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  1. Abstract

    In the South Atlantic Bight (SAB), responses of zooplankton communities to physical dynamics were evaluated monthly at two sites on the continental shelf offshore from Savannah, GA, USA, between December 2015 and December 2017. Zooplankton were collected in oblique net tows (202-μm). Samples were collected in two regions of the middle shelf: inner edge (Site 1: 25 m isobath, n = 22) and outer edge (Site 2: 40 m isobath, n = 21). Samples were also collected at a third site on the 40 m isobath, ~20 nm south of Site 2 in July and August 2016. Temperature, salinity and fluorescence data were recorded at each site. Overall, 57 taxa were identified with total abundances varying from 1 × 103 to 81 × 103 ind.m−3. Small copepods predominated; notably Paracalanus spp. The highest abundance was recorded in October 2016 at Site 1, following deep mixing induced by Hurricane Matthew. Interannual variability of zooplankton abundance was significant, with higher abundances in 2016 compared with 2017, reflecting higher river runoff in 2016. Samples from Site 3 yielded the largest Dolioletta gegenbauri bloom documented in the SAB. This 2-year time-series, for the first time, suggests that zooplankton communities on the SAB middle shelf region are significantly influenced by continental precipitationmore »patterns.

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  2. Bloom-forming gelatinous zooplankton occur circumglobally and significantly influence the structure of pelagic marine food webs and biogeochemical cycling through interactions with microbial communities. During bloom conditions especially, gelatinous zooplankton are keystone taxa that help determine the fate of primary production, nutrient remineralization, and carbon export. Using the pelagic tunicate Dolioletta gegenbauri as a model system for gelatinous zooplankton, we carried out a laboratory-based feeding experiment to investigate the potential ecosystem impacts of doliolid gut microbiomes and microbial communities associated with doliolid faecal pellets and the surrounding seawater. Metabarcoding targeting Bacteria and Archaea 16S rRNA genes/Archaea and qPCR approaches were used to characterize microbiome assemblages. Comparison between sample types revealed distinct patterns in microbial diversity and biomass that were replicable across experiments. These observations support the hypothesis that through their presence and trophic activity, doliolids influence the structure of pelagic food webs and biogeochemical cycling in subtropical continental shelf systems where tunicate blooms are common. Bacteria associated with starved doliolids (representative of the resident gut microbiome) possessed distinct low-biomass and low-diversity microbial assemblages, suggesting that the doliolid microbiome is optimized to support a detrital trophic mode. Bacterial genera Pseudoalteromomas and Shimia were the most abundant potential core microbiome taxa, similar tomore »patterns observed in other marine invertebrates. Exploratory bioinformatic analyses of predicted functional genes suggest that doliolids, via their interactions with bacterial communities, may affect important biogeochemical processes including nitrogen, sulphur, and organic matter cycling.« less
    Free, publicly-accessible full text available July 1, 2023
  3. Abstract

    The study of invasive species often focuses on regions of recent introduction rather than native habitats. Understanding an invasive species in its natural environment, however, can provide important insights regarding the long-term outcome of invasions. In this study we investigated the diet of the invasive spiny water flea, Bythotrephes longimanus, in two Austrian perialpine lakes, where it is native. The gut contents of wild-caught Bythotrephes individuals were estimated by quantitative polymerase chain reaction, targeting species-specific fragments of the barcoding region of the cytochrome c oxidase I gene of potential prey. The observed prey spectrum of Bythotrephes in the study lakes consisted primarily of Eudiaptomus gracilis and Diaphanosoma brachyurum. The Daphnia longispina complex, Leptodora kindtii and Mesocyclops leuckarti also contributed to the diet. Results indicate that Bythotrephes is a generalist feeder with a preference for epilimnetic prey.