Experimental growth characteristics, cell size, yessotoxin values and bioassay data of Protoceratium reticulatum (Dinophyceae)

Harmful algal blooms are mainly caused by marine dinoflagellates and are known to produce potent toxins that may affect the ecosystem, human activities and health. Such events have increased in frequency and intensity worldwide in the past decades. Numerous processes involved in Global Change are amplified in the Arctic, but little is known about species specific responses of arctic dinoflagellates. The aim of this work was to perform an exhaustive morphological, phylogenetical and toxinological characterization of Greenland Protoceratium reticulatum and, in addition, to test the effect of temperature on growth and production of bioactive secondary metabolites. Seven clonal isolates, the first isolates of P. reticulatum available from arctic waters, were phylogenetically characterized by analysis of the LSU rDNA. Six isolates were further characterized morphologically and were shown to produce both yessotoxins (YTX) and lytic compounds, representing the first report of allelochemical activity in P. reticulatum. As shown for one of the isolates, growth was strongly affected by temperature with a maximum growth rate at 15 °C, a significant but slow growth at 1 °C, and cell death at 25 °C, suggesting an adaptation of P. reticulatum to temperate waters. Temperature had no major effect on total YTX cell quota or lytic activity but both were affected by the growth phase with a significant increase at stationary phase. A comparison of six isolates at a fixed temperature of 10 °C showed high intraspecific variability for all three physiological parameters tested. Growth rate varied from 0.06 to 0.19 per day, and total YTX concentration ranged from 0.3 to 15.0 pg YTX/cell and from 0.5 to 31.0 pg YTX/cell at exponential and stationary phase, respectively. All six isolates performed lytic activity; however, for two isolates lytic activity was only detectable at higher cell densities in stationary phase.

(Table 2) Survivorship of transplanted seedlings of Picea glauca inside and outside three tree islands in 1994, 1995, 2009 and after 15 years

The northern boundary of boreal forest and the ranges of tree species are expected to shift northward in response to climate warming, which will result in a decrease in the albedo of areas currently covered by tundra vegetation, an increase in terrestrial carbon sequestration, and an alteration of biodiversity in the current Low Arctic. Central to the prediction of forest expansion is an increase in the reproductive capacity and establishment of individual trees. We assessed cone production, seed viability, and transplanted seedling success of Picea glauca (Moench.) Voss. (white spruce) in the early 1990s and again in the late 2000s at four forest stand sites and eight tree island sites (clonal populations beyond present treeline) in the Mackenzie Delta region of the Northwest Territories, Canada. Over the past 20 years, average temperatures in this region have increased by 0.9 °C. This area has the northernmost forest-tundra ecotone in North America and is one of the few circumpolar regions where the northern limit of conifer trees reaches the Arctic Ocean. We found that cone production and seed viability did not change between the two periods of examination and that both variables decreased northward across the forest-tundra ecotone. Nevertheless, white spruce individuals at the northern limit of the forest-tundra ecotone produced viable seeds. Furthermore, transplanted seedlings were able to survive in the northernmost sites for 15 years, but there were no signs of natural regeneration. These results indicate that if climatic conditions continue to ameliorate, reproductive output will likely increase, but seedling establishment and forest expansion within the forest-tundra of this region is unlikely to occur without the availability of suitable recruitment sites. Processes that affect the availability of recruitment sites are likely to be important elsewhere in the circumpolar ecotone, and should be incorporated into models and predictions of climate change and its effects on the northern forest-tundra ecotone.

Intraspecific facilitation by allelochemical mediated grazing protection within a toxigenic dinoflagellate population, link to supplementary material

Dinoflagellates are a major cause of harmful algal blooms, with consequences for coastal marine ecosystem functioning and services. Alexandrium tamarense is one of the most abundant and widespread toxigenic species in the temperate northern and southern hemisphere, and produces paralytic shellfish poisoning toxins as well as lytic allelochemical substances. These bioactive compounds may support the success of A. tamarense and its ability to form blooms. Here we investigate the impact of grazing on monoclonal and mixed set-ups of highly (Alex2) and moderately (Alex4) allelochemically active A. tamarense strains and on a non-allelochemically active conspecific (Alex5) by the heterotrophic dinoflagellate Polykrikos kofoidii. While Alex4 and particularly Alex5 were strongly grazed by P. kofoidii when offered alone, both strains grew well in the mixed assemblages (Alex4+Alex5 and Alex2+Alex5). Hence, the allelochemical active strains facilitated growth of the non-active strain by protecting the population as a whole against grazing. Based on our results, we argue that facilitation among clonal lineages within a species may partly explain the high genotypic and phenotypic diversity of Alexandrium populations. Populations of Alexandrium may comprise multiple cooperative traits that act in concert with intraspecific facilitation, and hence promote the success of this notorious harmful algal bloom species.

