Biogeography of bloom-forming microcystin producing and non-toxigenic populations of Dolichospermum lemmermannii (Cyanobacteria)

In the last decades, the cyanobacterium Dolichospermum lemmermannii showed an increasing spread to Southern Europe, raising serious concerns due to its ability to produce cyanotoxins. The widening of its geographic distribution and the observation of strains showing high optimum temperature underline its ecological heterogeneity, suggesting the existence of different ecotypes. To investigate its biogeography, new isolates from different European water bodies, together with strains maintained by the Norwegian Institute for Water Research Culture Collection of Algae, were genetically characterised for the 16S rRNA gene and compared with strains obtained from public repositories. Geographic distance highly influenced the differentiation of genotypes, further suggesting the concurrent role of geographic isolation, physical barriers and environmental factors in promoting the establishment of phylogenetic lineages adapted to specific habitats. Differences among populations were also examined by morphological analysis and evaluating the toxic potential of single strains, which revealed the exclusive ability of North European strains to produce microcystins, whereas the populations in Southern Europe tested negative for a wide range of cyanotoxins. The high dispersion ability and the existence of toxic genotypes indicate the possible spread of harmful blooms in other temperate regions.     

ANNA – Artificial Neural Network model for predicting species abundance and succession of blue-green algae

Predictive potential of deductive and inductivephytoplankton models are compared regarding theirusefulness for forecasting and control of harmfulalgal blooms. While applications of deductive modelsstill seem to be restricted by lack of knowledge, ad hocinductive models sometimes prove to bestraightforward and useful. The inductive neuralnetwork model ANNA is documented by means of anapplication to Lake Kasumigaura, Japan. ANNA wasvalidated for five blue-green algae species wherepredictive accuracy has improved with increased eventand time resolution of training data. A scenarioanalysis on species succession has demonstrated thepotential of ANNA for hypothesis testing. Finally,implications for use of ANNA for operational algalbloom control are discussed.     

Alteration of plankton communities and biogeochemical cycles by harmful Cochlodinium polykrikoides (Dinophyceae) blooms

Cochlodinium polykrikoides is a globally distributed, ichthyotoxic, bloom-forming dinoflagellate. Blooms of C. polykrikoides manifest themselves as large (many km²) and distinct patches with cell densities exceeding 10³ ml⁻¹ while water adjacent to these patches can have low cell densities (<100 cells ml⁻¹). While the effect of these blooms on fish and shellfish is well-known, their impacts on microbial communities and biogeochemical cycles are poorly understood. Here, we investigated plankton communities and the cycling of carbon, nitrogen, and B-vitamins within blooms of C. polykrikoides and compared them to areas in close proximity (<100 m) with low C. polykrikoides densities. Within blooms, C. polykrikoides represented more than 90% of microplankton (>20 μm) cells, and there were significantly more heterotrophic bacteria and picoeukaryotic phytoplankton but fewer Synechococcus. Terminal restriction fragment length polymorphism analysis of 16S and 18S rRNA genes revealed significant differences in community composition between bloom and non-bloom samples. Inside the bloom patches, concentrations of vitamin B₁₂ were significantly lower while concentrations of dissolved oxygen were significantly higher. Carbon fixation and nitrogen uptake rates were up to ten times higher within C. polykrikoides bloom patches. Ammonium was a more important source of nitrogen, relative to nitrate and urea, for microplankton within bloom patches compared to non-bloom communities. While uptake rates of vitamin B₁ were similar in bloom and non-bloom samples, vitamin B₁₂ was taken up at rates five-fold higher (>100 pmol⁻¹ L⁻¹ d⁻¹) in bloom samples, resulting in turn-over times of hours during blooms. This high vitamin demand likely led to the vitamin B₁₂ limitation of C. polykrikoides observed during nutrient amendment experiments conducted with bloom water. Collectively, this study revealed that C. polykrikoides blooms fundamentally change microbial communities and accelerate the cycling of carbon, some nutrients, and vitamin B₁₂.     

Validation of the detection of Pseudo-nitzschia spp. using specific RNA probes tested in a microarray format: Calibration of signal based on variability of RNA content with environmental conditions

Harmful algal blooms (HAB) occur worldwide and cause health problems and economic damage to fisheries and tourism. Monitoring for toxic algae is therefore essential but is based primarily on light microscopy, which is time consuming and can be limited by insufficient morphological characters such that more time is needed to examine critical features with electron microscopy. Monitoring with molecular tools is done in only a few places world-wide. EU FP7 MIDTAL (Microarray Detection of Toxic Algae) used SSU and LSU rRNA genes as targets on microarrays to identify toxic species. In order to comply with current monitoring requirements to report cell numbers as the relevant threshold measurement to trigger closure of fisheries, it was necessary to calibrate our microarray to convert the hybridisation signal obtained to cell numbers. Calibration curves for two species of Pseudo-nitzschia for use with the MIDTAL microarray are presented to obtain cell numbers following hybridisation. It complements work presented by Barra et al. (2012b. Environ. Sci. Pollut. Res. doi: 10.1007/s11356-012-1330-1v) for two other Pseudo-nitzschia spp., Dittami and Edvardsen (2012a. J. Phycol. 48, 1050) for Pseudochatonella, Blanco et al. (2013. Harmful Algae 24, 80) for Heterosigma, McCoy et al. (2013. FEMS. doi: 10.1111/1574-6941.12277) for Prymnesium spp., Karlodinium veneficum, and cf. Chatonella spp. and Taylor et al. (2014. Harmful Algae, in press) for Alexandrium.     

