| 1. |
- Lundgren, Veronica, et al.
(författare)
-
Metabolic and physiological changes in Prymnesium parvum when grown under, and grazing on prey of, variable nitrogen:phosphorus stoichiometry
- 2016
-
Ingår i: Harmful Algae. - : Elsevier BV. - 1568-9883 .- 1878-1470. ; 55, s. 1-12
-
Tidskriftsartikel (refereegranskat)abstract
- Mixotrophy is found in almost all classes of phytoplankton in a wide range of aquatic habitats ranging from oligotrophic to eutrophic marine and freshwater systems. Few studies have addressed how the nutritional status of the predator and/or the prey affects mixotrophic metabolism despite the realization that mixotrophy is important ecologically. Laboratory experiments were conducted to examine changes in growth rates and physiological states of the toxic haptophyte Prymnesium parvum when fed Rhodomonas sauna of varying nutritional status. Haemolytic activity of P. parvum and prey mortality of R. sauna were also measured. P. parvum cultures grown to be comparatively low in nitrogen (low-N), phosphorus (low-P) or low in both nutrients (low-NP) were mixed with low-NP, low-N, and low-P R. saline in all possible combinations, i.e., a 3 x 3 factorial design. N deficiency was obtained in the low-N cultures, while true P deficiency may not have been obtained in the low-P cultures. Mortality rates of R. salina (both due to ingestion and/or cell rupture as a function of grazing or toxic effects) were higher when R. sauna cells were low-P, N-rich, regardless of the nutritional state of P. parvum. Mortality rates were, however, directly related to the initial prey:predator cell ratios. On the other hand, growth of the predator was a function of nutritional status and a significant positive correlation was observed between growth rates of P. parvum and cell-specific depletion rates of N, whereas no such relationship was found between P. parvum growth rates and depletion rates of P. In addition, the greatest changes in chlorophyll content and stoichiometric ratios of P. parvum were observed in high N:P conditions. Therefore, P. parvum may show enhanced success under conditions of higher inorganic N:P, which are likely favored in the future due to increases in eutrophication and altered nutrient stoichiometry driven by anthropogenic nutrient loads that are increasingly enriched in N relative to P. (C) 2016 Elsevier B.V. All rights reserved.
|
|
| 2. |
- Granéli, Edna, et al.
(författare)
-
Can increases in temperature stimulate blooms of the toxic benthic dinoflagellate Ostreopsis ovata?
- 2011
-
Ingår i: Harmful Algae. - : Elsevier. - 1568-9883 .- 1878-1470. ; 10:2, s. 165-172
-
Tidskriftsartikel (refereegranskat)abstract
- Ostreopsis ovata Fukuyo is an epiphytic, toxic dinoflagellate, inhabiting tropical and sub-tropical waters worldwide and also in certain temperate waters such as the Mediterranean Sea. Toxic blooms of O. ovata have been reported in SE Brazil in 1998/99 and 2001/02 and the French-Italian Riviera in 2005 and 2006. These blooms had negative effects on human health and aquatic life. Chemical analyses have indicated that O. ovata cells produce palytoxin, a very strong toxin, only second in toxicity to botulism. Increase in water temperature by several degrees has been suggested as the reason for triggering these blooms. Four laboratory experiments were performed with O. ovata isolated from Tyrrhenian Sea, Italy to determine the effects of water temperature and co-occurring algae on the cell growth and/or the toxicity of O. ovata. The cells were grown under different temperatures ranging from 16 °C to 30 °C, and cell densities, growth rates and the cell toxicities were studied. Results indicated high water temperatures (26-30 °C) increased the growth rate and biomass accumulation of O. ovata. In mixed cultures of O. ovata with other co-occurring algae, biomass decreased due to grazing by ciliates. Cell toxicity on the other hand was highest at lower temperatures, i.e., between 20 and 22 °C. The present study suggests that sea surface temperature increases resulted by global warming could play a crucial role inducing the geographical expansion and biomass accumulation by blooms of O. ovata.
|
|
| 3. |
- Vidyarathna, Nayani K., 1979-
(författare)
-
Influence of Human-induced Environmental Changes on the Physiology of the Harmful Benthic Marine Microalga Ostreopsis ovata
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focus on the influence of human-induced environmental changes on the physiology of Ostreopsis ovata; a toxic, benthic dinoflagellate, which form blooms in tropical and temperate marine waters. O. ovata produces palytoxin and ovatoxins and copious amount of mucilage, all of which have significant negative ecological impacts on the benthic ecosystems where they occur. Understanding the factors affecting O. ovata growth and toxin production is therefore of great importance if we are to understand how this species form such successful blooms. To accomplish this, growth, toxicity, carbohydrate accumulation and related physiological traits of two strains of O. ovata (one from Japanese waters and the other from Mediterranean waters) were studied in laboratory experiments. The cells were grown under the conditions simulating climate-induced changes (higher temperatures and acidification of marine waters) and eutrophication (increase of nitrogen and phosphorus in coastal ecosystems).O. ovata showed strain-specific responses to the tested environmental changes. Higher temperatures increased growth and reduced the cell toxin quota of the Mediterranean strain while it decreased the growth and toxicity of the Japanese strain. Nutrient (nitrogen-N and phosphorus-P) sufficiency significantly increased O. ovata biomass accumulation. N deficiency markedly decreased the growth while it increased cell toxicity. Lower temperatures (20 - 25 °C) increased the particulate carbohydrate accumulation in both strains. Cell volumes, C (carbon), N and P cell quotas and atomic ratios of O. ovata were significantly higher when grown at 20 °C, than those grown at 30 °C. Acidification did not significantly affect growth and cell toxicity, but increased particulate carbohydrate accumulation. The combined effect of higher temperature and acidification delayed the onset of the blooms by 3 - 5 days, in relation to present temperature and pH conditions.When extrapolating these results to natural marine ecosystems, it can be inferred that O. ovata occurring in lower-latitudes are growing optimally in the present climate conditions. On the other hand, the strains of O. ovata in higher-latitudes seem to have higher temperature optima than they have now at present conditions. Therefore, further expansion of O. ovata blooms is most likely possible in the warm, eutrophic coastal waters in higher-latitudes.
|
|
| 4. |
- Vidyarathna, Nayani K., et al.
