Thabet Ali A.

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Ali A.

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  • Preprint
    Life cycle and early development of the thecosomatous pteropod Limacina retroversa in the Gulf of Maine, including the effect of elevated CO2 levels
    ( 2015-10) Thabet, Ali A. ; Maas, Amy E. ; Lawson, Gareth L. ; Tarrant, Ann M.
    Thecosome pteropods are pelagic molluscs with aragonitic shells. They are considered to be especially vulnerable among plankton to ocean acidification (OA), but to recognize changes due to anthropogenic forcing a baseline understanding of their life history is needed. In the present study, adult Limacina retroversa were collected on five cruises from multiple sites in the Gulf of Maine (between 42° 22.1’–42° 0.0’ N and 69° 42.6’–70° 15.4’ W; water depths of ca. 45–260 m) from October 2013−November 2014. They were maintained in the laboratory under continuous light at 8° C. There was evidence of year-round reproduction and an individual life span in the laboratory of 6 months. Eggs laid in captivity were observed throughout development. Hatching occurred after 3 days, the veliger stage was reached after 6−7 days, and metamorphosis to the juvenile stage was after ~ 1 month. Reproductive individuals were first observed after 3 months. Calcein staining of embryos revealed calcium storage beginning in the late gastrula stage. Staining was observed in the shell gland, shell field, mantle, and shell margin in later stages. Exposure of two batches of larvae at the gastrula stage to elevated CO2 levels (800 and 1200 ppm) resulted in significantly increased mortality in comparison with individuals raised under ambient (~400 ppm) conditions and a developmental delay in the 1200 ppm treatment compared with the ambient and 800 ppm treatments.
  • Preprint
    Assembly of a reference transcriptome for the gymnosome pteropod Clione limacina and profiling responses to short-term CO2 exposure
    ( 2017-03) Thabet, Ali A. ; Maas, Amy E. ; Saber, Samy A. ; Tarrant, Ann M.
    The gymnosome (unshelled) pteropod Clione limacina is a pelagic predatory mollusc found in polar and sub-polar regions. It has been studied for its distinctive swimming behavior and as an obligate predator on the closely related thecosome (shelled) pteropods. As concern about ocean acidification increases, it becomes useful to compare the physiological responses of closely-related calcifying and non-calcifying species to acidification. The goals of this study were thus to generate a reference transcriptome for Clione limacina, to expose individuals to CO2 for a period of 3 days, and to explore differential patterns of gene expression. Our Trinity assembly contained 300,994 transcripts of which ~26% could be annotated. In total, only 41 transcripts were differentially expressed following the CO2 treatment, consistent with a limited physiological response of this species to short-term CO2 exposure. The differentially expressed genes identified in our study were largely distinct from those identified in previous studies of thecosome pteropods, although some similar transcripts were identified, suggesting that comparison of these transcriptomes and responses may provide insight into differences in OA responses among phylogenetically and functionally distinct molluscan lineages.