Elsevier

Harmful Algae

Volume 84, April 2019, Pages 195-209
Harmful Algae

Species composition and toxicity of the genus Pseudo-nitzschia in Taiwan Strait, including P. chiniana sp. nov. and P. qiana sp. nov.

https://doi.org/10.1016/j.hal.2019.04.003Get rights and content

Highlights

  • Fourteen Pseudo-nitzschia taxa were identified in the Taiwan Strait.

  • Two novel species were described, i.e., P. chiniana sp. nov. and P. qiana sp. nov.

  • Three taxa were detected to produce domoic acid, i.e. P. multiseries, P. pseudodelicatissima and P. lundholmiae.

  • It was proofed that brine shrimp can induce toxic Pseudo-nitzschia to produce more DA.

Abstract

In a field survey in the Taiwan Strait during April 2016, the species composition and the domoic acid production of the diatom genus Pseudo-nitzschia were investigated. A total of 80 strains of Pseudo-nitzschia were established, and species identification was determined based on a combination of morphological and molecular data. Fourteen taxa were recognized, i.e., P. americana, P. brasiliana, P. calliantha, P. cuspidata, P. galaxiae, P. lundholmiae, P. multiseries, P. multistriata, P. pseudodelicatissima, P. pungens var. aveirensis, P. pungenus var. pungens and P. sabit, as well as two novel species P. chiniana C.X. Huang & Yang Li and P. qiana C.X. Huang & Yang Li. Morphologically, P. chiniana is characterized by striae comprising one or two rows of poroids, and valve ends that are normally dominated by two rows of poroids within each stria. Whereas P. qiana is unique by having a narrow valve width (1.3–1.5 μm) and sharply pointed valve ends. Both taxa constitute their own monophyletic lineage in the phylogenetic analyses inferred from LSU and ITS2 rDNA, and are well differentiated from other Pseudo-nitzschia species. Pseudo-nitzschia chiniana forms a group with P. abrensis and P. batesiana in LSU and ITS trees, whereas P. qiana is sister to P. lineola. When comparing ITS2 secondary structure, five CBCs and seven HCBCs are recognized between P. chiniana and P. abrensis, and four CBCs and ten HCBCs between P. chiniana and P. batesiana. Two CBCs and eight HCBCs are found between P. qiana with P. lineola. The ability of the strains to produce domoic acid was assessed, including a potential toxin induction by the presence of brine shrimps. Results revealed production of domoic acid in six strains belonging to three species. Without presence of brine shrimps, cellular DA (pDA) was detected in four P. multiseries strains (1.6 ± 0.3, 26.6 ± 2.7, 68.3 ± 4.2 and 56.9 ± 4.7 fg cell−1, separately), one strain of P. pseudodelicatissima (0.8 ± 0.2 fg cell−1) and one strain of P. lundholmiae (2.5 ± 0.4 fg cell−1). In the presence of brine shrimps, pDA contents increased significantly (p < 0.05) in P. lundholmiae (strain MC4218) and P. multiseries (strain MC4177), from 2.5 ± 0.4 to 8.9 ± 0.7 and 1.6 ± 0.3 to 37.2 ± 2.5 fg cell−1 respectively.

Introduction

The Taiwan Strait (TS) is located between the Chinese mainland and Taiwan Island, and constitutes the southern part of the East China Sea. It covers from northeast to southwest an area of about 80 thousand square kilometers. The strait connecting the East China Sea and the South China Sea, has significant importance to international shipping, especially in East Asian trading with South Asian or Indian Ocean countries (Cai and Shi, 2009). On the other hand, TS is also rich in marine biological resources, and it is one of the traditional fishing areas in China (Dai, 2011). Several warm and cold currents interact here, especially the Fujian-Taiwan upwelling, the Chinese coastal Current and Taiwan Current (a branch of Kuroshio Current) (Xiao et al., 2002; Cai and Shi, 2009). These currents bring nutrients to the water column in TS. Sufficient nutrients, as well as the rapid increase in water temperature in spring often trigger blooms, and could explain why blooms in TS always occur in spring (Lu et al., 2014; Deng et al., 2016).

Spanning sub-tropical climate zones, TS experiences warm temperatures and significant rainfall. It makes up a major harmful algal bloom (HAB) area in China due to heavy eutrophication resulting from a high-speed economic development during the past thirty years. The number and intensity of the yearly outbreaks of HABs have been increasing dramatically in the region since the 1980s (Lu et al., 2014). Presently, the frequency of HABs and the diversity of toxic microalgae reported along TS are higher than in most other Chinese regions, with the dominating HAB species being Karenia mikimotoi Hansen & Moestrup, Prorocentrum donghaiensis Lu, Phaeocystis globosa Scherffel, Skeletonema tropicum Cleve, Noctiluca scintillans (Macartney) Kofoid & Swezy, as well as Pseudo-nitzschia spp. (Xu et al., 2010; Lu et al., 2014; Deng et al., 2016).

