Gustaaf M. Hallegraeff

OCEAN CLIMATE CHANGE, PHYTOPLANKTON COMMUNITY RESPONSES, AND HARMFUL ALGAL BLOOMS: A FORMIDABLE PREDICTIVE CHALLENGE

Prediction of the impact of global climate change on marine HABs is fraught with difficulties. However, we can learn important lessons from the fossil record of dinoflagellate cysts; long‐term monitoring programs, such as the Continuous Plankton Recorder surveys; and short‐term phytoplankton community responses to El Niño Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) episodes. Increasing temperature, enhanced surface stratification, alteration of ocean currents, intensification or weakening of local nutrient upwelling, stimulation of photosynthesis by elevated CO2, reduced calcification through ocean acidification (“the other CO2 problem”), and heavy precipitation and storm events causing changes in land runoff and micronutrient availability may all produce contradictory species‐ or even strain‐specific responses. Complex factor interactions exist, and simulated ecophysiological laboratory experiments rarely allow for sufficient acclimation and rarely take into account physiological plasticity and genetic strain diversity. We can expect: (i) range expansion of warm‐water species at the expense of cold‐water species, which are driven poleward; (ii) species‐specific changes in the abundance and seasonal window of growth of HAB taxa; (iii) earlier timing of peak production of some phytoplankton; and (iv) secondary effects for marine food webs, notably when individual zooplankton and fish grazers are differentially impacted (“match‐mismatch”) by climate change. Some species of harmful algae (e.g., toxic dinoflagellates benefitting from land runoff and/or water column stratification, tropical benthic dinoflagellates responding to increased water temperatures and coral reef disturbance) may become more successful, while others may diminish in areas currently impacted. Our limited understanding of marine ecosystem responses to multifactorial physicochemical climate drivers as well as our poor knowledge of the potential of marine microalgae to adapt genetically and phenotypically to the unprecedented pace of current climate change are emphasized. The greatest problems for human society will be caused by being unprepared for significant range expansions or the increase of algal biotoxin problems in currently poorly monitored areas, thus calling for increased vigilance in seafood‐biotoxin and HAB monitoring programs. Changes in phytoplankton communities provide a sensitive early warning for climate‐driven perturbations to marine ecosystems.

Transport of toxic dinoflagellate cysts via ships' ballast water☆

Toxic dinoflagellate species that are not endemic to an area can be inadvertently introduced when their cysts are discharged with the ballast tank sediments of bulk container ships. These species, which can affect fish- and shellfish-farms, pose a serious threat to public health and aquaculture. Among 80 cargo vessels entering Australian ports, 40% contained viable dinoflagellate cysts and 6% carried the cysts of the toxic dinoflagellates Alexandrium catenella and A. tamarense (up to an estimated 300 million cysts per ship). The introduction of new Australian quarantine measures is discussed; however, the implications of this potential spreading of toxic algae are global.

Vegetative reproduction and sexual life cycle of the toxic dinoflagellate Gymnodinium catenatum from Tasmania, Australia

The toxic, chain‐forming dinoflagellate Gymnodinium catenatum Graham was cultured from vegetative cells and benthic resting cysts isolated from estuarine waters in Tasmania, Australia. Rapidly dividing, log phase cultures formed long chains of up to 64 cells whereas stationary phase cultures were composed primarily of single cells (23‐41 pm long, 27‐36 pm wide). Vegetative growth (mean doubling time 3‐4 days) was optimal at temperatures from 14.5‐20° C, salinities of 23‐34% and light irradiances of 50‐300 μE·m−2·s−1.

Comparative study on paralytic shellfish toxin profiles of the dinoflagellate Gymnodinium catenatum from three different countries

Paralytic shellfish toxin profiles of the dinoflagellate Gymnodinium catenatum Graham were investigated as a possible biochemical marker to distinguish different geographic populations of this species. Isolates obtained between 1986 and 1988 from Japan, Tasmania (Australia) and Galicia (Spain) were cultured under similar conditions and the toxins produced were analyzed using HPLC. Variations in temperature, salinity, and nitrate and phosphate levels in the culture medium had no significant effect on the toxin profile, suggesting that toxins can be used as a stable biochemical marker for this dinoflagellate. All the isolates produced mainly toxins of the N-sulfocarbamoyl group (C1–C4, gonyautoxins 5 and 6) but their relative abundance differed according to their geographic origin. Furthermore, only the Australian population produced the newly found 13-deoxydecarbamoyl toxins, and these could readily be used to distinguish the Australian populations from those of the other two countries.

