Net heterotrophy in High Arctic first-year and multi-year spring sea ice

The net productivity of sea ice is determined by the physical and geochemical characteristics of the ice–ocean system and the activity of organisms inhabiting the ice. Differences in habitat suitability between first-year and multi-year sea ice can affect the ice algal community composition and acclimation state, introducing considerable variability to primary production within each ice type. In this study, we characterized the biogeochemical variability between adjacent first-year and multi-year sea ice floes in the Lincoln Sea of the Canadian High Arctic, during the May 2018 Multidisciplinary Arctic Program—Last Ice sampling campaign. Combining measurements of transmitted irradiance from a remotely operated underwater vehicle with laboratory-based oxygen optode incubations, this work shows widespread heterotrophy (net oxygen uptake) in the bottom 10 cm of both ice types, particularly in thick multi-year ice (>2.4 m) and early morning of the 24-h day. Algal acclimation state and species composition varied between ice types despite similar net community production due to widespread light and nutrient limitation. The first-year ice algal community was increasingly dominated over spring by the potentially toxin-producing genus Pseudonitzschia that was acclimated to high and variable light conditions characteristic of a thinner ice habitat with mobile snow cover. In comparison, the multi-year ice harbored more shade-acclimated algae of mixed composition. This work highlights the potential for heterotrophy in sea ice habitats of the High Arctic, including first measurements of such O2-uptake in multi-year ice floes. Observed differences in photophysiology between algae of these sea ice types suggests that a shift toward higher light availability and a younger sea ice cover with climate change does not necessarily result in a more productive system. Instead, it may favor future sea ice algal communities of different species composition, with lower photosynthetic potential but greater resilience to stronger and more variable light conditions.

Silicon Concentrations and Stoichiometry in Two Agricultural Watersheds: Implications for Management and Downstream Water Quality

Agriculture alters the biogeochemical cycling of nutrients such as nitrogen (N), phosphorus (P), and silicon (Si) which contributes to the stoichiometric imbalance among these nutrients in aquatic systems. Limitation of Si relative to N and P can facilitate the growth of non-siliceous, potentially harmful, algal taxa which has severe environmental and economic impacts. Planting winter cover crops can retain N and P on the landscape, yet their effect on Si concentrations and stoichiometry is unknown. We analyzed three years of biweekly concentrations and loads of dissolved N, P, and Si from subsurface tile drains and stream water in two agricultural watersheds in northern Indiana. Intra-annual patterns in Si concentrations and stoichiometry showed that cover crop vegetation growth did not reduce in-stream Si concentrations as expected, although, compared to fallow conditions, winter cover crops increased Si:N ratios to conditions more favorable for diatom growth. To assess the risk of non-siliceous algal growth, we calculated a stoichiometric index to quantify biomass growth facilitated by excess N and P relative to Si. Index values showed a divergence between predicted algal growth and what we observed in the streams, indicating other factors influence algal community composition. The stoichiometric imbalance was more pronounced at high flows, suggesting increased risk of harmful blooms as environmental change increases the frequency and intensity of precipitation in the midwestern U.S. Our data include some of the first measurements of Si within small agricultural watersheds and provide the groundwork for understanding the role of agriculture on Si export and stoichiometry.

Toward understanding the impact of nuisance algae bloom on the reduction of rice seedling emergence and establishment

California rice (Oryza sativa L.) production has been recently challenged by the early season bloom of nuisance algae. The algal community in rice is a complex of green algae (Nostoc spongiforme Agardh ex Bornet) and cyanobacteria species that could develop a thick algal mat on the surface of the water and interfere with the emergence and establishment of rice seedlings. The objective of this research was to determine the impact of algae infestation level on rice seedling emergence. A mesocosm study was conducted in 57 L tubs. Three levels of algae infestation (low, medium, and high) were produced by adding fertilizer N:P amount into the tubs including 0:0, 75:35, and 150:70 kg-1ha. Sixty rice seeds (M-206) were soaked for 24 hours and spread into tubs filled with water. Photosynthetic Active Radiation (PAR), Chlorophyll a concentration as the quantitative measure of algae, number of emerged rice seedlings, and their dry biomass were studied during the experiment. Results showed that algae infestation can directly change the amount of light received into the water. Minimum, maximum and mean percentage of PAR inside the water declined by the increase of algae infestation level. As a consequence, rice seedling emergence dropped under the high algae pressure. At very high algae infestation (i.e. chlorophyll a concentration of above 500 µg ml-1), rice seedling emergence reduced up to 90%. Furthermore, rice seedling emergence was delayed under algae infestation. When algae infestation was low, time to 50% of rice seedling emergence (t50) ranged between five and ten days, while at high algae infestation t50 ranged between twelve and twenty days. Moreover, individual rice seedling biomass reduced from one gram to 0.01 gram by the increase of algae infestation. The results from this study indicate that uncontrolled algae at the beginning of the rice-growing season could reduce rice seedling emergence, establishment, and rice stand. Given that algae infestation in field has a patchy pattern, loss of rice stand in these patches could provide empty niches for other weeds to grow.

