmful algal blooms (HABs) of the species Dinophysis acuminata and Alexandrium fundyense, which can generate shellfish toxicity and pose risks to human health. The authors' model predicts an increase in the growth rate and in the duration of the bloom season for these species, with a "hot spot" being the North Eastern Atlantic (NEA) and North Sea (NS) waters surrounding the United Kingdom. Using ships of opportunity, the Continuous Plankton Recorder (CPR) has surveyed offshore phytoplankton populations (including Dinophysis, but not Alexandrium) in this region since 1958 (2). We used Dinophysis spp. data to evaluate the model's predictions, as species data were not available before 2004.Growth rate is not easily calculated from in situ data, but one might reasonably expect enhanced growth to lead to increased cell abundance. We therefore determined the annual mean CPR surveyed Dinophysis concentration in the NEA and NS. Using the modified Chelton method to remove serial autocorrelation (3), we found that over the modeled period and the whole CPR time series there was no statistically significant positive relationship between Dinophysis abundance and seasurface temperature (4) in the modeled area over either the whole year or the April to September growth season, a result consistent with a previous study (5).Dinophysis-generated shellfish toxicity is related to short-term "bloom" events of elevated abundance. Harm from Dinophysis could therefore increase despite annual abundance decreases, should more frequent or larger blooms occur. Fig. 1 shows that, while there have been periods of large Dinophysis blooms in the region, these mostly occurred during the early 1970s and the late 1980s, and have been followed by a period of briefer bloom events from the mid-2000s until 2014. In Fig. 2, by calculating the percentage of days per year that Dinophysis abundance was greater than two SDs above the mean of the whole series, we also show that there is no increasing trend in number or annual duration of blooms.Understanding the long-term trends of Dinophysis concentrations is important in NEA waters as significant increases in shellfish aquaculture are planned in the region. The work of Gobler et al. (1) is valuable in demonstrating the potential for increasing water temperature to increase the associated HAB risk. However, our data indicate that the modeled increases in D. acuminata growth rate are not evident in terms of increases in the annual mean, number of Dinophysis blooms, or their duration. Gobler et al. used empirical laboratory evidence of increasing D. acuminata growth rate with increasing temperature to parameterize an individual-based model. Dinophysis populations exist within a complex planktonic food web and are often comprised of more than one species, with different environmental preferences. Our results suggest that other factors, such as prey availability, predation, or ecological interactio...

Temporal and Spatial Patterns of Harmful Algae Affecting Scottish Shellfish Aquaculture

“…Dinophysis presented the greatest bloom frequency. The countrywide interannual patterns observed are consistent with abundance observations at two targeted locations on the west coast of Scotland (Swan et al, 2018) and offshore patterns found in the Northeast Atlantic from Continuous Plankton Recorder data (Dees et al, 2017), and do not confirm the model based predictions of Gobler et al (2017) of a climate driven increase in the abundance of Dinophysis acuminata in the region. The monthly and annual Dinophysis analysis using K-means categories, determined that the blooms respond similarly between clusters at a regional scale, but with varying levels of risk.…”

“…The occurrence, intensity and distribution of HABs is a problem worldwide (Hallegraeff, 1993(Hallegraeff, , 2010Van Dolah, 2000;Smayda, 2002;Glibert et al, 2005;Anderson et al, 2017;Gobler et al, 2017;Wells et al, 2019). However, trends of increasing HAB frequency and/or abundance are not evident in all studies (Moore et al, 2009;Díaz et al, 2016;Dees et al, 2017) suggesting that local or regional variability is likely in any overall trend. This is consistent with recent results from Hallegraeff et al (2021) who used a metaanalysis of Harmful Algae Event Database and Ocean Biodiversity Information system data to demonstrate that there is no empirical support for a global increase in HAB events.…”

“…Characterizing the spatial and temporal trends of different HAB genera over multiple years is therefore not straightforward. Many authors have attempted to understand HAB dynamics, using linear modeling in relation to single or multiple environmental drivers (Hinder et al, 2012;Ruiz-Villarreal et al, 2016;Dees et al, 2017), but such approaches are best suited to the evaluation of decadal trends. Aquaculture practitioners and coastal zone managers have a more pressing need to better understand the likely timing and location of HAB taxa and biotoxins to allow more informed farm management and regulatory decision-making.…”

Dinophysis acuta in Scottish Coastal Waters and Its Influence on Diarrhetic Shellfish Toxin Profiles

“…Based on a modelling study, Gobler et al [ 36 ] proposed that ocean warming had increased the growth rate and duration of the bloom season of D. acuminata over the period 1982–2006 in the North East Atlantic around the UK. However, following analysis of data from the Continuous Plankton Recorder (CPR) from the region, Dees et al [ 37 ] did not find any increase in the number or annual duration of Dinophysis blooms. While the greatest number of D. acuminata above threshold counts occurred in each of the last three years (2015–2017), our results ( Figure 2 and Figure 5 ), albeit over a shorter timescale than that modelled by Gobler et al [ 36 ], concur with the conclusion that there is no clear temporal increase in D. acuminata blooms.…”

Current Status of Forecasting Toxic Harmful Algae for the North-East Atlantic Shellfish Aquaculture Industry

“…Links between increasing sea surface temperatures and wind intensity have led to an increase in the potentially toxic diatom Pseudo-nitzschia in the NEA since the mid-1990s (Hinder et al, 2012). Climate change effect on the timing and severity of toxic events is still uncertain (Wells et al, 2019) with model predictions and in situ data not always coinciding (Dees et al, 2017;Gobler et al, 2017).…”