Genotypic data for nine microsatellite loci for the seagrass Zostera muelleri collections from Lake Macquarie, NSW, Australia

Seagrasses are ecosystem engineers that offer important habitat for a large number of species and provide a range of ecosystem services. Many seagrass ecosystems are dominated by a single species; with research showing that genotypic diversity at fine spatial scales plays an important role in maintaining a range of ecosystem functions. However, for most seagrass species, information on fine-scale patterns of genetic variation in natural populations is lacking. In this study we use a hierarchical sampling design to determine levels of genetic and genotypic diversity at different spatial scales (centimeters, meters, kilometers) in the Australian seagrass Zostera muelleri. Our analysis shows that at fine-spatial scales (< 1 m) levels of genotypic diversity are relatively low (R (Plots) = 0.37 ± 0.06 SE), although there is some intermingling of genotypes. At the site (10's m) and meadow location (km) scale we found higher levels of genotypic diversity (R (sites) = 0.79 ± 0.04 SE; R (Locations) = 0.78 ± 0.04 SE). We found some sharing of genotypes between sites within meadows, but no sharing of genotypes between meadow locations. We also detected a high level of genetic structuring between meadow locations (FST = 0.278). Taken together, our results indicate that both sexual and asexual reproduction are important in maintaining meadows of Z. muelleri. The dominant mechanism of asexual reproduction appears to occur via localised rhizome extension, although the sharing of a limited number of genotypes over the scale of 10's of metres could also result from the localised dispersal and recruitment of fragments. The large number of unique genotypes at the meadow scale indicates that sexual reproduction is important in maintaining these populations, while the high level of genetic structuring suggests little gene flow and connectivity between our study sites. These results imply that recovery from disturbances will occur through both sexual and asexual regeneration, but the limited connectivity at the landscape-scale implies that recovery at meadow-scale losses is likely to be limited.

Short- versus long-term responses to changing CO2 in a coastal dinoflagellate bloom

Increasing pCO2 (partial pressure of CO2 ) in an "acidified" ocean will affect phytoplankton community structure, but manipulation experiments with assemblages briefly acclimated to simulated future conditions may not accurately predict the long-term evolutionary shifts that could affect inter-specific competitive success. We assessed community structure changes in a natural mixed dinoflagellate bloom incubated at three pCO2 levels (230, 433, and 765 ppm) in a short-term experiment (2 weeks). The four dominant species were then isolated from each treatment into clonal cultures, and maintained at all three pCO2 levels for approximately 1 year. Periodically (4, 8, and 12 months), these pCO2 -conditioned clones were recombined into artificial communities, and allowed to compete at their conditioning pCO2 level or at higher and lower levels. The dominant species in these artificial communities of CO2 -conditioned clones differed from those in the original short-term experiment, but individual species relative abundance trends across pCO2 treatments were often similar. Specific growth rates showed no strong evidence for fitness increases attributable to conditioning pCO2 level. Although pCO2 significantly structured our experimental communities, conditioning time and biotic interactions like mixotrophy also had major roles in determining competitive outcomes. New methods of carrying out extended mixed species experiments are needed to accurately predict future long-term phytoplankton community responses to changing pCO2 .

Short- and long-term conditioning of a temperate marine diatom community to acidification and warming

Ocean acidification and greenhouse warming will interactively influence competitive success of key phytoplankton groups such as diatoms, but how long-term responses to global change will affect community structure is unknown. We incubated a mixed natural diatom community from coastal New Zealand waters in a short-term (two-week) incubation experiment using a factorial matrix of warming and/or elevated pCO2 and measured effects on community structure. We then isolated the dominant diatoms in clonal cultures and conditioned them for 1 year under the same temperature and pCO2 conditions from which they were isolated, in order to allow for extended selection or acclimation by these abiotic environmental change factors in the absence of interspecific interactions. These conditioned isolates were then recombined into 'artificial' communities modelled after the original natural assemblage and allowed to compete under conditions identical to those in the short-term natural community experiment. In general, the resulting structure of both the unconditioned natural community and conditioned 'artificial' community experiments was similar, despite differences such as the loss of two species in the latter. pCO2 and temperature had both individual and interactive effects on community structure, but temperature was more influential, as warming significantly reduced species richness. In this case, our short-term manipulative experiment with a mixed natural assemblage spanning weeks served as a reasonable proxy to predict the effects of global change forcing on diatom community structure after the component species were conditioned in isolation over an extended timescale. Future studies will be required to assess whether or not this is also the case for other types of algal communities from other marine regimes.