Characterising the benthic Phormidium autumnale-dominated biofilm community and anatoxin production throughout biofilm succession

<p>There has been an increase in the prevalence and intensity of Phormidium autumnale-dominated benthic blooms in New Zealand over the last decade. This species produces the potent neurotoxins Anatoxin-a, Homoanatoxin-a and their derivatives, and consumption of P. autumnale biofilms has led to over 70 dog deaths since 2005. The mechanisms regulating the dominance and toxicity of P. autumnale are still unclear, as these blooms can reach high biomass in low nutrient conditions. Benthic biofilms are composed of multiple taxa and usually harbor a complex community of bacteria and other microbes, which can change over time and interact to facilitate biofilm development and metabolic processing. Prior to this thesis, the microbial composition of P. autumnale-dominated biofilms was unknown. This study provides insights into the relationships of this neurotoxic cyanobacterium with microbial components of the biofilm community. Benthic biofilms were sampled every two to four days for 32 days from three sites in the Hutt River (Wellington) following a high flow event. A combination of microscopy and molecular techniques (bacterial ARISA and Illumina™ sequencing) were used to identify the micro-algal and bacterial components of the biofilm throughout its development. Variation in total anatoxin production was measured using LC-MS and changes in toxic P. autumnale cell numbers were quantified using QPCR. A suite of environmental variables (point velocity, depth, flow, conductivity, temperature and nutrients) were also monitored throughout the study period. Three distinct phases of microbial succession were identified (early, mid and late) using non-metric multidimensional cluster analyses. The micro-algal community composition (including P. autumnale) shifted from early to mid-phase ca. 16 days after the flushing flow and from mid to late phase at ca. day 30. The ARISA and Illumina™ sequencing showed the bacterial community shifts occurred ca. 4 and 9 days before the respective micro-algal community shifts. These analyses indicate a close coupling of the micro-algal and bacterial communities and may suggest bacterial driven succession. However, bacteria are likely to depend on micro-algal by-products for nutrition from the mid-phases onward and assessment of the metabolic processes occurring within the biofilms is needed to clarify this. Phormidium autumnale was dominant in the biofilm from an early stage in development and grew exponentially despite an influx of diatoms at day 20. None of the environmental parameters measured could explain the temporal variation in micro-algal and bacterial communities, which suggested that intrinsic rather than extrinsic factors were more important in regulating succession. This further supports the hypothesis that biofilm microbes may facilitate P. autumnale dominance. There was a significant variation in anatoxins per cell over time (p = 0.034). Production of anatoxins was greatest in the mid-phase of succession (208 fg cell⁻¹), coinciding with an increase in diatom biomass, which could implicate anatoxins as allelopathic chemicals that alleviate the effects of competition on P. autumnale. Changes in proportions of the different anatoxin variants produced over time also aligned with the three successional phases in both the micro-algal and bacterial communities, providing further evidence of a relationship between anatoxin production and microbial biofilm components. Bacterial taxa of the Alphaproteobacteria were dominant within the early bacterial community, but were surpassed by the Betaproteobacteria and Flavobacteria in mid and late phases. Bacterial genera involved in exopolysaccharide production, alkaline phosphatase activity and biopolymer degradation were identified. These attributes are important in the formation, maintenance and break-down of biofilms and therefore strengthen the likelihood of linkages between the micro-algal and bacterial community. Further investigations into functional roles of the biofilm components are needed to infer relationships between P. autumnale and the bacterial community. A clear pattern of microbial succession is described here and linkages between the micro-algal and bacterial communities are evident. Future work should focus on the functional attributes of microbes occurring at different stages of succession to further understand how P. autumnale dominates these benthic communities.</p>

