Microphytobenthic dynamics in a Wadden Sea intertidal flat – Part II: Seasonal and spatial variability of non-diatom community components in relation to abiotic parameters

Abstract

The microphytobenthos colonizing the intertidal flats forms an important component of the Wadden Sea. Ten sampling points along a 1-km transect were studied in a fringe area of the Soltho¨rn tidal flat, southern North Sea, in order to determine seasonal differences in the microphytobenthos. An accompanying paper deals with the major component of the flora, the diatoms; here we, focus on the minor taxonomic groups. From May 2008 to May 2009 surface sediments were collected during low tide. Variation of environmental factors as well as microphytobenthic density (abundance and chlorophyll a) were monitored. The area investigated was a mixed-sediment mudflat, with a gradient from coarse to fine. Highest biomass was obtained in summer 2008 with 215.9 AE 12.6 mg chlorophyll a m -2 . In late autumn the chlorophyll a concentration decreased continuously at all investigated stations. Lowest values were detected in December 2008. Species abundances varied considerably both along the transect and seasonally, depending on species-specific requirements as well as hydrodynamic conditions (tidal currents). Higher densities of benthic pro-and eukaryotic microalgae were observed in sites characterized by fine sediments. Apart from the diatoms, the most abundant microphytobenthic group was the cyanophytes. Coccoid cyanophytes, mainly Merismopedia sp., were most abundant during summer, with cell numbers up to 5.72 Â 10 6 cells cm À2, while diatoms dominated in winter, spring and autumn. Filamentous cyanophytes, particularly Microcoleus chthonoplastes, were most abundant during autumn, while coccoid chlorophytes (spring: Chlorococcum submarinum, Crucigenia tetrapedia, Tetraselmis suecica), euglenophytes (summer: Euglena obtusa), dinophytes (autumn: Amphidinium operculatum, A. herdmanii) and cryptophytes (autumn: Hillea marina, Hemiselmis virescens) contributed to the microphytobenthos during warmer seasons. The statistical analysis confirmed that the composition of the microphytobenthos was related to sediment features and to characteristics of particular seasons.

Compatible solutes in three marine intertidal microphytobenthic Wadden Sea diatoms exposed to different salinities

“…Cultures were adapted to the standard conditions described above at a saturating nitrogen concentration (800 mM), reducing the N level to 90% relative to full-strength f/2. The N:P ratio of the medium in all treatments was 17:1, which is comparable to low-tide ratios in the Soltho¨rn tidal flat (Scholz & Liebezeit, 2012b). The initial nitrogen concentration was five times higher than found in the environment of the isolates during winter 2008/2009, which was the season with the highest nutrient concentrations in the Soltho¨rn tidal flat.…”

“…Samples were taken at low tide from sediments characterized by mixed sands at bi-weekly intervals from 9 June to 22 August 2008; the three taxa reached their highest abundances during this time, which was determined by analysis of permanent slides (cf. Scholz & Liebezeit, 2012b). In the first step in the isolation of clones, subsamples of approximately 2-3 g were placed in glass Petri dishes, diluted with 10 ml sterile filtered sea water from the sampling area, and stored until isolation at 18 AE 2 C and a photosynthetic active radiation (PAR) of 400 mmol photons m -2 s…”

“…All salinities are according to the Practical Salinity Scale (psu). Diatom identification was as described in Scholz & Liebezeit (2012b).…”

Effects of UV radiation on five marine microphytobenthic Wadden sea diatoms, isolated from the Solthörn tidal flat (Lower Saxony, southern North Sea) – Part II: changes in carbohydrate, amino acid and fatty acid composition

“…Photosynthetic active radiation (PAR, 400-700 nm) and UV-A were provided for 14 h daily, supplemented with 4 h of UV-B. Care was taken to obtain realistic PAR+UV-A+UV-B ratios and relatively high values of PAR, such as found at the sediment surface in the Solthörn tidal flat during summer 2008 (Scholz & Liebezeit, 2012c). UV-A radiation was supplied from four Philips TLK09N 40 W fluorescent tubes (maximum emission at 354 nm) and UV-B from two Spectroline EB160C fluorescent tubes (Laboratory Products Sales, Rochester, New York, USA; maximum emission at 312 nm) pre-burned for c. 110 h to stabilize the lamp output.…”

“…The present study is the second part of a study of five intertidal microphytobenthic diatoms, in which they were subjected to photosynthetically active radiation (PAR) supplemented with different UV combinations (UV-A, UV-B and UV-A+UV-B) during short-(6 h) and longterm experiments (30 days, with a daily dose of 4 h). The taxa were isolated from the Solthörn tidal flat in summer 2008, when relatively high levels of UV were recorded on the sediment surface (up to 118 Wm −2 in June 2008; Scholz & Liebezeit 2012c). Whereas the first part of our study (Scholz et al, 2014) dealt with the influence of UV on growth and antioxidative defence strategies, the main objectives of the present study were to determine (1) variations in carbohydrate and lipid content, which might give evidence on the overall physiological status of the cells; (2) carbohydrate composition, particularly with regard to EPS production and the possible role of particular carbohydrates as compatible solutes; (3) differences in fatty acid composition including likely changes in membrane composition; and (4) amino acid composition, with special emphasis on proline, including the activities of enzymes involved in proline metabolism.…”