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Diatoms, dinoflagellates, and coccolithophores are dominant groups of marine eukaryotic phytoplankton that are collectively responsible for the majority of primary production in the ocean.1 These phytoplankton contain additional intracellular membranes around their chloroplasts, which are derived from ancestral engulfment of red microalgae by unicellular heterotrophic eukaryotes that led to secondary and tertiary endosymbiosis.2 However, the selectable evolutionary advantage of these membranes and the physiological significance for extant phytoplankton remain poorly understood. Since intracellular digestive vacuoles are ubiquitously acidified by V-type H+-ATPase (VHA),3 proton pumps were proposed to acidify the microenvironment around secondary chloroplasts to promote the dehydration of dissolved inorganic carbon (DIC) into CO2, thus enhancing photosynthesis.4,5 We report that VHA is localized around the chloroplasts of centric diatoms and that VHA significantly contributes to their photosynthesis across a wide range of oceanic irradiances. Similar results in a pennate diatom, dinoflagellate, and coccolithophore, but not green or red microalgae, imply the co-option of phagocytic VHA activity into a carbon-concentrating mechanism (CCM) is common to secondary endosymbiotic phytoplankton. Furthermore, analogous mechanisms in extant photosymbiotic marine invertebrates6,7,8 provide functional evidence for an adaptive advantage throughout the transition from endosymbiosis to symbiogenesis. Based on the contribution of diatoms to ocean biogeochemical cycles, VHA-mediated enhancement of photosynthesis contributes at least 3.5 Gtons of fixed carbon per year (or 7% of primary production in the ocean), providing an example of a symbiosis-derived evolutionary innovation with global environmental implications.

Anthropogenic climate change is warming our oceans and thus has the potential to dramatically alter marine ecosystems. Recent ocean temperatures have been shown to impact the distribution and availability of prey species, which may lead to periodic or permanent range shifts of the predators relying on them. Since seabirds are solely dependent on marine prey, changes in seabirds’ distribution may be valuable alerts for ecosystem health. We expand upon previous investigations of range and seabird community composition within the California Current Ecosystem (CCE) form 1980-2017 by selecting a “warm water” and “cool water” seabird species. We investigated these potential trends in Craveri’s murrelets (CRMU), the “warm water” species, and ancient murrelets (ANMU), the “cool water” species, as their northern and southern range, respectively, overlap in the southern CCE region. They are comparable in size, natural history, and prey type. We hypothesized that the trends in their distribution would reflect the northward expansion of warm water over time and periods of warm water associated with El Niño Southern Oscillation (ENSO). We expected CRMUs to increase in frequency and northward distribution over time and during El Niño events. For ANMUs, we expected to see a decrease in their frequency and a shift northward over time and with El Niño events. We calculated multiple linear regression models to analyze the relationships between species density (frequency of sightings/km2) with latitude, upwelling, and year. We found a decrease in density of both species and that latitude was the only significant predictor for both species’ density. This research will provide a foundation for future investigations of seabird range shifts in the CCE and assist in further understanding changes in upwelling ecosystems.

As the Western Antarctic Peninsula (WAP) region responds to a warmer climate, the impacts of glacial meltwater on the Southern Ocean are expected to intensify. The Antarctic Peninsula fjord system offers an ideal system to understand meltwater's properties, providing an extreme in the meltwater's spatial gradient from the glacio-marine boundary to the WAP continental shelf. Glacial meltwater discharge in Arctic and Greenland fjords is typically characterized as relatively lower temperature, fresh and with high turbidity. During two cruises conducted in December 2015 and April 2016 in Andvord Bay, we found a water lens of low salinity and low temperature along the glacio-marine interface. Oxygen isotope ratios identified this water lens as a mixture of glacial ice and deep water in Gerlache Strait suggesting this is glacial meltwater. Conventional hydrographic measurements were combined with optical properties to effectively quantify its spatial extent. Fine suspended sediments associated with meltwater (nanoparticles of ~ 5nm) had a significant impact on the underwater light field and enabled the detection of meltwater characteristics and spatial distribution. In this study, we illustrate that glacial meltwater in Andvord Bay alters the inherent and apparent optical properties of the water column, and develop statistical models to predict the meltwater content from hydrographic and optical measurements. The predicted meltwater fraction is in good agreement with in-situ values. These models offer a potential for remote sensing and high-resolution detection of glacial meltwater in Antarctic waters. Furthermore, the possible influence of meltwater on phytoplankton abundance in the surface is highlighted; a significant correlation is found between meltwater fraction and chlorophyll concentration.