Dinoflagellate Gymnodinium catenatum as the source of paralytic shellfish toxins in Tasmanian shellfish

Paralytic shellfish toxins in both cultured cells and natural phytoplankton blooms of the dinoflagellate Gymnodinium catenatum from inshore Tasmanian waters (Australia) were analyzed by high performance liquid chromatography, thin layer chromatography and electrophoresis techniques. The dinoflagellate toxins were dominated by low potency sulfocarbamoyl saxitoxin derivatives (98-99 mole% in total), including gonyautoxin VIII (C2) and its epimer (C1) and sulfocarbamoyl gonyautoxins I and IV (C3 and C4). Mussels and oysters contaminated by the dinoflagellate showed similar toxins, but contained larger proportions of C3 (40-57 mole%) and more potent carbamate toxins (7-23 mole% total).

Dinoflagellate cysts in recent marine sediments from Tasmania, Australia

Thirty-four cyst types capable of seeding plankton dinoflagellate populations have been identified in Tasmanian estuarine sediments. The most common cysts were those of Gonyaulax grindleyi, G. spinifera, Gymnodinium catenatum, Gyrodinium sp., Polykrikos schwartzii, Protoperidinium conicum, P. pentagonum, P. subinerme, Scrippsiella spp. and Zygabikodiniwn lenticuiatum. Also common were ovoid to spherical Alexandrium tamarense-like cysts, which lack distinctive taxonomic features and mucilaginous covering. These latter cysts could only be identified by incubation experiments, which produced living cells of Scrippsiella (2 spp.), Gyrodinium sp. and Alexandrium cf. excavatum. While Tasmanian dinoflagellate cyst assemblages resemble those of New South Wales, Australia, and New Zealand, one notable difference is the cyst of the toxic dinoflagellate Gymnodinium catenatum which appears to be confined to south-eastern Tasmania.

Ichthyotoxicity of Chattonella marina (Raphidophyceae) to damselfish ( Acanthochromis polycanthus ): the synergistic role of reactive oxygen species and free fatty acids

This investigation aimed to elucidate the relative roles of putative brevetoxins, reactive oxygen species and free fatty acids as the toxic principle of the raphidophyte Chattonella marina, using damselfish as the bioassay. Our investigations on Australian C. marina demonstrated an absence or only very low concentrations of brevetoxin-like compounds by radio-receptor binding assay and liquid chromatography-mass spectroscopy techniques. Chattonella is unique in its ability to produce levels of reactive oxygen species 100 times higher than most other algal species. However, high levels of superoxide on their own were found not to cause fish mortalities. Lipid analysis revealed this raphidophyte to contain high concentrations of the polyunsaturated fatty acid eicosapentaenoic acid (EPA; 18-23% of fatty acids), which has demonstrated toxic properties to marine organisms. Using damselfish as a model organism, we demonstrated that the free fatty acid (FFA) form of EPA produced a mortality and fish behavioural response similar to fish exposed to C. marina cells. This effect was not apparent when fish were exposed to other lipid fractions including a triglyceride containing fish oil, docosahexaenoate-enriched ethyl ester, or pure brevetoxin standards. The presence of superoxide together with low concentrations of EPA accelerated fish mortality rate threefold. We conclude that the enhancement of ichthyotoxicity of EPA in the presence of superoxide can account for the high C. marina fish killing potential

Takayama Gen, Nov (Gymnodiniales, Dinophyceae), a new genus of unarmored Dinoflagellates with sigmoid apical grooves, including the description of two new species

