Abstract

Karenia brevis is the dominant toxic red tide algal species in the Gulf of Mexico. It produces potent neurotoxins (brevetoxins [PbTxs]), which negatively impact human and animal health, local economies, and ecosystem function. Field measurements have shown that cellular brevetoxin contents vary from 1–68 pg/cell but the source of this variability is uncertain. Increases in cellular toxicity caused by nutrient-limitation and inter-strain differences have been observed in many algal species. This study examined the effect of P-limitation of growth rate on cellular toxin concentrations in five Karenia brevis strains from different geographic locations. Phosphorous was selected because of evidence for regional P-limitation of algal growth in the Gulf of Mexico. Depending on the isolate, P-limited cells had 2.3- to 7.3-fold higher PbTx per cell than P-replete cells. The percent of cellular carbon associated with brevetoxins (%C-PbTx) was ∼ 0.7 to 2.1% in P-replete cells, but increased to 1.6–5% under P-limitation. Because PbTxs are potent anti-grazing compounds, this increased investment in PbTxs should enhance cellular survival during periods of nutrient-limited growth. The %C-PbTx was inversely related to the specific growth rate in both the nutrient-replete and P-limited cultures of all strains. This inverse relationship is consistent with an evolutionary tradeoff between carbon investment in PbTxs and other grazing defenses, and C investment in growth and reproduction. In aquatic environments where nutrient supply and grazing pressure often vary on different temporal and spatial scales, this tradeoff would be selectively advantageous as it would result in increased net population growth rates. The variation in PbTx/cell values observed in this study can account for the range of values observed in the field, including the highest values, which are not observed under N-limitation. These results suggest P-limitation is an important factor regulating cellular toxicity and adverse impacts during at least some K. brevis blooms.

Highlights

  • Blooms of the toxic dinoflagellate Karenia brevis produce a suite of structurally related neurotoxins, brevetoxins (PbTxs), which adversely affect both human and ecosystem health

  • Shellfish feeding on K. brevis accumulate PbTxs, which can lead to neurotoxic shellfish poisoning (NSP)

  • In this study we investigated the effect of P-limitation on cellular growth rate, and cellular content of chlorophyll a, carbon (C), phosphorus (P), nitrogen (N) and PbTxs in laboratory cultures of K. brevis

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Summary

Introduction

Blooms of the toxic dinoflagellate Karenia brevis produce a suite of structurally related neurotoxins, brevetoxins (PbTxs), which adversely affect both human and ecosystem health. These toxins bind to voltage-gated sodium channels which results in persistent activation of neuronal, skeletal muscle and cardiac cells [1]. Exposure is enhanced when K brevis cells are disrupted by breaking waves and form toxic aerosols [4]. Onshore winds transport these aerosols over beaches and nearshore communities, causing respiratory related illnesses [4,5,6]. The adverse environmental and health effects of K. brevis blooms, in conjunction with the associated negative publicity, result in significant economic losses in local communities that depend on tourism and recreational fishing [11–

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