Distribution of Gymnodinium catenatum Graham cysts and its relation to harmful algae blooms in the northern Gulf of California

Germination of cysts serves as inoculum for the proliferation of some dinoflagellates, and cyst abundance in sediments represents crucial information to understand and possibly predict Harmful Algae Blooms (HABs). Cyst distribution is related to the physical characteristics of the sediments and the hydrodynamics (circulation) of a particular region. In the northern Gulf of California (nGC) several Gymnodinium catenatum HABs have been recorded. However, the presence of resting cysts and the effect of hydrodynamics on their distribution in the nGC have not been investigated. This study evaluated cyst abundance, distribution and their relation to local circulation in surface sediments during two periods that coincided with a non-bloom year condition (July 2016) and after a major HAB registered in the nGC that occurred in January 2017. Also, a numerical ocean model was implemented to characterize the transport and relocation of cysts and sediments in the region. Gymnodinium catenatum cysts were heterogeneously distributed with some areas of high accumulation (as high as 158 cyst g−1, and 27% of total cyst registered). Cysts seemed to be transported in an eastward direction after deposition and accumulated in an extensive area that probably is the seedbed responsible for the initiation of HABs in the region. The nGC is a retention area of cysts (and sediments) that permit the formation of seedbeds that could be important for G. catenatum HAB development. Our results provide key information to understand G. catenatum ecology and specifically, to understand the geographic and temporal appearance of HABs in the nGC.

Cell Death and Metabolic Stress in Gymnodinium catenatum Induced by Allelopathy

Allelopathy between phytoplankton species can promote cellular stress and programmed cell death (PCD). The raphidophyte Chattonella marina var. marina, and the dinoflagellates Margalefidinium polykrikoides and Gymnodinium impudicum have allelopathic effects on Gymnodinium catenatum; however, the physiological mechanisms are unknown. We evaluated whether the allelopathic effect promotes cellular stress and activates PCD in G. catenatum. Cultures of G. catenatum were exposed to cell-free media of C. marina var. marina, M. polykrikoides and G. impudicum. The mortality, superoxide radical (O2●−) production, thiobarbituric acid reactive substances (TBARS) levels, superoxide dismutase (SOD) activity, protein content, and caspase-3 activity were quantified. Mortality (between 57 and 79%) was registered in G. catenatum after exposure to cell-free media of the three species. The maximal O2●− production occurred with C. marina var. marina cell-free media. The highest TBARS levels and SOD activity in G. catenatum were recorded with cell-free media from G. impudicum. The highest protein content was recorded with cell-free media from M. polykrikoides. All cell-free media caused an increase in the activity of caspase-3. These results indicate that the allelopathic effect in G. catenatum promotes cell stress and caspase-3 activation, as a signal for the induction of programmed cell death.

Ancient DNA and microfossils reveal dynamics of three harmful dinoflagellate species off Eastern Tasmania, Australia, over the last 9,000 years

Harmful algal blooms (HABs) have significantly impacted the seafood industry along the Tasmanian east coast over the past three decades, and are expected to change in frequency and magnitude due to climate change induced changing oceanographic conditions. To investigate the long-term history of regional HABs, a combination of palynological and sedimentary ancient DNA (sedaDNA) analyses was applied to marine sediment cores from inshore (up to 145 years old) and offshore (up to ~9,000 years) sites at Maria Island, southeast Tasmania. Analyses focused Paralytic Shellfish Toxin (PST) producing dinoflagellates Alexandrium catenella and Gymnodinium catenatum, and the red-tide dinoflagellate Noctiluca scintillans, which were specifically targeted using a hybridization capture sedaDNA technique. Identification of primulin-stained A. catenella cysts throughout the inshore sediment core, together with sedaDNA evidence of a bloom-phase of Alexandrium ~15 years ago, indicates recent stimulation of a cryptic endemic population. Morphologically similar but unstained Alexandrium cysts were observed throughout the offshore core, with sedaDNA confirming the presence of A. catenella from ~8,300 years ago to present. Gymnodinium catenatum cysts were detected only in inshore surface sediments from 30 years ago to present, supporting previous evidence of a 1970s introduction via shipping ballast water. sedaDNA confirmed the presence of G. catenatum-related sequences in the inshore and offshore cores, however, unambiguous species identification could not be achieved due to limited reference sequence coverage of Gymnodinium. Our hybridization capture sedaDNA data also confirmed the historically recent dispersal of the non-fossilizing dinoflagellate Noctiluca scintillans, detected inshore from ~30 years ago, matching first observations of this species in Tasmanian waters in 1994. At the offshore site, N. scintillans sedaDNA was detected only in surface sediments, confirming a recent climate-driven range expansion this species. This study provides new insights into the distribution and abundance of three HAB species in the Tasmanian region, including clues to past bloom phases. Further research into paleo-environmental conditions and paleo-community structure are required to identify the factors driving bloom phases through time and predict plankton community responses under different future climate scenarios.HighlightsDinocyst and sedaDNA analyses were applied to marine sediments off TasmaniaAlexandrium catenella has been endemic to Australia for at least ~9,000 yearsRecent A. catenella blooms are likely induced by climate and oceanographic changeGymnodinium catenatum cysts in recent (~30y) sediments confirm a 1970s introductionNoctiluca scintillans sedaDNAin recent (~30y) sediments matches a 1994 introduction

Harmful micro-algal blooms and local environmental conditions of the coastal fringe: Moroccan Mediterranean coasts as a case study

The dynamic study of harmful phytoplankton, conducted from June 2013 to May 2014, has tracked the evolution of the microalgae community at four sites located along the Moroccan western Mediterranean coast. 91 species and genera of phytoplankton were identified, 8 of which are recognized as potentially toxic. The genus Pseudo-nitzschia, a diatom known to produce domoic acid, is quite prevalent in all four sites, particularly in spring. The toxic dinoflagellate species detected in our study are Gymnodinium catenatum, Alexandrium sp PSP producers, Prorocentruml Lima, Dinophysis acuminata, D. caudata, D. fortii DSP producer, and Ostreopsis sp known palytoxin producer. The species Gymnodinium catenatum proliferates intensively from S1 to S3 in winter and S4 in summer, while Alexandrium sp proliferates mainly during spring and late summer with an exceedance of the threshold. Significant blooms of Dinophysis sp were recorded during the summer at all sites. On the other hand, the abundance of Ostreopsis sp was noted during the spring summer period with low concentrations. Discriminant analysis (DFA) of nutrients, toxic species identifies perfect seasonal discrimination. Winter and fall are characterized by high nutrient inputs, but algal biomass is low. On the contrary, spring and summer are characterized by a depletion of nutrients in the environment following the assimilation of these elements by phytoplankton.