Characterising the benthic Phormidium autumnale-dominated biofilm community and anatoxin production throughout biofilm succession

<p>There has been an increase in the prevalence and intensity of Phormidium autumnale-dominated benthic blooms in New Zealand over the last decade. This species produces the potent neurotoxins Anatoxin-a, Homoanatoxin-a and their derivatives, and consumption of P. autumnale biofilms has led to over 70 dog deaths since 2005. The mechanisms regulating the dominance and toxicity of P. autumnale are still unclear, as these blooms can reach high biomass in low nutrient conditions. Benthic biofilms are composed of multiple taxa and usually harbor a complex community of bacteria and other microbes, which can change over time and interact to facilitate biofilm development and metabolic processing. Prior to this thesis, the microbial composition of P. autumnale-dominated biofilms was unknown. This study provides insights into the relationships of this neurotoxic cyanobacterium with microbial components of the biofilm community. Benthic biofilms were sampled every two to four days for 32 days from three sites in the Hutt River (Wellington) following a high flow event. A combination of microscopy and molecular techniques (bacterial ARISA and Illumina™ sequencing) were used to identify the micro-algal and bacterial components of the biofilm throughout its development. Variation in total anatoxin production was measured using LC-MS and changes in toxic P. autumnale cell numbers were quantified using QPCR. A suite of environmental variables (point velocity, depth, flow, conductivity, temperature and nutrients) were also monitored throughout the study period. Three distinct phases of microbial succession were identified (early, mid and late) using non-metric multidimensional cluster analyses. The micro-algal community composition (including P. autumnale) shifted from early to mid-phase ca. 16 days after the flushing flow and from mid to late phase at ca. day 30. The ARISA and Illumina™ sequencing showed the bacterial community shifts occurred ca. 4 and 9 days before the respective micro-algal community shifts. These analyses indicate a close coupling of the micro-algal and bacterial communities and may suggest bacterial driven succession. However, bacteria are likely to depend on micro-algal by-products for nutrition from the mid-phases onward and assessment of the metabolic processes occurring within the biofilms is needed to clarify this. Phormidium autumnale was dominant in the biofilm from an early stage in development and grew exponentially despite an influx of diatoms at day 20. None of the environmental parameters measured could explain the temporal variation in micro-algal and bacterial communities, which suggested that intrinsic rather than extrinsic factors were more important in regulating succession. This further supports the hypothesis that biofilm microbes may facilitate P. autumnale dominance. There was a significant variation in anatoxins per cell over time (p = 0.034). Production of anatoxins was greatest in the mid-phase of succession (208 fg cell⁻¹), coinciding with an increase in diatom biomass, which could implicate anatoxins as allelopathic chemicals that alleviate the effects of competition on P. autumnale. Changes in proportions of the different anatoxin variants produced over time also aligned with the three successional phases in both the micro-algal and bacterial communities, providing further evidence of a relationship between anatoxin production and microbial biofilm components. Bacterial taxa of the Alphaproteobacteria were dominant within the early bacterial community, but were surpassed by the Betaproteobacteria and Flavobacteria in mid and late phases. Bacterial genera involved in exopolysaccharide production, alkaline phosphatase activity and biopolymer degradation were identified. These attributes are important in the formation, maintenance and break-down of biofilms and therefore strengthen the likelihood of linkages between the micro-algal and bacterial community. Further investigations into functional roles of the biofilm components are needed to infer relationships between P. autumnale and the bacterial community. A clear pattern of microbial succession is described here and linkages between the micro-algal and bacterial communities are evident. Future work should focus on the functional attributes of microbes occurring at different stages of succession to further understand how P. autumnale dominates these benthic communities.</p>

The Influences of Nutrients and Snow on the Spatial and Temporal Variability of Sea Ice Algae

