Elisa Berdalet

EFFECTS OF TURBULENCE ON THE MARINE DINOFLAGELLATE GYMNODINIUM NELSONII1

Laboratory experiments were conducted to study the effects of agitation on growth, cell division, and nucleic acid dynamics of the dinoflagellate Gymnodinium nelsonii Martin. When cultures were placed on an orbital shaker at 100 rpm, cell division was prevented, cellular volume increased up to 1.5 times that of the nonperturbed cells, the form and location of the cell nucleus were modified, and the RNA and DNA concentrations per cell increased up to 10 times those of the controls. When shaking was stopped after 10 days, cells divided immediately at about 2/3 of the division rate of the unshaken populations, and all the altered parameters were restored. If the agitation continued for more than 20 days, total cell death and disintegration occurred. Several cellular types differing in size and shape were observed in the control and shaken cultures. One possible hypothesis for these results is that failure of the cell to divide results from physical disturbance of the microtubule assemblage associated with chromosome separation during mitosis. My study suggests that small‐scale oceanic turbulence of sufficient intensity may inhibit growth of individual dinoflagellate cells, but immediate development of the population may continue when calm weather follows the active mixing period.

DETECTION OF THE TOXIC DINOFLAGELLATE ALEXANDRIUM FUNDYENSE (DINOPHYCEAE) WITH OLIGONUCLEOTIDE AND ANTIBODY PROBES: VARIABILITY IN LABELING INTENSITY WITH PHYSIOLOGICAL CONDITION

 The toxic dinoflagellate Alexandrium fundyense Balech was grown under temperature‐ and nutrient‐limited conditions, and changes in labeling intensity on intact cells were determined for two probe types: an oligonucleotide probe targeting rRNA and a monoclonal antibody (MAb) targeting a cell surface protein. In nutrient‐replete batch culture, labeling with the rRNA probe was up to 400% brighter during exponential phase than during stationary phase, whereas MAb labeling did not change significantly with growth stage at the optimal growth temperature. In cultures grown at suboptimal, low temperatures, there was a significant difference between labeling intensity in stationary versus exponential phase for both probe types, with exponential cells labeling brighter with the rRNA probe and slightly weaker with the MAb. The decrease in rRNA probe labeling with increasing culture age was likely due to lower abundance of the target nucleic acid, as extracted RNA varied in a similar manner. With the MAb and the rRNA probes, slower growing cultures at low, nonoptimal temperature labeled 35% and 50% brighter than cells growing faster at warmer temperatures. Some differences in labeling intensity per cell disappeared when the data were normalized to surface area or volume, which indicated that the number of target antigens or rRNA molecules was relatively constant per unit area or volume, respectively. Slow growth accompanying phosphorus and nitrogen limitation resulted in up to a 400% decrease in labeling intensity with the rRNA probe compared to nutrient‐replete levels, whereas the MAb labeling intensity increased by a maximum of 60%. With both probes, labeling was more intense under phosphorus limitation than under nitrogen limitation, and for all conditions tested, labeling intensity was from 600% to 3600% brighter with the MAb than with the rRNA probe. Thus, it is clear that significant levels of variability in labeling intensity can be expected with both probe types because of the influence of environmental conditions and growth stage on cellular biochemistry, cell size,rRNA levels, and the number or accessibility of cell surface proteins. Of the two probes tested, the rRNA probe was the most variable, suggesting that in automated, whole‐cell assays, it can be used only in a semiquantitative manner. For manual counts, the human eye will likely accommodate the labeling differences. The MAb probe was less variable, and thus should be amenable to both manual and automated counts.

Dissolved and particulate organic carbon and nitrogen in the Northwestern Mediterranean

