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Temporal and light-dependent variability of algal communities in land-fast Arctic sea ice

Description
Sea ice algae dominated by diatoms inhabit the brine channels of the Arctic sea ice and serve as the base of the Arctic marine food web in the spring. I studied sea ice diatoms in the bottom 10 cm of first year land-fast sea ice off the coast of Barrow,…

Sea ice algae dominated by diatoms inhabit the brine channels of the Arctic sea ice and serve as the base of the Arctic marine food web in the spring. I studied sea ice diatoms in the bottom 10 cm of first year land-fast sea ice off the coast of Barrow, AK, in spring of 2011, 2012, and 2013. I investigated the variability in the biomass and the community composition of these sea-ice diatoms between bloom phases, as a function of overlying snow depth and over time. The dominant genera were the pennate diatoms Nitzschia, Navicula, Thalassiothrix, and Fragilariopsis with only a minor contribution by centric diatoms. While diatom biomass as estimated by organic carbon changed significantly between early, peak, and declining bloom phases (average of 1.6 mg C L-1, 5.7 mg C L-1, and 1.0 mg C L-1, respectively), the relative ratio of the dominant diatom groups did not change. However, after export, when the diatoms melt out of the ice into the underlying water, diatom biomass dropped by ~73% and the diatom community shifted to one dominated by centric diatoms. I also found that diatom biomass was ~77% lower under high snow cover (>20 cm) compared to low snow cover (<8 cm); however, the ratio of the diatom categories relative to particulate organic carbon (POC) was again unchanged. The diatom biomass was significantly different between the three sampling years (average of 2.4 mg C L-1 in 2011, 1.1 mg C L-1 in 2012, and 5.4 mg C L-1 in 2013, respectively) as was the contribution of all of the dominant genera to POC. I hypothesize the latter to be due to differences in the history of ice sheet formation each year. The temporal variability of these algal communities will influence their availability for pelagic or benthic consumers. Furthermore, in an Arctic that is changing rapidly with earlier sea ice and snowmelt, this time series study will constitute an important baseline for further studies on how the changing Arctic influences the algal community immured in sea ice.
ContributorsKinzler, Kyle (Author) / Neuer, Susanne (Thesis advisor) / Juhl, Andrew (Committee member) / Hartnett, Hilairy (Committee member) / Arizona State University (Publisher)
Created2014
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Growth and grazing mortality of pico- and nano-phytoplankton and their role in the carbon export in the Sargasso Sea

Description
The ocean sequesters more than 25% of the carbon released by anthropogenic action every year, and oligotrophic oceans, such as the Sargasso Sea, are responsible for about 50% of the global carbon export. Pico- and nano-phytoplankton (cells < 5 µm), mostly unicellular eukaryotes (protists) and cyanobacteria, dominate the primary production…

The ocean sequesters more than 25% of the carbon released by anthropogenic action every year, and oligotrophic oceans, such as the Sargasso Sea, are responsible for about 50% of the global carbon export. Pico- and nano-phytoplankton (cells < 5 µm), mostly unicellular eukaryotes (protists) and cyanobacteria, dominate the primary production in the Sargasso Sea; however, little is known about their contribution to the export of carbon into the deep ocean via sinking particles. The overall goal of this study is to examine the link between growth and grazing rates of pico- and nano-phytoplankton and the carbon export in the Sargasso Sea. I investigate three aspects: 1) how microzooplankton grazing and physical forcing affect taxon-specific primary productivity in this region, 2) how these microbial trophic dynamics impact their contribution to the export of particulate matter, and 3) how much pico-phytoplankton, specifically the pico-cyanobacteria Synechococcus and Prochlorococcus, contribute to the carbon export. I collected seawater samples within the sunlit (euphotic) zone, and sinking particles at 150 m depth using particle traps in the Sargasso Sea during the winter and summer seasons of 2011 and 2012. I conducted dilution experiments to determine the growth and grazing rates of the pico- and nano-phytoplankton community, and used 454 pyrosequencing and quantitative Polymerase Chain Reaction to measure the relative and absolute contribution of these primary producers to the plankton community within the euphotic zone and in the sinking particles. I found that micrograzing controls taxon-specific primary production, and that microbial trophic dynamics impact directly the taxonomical composition of the sinking particles. For the first time, I was able to quantify clade-specific carbon export of pico-cyanobacteria and found that, despite their small size, these tiny primary producers are capable of sinking from the surface to the deeper oceans. However, their contribution to the carbon flux is often less than one tenth of their biomass contribution in the euphotic zone. Our study provides a comprehensive approach to better understand the role of pico- and nano-phytoplankton in the carbon cycle of oligotrophic oceans, and a baseline to study changes in the carbon export in future warmer oceans.
ContributorsDe Martini, Francesca (Author) / Neuer, Susanne (Thesis advisor) / Garcia-Pichel, Ferran (Committee member) / Hartnett, Hilairy (Committee member) / Lomas, Michael (Committee member) / Arizona State University (Publisher)
Created2016

The Intertidal Ecosystems of Puerto Peñasco: A Collaboration with CEDO and the Clean Beaches Committee of Puerto Peñasco to Educate Beach Visitors on Local Biodiversity

Description

The Northern Gulf of California is characterized by an extreme tidal range and temperature fluctuations between seasons, as well as a large variation in microhabitats along its shoreline. As a result, the intertidal regions exhibit a diverse and distinct collection of species that have adapted to these environmental conditions, with…

The Northern Gulf of California is characterized by an extreme tidal range and temperature fluctuations between seasons, as well as a large variation in microhabitats along its shoreline. As a result, the intertidal regions exhibit a diverse and distinct collection of species that have adapted to these environmental conditions, with roughly 4.6 percent being endemic. Minimal knowledge of these ecosystems existed until the 1940’s, when the renowned author John Steinbeck accompanied marine biologist Edward Ricketts on an expedition with the purpose of documenting the biodiversity of the Sea of Cortez. Today, the majority of research in the Northern Gulf of California is directed by CEDO, the Intercultural Center for the Study of Deserts and Oceans. The purpose of this project is to compile a literature review of research on the intertidal areas of the Northern Gulf and produce an illustrated brochure that educates beach visitors on local biodiversity as a collaboration with CEDO and the Clean Beaches Committee of Puerto Peñasco. This brochure aims to increase respect and appreciation for these species, as increased tourism over the past few decades has led to detrimental effects on the ecosystem. Additionally, it serves to promote the success of the Blue Flag certification of El Mirador beach in front of Manny’s Beach Club.
ContributorsPotter, Jessica Noel (Co-author) / Potter, Jessica (Co-author) / Neuer, Susanne (Thesis director) / Mangin, Katrina (Committee member) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05