(författare)
-
Influence of temperature on growth, toxicity and carbohydrate production of a Japanese Ostreopsis ovata strain, a toxic-bloom-forming dinoflagellate
- 2012
-
Ingår i: Aquatic Microbial Ecology. - : Inter-Research Science Center. - 0948-3055 .- 1616-1564. ; 65:3, s. 261-270
-
Tidskriftsartikel (refereegranskat)abstract
- Ostreopsis ovata is a benthic dinoflagellate that produces palytoxin and its analogues.Since the end of the 1990s, toxic blooms of O. ovata have been recorded in many tropicaland temperate marine waters. These blooms often kill benthic invertebrates and cause healthproblems for humans. We hypothesize that increases in seawater temperature might induce theseblooms. A strain of O. ovata isolated from the southern coast of Japan was selected for study. O.ovata cells were exposed to 7 different temperatures from 24 to 30°C for 30 d, and growth rateswere noted. The specific growth rate was found to be highest at 25°C, next highest at 24°C andlower at 26, 28, 27, 30 and 29°C, in that order. The hypothesis that increased seawater temperaturecauses increases in growth rate was thus not supported. The cell toxicity and car bohydrate productionof O. ovata were highest at the temperature range that is optimal for cell growth. Increasesingsea surface temperature, as a result of global warming, is therefore not likely to have asubstantial effect on the bloom formation and toxicity of this Japanese strain of O. ovata.
|
|
| 5. |
- Vidyarathna, Nayani K., et al.
(författare)
-
Physiological responses of Ostreopsis ovata to changesin N and P availability and temperature increase
- 2013
-
Ingår i: Harmful Algae. - : Elsevier. - 1568-9883 .- 1878-1470. ; 21-22, s. 54-63
-
Tidskriftsartikel (refereegranskat)abstract
- Ostreopsis ovata is a benthic dinoflagellate that produces palytoxin and ovatoxins. Blooms of O. ovata causing human health problems and mortality of benthic fauna have been reported from many tropical and temperate marine waters. In the present study we examined the combined effects of temperature and different nutrient conditions on the biochemical composition, growth, toxicity and carbohydrate production of an O. ovata strain originating from the Tyrrhenian Sea. O. ovata cultures with N:P ratios of 1.6, 16 and 160 (N deficient, NP sufficient and P deficient, respectively) were grown at 20 °C and 30 °C. Biomass accumulation, growth rates, cell volumes, biochemical composition, cell toxicity and carbohydrate production in each treatment were studied. Results indicated that under nutrient sufficiency O. ovata biomass accumulation increased significantly compared to N and P deficiency and also that N limitation severely affected growth. The highest growth rates were recorded at 30 °C. Cellular contents and the atomic ratios of C, N and P were higher in the cells grown at 20 °C than in those grown at 30 °C. O. ovata cell volumes increased at 20 °C. N deficiency significantly increased cell toxicity. Toxicity per cell was higher at 20 °C, but per carbon was highest at 30 °C. The highest carbohydrate production was found in conditions of N deficiency and at the lower temperature.Our study suggests that temperature increases due to global warming and nutrient enrichment of coastal waters stimulate the proliferation of O. ovata, particularly for the strains that have become adapted to warm temperate waters.
|
|
| 6. |
- Vidyarathna, Nayani K., et al.
(författare)
-
The effects of aeration on growth and toxicity of Prymnesium parvum grown with and without algal prey.
- 2014
-
Ingår i: Harmful Algae. - : Elsevier. - 1568-9883 .- 1878-1470. ; 39, s. 55-63
-
Tidskriftsartikel (refereegranskat)abstract
- We investigated the effects of aeration on growth and toxicity of the haptophyte Prymnesium parvum in the presence and absence of the algal prey Rhodomonas salina. Batch monocultures of P-limited P. parvum and N and P sufficient R. salina and mixed cultures of the two microalgae were grown with no, low (20) and high (100) ml min1 aeration for 18 days. Cell growth of P. parvum and R. salina and cell toxicity of P.parvum were studied over the experimental period. The highest specific growth rates of P. parvum were found at low aeration rates. R. salina in monocultures showed typical growth patterns, while R. salina numbers declined rapidly in the mixed cultures. Of the initial cell densities, 98–100% of the R. salina cells were lysed or ingested within 24 h of mixing with P. parvum cells. The maxima P. parvum biomasses were significantly higher in the mixed cultures than in the monocultures. Cell toxicity of P. parvum increased significantly in response to aeration rates and the highest levels were found in the high aeration condition. Availability of prey and resupply of inorganic nutrients decreased P. parvum cell toxicity. Our study suggests that P. parvum is tolerant and is able to grow over a broad range of aeration and associated turbulence effects though low aeration represents an optimal condition for growth. As P. parvum toxicity was higher in the high aeration treatment we suggest that the higher concentrations of oxygen cause more toxins to be produced, as these are oxygen rich compounds. We suggest that oxygenation and turbulence of surface waters caused by mixing may be involved in promoting high toxic P. parvum blooms in shallow lakes and coastal waters.
|
|
