Seagrass as major source of transparent exopolymer particles in the oligotrophic Mediterranean coast

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Iuculano, Francesca ; Duarte, Carlos M. ; Marbà, Núria ; Augustí, Susana (2017)

The role of seagrass, Posidonia oceanica, meadows as a source of transparent exopolymer particles (TEP) to Mediterranean coastal waters was tested by comparing the TEP dynamics in two adjacent coastal waters in the oligotrophic NW Mediterranean Sea, one characterized by oligotrophic open-sea waters and the other accumulating seagrass leaf litter, together with an experimental examination of TEP release by seagrass litter. TEP concentrations ranged from 4.6&thinsp;µg&thinsp;XG&thinsp;Eq&thinsp;L<sup>&minus;1</sup> to 90.6&thinsp;µg&thinsp;XG&thinsp;Eq&thinsp;L<sup>&minus;1</sup>, with mean (±SE) values of 38.7 (±2.02)&thinsp;µg&thinsp;XG&thinsp;Eq&thinsp;L<sup>&minus;1</sup> in the site devoid of seagrass litter, whereas the coastal beach site accumulating leaf litter had >&thinsp;10-fold mean TEP concentrations of 487.02 (±72.8)&thinsp;µg&thinsp;XG&thinsp;Eq&thinsp;L<sup>&minus;1&thinsp;</sup>. Experimental evaluation confirmed high rates of TEP production by <i>P. oceanica</i> litter, allowing calculations of the associated TEP yield. We demonstrated that <i>P. oceanica</i> is an important source of TEP to the Mediterranean Sea, contributing an estimated 0.10&thinsp;Tg&thinsp;C as TEP annually. TEP release by <i>P. oceanica</i> seagrass explains the elevated TEP concentration relative to the low chlorophyll <i>a</i> concentration in the Mediterranean Sea.
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