Characterization of the Parasitic Dinoflagellate Amoebophrya sp. Infecting Akashiwo sanguinea in Coastal Waters of China

The endoparasitic dinoflagellate Amoebophrya infects a number of free‐living marine dinoflagellates, including harmful algal bloom species. The parasitoid eventually kills its host and has been proposed to be a significant loss factor for dinoflagellate blooms in restricted coastal waters. For several decades, the difficulties of culturing host‐parasitoid systems have been a great obstacle for further research on the biology of Amoebophrya. Here, we established an Akashiwo sanguinea‐Amoebophrya sp. coculture from Chinese coastal waters and studied the parasitoid's generation time, dinospore survival and infectivity, as well as its host specificity. The lifespan of Amoebophrya sp. ex. A. sanguinea was approximately 58 h. The infective dinospores can survive up to 78 h in ambient waters but gradually lose their infectivity. The parasitoid was unable to infect other dinoflagellate species, its infection rate reached as high as 91% when the ratio of dinospores to host cells was 20:1. The high infectivity of dinospores suggests that the Amoebophrya strain was capable of removing a considerable fraction of host biomass within a short period, but that it is probably unable to maintain high infection levels under nonbloom conditions of its host, due to limited survival and time constraints in encountering host cells.     

Ocean current connectivity propelling the secondary spread of a marine invasive comb jelly across western Eurasia

Aim

Invasive species are of increasing global concern. Nevertheless, the mechanisms driving further distribution after the initial establishment of non‐native species remain largely unresolved, especially in marine systems. Ocean currents can be a major driver governing range occupancy, but this has not been accounted for in most invasion ecology studies so far. We investigate how well initial establishment areas are interconnected to later occupancy regions to test for the potential role of ocean currents driving secondary spread dynamics in order to infer invasion corridors and the source–sink dynamics of a non‐native holoplanktonic biological probe species on a continental scale.

Location

Western Eurasia.

Time period

1980s–2016.

Major taxa studied

‘Comb jelly’ Mnemiopsis leidyi.

Methods

Based on 12,400 geo‐referenced occurrence data, we reconstruct the invasion history of M. leidyi in western Eurasia. We model ocean currents and calculate their stability to match the temporal and spatial spread dynamics with large‐scale connectivity patterns via ocean currents. Additionally, genetic markers are used to test the predicted connectivity between subpopulations.

Results

Ocean currents can explain secondary spread dynamics, matching observed range expansions and the timing of first occurrence of our holoplanktonic non‐native biological probe species, leading to invasion corridors in western Eurasia. In northern Europe, regional extinctions after cold winters were followed by rapid recolonizations at a speed of up to 2,000 km per season. Source areas hosting year‐round populations in highly interconnected regions can re‐seed genotypes over large distances after local extinctions.

Main conclusions

Although the release of ballast water from container ships may contribute to the dispersal of non‐native species, our results highlight the importance of ocean currents driving secondary spread dynamics. Highly interconnected areas hosting invasive species are crucial for secondary spread dynamics on a continental scale. Invasion risk assessments should consider large‐scale connectivity patterns and the potential source regions of non‐native marine species.

     

Student's tutorial on bloom hypotheses in the context of phytoplankton annual cycles

Phytoplankton blooms are elements in repeating annual cycles of phytoplankton biomass and they have significant ecological and biogeochemical consequences. Temporal changes in phytoplankton biomass are governed by complex predator–prey interactions and physically driven variations in upper water column growth conditions (light, nutrient, and temperature). Understanding these dependencies is fundamental to assess future change in bloom frequency, duration, and magnitude and thus represents a quintessential challenge in global change biology. A variety of contrasting hypotheses have emerged in the literature to explain phytoplankton blooms, but over time the basic tenets of these hypotheses have become unclear. Here, we provide a “tutorial” on the development of these concepts and the fundamental elements distinguishing each hypothesis. The intent of this tutorial is to provide a useful background and set of tools for reading the bloom literature and to give some suggestions for future studies. Our tutorial is written for “students” at all stages of their career. We hope it is equally useful and interesting to those with only a cursory interest in blooms as those deeply immersed in the challenge of understanding the temporal dynamics of phytoplankton biomass and predicting its future change.     