Pseudo-nitzschia Peragallo is a group of marine planktonic chain-forming diatoms, in which some taxa have been reported to form massive blooms worldwide (Bates et al., 2018). Because some species produce the neurotoxin domoic acid (DA), a toxin associated with amnesic shellfish poisoning (ASP), Pseudo-nitzschia has become one of the most intensively studied diatom genera (Lelong et al., 2012; Trainer et al., 2012; Bates et al., 2018). In order to explore the presence of cryptic/pseudo-cryptic species in the genus Pseudo-nitzschia, a combined approach including morphological characteristics, molecular phylogeny, ITS2 secondary structure, as well as sexual compatibility and physiological traits, have resulted in great advances in species delineation (Lundholm et al., 2002b, 2003, 2006, 2012, Amato et al., 2007; Amato and Montresor, 2008; Quijano-Scheggia et al., 2009; Lim et al., 2012; Orive et al., 2013; Teng et al., 2014, 2015, 2016; Li et al., 2017, 2018). More than 20 new species have been described during the past two decades, making the total number of Pseudo-nitzschia species reach 52, of which 26 have been reported to produce DA (Lundholm, 2018).

The first ASP event in Prince Edward Island, eastern Canada, was caused by consumption of blue mussels (Mytilus edulis L.) contaminated with DA, and resulted in at least three deaths and over 100 illnesses (Bates et al., 1989; Trainer et al., 2008). The toxin was traced to a bloom of P. multiseries, upon which the mussels had been feeding. This was the first time that a diatom was shown to produce a neurotoxin. Since then, no casualty has been confirmed due to ASP, although the prevalence of DA, its isomers and toxic diatoms, have been reported globally (Bates et al., 2018). Domoic acid is also harmful to animals in the marine food web, and fatalities have been recorded all over the world (Bates et al., 2018). Seabirds like pelicans and Brandt’s cormorants have been intoxicated and dead following ingestion of DA-contaminated anchovies (Fritz et al., 1992). Marine mammals are regularly affected by Pseudo-nitzschia and DA contamination along west coast of USA (McCabe et al., 2016). Seals, otters, walruses and cetaceans have been recorded stranded and dead with high DA concentrations in tissue or urine (Lefebvre et al., 2016; Nash et al., 2017).

Pseudo-nitzschia species are frequently observed in field surveys in TS, especially as dominant species or forming blooms in spring and summer (Xu et al., 2010). Almost all studies have recorded the dominant or common species as P. pungens (Grunow & Cleve) Hasle, because the identification was usually conducted using only light microscopy (Xu et al., 2010; Li, 2012). Combined morphological and molecular data confirmed the presence of one species, P. brasiliana (Wang et al., 2012). Thus the true Pseudo-nitzschia diversity along TS has not been assessed. Recently, however, high diversity including several new species have been discovered in the adjacent northern coast of the South China Sea (Lü et al., 2012; Li et al., 2017, 2018).

The Fujian Provincial coast on the western side of TS is the key aquaculture base in China, contributing with a gross economic output of about 300 billion Chinese Yuan in 2017 (Fujian Provincial Department of Ocean and Fisheries, 2017). Shellfish are the dominating cultured organisms and a potential vector for algal toxins. Algal blooms or algal toxins result in economic loss for the shellfish industry annually, with the worst occurring in 2012, with large-scale death of abalone during a K. mikimotoi bloom and an economic loss of more than 2 billion Chinese Yuan (Deng et al., 2016). So far, no ASP events have been reported in TS but DA has already been detected in several shellfishes, for example green mussels (Mytilus coruscus Gould), clams (Moerella iridescens Benson, Cyclina sinensis Gmelin and Mactra veneriformis Reeve) and sea snails (Rapana venosa Valenciennes, Mammilla maura Lamarck) collected from Zhoushan, the north coast of the East China Sea, although the DA concentration was low (Wang, 2011). Therefore, knowledge on species diversity and toxicity of Pseudo-nitzschia along TS is highly needed.

Section snippets

Sampling and collection

A cruise was carried out in TS during spring (April 2016). Eight transects perpendicular to the Chinese mainland coast with nineteen stations were selected for Pseudo-nitzschia sampling (Fig. 1). Coordinates of the sampling stations are listed in supplemental Table S1. Net samples were collected at each station using a 10 μm plankton net (˜30 cm diameter) hauled vertically through the upper photic zone (˜20 m). Part of the net sample was fixed in acidic Lugol’s solution and another part was

Species identifications

Thirteen distinct species and one variety were recognized among the 80 established strains: P. americana, P. brasiliana, P. calliantha, P. cuspidata, P. galaxiae, P. lundholmiae, P. multiseries, P. multistriata, P. pseudodelicatissima, P. pungens var. pungens, P. pungens var. aveirensis and P. sabit, as well as two novel species P. chiniana sp. nov. and P. qiana sp. nov. Species identification was based on the combination of morphological and molecular data, mainly TEM micrographs and

Comparison between two new species and closely related species

Based on morphological characters, P. qiana belongs most closely to the P. pseudodelicatissima complex, which is characterized by the striae with one row of poroids, a central nodule and a transapical axis < 3 μm (Lundholm et al., 2003, 2012, Lim et al., 2013; Orive et al., 2013). The P. pseudodelicatissima complex is a morphological species complex (Lundholm et al., 2012) and the complex is not monophyletic (Lim et al., 2018). The P. delicatissima complex comprises species with two rows of

Acknowledgements

We thank Antonio Calado for help with the naming of the species. This work was supported by grants from the National Natural Science Foundation of China (31570205), Science & Technology Basic Resources Investigation Program of China (2018FY100200) and Special Funds of Guangdong Province for Promoting Economic Development for 2019 (For the Development of Marine Economy). [CG]

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