<p>Polar marine regions are dominated by sea ice, where large gradients in temperature, salinity, nutrients and light occur. Despite this, a rich community exists within the sea ice, consisting of prokaryotic organisms, several algal groups and small zooplankton. Prokaryotes are present in the largest abundance in the sea ice; however, diatoms dominate in biomass. Diatoms are the main primary producers within the ice and they form a vital food source for many organisms. However, factors determining species composition, abundance, spatial and temporal variability and nutrient requirement are relatively poorly understood. In order to increase understanding of these processes, an integrated approach was used in this thesis to provide an insight into the potential changes to the ecology of the Southern Ocean in relation to predicted climate change. In this thesis, I studied ice algal community structure, diversity and nutrient requirements at several locations in the sea ice of the Ross Sea, Antarctica. Though many previous studies have focussed on these organisms, this is the first study to I) integrate recent and historical data collected over 30 years and to compare spatial and temporal differences in sea ice communities, II) use the near real time nutrient induced fluorescence transient (NIFT) method to study nutrient limitation in sea ice and further develop this method for use with the imaging pulse amplitude modulator (I-PAM), III) show that Antarctic diatoms may be more susceptible to silica limitation than previously thought, despite the fact that the silica concentration in the Southern Ocean are relatively high. Results from these studies provide important new information on community structure and how it is influenced by and responds to the environment ...</p>

The Influences of Nutrients and Snow on the Spatial and Temporal Variability of Sea Ice Algae

<p>Polar marine regions are dominated by sea ice, where large gradients in temperature, salinity, nutrients and light occur. Despite this, a rich community exists within the sea ice, consisting of prokaryotic organisms, several algal groups and small zooplankton. Prokaryotes are present in the largest abundance in the sea ice; however, diatoms dominate in biomass. Diatoms are the main primary producers within the ice and they form a vital food source for many organisms. However, factors determining species composition, abundance, spatial and temporal variability and nutrient requirement are relatively poorly understood. In order to increase understanding of these processes, an integrated approach was used in this thesis to provide an insight into the potential changes to the ecology of the Southern Ocean in relation to predicted climate change. In this thesis, I studied ice algal community structure, diversity and nutrient requirements at several locations in the sea ice of the Ross Sea, Antarctica. Though many previous studies have focussed on these organisms, this is the first study to I) integrate recent and historical data collected over 30 years and to compare spatial and temporal differences in sea ice communities, II) use the near real time nutrient induced fluorescence transient (NIFT) method to study nutrient limitation in sea ice and further develop this method for use with the imaging pulse amplitude modulator (I-PAM), III) show that Antarctic diatoms may be more susceptible to silica limitation than previously thought, despite the fact that the silica concentration in the Southern Ocean are relatively high. Results from these studies provide important new information on community structure and how it is influenced by and responds to the environment ...</p>

Ecological Effects of Undaria pinnatifida (Harvey) Suringar and Nutrient-Enrichment on Intertidal Assemblages in the Wellington Region of New Zealand

<p>The introduction of non-native species and the alteration of seawater nutrient regimes due to anthropogenic impacts are two important threats to marine environments. Moreover, these disturbances may interact in such a way that promotes the success of invasive species in coastal habitats. This thesis contributes to current gaps in knowledge in these areas for low-intertidal communities. Algal community dynamics and ecological effects of the invasive kelp Undaria pinnatifida on low shores in the Wellington region, New Zealand, were examined, using field surveys and experiments. In addition, the role of variability in nutrient concentrations in coastal waters in mediating algal community structure and diversity, and the success of U. pinnatifida reproduction were investigated. Algal surveys were used in two locations thought to differ in nutrient regimes, the Wellington Harbour and the Wellington south coast, to explore the structure and dynamics of algal assemblages. Results showed high variability of low-intertidal algal communities among sites, but no consistent differences in algal community composition were found between the two locations, despite higher U. pinnatifida cover in the harbour. Over the duration of the study, nutrient regimes did not differ greatly between the locations. The response of rocky intertidal algal assemblages to chronic exposure to high nutrient effluent was investigated using two nearshore sewage outfalls in the Wellington region. The Titahi Bay outfall showed a stronger relationship between nutrients and algal community composition. Variation in algal assemblage structure and diversity was best explained by phosphate concentrations. By contrast, at the more wave-exposed Pencarrow outfall, patterns of change in the algal community were less clear and there was a much weaker relationship with seawater nutrients. Because removal of native algal canopy species may facilitate the establishment of invasive macroalgae, the invasion process of U. pinnatifida in disturbed patches in a rocky low-intertidal habitat was investigated. In a site where U. pinnatifida had not yet established, patches were scraped clear of native algal cover at two different times of year, and recruitment of U. pinnatifida was monitored. While U. pinnatifida invaded the site, it recruited in control plots at a similar rate as cleared plots, suggesting that physical disturbance of the native algal assemblage is not a key requirement for this kelp to invade and establish in new areas in the low intertidal zone. The response of native algal assemblages to removal of U. pinnatifida individuals was investigated at intertidal sites in the Wellington Harbour and on the south coast. No significant effect of U. pinnatifida on community composition, diversity, and species richness was detected. Removal of this invader did not change native intertidal assemblage structure in either harbour or south coast sites. Lastly, effects of different nutrient regimes and light intensities on early development and reproduction of U. pinnatifida were studied using a laboratory experiment. Under low light conditions U. pinnatifida gametophyte growth and reproduction stalled and was not increased by the addition of nutrients. However, at medium and high light levels, gametophyte growth and reproduction, and particularly early stage sporophyte growth rates increased when exposed to higher nutrient concentrations.These effects could have implications for U. pinnatifida population dynamics in intertidal habitats where light is not often a limiting resource. This research contributed to a better understanding of factors that underlie invasion dynamics, distribution, and ecological effects of U. pinnatifida and seawater nutrient regimes on low-intertidal assemblages in the Wellington region. The outcomes can assist in setting up strategic environmental protection and conservation plans.</p>