A new potentially ichthyotoxic dinoflagellate genus, Takayama de Salas, Bolch, Botes et Hallegraeff gen. nov., is described with two new species isolated from Tasmanian (Australia) and South African coastal waters: T. tasmanica de Salas, Bolch et Hallegraeff, sp. nov. and T. helix, de Salas, Bolch, Botes et Hallegraeff, sp. nov. The genus and two species are characterized by LM and EM of field samples and laboratory cultures as well as large subunit rDNA sequences and HPLC pigment analyses of several cultured strains. The new Takayama species have sigmoid apical grooves and contain fucoxanthin and its derivatives as the main accessory pigments. Takayama tasmanica is similar to the previously described species Gymnodinium pulchellum Larsen, Gyrodinium acrotrochum Larsen, and G. cladochroma Larsen in its external morphology but differs from these in having two ventral pores, a large horseshoe‐shaped nucleus, and a central pyrenoid with radiating chloroplasts that pass through the nucleus. It contains gyroxanthin‐diester and a gyroxanthin‐like accessory pigment, both of which are missing in T. helix. Takayama helix has an apical groove that is nearly straight while still being clearly inflected. A ventral pore or slit is present. It has numerous peripheral, strap shaped, and spiraling chloroplasts with individual pyrenoids and a solid ellipsoidal nucleus. The genus Takayama has close affinities to the genera Karenia and Karlodinium.

Reproductive compatibility among four global populations of the toxic dinoflagellate Gymnodinium catenatum (Dinophyceae)

Abstract Reproductive compatibility was examined among 21 strains of Gymnodinium catenatum derived from four different populations from across the globe: Tasmania, Australia (15 strains), Japan (2 strains), Spain (2 strains) and Portugal (2 strains). Pairwise crossing of strains demonstrated extensive intrapopulation compatibility (to resting cyst formation) among all four populations. The observations were most consistent with a heterothallic, multiple-group mating system, requiring more than two groups to explain the pairwise crossing data. Despite the ability of strains from different populations to produce resting cysts, the viability of progeny was highly variable among interpopulation crosses. Cysts from all crosses showed a high germination percentage (93–100%) and released a swimming planomeiocyte. Crosses between different Tasmanian strains, and those between Spanish and Japanese strains, showed high post-meiotic viability (65% and 80%, respectively). However, progeny from Tasmanian–Spanish and Tasmanian–Japanese crosses showed very low post-meiotic viability (5–10%), indicating a higher level of somatic incompatibility between these populations. Significant differences in sexual life-history (e.g. rate of gamete formation and cyst dormancy) were also noted between interpopulation crosses, suggesting genetically determined strain- and population-level differences. The crossing data indicate a high level of mating diversity within the Australian population and show that the Japanese and Spanish populations are more closely related to each other than to Australian populations; this is supported by molecular studies. Implications for the proposed global dispersal of G. catenatum and the use of interbreeding to examine population relationships are discussed. New measures are proposed for examining strain (RCs) and population (RCp) levels of reproductive compatibility, respectively, which are calculated as the product of proportion of successful matings (termed the compatibility index) and the number of cysts produced (average vigour) in successful crosses.

Harmful algal blooms in the Australian region

Abstract In the past two decades, there has been an apparent increase in the frequency, intensity and geographical distribution of harmful algal blooms in Australian coastal, estuarine and fresh waters. Wild and cultured fish kills have been associated with blooms of the dinoflagellates Scrippsiella trochoidea (through the generation of anoxic conditions), Cochlodinium cf. helix, Gymnodinium cf. galatheanum, Gymnodinium mikimotoi and the golden-brown flagellate Prymnesium parvum (most likely through the production of substances affecting the gills of fish). Contamination of shellfish products with algal toxins has been caused by the diatoms Rhizosolenia cf. chunii (bitter-tasting compound), the dinoflagellates Alexandrium catenella, A. minutum and Gymnodinium catenatum (paralytic shellfish poisons) and, to a lesser extent, the dinoflagellates Dinophysis acuminata and D. fortii (diarrhetic shellfish poisons). Poisoning of cattle and wildlife or contamination of drinking water supplies by blue-green algal toxins from Nodularia spumigena (brackish water), Anabaena circinalis and Microcystis aeruginosa (freshwater) is also an increasing problem. The management of nutrient discharges to inland and coastal waterways is crucial to arrest the increasing impact of harmful algal blooms.