Assessing water quality and classifying trophic status for scientifically based managing the water resources of the Lake Timsah,the lake with salinity stratification along the Suez Canal

Lake Timsah is considered as the biggest water body at Ismailia City with a surface area of 14?km². It is a saline shallow water basin lies approximately mid-way between the south city of Suez and the north city of Port Said at 30^o35′46.55“N and 32^o19′30.54″E. Because it receives water with high and low salinities, salinity stratification is producing in the Lake Timsah, with values of 14–40‰ for the surface water and over 40‰ for the bottom water. The temperature of the lake water decreased to below 19 °C in the winter and rose to above 29?°C in the summer; the concentration of dissolved oxygen ranged between 6.5 and 12.2?l^?1 and the pH fluctuated between 7.9 in its lower value and 8.2 in its higher value. Water transparency was very low as indicated by Secchi disc readings recorded during this study and varied between 0.3 and 2.7?m. The main chemical nutrient (phosphorus) reached its highest levels of 96?µg?l^?1 in winter and their lowest values of 24?µg?l^?1 during summer. This nutrient concentration is high especially by comparing with those of unpolluted marine waters, but is typical of the more eutrophic coastal waters worldwide. The composition and abundance of phytoplankton with dominancy of diatoms and increased population density (20,986 cell l^?1) reflect the eutrophic condition of the lake. The intensive growth of phytoplankton was enriched by high concentration of chlorophyll a with annual values ranged between 6.5 and 56?µg?l^?1. The objective of the present work was quantitative assessment of the quality of the water of the Lake Timsah using different approaches. During the present study, three different approaches were applied for the quantitative assessment of Lake Timsah water quality: the trophic state index (TST); trophic level index (TLI) and water quality index (WQI). Application of the trophic state and trophic level indices (TSI & TLI) revealed that the Lake Timsah has trophic indices of 60 and 5.2 for TSI and TLI, respectively. Both indices reflected the eutrophic condition of the lake waters and confirmed that the eutrophication is a major threat in the Lake Timsah. On the other hand, the WQI calculated for the Lake Timsah during the present study with an average of 49 demonstrated that the water of the Lake Timsah is bad and unsuitable for main and/or several uses. Moreover, WQI allows accounting for several water resource uses and can serve a more robust than TSI and/or TLI and can be used effectively as a comprehensive tool for water quality quantification. In conclusion, the three subjective indices used for the assessment process for the lake water are more suitable and effective for needs of the sustainable water resources protection and management of the Lake Timsah.     

NEW JELLYFISH TAXA FROM THE UPPER JURASSIC LITHOGRAPHIC LIMESTONES OF CERIN (FRANCE): TAPHONOMY AND ECOLOGY

Abstract:  Abundant well-preserved jellyfish impressions are described from the Cerin Lagerstätte (Ain, eastern France). The enclosing sediments are lithographic limestones deposited in a Late Kimmeridgian lagoon lying on an emergent reef complex. Two new taxa of Scyphozoa are proposed: Paraurelia cerinensis gen. et sp. nov. (abundant) and Paraurelia sp. A (rare), and two new taxa of Cubozoa: Bipedalia cerinensis gen. et sp. nov. (rare) and Paracarybdea lithographica gen. et sp. nov. (very rare). Rapid covering by a microbial mat helped the preservation of the animals. Many specimens of Paraurelia cerinensis are deformed by slippage down the palaeoslope, which characterizes the margin of the lagoon. Their resultant morphology and their orientation clearly indicate the downslope direction. Tentacles of Bipedalia cerinensis and Paracarybdea lithographica are also orientated according to the palaeoslope. The jellyfish were probably dead individuals occasionally introduced into the Cerin lagoon. However, another hypothesis may be considered with reference to the model of the present-day jellyfish lakes in Palau (Caroline Islands, Western Pacific). Jellyfish could have lived in the more oxygenated upper layer of water of the Cerin lagoon that allowed pelagic life. This situation could have corresponded to short periods of easier communication between the open sea and the lagoon. Jellyfish are only found in the lower beds of the lithographic limestones and their distribution illustrates the supposed evolution of the Cerin lagoon. Initially, it was deep, mainly flooded, with possibly autochthonous jellyfish and allochthonous animals indicating clear marine influence. Later, the lagoon shallowed and its sediments often emerged with marginal marine burrows and plants indicating increasing terrestrial influence.     

Circumtropical distribution of the epiphytic dinoflagellate Coolia malayensis (Dinophyceae): Morphology and molecular phylogeny from Puerto Rico and Brazil

The dinoflagellate genus Coolia, which contains potentially toxic species, is an important component of epiphytic assemblages in marine ecosystems. The morphology of C. malayensis has been illustrated from strains isolated in Asia and Oceania. In this study, strains of C. malayensis isolated from the Caribbean Sea in Puerto Rico, and for the first time from the South Atlantic Ocean in Brazil, were investigated by light, epifluorescence and scanning electron microscopies. No significant morphological differences between these new strains and other geographically distant strains of C. malayensis were observed. In the LSU rDNA phylogeny, the C. malayensis sequences from Brazil and Puerto Rico branched within the clade of strains from Oceania and Asia. The recently described species C. santacroce branched as a sister group of C. monotis, and C. palmyrensis was basal to the combined group of C. monotis/C. malayensis/C. santacroce. A tentative undescribed species from Florida and New Zealand branched as a sister group of C. malayensis. Our results confirm that C. malayensis showed a cosmopolitan distribution in tropical to subtropical waters, while the type species C. monotis remains endemic for the Mediterranean Sea and the temperate North Atlantic.