Kathryn M. Schoenrock

Multi-frequency observations of seawater carbonate chemistry on the central coast of the western Antarctic Peninsula

Assessments of benthic coastal seawater carbonate chemistry in Antarctica are sparse. The studies have generally been short in duration, during the austral spring/summer, under sea ice, or offshore in ice-free water. Herein we present multi-frequency measurements for seawater collected from the shallow coastal benthos on a weekly schedule over one year (May 2012–May 2013), daily schedule over three months (March–May 2013) and semidiurnal schedule over five weeks (March–April 2013). A notable pH increase (max pH = 8.62) occurred in the late austral spring/summer (November–December 2012), coinciding with sea-ice break-out and subsequent increase in primary productivity. We detected semidiurnal variation in seawater pH with a maximum variation of 0.13 pH units during the day and 0.11 pH units during the night. Daily variation in pH is likely related to biological activity, consistent with previous research. We calculated the variation in dissolved inorganic carbon (DIC) over each seawater measurement frequency, focusing on the primary DIC drivers in the Palmer Station region. From this, we estimated net biological activity and found it accounts for the greatest variations in DIC. Our seasonal data suggest that this coastal region tends to act as a carbon dioxide source during austral winter months and as a strong sink during the summer. These data characterize present-day seawater carbonate chemistry and the extent to which these measures vary over multiple time scales. This information will inform future experiments designed to evaluate the vulnerability of coastal benthic Antarctic marine organisms to ocean acidification.

Life history bias in endophyte infection of the Antarctic rhodophyte, Iridaea cordata

Abstract Endophytic organisms are known to have varied effects on their host organism in terrestrial and marine environments. In previous studies on marine algae, these symbioses range from innocuous to pathogenic depending on the host and endophyte species. The present study further assessed a pathogenic relationship between filamentous algal endophytes and a red algal host from the western Antarctic Peninsula. We analyzed endophyte presence (appearance of filamentous thalli) in the three life history stages of Iridaea cordata and potential impacts on fertility in the fertilized female gametophytes (carposporophytes) and tetrasporophytes. We found that endophytes proliferate throughout significantly more thallus area in tetrasporophyte and unfertilized gametophyte hosts than in carposporophyte hosts, but there was no correlation between endophyte cover and fertility in these individuals. This study also provides a demographic analysis of I. cordata populations surrounding Palmer Station, Antarctica, showing that these populations are haploid dominated (∼78% of individuals). The differential presence of filamentous algal endophytes indicates that endophyte pathogenicity indirectly has greater effect on tetrasporophytes and unfertilized gametophytes than on the carposporophytes, which house the products of sexual recombination.

Endophyte presence as a potential stressor on growth and survival in Antarctic macroalgal hosts

Schoenrock K.M., Amsler C.D., McClintock J.B. and Baker B.J. 2013. Endophyte presence as a potential stressor on growth and survival in Antarctic macroalgal hosts. Phycologia 52: 595–599. DOI: 10:2216/13–188.1 Filamentous algal endophytes are common in many species of macroalgae along the Antarctic Peninsula, but their influence on host physiology is unknown. However, worldwide endophyte–macroalgae symbioses are known to be detrimental to vital functions of a host. The growth and survival of four Antarctic rhodophyte species were examined in situ under varying loads of endophyte infection. Growth was measured through relative growth rate and surface-area-corrected growth rate, and survivorship of individuals was documented throughout the experiment. The relationship between hosts and their endophytes was best described as innocuous in Myriogramme manginii, mildly pathogenic in Gymnogongrus turquetii and Trematocarpus antarcticus, and pathogenic in Iridaea cordata. Deterioration of thalli and decreased growth rates may be natural in the late austral summer when this experiment took place; however, the effects of increased infection probably expedited deterioration of the host. Endophytes in this study were pigmented green and brown filamentous algae, most of which are never seen as free-living thalli, and some of which may be obligate endophytes.

A comprehensive study of Antarctic algal symbioses: minimal impacts of endophyte presence in most species of macroalgal hosts

Many species of macroalgae along the western Antarctic Peninsula have a high coverage of filamentous algal endophytes. A previous field study showed that endophyte presence negatively impacts growth and survival in some Antarctic algae, but can have no impact on others. We examined nine species of common macroalgal hosts from the area surrounding Palmer Station, Antarctica, to examine fine-scale impacts of endophyte presence on host physiology. Physiological parameters were selected based on their potential to influence fitness of host algae. These included photosynthetic parameters, thallus toughness and susceptibility to grazers in those species previously known to be chemically defended. We found that few macroalgal hosts are impacted by the presence of endophytes and that these impacts are not consistent across all physiological parameters. Iridaea cordata and Pachymenia sp. were the only species among the nine examined that demonstrated physiological stress in the presence of endophytes. Out of four species in a previous study, I. cordata was also the most heavily impacted by endophyte presence.

Structure and Function of Macroalgal Natural Products

Since the initial discovery of marine phyco-derived secondary metabolites in the 1950s there has been a rapid increase in the description of new algal natural products. These metabolites have multiple ecological roles as well as commercial value as potential drugs or lead compounds. With the emergence of resistance to our current arsenal of drugs as well as the development of new chemotherapies for currently untreatable diseases, new compounds must be sourced. As outlined in this chapter algae produce a diverse range of chemicals many of which have potential for the treatment of human afflictions.In this chapter we outline the classes of metabolites produced by this chemically rich group of organisms as well as their respective ecological roles in the environment. Algae are found in nearly every environment on earth, with many of these organisms possessing the ability to shape the ecosystem they inhabit. With current challenges to climate stability, understanding how these important organisms interact with their environment as well as one another might afford better insight into how they respond to a changing climate.