Ecological Effects of Undaria pinnatifida (Harvey) Suringar and Nutrient-Enrichment on Intertidal Assemblages in the Wellington Region of New Zealand

<p>The introduction of non-native species and the alteration of seawater nutrient regimes due to anthropogenic impacts are two important threats to marine environments. Moreover, these disturbances may interact in such a way that promotes the success of invasive species in coastal habitats. This thesis contributes to current gaps in knowledge in these areas for low-intertidal communities. Algal community dynamics and ecological effects of the invasive kelp Undaria pinnatifida on low shores in the Wellington region, New Zealand, were examined, using field surveys and experiments. In addition, the role of variability in nutrient concentrations in coastal waters in mediating algal community structure and diversity, and the success of U. pinnatifida reproduction were investigated. Algal surveys were used in two locations thought to differ in nutrient regimes, the Wellington Harbour and the Wellington south coast, to explore the structure and dynamics of algal assemblages. Results showed high variability of low-intertidal algal communities among sites, but no consistent differences in algal community composition were found between the two locations, despite higher U. pinnatifida cover in the harbour. Over the duration of the study, nutrient regimes did not differ greatly between the locations. The response of rocky intertidal algal assemblages to chronic exposure to high nutrient effluent was investigated using two nearshore sewage outfalls in the Wellington region. The Titahi Bay outfall showed a stronger relationship between nutrients and algal community composition. Variation in algal assemblage structure and diversity was best explained by phosphate concentrations. By contrast, at the more wave-exposed Pencarrow outfall, patterns of change in the algal community were less clear and there was a much weaker relationship with seawater nutrients. Because removal of native algal canopy species may facilitate the establishment of invasive macroalgae, the invasion process of U. pinnatifida in disturbed patches in a rocky low-intertidal habitat was investigated. In a site where U. pinnatifida had not yet established, patches were scraped clear of native algal cover at two different times of year, and recruitment of U. pinnatifida was monitored. While U. pinnatifida invaded the site, it recruited in control plots at a similar rate as cleared plots, suggesting that physical disturbance of the native algal assemblage is not a key requirement for this kelp to invade and establish in new areas in the low intertidal zone. The response of native algal assemblages to removal of U. pinnatifida individuals was investigated at intertidal sites in the Wellington Harbour and on the south coast. No significant effect of U. pinnatifida on community composition, diversity, and species richness was detected. Removal of this invader did not change native intertidal assemblage structure in either harbour or south coast sites. Lastly, effects of different nutrient regimes and light intensities on early development and reproduction of U. pinnatifida were studied using a laboratory experiment. Under low light conditions U. pinnatifida gametophyte growth and reproduction stalled and was not increased by the addition of nutrients. However, at medium and high light levels, gametophyte growth and reproduction, and particularly early stage sporophyte growth rates increased when exposed to higher nutrient concentrations.These effects could have implications for U. pinnatifida population dynamics in intertidal habitats where light is not often a limiting resource. This research contributed to a better understanding of factors that underlie invasion dynamics, distribution, and ecological effects of U. pinnatifida and seawater nutrient regimes on low-intertidal assemblages in the Wellington region. The outcomes can assist in setting up strategic environmental protection and conservation plans.</p>