Bergan
Alexander J.
Bergan
Alexander J.
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ArticleExposure to CO2 influences metabolism, calcification and gene expression of the thecosome pteropod Limacina retroversa(The Company of Biologists, 2018-02-13) Maas, Amy E. ; Lawson, Gareth L. ; Bergan, Alexander J. ; Tarrant, Ann M.Thecosomatous pteropods, a group of aragonite shell-bearing zooplankton, are becoming an important sentinel organism for understanding the influence of ocean acidification on pelagic organisms. These animals show vulnerability to changing carbonate chemistry conditions, are geographically widespread, and are both biogeochemically and trophically important. The objective of this study was to determine how increasing duration and severity of CO2 treatment influence the physiology of the thecosome Limacina retroversa, integrating both gene expression and organism-level (respiration and calcification) metrics. We exposed pteropods to over-saturated, near-saturated or under-saturated conditions and sampled individuals at 1, 3, 7, 14 and 21 days of exposure to test for the effect of duration. We found that calcification was affected by borderline and under-saturated conditions by week two, while respiration appeared to be more strongly influenced by an interaction between severity and duration of exposure, showing complex changes by one week of exposure. The organismal metrics were corroborated by specific gene expression responses, with increased expression of biomineralization-associated genes in the medium and high treatments throughout and complex changes in metabolic genes corresponding to both captivity and CO2 treatment. Genes associated with other physiological processes such as lipid metabolism, neural function and ion pumping had complex responses, influenced by both duration and severity. Beyond these responses, our findings detail the captivity effects for these pelagic organisms, providing information to contextualize the conclusions of previous studies, and emphasizing a need for better culturing protocols.
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ThesisPteropod shell condition, locomotion, and long-term population trends in the context of ocean acidification and environmental change(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2017-06) Bergan, Alexander J.Thecosome pteropods are planktonic mollusks that form aragonite shells and that may experience increased dissolution and other adverse effects due to ocean acidification. This thesis focuses on assessing the possible biological effects of ocean acidification on the shells and locomotion of pteropods and examining the response of a local pteropod population to environmental change over time. I analyzed shell condition after exposing pteropods to elevated CO2 as well as in natural populations to investigate the sensitivity of the shells of different species to aragonite saturation state (ΩA). The pteropods (Limacina retroversa) from laboratory experiments showed the clearest pattern of shell dissolution in response to decreased ΩA, while wild populations either had non-significant regional trends in shell condition (Clio pyramidata) or variability in shell condition that did not match expectations due to regional variability in ΩA (Limacina helicina). At locations with intermediate ΩA (1.5-2.5) the variability seen in L. helicina shell condition might be affected by food availability more than ΩA. I examined sinking and swimming behaviors in the laboratory in order to investigate a possible fitness effect of ocean acidification on pteropods. The sinking rates of L. retroversa from elevated CO2 treatments were slower in conjunction with worsened shell condition. These changes could increase their vulnerability to predators in the wild. Swimming ability was mostly unchanged by elevated CO2 after experiments that were up to three weeks in duration. I used a long-term dataset of pteropods in the Gulf of Maine to directly test whether there has been a population effect of environmental change over the past several decades. I did not observe a population decline between 1977 and 2015, and L. retroversa abundance in the fall actually increased over the time series. Analysis of the habitat use of L. retroversa revealed seasonal associations with temperature, salinity, and bottom depths. The combination of laboratory experiments and field surveys helped to address gaps in knowledge about pteropod ecology and improve our understanding of the effects of ocean acidification on pteropods.
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PreprintThe effect of elevated carbon dioxide on the sinking and swimming of the shelled pteropod Limacina retroversa( 2017-01) Bergan, Alexander J. ; Lawson, Gareth L. ; Maas, Amy E. ; Wang, Zhaohui AleckShelled pteropods are planktonic molluscs that may be affected by ocean acidification. Limacina retroversa from the Gulf of Maine were used to investigate the impact of elevated carbon dioxide (CO2) on shell condition as well as swimming and sinking behaviours. Limacina retroversa were maintained at either ambient (ca. 400 μatm) or two levels of elevated CO2 (800 and 1200 μatm) for up to four weeks, and then examined for changes in shell transparency, sinking speed, and swimming behaviour assessed through a variety of metrics (e.g., speed, path tortuosity, wing beat frequency). After exposures to elevated CO2 for as little as four days, the pteropod shells were significantly darker and more opaque in the elevated CO2 treatments. Sinking speeds were significantly slower for pteropods exposed to medium and high CO2 in comparison to the ambient treatment. Swimming behaviour showed less clear patterns of response to treatment and duration of exposure, but overall, swimming did not appear to be hindered under elevated CO2. Sinking is used by L. retroversa for predator evasion, and altered speeds and increased visibility could increase the susceptibility of pteropods to predation.
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ArticleShelled pteropods in peril : assessing vulnerability in a high CO2 ocean(Elsevier, 2017-04-09) Manno, Clara ; Bednarsek, Nina ; Tarling, Geraint A. ; Peck, Vicky L. ; Comeau, Steeve ; Adhikari, Deepak ; Bakker, Dorothee ; Bauerfeind, Eduard ; Bergan, Alexander J. ; Berning, Maria I. ; Buitenhuis, Erik T. ; Burridge, Alice K. ; Chierici, Melissa ; Flöter, Sebastian ; Fransson, Agneta ; Gardner, Jessie ; Howes, Ella L. ; Keul, Nina ; Kimoto, Katsunori ; Kohnert, Peter ; Lawson, Gareth L. ; Lischka, Silke ; Maas, Amy E. ; Mekkes, Lisette ; Oakes, Rosie L. ; Pebody, Corinne ; Peijnenburg, Katja T. C. A. ; Seifert, Miriam ; Skinner, Jennifer ; Thibodeau, Patricia S. ; Wall-Palmer, Deborah ; Ziveri, PatriziaThe impact of anthropogenic ocean acidification (OA) on marine ecosystems is a vital concern facing marine scientists and managers of ocean resources. Euthecosomatous pteropods (holoplanktonic gastropods) represent an excellent sentinel for indicating exposure to anthropogenic OA because of the sensitivity of their aragonite shells to the OA conditions less favorable for calcification. However, an integration of observations, experiments and modelling efforts is needed to make accurate predictions of how these organisms will respond to future changes to their environment. Our understanding of the underlying organismal biology and life history is far from complete and must be improved if we are to comprehend fully the responses of these organisms to the multitude of stressors in their environment beyond OA. This review considers the present state of research and understanding of euthecosomatous pteropod biology and ecology of these organisms and considers promising new laboratory methods, advances in instrumentation (such as molecular, trace elements, stable isotopes, palaeobiology alongside autonomous sampling platforms, CT scanning and high-quality video recording) and novel field-based approaches (i.e. studies of upwelling and CO2 vent regions) that may allow us to improve our predictive capacity of their vulnerability and/or resilience. In addition to playing a critical ecological and biogeochemical role, pteropods can offer a significant value as an early-indicator of anthropogenic OA. This role as a sentinel species should be developed further to consolidate their potential use within marine environmental management policy making.