The distribution of dissolved organic carbon (DOC) and nitrogen (DON) and particulate organic carbon (POC) and nitrogen (PON) was studied on a transect perpendicular to the Catalan coast in the NW Mediterranean in June 1995. The transect covered a hydrographically diverse zone, including coastal waters and two frontal structures (the Catalan and the Balear fronts). The cruise was conducted during the stratified period, characterized by inorganic nutrient depletion in the photic zone and a well established deep chlorophyll a maximum. DOC concentrations were measured using a high-temperature catalytic oxidation method, and DON was determined directly, with an update of the Kjeldahl method, after removal of inorganic nitrogen. The ranges of DOC and DON concentrations were 44–95 μM-C and 2.8–6.2 μM-N. The particulate organic matter ranged between 0.9 and 14.9 μM-C and from 0.1 to 1.7 μM-N. The DOC : DON molar ratio averaged 15.5±0.4, and the mean POC : PON ratio was 8.6±0.6. The distribution of dissolved organic matter (DOM) was inverse to that of the salinity. The highest concentrations of DOM were found in coastal waters and in the stations affected by the Catalan front, located at the continental shelf break. It was estimated that recalcitrant DOM constituted 67% of the DOM pool in the upper 50 m. The data suggest that accumulation of DOC due to the decoupling of production and consumption may occur in the NW Mediterranean during stratification and that the organic matter exported from the photic layer is dominated by C-rich material.

Marine harmful algal blooms, human health and wellbeing: challenges and opportunities in the 21st century

Microalgal blooms are a natural part of the seasonal cycle of photosynthetic organisms in marine ecosystems. They are key components of the structure and dynamics of the oceans and thus sustain the benefits that humans obtain from these aquatic environments. However, some microalgal blooms can cause harm to humans and other organisms. These harmful algal blooms (HABs) have direct impacts on human health and negative influences on human wellbeing, mainly through their consequences to coastal ecosystem services (fisheries, tourism and recreation) and other marine organisms and environments. HABs are natural phenomena, but these events can be favoured by anthropogenic pressures in coastal areas. Global warming and associated changes in the oceans could affect HAB occurrences and toxicity as well, although forecasting the possible trends is still speculative and requires intensive multidisciplinary research. At the beginning of the 21st century, with expanding human populations, particularly in coastal and developing countries, mitigating HABs impacts on human health and wellbeing is becoming a more pressing public health need. The available tools to address this global challenge include maintaining intensive, multidisciplinary and collaborative scientific research, and strengthening the coordination with stakeholders, policymakers and the general public. Here we provide an overview of different aspects of the HABs phenomena, an important element of the intrinsic links between oceans and human health and wellbeing.

Species-specific physiological response of dinoflagellates to quantified small-scale turbulence

Turbulence has been shown to alter different aspects of the physiology of some dinoflagellates. The response appears to be species‐specific and dependent on the experimental design and setup used to generate small‐scale turbulence. We examined the variability of the response of three dinoflagellate species to the turbulence, following the same experimental design used by Berdalet (1992) on Akashiwo sanguinea (Hirasaka) Ge. Hansen et Moestrup (=Gymnodinium nelsonii G. W. Martin). In all experiments, turbulence was generated by an orbital shaker at 100 rpm, which corresponded on bulk average, to dissipation rates (ε, quantified using an acoustic Doppler velocimeter) of ≈2 cm2 · s−3. Turbulence did not appreciably affect Gymnodinium sp., a small dinoflagellate. However, Alexandrium minutum Halim and Prorocentrum triestinum J. Schiller exhibited a reduced net growth rate (33% and 28%, respectively) when shaken during the exponential growth phase. Compared to the still cultures, the shaken treatments of A. minutum and P. triestinum increased the mean cell volume (up to 1.4‐ and 2.5‐fold, respectively) and the mean DNA content (up to 1.8‐ and 5.3‐fold, respectively). Cultures affected by turbulence recovered their normal cell properties when returned to still conditions. The swimming speed of the cells exposed to agitation was half that of the unshaken ones. Overall, the response of A. minutum and P. triestinum was similar, but with lower intensity, to that observed previously on A. sanguinea. We found no clear trends related to taxonomy or morphology.

An Updated Review of Ciguatera Fish Poisoning: Clinical, Epidemiological, Environmental, and Public Health Management

Ciguatera Fish Poisoning (CFP) is the most frequently reported seafood-toxin illness in the world. It causes substantial human health, social, and economic impacts. The illness produces a complex array of gastrointestinal, neurological and neuropsychological, and cardiovascular symptoms, which may last days, weeks, or months. This paper is a general review of CFP including the human health effects of exposure to ciguatoxins (CTXs), diagnosis, human pathophysiology of CFP, treatment, detection of CTXs in fish, epidemiology of the illness, global dimensions, prevention, future directions, and recommendations for clinicians and patients. It updates and expands upon the previous review of CFP published by Friedman et al. (2008) and addresses new insights and relevant emerging global themes such as climate and environmental change, international market issues, and socioeconomic impacts of CFP. It also provides a proposed universal case definition for CFP designed to account for the variability in symptom presentation across different geographic regions. Information that is important but unchanged since the previous review has been reiterated. This article is intended for a broad audience, including resource and fishery managers, commercial and recreational fishers, public health officials, medical professionals, and other interested parties.

