Sub-tropical benthic/epiphytic dinoflagellates of Aotearoa New Zealand and Rangitahua Kermadec Islands.

Temperatures and temperature anomalies have been increasing in the sub-tropical regions of Aotearoa New Zealand and these changes may impact on harmful algal bloom (HAB) events. Benthic and epiphytic dinoflagellates, particularly the toxin producers, are the focus of this study as it is predicted that under future climate conditions they may produce more toxins or marine animals may become more susceptible to them. The results of past expeditions to Rangitahua Kermadec Islands and sampling trips to Northland, Aotearoa New Zealand, are summarised and the results of the most recent trips to both regions are presented. The macroalgal habitats of the dinoflagellates are also characterised. Dinoflagellate species not previously identified in Rangitahua include Coolia canariensis, C. palmyrensis, and C. tropicalis, all identified by DNA sequencing of the large subunit ribosomal RNA region. Gambierdiscus polynesiensis was again isolated and produced 44-methylgambierone and gambierone, and one isolate produced ciguatoxins, the cause of Ciguatera Poisoning. An Ostreopsis tairoto isolate, as analysed by the oxidative cleavage method, produced a palytoxin (PLTX)-like amine oxidation fragment, but when analysed for PLTX-like analogues using a new intact method none were detected indicating an 'unknown' PLTX-like compound is produced by this isolate. Isolates of O. cf. siamensis (Ostreopsis sp. 9), collected in Northland, were also analysed using the oxidative cleavage method, with the common PLTX-like amine fragment and the amide fragment corresponding to bishomoPLTX detected in all isolates. Again, the intact method indicated no detections in the isolates, again suggesting an unknown compound was being produced by these isolates. Prorocentrum hoffmannianum isolates produced okadaic acid (OA) and isoDTX-1 and P. lima isolates produced OA, DTX-1, and isoDTX-1. It is expected that new species of potentially harmful, benthic dinoflagellates will continue to be recorded in Aotearoa New Zealand and the results from Rangitahua provide a guide to the HAB species to expect in sub-tropical Northland as the oceans continue to warm.

Molecular Identification of Gambierdiscus and Fukuyoa (Dinophyceae) from Environmental Samples.

Ciguatera Fish Poisoning (CFP) is increasing across the Pacific and the distribution of the causative dinoflagellates appears to be expanding. Subtle differences in thecal plate morphology are used to distinguish dinoflagellate species, which are difficult to determine using light microscopy. For these reasons we sought to develop a Quantitative PCR assay that would detect all species from both Gambierdiscus and Fukuyoa genera in order to rapidly screen environmental samples for potentially toxic species. Additionally, a specific assay for F. paulensis was developed as this species is of concern in New Zealand coastal waters. Using the assays we analyzed 31 samples from three locations around New Zealand and the Kingdom of Tonga. Fourteen samples in total were positive for Gambierdiscus/Fukuyoa and two samples were also positive using the F. paulensis assay. Samples from the Kermadec Islands were further characterized using high-throughput sequencing metabarcoding. The majority of reads corresponded to Gambierdiscus species with three species identified at all sites (G. australes, G. honu and G. polynesiensis). This is the first confirmed identification of G. polynesiensis, a known ciguatoxin producer, in New Zealand waters. Other known toxin-producing genera were also detected, included Alexandrium, Amphidinium, Azadinium, Dinophysis, Ostreopsis, and Prorocentrum.

The Epiphytic Genus Gambierdiscus (Dinophyceae) in the Kermadec Islands and Zealandia Regions of the Southwestern Pacific and the Associated Risk of Ciguatera Fish Poisoning.

Species in the genus Gambierdiscus produce ciguatoxins (CTXs) and/or maitotoxins (MTXs), which may cause ciguatera fish poisoning (CFP) in humans if contaminated fish are consumed. Species of Gambierdiscus have previously been isolated from macroalgae at Rangitahua (Raoul Island and North Meyer Islands, northern Kermadec Islands), and the opportunity was taken to sample for Gambierdiscus at the more southerly Macauley Island during an expedition in 2016. Gambierdiscus cells were isolated, cultured, and DNA extracted and sequenced to determine the species present. Bulk cultures were tested for CTXs and MTXs by liquid chromatography-mass spectrometry (LC-MS/MS). The species isolated were G. australes, which produced MTX-1 (ranging from 3 to 36 pg/cell), and G. polynesiensis, which produced neither MTX-1 nor, unusually, any known CTXs. Isolates of both species produced putative MTX-3. The risk of fish, particularly herbivorous fish, causing CFP in the Zealandia and Kermadec Islands region is real, although in mainland New Zealand the risk is currently low. Both Gambierdiscus and Fukuyoa have been recorded in the sub-tropical northern region of New Zealand, and so the risk may increase with warming seas and shift in the distribution of Gambierdiscus species.