Identification of dissolved and particulate carbonyl compounds produced by marine harmful algal bloom species

Abstract

Carbonyl compounds, especially polyunsaturated aldehydes (PUAs), are increasingly reported as teratogenic to grazers and deleterious to phytoplankton. While PUAs have been considered to be mainly produced by diatoms after cell wounding, little is known about whether microalgae other than diatoms, particularly harmful algal bloom (HAB)-forming species, produce carbonyl compounds. In this study, we analyzed the carbonyl compounds from eight common HAB-forming species (Akashiwo sanguinea, Karenia mikimotoi, Karlodinium veneficum, Margalefidinium polykrikoides, Prorocentrum donghaiense, P. minimum, Scrippsiella trochoidea, and Heterosigma akashiwo) using gas chromatography-mass spectrometry in full scan and selected ion monitoring (SIM) modes. Our results show a ubiquitous presence of carbonyl compounds in both dissolved and particulate forms in all species we examined. In the full scan mode, 133 chromatographic peaks were detected from 51 samples altogether. Both the varieties of carbonyl compounds and their quantities were algal species dependent, although most of the carbonyl compounds could not be fully identified according to the mass spectral database only due to the unavailability of enough standards for all analytes. Aided with nine standards in SIM mode, we further identified and quantified all nine aldehydes (2-methyl-2-pentenal, trans-2-nonenal, cis-6-nonenal, 2,6-dimethyl-5-heptenal, trans-2-hexenal, trans-2-decenal, 2,4-heptadienal, trans-trans-2,4-octadienal, and trans-trans-2,4-decadienal). Four of these nine aldehydes were detected in particulate form, which confirmed that trans-2-nonenal could be produced by K. mikimotoi, Karl. veneficum, P. donghaiense, P. minimum, S. trochoidea, and H. akashiwo, 2,4-heptadienal and trans-trans-2,4-decadienal by A. sanguinea, M. polykrikoides, and S. trochoidea, and trans, trans-2,4-octadienal by S. trochoidea, respectively. We proved that some dinoflagellate and raphidophyte species could contribute to the pool of carbonyl compounds including PUAs in a marine ecosystem. Some carbonyl compounds, particularly those in high cell quota and/or dissolved concentration, may be related to fish-killing or allelopathy which needs further identification and quantification.