Ocean warming since 1982 has expanded the niche of toxic algal blooms in the North Atlantic and North Pacific oceans

Abstract

Global ocean temperatures are rising, yet the impacts of such changes on harmful algal blooms (HABs) are not fully understood. Here we used high-resolution sea-surface temperature records (1982 to 2016) and temperature-dependent growth rates of two algae that produce potent biotoxins, Alexandrium fundyense and Dinophysis acuminata, to evaluate recent changes in these HABs. For both species, potential mean annual growth rates and duration of bloom seasons significantly increased within many coastal Atlantic regions between 40°N and 60°N, where incidents of these HABs have emerged and expanded in recent decades. Widespread trends were less evident across the North Pacific, although regions were identified across the Salish Sea and along the Alaskan coastline where blooms have recently emerged, and there have been significant increases in the potential growth rates and duration of these HAB events. We conclude that increasing ocean temperature is an important factor facilitating the intensification of these, and likely other, HABs and thus contributes to an expanding human health threat.

Keywords: Alexandrium; Dinophysis; bloom duration; climate change; sea-surface temperature.

Fig. 1.

Modeled trend in bloom season (d⋅y⁻¹) over the period 1982 to 2016 for A. fundyense in the North Atlantic (A) and North Pacific (B). Modeled trend in mean annual growth rate (d⁻¹⋅y⁻¹) over the same time period in the North Atlantic (C) and North Pacific (D). Stippling indicates regions where trends are statistically significant (S < 0.05). Boxes indicate two coastal regions of significantly enhanced temperature, growth rates, bloom season, and record of bloom occurrence: NW Atlantic (40.625°N to 50.325°N; 287.875°W to 307.125°W) and NE Atlantic (49.125°N to 60.125°N; 0.125°E to 10.125°E).

Fig. 2.

Modeled trend in bloom season (d⋅y⁻¹) over the period 1982 to 2016 for D. acuminata in the North Atlantic (A) and North Pacific (B). Modeled trend in mean annual growth rate (d⁻¹⋅y⁻¹) over the same time period in the North Atlantic (C) and North Pacific (D). Stippling indicates regions where trends are statistically significant (S < 0.05). Boxes indicate two coastal regions of significantly enhanced temperature, growth rates, bloom season, and record of bloom occurrence: NW Atlantic (40.625°N to 50.325°N; 287.875°W to 307.125°W) and NE Atlantic (49.125°N to 60.125°N; 0.125°E to 10.125°E).

Fig. 3.

Annual mean of bloom season (A and B; d⋅y⁻¹) and growth rate (C and D; d⁻¹⋅y⁻¹) from 1982 to 2016 for A. fundyense within the two coastal regions defined in Fig. 1. Shaded region shows range of growth-curve uncertainty, corresponding to the range of outcomes between 2.5th and 97.5th percentiles of bootstrapped growth curves. All time series exhibit statistically significant trends (S < 0.01) as shown in Table 1.

Fig. 4.

Annual mean of bloom season (A and B; d⋅y⁻¹) and growth rate (C and D; d⁻¹⋅y⁻¹) from 1982 to 2016 for D. acuminata within the two coastal regions defined in Fig. 1. Shaded region shows range of growth-curve uncertainty, corresponding to the range of outcomes between 2.5th and 97.5th percentiles of bootstrapped growth curves. All time series exhibit statistically significant trends (S < 0.01) as shown in Table 1.