Hydrography and biochemical indicators of microplankton biomass in the Bransfield Strait (Antarctica) during January 1994

The relationships between hydrography and spatial distribution of several biochemical indicators of microplankton biomass (chlorophyll, protein and ATP) were studied in an area covering the eastern part of the Bransfield Strait and the northern part of the Weddell Sea, during Antarctic summer (January 1994). Four hydrographic zones were identified: (a) the northern part of the Bransfield Strait, covered by waters of Bellings- hausen Sea origin; (b) a Weddell Sea water mass that affected most of the study area; (c) the Weddell-Scotia Confluence waters, observed north of Elephant Island; and (d) waters influenced by ice melting, found towards the southeastern part of the sampled area. The highest values of biomass indicators (chlorophyll a, ATP and protein) were found in the zones affected by ice-melting processes and in waters from the Bellingshausen Sea. The lowest values of all biochemical parameters were found in the Weddell Sea and in the Weddell-Scotia Confluence waters. A high variability in the hydrographic structure and the distribution of biochemical indicators was observed. The degree of stabilization of the water column, the depth of the upper mixed layer and the grazing pressure of herbivorous zooplankton played a major role in the development, accumulation and spatial variability of microplankton biomass.

Variations in biochemical parameters of Heterocapsa sp. and Olisthodiscus luteus grown in 12:12 light:dark cycles I. Cell cycle and nucleic acid composition

The division cycle of two phytoplankton species, Olisthodiscus luteus and Heterocapsa sp. was studied in relation to a 12:12 light:dark cycle. Batch cultures in exponential phase were sampled every three hours during 48 hours. Cell number, cellular volume and DNA and RNA concentrations were measured. Microscopic observations of the nuclei of Heterocapsa sp. were also performed. In both species, cell division took place in the dark. In Heterocapsa sp., DNA and RNA showed a similar diel variability pattern, with synthesis starting at the end of the light period, previously to mitosis and cytokinesis. In O. luteus. Major RNA synthesis occurred during darkness, and DNA was produced almost continuously. Both species presented different values and diel rhythmicity on the RNA/DNA ratios.

DETERMINATION OF RNA AND DNA CONCENTRATIONS IN NATURAL PLANKTON SAMPLES USING THIAZOLE ORANGE IN COMBINATION WITH DNASE AND RNASE DIGESTIONS

A fluorometric technique, based on the combination of RNase and DNase incubation with the use of thiazole orange (RNase/DNase method), was investigated to determine DNA and RNA concentrations in marine plankton. Tests were performed to optimize both RNase and DNase assay conditions. The RNase assay should be conducted at 37° C for 20 min with 0.5 μg·mL−1 of DNase‐free RNase. An incubation at 25° C for 20 min with 10 units ·mL‐1 of RNase‐free DNase were the optimal conditions required for DNA digestion by DNase. The detection limits in terms of minimum biomass for reliable measurements of DNA and RNA were 7.5 and 10 μg of protein · (mL assay)−1, respectively.

Variations in biochemical parameters of Heterocapsa sp. and Olisthodiscus luteus grown in 12:12 light:dark cycles II. Changes in pigment composition

Photosynthetic pigment composition was studied in batch cultures of Heterocapsa sp. and Olisthodiscus luteus growing exponentially in a 12:12 light:dark cycle. Both species divided in the dark. The synthesis of pigments was continuous for both species. However for chlorophyll c and peridinin, in Heterocapsa sp., and chlorophyll c and fucoxanthin, in O. luteus, (pigments belonging to light harvesting complexes) the synthesis was significantly higher during the light period. Concentrations per total cell volume (TCV) of chlorophyll a, chlorophyll c, peridinin and diadinoxanthin in Heterocapsa sp., and chlorophyll a, chlorophyll c, fucoxanthin and violaxanthin in O. luteus, showed a maximum at the onset of light and decreased during the light period. The values of the chlorophyll a:chlorophyll c, chlorophyll a:peridinin and chlorophyll a:fucoxanthin ratios are compared with data reported in the literature.