Toxic bloom of Pseudo-nitzschia cuspidata (Bacillariophyceae) and domoic acid contamination of bivalve molluscs in Malaysia Borneo

Mapping harmful microalgal species by eDNA monitoring: A large-scale survey across the southwestern South China Sea

A large-scale sampling was undertaken during a research cruise across the South China Sea in August 2016, covering an area of about 100,000 km2 to investigate the molecular diversity and distributions of micro-eukaryotic protists, with a focus on the potentially harmful microalgal (HAB) species along the east coast of Peninsular Malaysia. Environmental DNAs from 30 stations were extracted and DNA metabarcoding targeting the V4 and V9 markers in the 18S rDNA was performed. Many protistan molecular units, including previously unreported HAB taxa, were discovered for the first time in the water. Our findings also revealed interesting spatial distribution patterns, with a marked signal of compositional turnover between latitudinal regimes of water masses, where dinophytes and diatom compositions were among the most strongly enhanced at the fronts, leading to distinct niches. Our results further confirmed the widespread distribution of HAB species, such as the toxigenic Alexandrium tamiyavaichii and Pseudo-nitzschia species, and the fish-killing Margalefidinium polykrikoides and Karlodinium veneficum. The molecular information obtained from this study provides an updated HAB species inventory and a toolset that could facilitate existing HAB monitoring schemes in the region to better inform management decisions.

First record of the diatom Nitzschia navis-varingica (Bacillariophyceae) producing amnesic shellfish poisoning-toxins from Papua New Guinea

To determine the species distribution of an amnesic shellfish poisoning (ASP) toxins-producing diatom Nitzschia navis-varingica outside its current restricted geographical distribution range in Asian coastal waters, samples were collected from two sites of Bootless Bay, located on southwest coast of Papua New Guinea near Port Moresby. A total of twenty-one strains of N. navis-varingica were isolated and the clonal cultures established. The species identity was confirmed by molecular characterization based on the ribosomal DNA markers. The LSU rDNA phylogenetic inference revealed a monophyletic clade of all strains, clustered with N. navis-varingica with high bootstrap supports. ASP toxin production in the strains was investigated by HPLC with fluorescence detection and subsequently confirmed for the representative isolates by LC-MS/MS with multiple reaction monitoring (MRM) mode. All eleven strains from site A showed presence of domoic acid (DA) and isodomoic acid (IB); the toxin quota ranged from 0.70 to 4.63 pg cell^-1 (average 2.75 ± 1.26 pg cell^-1, n = 11), with the composition of DA and IB of 21 DA: 79 IB. While for strains from site B, four out of ten strains showed presence of DA and IB, with the toxin quota ranged from 1.40 to 3.84 (average 2.57 ± 1.17 pg cell^-1, n = 4); the composition was 52 DA: 48 IB. The strains examined in this study were divided into toxic and probably non-toxic groups in ITS2 phylogeny. This represents the first record of domoic acid-producing Nitzschia navis-varingica from Papua New Guinea.

Spatial-temporal variability of microphytoplankton assemblages including harmful microalgae in a tropical semi-enclosed strait (Johor Strait, Malaysia)

Harmful algal blooms (HABs) were not new to the tropical semi-enclosed Johor Strait, with incident records that could trace back to the 1980s. HAB monitoring in the area, often, is reactive, focusing only on HAB taxa previously causing problems but neglecting potential emerging HABs. To develop datasets on HABs that can better inform and improve management practices, monitoring should expand to sample whole microphytoplankton communities. In this study, microphytoplankton community structure across the Strait was investigated. Abundances of microphytoplankton and a suite of in situ water parameters of temperatures, salinity, pH, dissolved oxygen levels, macronutrients, and chlorophyll-a contents were collected at ten sites across the Strait at monthly intervals from January 2017 to December 2018. A total of 48 genera (51 taxa) microphytoplankton were identified microscopically. Diatom was the most diverse group (32 genera), followed by dinophyte (15 genera). Bloom-forming species included diatoms Chaetoceros, Coscinodiscus, Eucampia, Pseudo-nitzschia, Rhizosolenia, Skeletonema, Thalassiosira, and dinophytes Blixaea quinquecornis and Scrippsiella. Diatom taxa that exhibit high in situ growth rates were predominant in the low-nutrient marine-influenced environment. Bloom-forming taxa including HAB taxa were found dominant in the environment with high nutrient levels and mesohaline, salinity-stratified conditions. This study provides valuable baseline data that could assist in monitoring and prediction of HABs in the Johor Strait and could be of reference to other similar tropical coastal systems.