Growth and biochemical composition of a microphytobenthic diatom (Entomoneis paludosa) exposed to shorebird (Calidris alpina) droppings

Intertidal mudflats are important feeding areas for migrating and wintering shorebird species. Partial release of organic and inorganic nutrients through bird excretion may enrich the nutrients flow of mudflat ecosystems, especially in areas with a low flushing rate. The objective of the present work was to experimentally evaluate the effect of Dunlin droppings on the growth and biochemical composition of the microphytobenthic diatom, Entomoneis paludosa (W. Smith) Reimer. Different nutritional conditions were tested to investigate the impact on E. paludosa growth rate, biomass, elemental (CHN) and biochemical composition (lipids, proteins, carbohydrates, pigments). Various culture media were used going from plain artificial seawater to F/2 culture media containing variable nitrate concentrations (0; 50 or 882 mu M-NO3) to which bird dropping extract was added or not. The faeces extracts contained inorganic nitrogen (9.1 mu M-NH4), inorganic phosphorus (8.2 mu M-PO4), traces of silicate (0.2 mu M-Si), organic nitrogen in the form of urea (16 mu M-N) and other dissolved organic nitrogen (120 mu M-N). Faeces extract inartificial seawater was sufficient to sustain E. paludosa growth (up to 6.8 cell divisions in 9 days). A significant growth rate increase (+ 20%) and higher biomasses were observed when faeces extract was added to inorganic media enriched with 50 mu M-NO3. Bird droppings had a significant effect in E. paludosa final biochemical composition with the addition of faeces extract to a culture medium containing 50 mu M-NO3 increasing E. paludosa protein content and decreasing carbohydrate content. Pigment content per cell increased with the addition of bird dropping extract but ratios of light-harvesting and photo-protective pigments to chlorophyll a were unaffected. E. paludosa grown with faeces extract showed high cellular nitrogen and carbon contents, close to those obtained when cells were grown in F/2 medium. This study showed that shorebird droppings, through the addition of dissolved material, can significantly affect microphytobenthic diatom growth and biochemical composition. (C) 2015 Elsevier B.V. All rights reserved.