Practical approaches to algal excretion

Release of dissolved organic carbon (DOC) by diatom cultures and by a mixed phytoplankton assemblage dominated by picophytoplankton was examined using filtration techniques; dialysis membrane based techniques were also investigated for their potential utility in studies of algal excretion. The inexpensive dialysis-diffusion system which was investigated shows promise as a method for obtaining phytoplankton exudate for physico-chemical characterization of exudate or for bacterial growth studies. Experimental results obtained using filtration techniques showed that at least a small amount of carbon fixed by photosynthesis is rapidly converted to DOC by rapidly growing cultures and that a larger proportion is converted to DOC by cells adapting to a change in irradiance, by senescent cells, and in a whole plankton community composed of a mixture of cells in unknown physiological condition. DOC production appears to occur simultaneously with photosynthesis and can be more than 10 % of total carbon fixation in cells which are not in complete metabolic equilibrium with the environment. Use of techniques which account for DOC release are, therefore, recommended for measurement of primary production in field situations unless the phytoplankton community is known to be in exponential growth

Summary table of previous deep-water disturbance studies relevant to mining (see Fig 1 for a map and Fig 2 for a timeline of these studies).

<p>Summary table of previous deep-water disturbance studies relevant to mining (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0171750#pone.0171750.g001" target="_blank">Fig 1</a> for a map and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0171750#pone.0171750.g002" target="_blank">Fig 2</a> for a timeline of these studies).</p

Flowchart of study identification and selection process.

<p>All systematic review and meta-analyses methods conducted according to PRISMA guidelines. See PRISMA checklist in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0171750#pone.0171750.s003" target="_blank">S3 Table</a>. <i>From</i>: Moher D, Liberati A, Tetzlaff J, Altman DG, The PRISMA Group (2009). <i>P</i>referred <i>R</i>eporting <i>I</i>tems for <i>S</i>ystematic Reviews and <i>M</i>eta-<i>A</i>nalyses: The PRISMA Statement. PLoS Med 6(7): e1000097. doi:<a href="http://dx.doi.org/10.1371/journal.pmed1000097" target="_blank">10.1371/journal.pmed1000097</a>. <b>For more information, visit</b> <a href="http://www.prisma-statement.org" target="_blank">www.prisma-statement.org</a>.</p

Timeline of deep-water seabed test mining or mining simulations.

<p>Bars represent time since initial disturbance to the seafloor. Upward ticks indicate the timing of pre-disturbance visits. Downward ticks indicate the timing of post-mining monitoring visits. Short name indicate in capitals and full name of each experiment indicated above each bar. OMI, OMA, OMCO, BIE-II, IOM BIE and JET experiments were carried out in the Clarion Clipperton Zone (also indicated as CCZ). The INDEX experiment was carried out in the Indian Ocean. Note OMCO disturbance investigated was sledge samples and not the mining vehicle test.</p

Initial impacts (first repeat visit and less than 1 year after disturbance) of mining activity on densities of a variety of faunal groups.

<p>Values represent standardised mean differences (SMD) between faunal densities at impacted sites and control sites and 95% confidence intervals. The horizontal line shows no difference between impacted and control sites. Colours represent different studies. Please note that the disturbances at DISCOL used a different disturbance mechanism than at the other sites. Filled symbols represent more robust data (>30 individuals per sample). Purple diamonds represent weighted means.</p

Recommendations for robust assessment of the impact of future test mining cases.

<p>Recommendations for robust assessment of the impact of future test mining cases.</p

Changes in effects of mining activities over time on faunal density and diversity.

<p>Changes shown for megafaunal density (top left), macrofaunal density (top right) and meiofaunal density (bottom left) and diversity (including evenness) of megafauna and meiofauna (bottom right). If totals were not available, the value for the most abundant taxon was plotted and indicated in the legend. Values represent standardised mean differences (SMD) between faunal densities or diversities at impacted sites and control sites and 95% confidence intervals. Diversity was reported as Shannon-Wiener diversity and evenness was Pielou evenness index in the studies used.</p

Maps of the locations of deep-sea mining simulations and test mining activities.

<p>A) Map of the world with deep-sea mining simulations and test mining activities marked as stars coloured according to the convention used throughout the paper; B) zoomed in map of the Clarion Clipperton Zone (extent indicated on map A); C-I) Maps of individual deep-sea mining simulations and test mining activities: C) DISCOL; D) OMI (DOMES A); E) JET; F) OMCO sled tracks investigated in [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0171750#pone.0171750.ref016" target="_blank">16</a>]; G) BIE-II (note that individual tracks not discernible, so map shows polygon of extent of tracks; H) IOM BIE; I) INDEX. Latitude and longitude labels are on the right and base of each map.</p