Abstract
Eutrophication has played a major role in the worldwide increase of harmful algal blooms (HABs). Higher input of key nutrients, such as nitrogen (N) and phosphorus (P), can stimulate the growth of harmful algal species in freshwater, estuarine, and coastal marine ecosystems. Some HAB-forming taxa, particularly several cyanobacteria and dinoflagellate species, are harmful through the production of N-rich toxins that have detrimental effects on the environment and human health. Here, we test how changes in nutrient availability affect N-rich toxin synthesis in cyanobacteria and dinoflagellates using a meta-analysis approach. Overall, N-rich toxin content showed an increase with P limitation, while it tended to decrease with N limitation, but we also observed substantial variation in responses both within and across genera and toxin groups. For instance, in response to N limitation, microcystin content varied from a 297% decrease up to a 273% increase, and paralytic shellfish poisoning (PSP) toxin content varied from a 204% decrease to an 82% increase. Cylindrospermopsin, produced by N2-fixing cyanobacteria, showed no clear direction in response to nutrient limitation, and cellular contents of this compound may thus vary independently of nutrient fluctuations. Our results confirm earlier reported stoichiometric regulation of N-rich phytoplankton toxins, showing increased toxin content with an increase in cellular N:P ratios, and vice versa. Thus, changes in N-rich toxin content largely follow the changes in relative cellular N content. Consequently, although nutrient limitation may limit bloom biomass and thereby bloom toxicity, our results warn that P limitation can cause accumulation of cellular toxins and thus lead to unexpected increases in bloom toxicity.
Highlights
Since the 1970s, the number of harmful algal bloom (HAB) outbreaks has increased dramatically worldwide [1,2]
Some HAB species produce potent toxins that can accumulate in the food chain, which can lead to the death of fish, seabirds, and marine mammals, and thereby disrupt ecosystem structure and functioning [13,14,15,16]
Toxic HAB outbreaks in coastal waters are often caused by dinoflagellates, while HABs in freshwater environments are typically caused by cyanobacteria [17,18,19]
Summary
Since the 1970s, the number of harmful algal bloom (HAB) outbreaks has increased dramatically worldwide [1,2]. Toxic HAB outbreaks in coastal waters are often caused by dinoflagellates, while HABs in freshwater environments are typically caused by cyanobacteria [17,18,19]. Toxins produced by both these phytoplankton groups can pose a risk to human health. Dinoflagellate toxins can accumulate in shellfish and may cause severe shellfish poisoning syndromes upon the ingestion of seafood [20,21,22] Cyanotoxins, such as microcystin, can cause acute liver failure, while chronic exposure to low concentrations through drinking water significantly increases the risk of liver and colorectal cancer [23,24,25]. Other symptoms of exposure to cyanotoxins may include, amongst others, abdominal pain, vomiting, diarrhea, skin irritation, weakness, sore throat, and headache [25,26]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
