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Virally-Mediated Versus Grazer-Induced Mortality Rates in a Warm-Temperate Inverse Estuary (Spencer Gulf, South Australia)

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Open Journal of Marine Science 2014年第4期4卷 257-278页

作者： Laurent Seuront mark doubell Paul Van Ruth CNRS UMR 8187 LOG Wimereux France School of Biological Sciences Flinders University Adelaide Australia Aquatic Sciences South Australian Research and Development Institute West Beach Australia

We investigated the seasonal dynamics of flow cytometrically-defined populations of viruses, heterotrophic bacteria, and the picoeukaryotic and prokaryotic phytoplankton at three sites in the temperate oligotrophic inverse estuary of Spencer Gulf (South Australia). We consistently identified two sub-populations of viruses, three sub-populations of heterotrophic bacteria, one population of picoeukaryotic phytoplankton and two populations of prokaryotic phytoplankton (cyanobacteria Prochlorococcus and Synechococcus). Both the cytometric community composition and the abundance of viruses, heterotrophic bacteria and both prokaryotic (Synechococcus and Prochlorococcus) and eukaryotic picophytoplankton were consistent with previous observations conducted in South Australian continental shelf waters. Noticeably LDNA bacteria (i.e. inactive or dormant cells) were consistently significantly the most abundant group of heterotrophic bacteria (totaling from 29% to 68% of total bacterial abundance) and were up to 10-fold more abundant than that previously reported in South Australian continental shelf waters, including the nearby Saint Vincent Gulf. These results suggest an overall low activity of the microbial community, and are consistent with previous evidence that LDNA cells may play a greater role in heterotrophic processes than HDNA cells in oligotrophic waters. In an attempt to further assess the qualitative and quantitative nature of the mortality of these organisms, we used a specific dilution assay to assess the relative contribution of viruses and microzooplankton grazers to the mortality rates of heterotrophic bacteria, and picoeukaryotic and prokaryotic phytoplankton. We consistently reported site-specific, population specific and sea-son-specific viral lysis and grazing rates of heterotrophic bacteria and the picoeukaryotic and prokaryotic (cyanobacteria Prochlorococcus and Synechococcus) phytoplankton across sites and seasons. Specifically, both viral lysis and micro-zooplankton grazing rates of heterotrophic b

关键词： Lysis Grazing Bacteria Viruses Prokaryotic and Eukaryotic Picophytoplankton Dilution Assay

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Evaluation of MODIS Products in the Great Australian Bight and Adjacent Coastal Waters

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Open Journal of Marine Science 2018年第4期8卷 431-449页

作者： Ana Redondo Rodriguez Edward King mark doubell Paul van Ruth South Australian Research and Development Institute West Beach SA Australia CSIRO Oceans and Atmosphere Flagship CSIRO Hobart Australia

Satellite remote sensing data can produce global environmental data and is easily accessible and widely used by the scientific and non-scientific community. However, to use satellite data, it is important to know its limitations and how it validates against in situ measurements for the different regions. Here, field measurements of chlorophyll-a concentration and euphotic depth within the Great Australian Bight, Gulf St Vincent and Spencer Gulf were used to validate ocean colour products derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Aqua satellite. The field data include in situ and in vivo chlorophyll-a concentration, which were compared against MODIS chlorophyll-a products derived from three algorithms (OC3M, Carder, and Garver-Siegel-Maritorena (GSM)), as well as euphotic depth measurements derived from photosynthetically active radiation (PAR) profiles, which were compared against two MODIS euphotic depth products (derived semi-analytically and from surface chlorophyll-a). The OC3M product performed well in open waters, with errors below the 35% NASA accepted limit, but it overestimated chlorophyll-a values in shallow (<50 m) waters. The GSM product produced the lowest errors, but also showed a smaller dynamic range, while the Carder product produced higher errors than GSM and it also showed small dynamic range. The relationships between the MODIS and in situ euphotic depth were robust, with errors lower than 20%. MODIS products showed weaker or no significant relationships to in situ measurements in the Eastern Great Australian Bight. This is thought to be due to the summertime subsurface upwelling pool that is characteristic of the area. Based on these results, the OC3M product provides the most reliable estimates of chlorophyll-a, and is recommended for further applications of MODIS imagery, if the limitations in shallow waters are taken into account. Alternatively, the GSM product could be a better option if the algorithm were locally adjusted. Changes in the sampling

关键词： Great Australian Bight MODIS Remote Sensing Ocean Color Chlorophyll Euphotic Depth

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