Abstract
Elevated pCO2 and warming may promote algal growth and toxin production, and thereby possibly support the proliferation and toxicity of harmful algal blooms (HABs). Here, we tested whether empirical data support this hypothesis using a meta‐analytic approach and investigated the responses of growth rate and toxin content or toxicity of numerous marine and estuarine HAB species to elevated pCO2 and warming. Most of the available data on HAB responses towards the two tested climate change variables concern dinoflagellates, as many members of this phytoplankton group are known to cause HAB outbreaks. Toxin content and toxicity did not reveal a consistent response towards both tested climate change variables, while growth rate increased consistently with elevated pCO2. Warming also led to higher growth rates, but only for species isolated at higher latitudes. The observed gradient in temperature growth responses shows the potential for enhanced development of HABs at higher latitudes. Increases in growth rates with more CO2 may present an additional competitive advantage for HAB species, particularly as CO2 was not shown to enhance growth rate of other non‐HAB phytoplankton species. However, this may also be related to the difference in representation of dinoflagellate and diatom species in the respective HAB and non‐HAB phytoplankton groups. Since the proliferation of HAB species may strongly depend on their growth rates, our results warn for a greater potential of dinoflagellate HAB development in future coastal waters, particularly in temperate regions.
Highlights
The atmospheric partial pressure of CO2 has been rising rapidly since the industrial revolution
Most of the harmful algal blooms (HABs) species tested for their response toward elevated pressure of CO2 (pCO2) and warming were dinoflagellates, and summarized HAB responses were mostly driven by the dinoflagellate responses (Table 1; Fig. 1)
paralytic shellfish poisoning (PSP) toxins produced by Alexandrium spp. decreased, while karlotoxins produced by Karlodinium veneficum and domoic acid (DA) produced by Pseudo-nitzschia spp. increased with elevated pCO2 (Fig. S2a)
Summary
The atmospheric partial pressure of CO2 (pCO2) has been rising rapidly since the industrial revolution. If greenhouse gas emissions are not reduced, they are expected to cause an increase in global mean temperatures of 3 to 5 ̊C by the end of this century (RCP scenario 8.5; IPCC 2014). These changes in the Earth’s climate will impact the oceans, leading to ocean acidification and warming of the surface layers, which, in turn, greatly affect marine life (Doney et al, 2009; Fabry et al, 2008; Poloczanska et al, 2013). In regions where HAB species already grow at their temperature optimum, warming may lead to decreases in HAB events (Kibler et al, 2015)
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