Long-term changes in intertidal estuarine diatom assemblages related to reduced input of organic waste

Abstract

A comparison is made of the species composition and density of benthic diatoms of an intertidal brackish mudflat in the Ems-Dollard estuary (NetherlanddGermany) under conditions of high (1977 to 1980) and reduced (1987 to 1993) organic waste input from the river LVesterwoldsche Aa. During the observation period (1977 to 1993) the epipelic diatom population on the mudflat was composed of only a limited number of species. From 1977 to 1980. every year broadly the same spatial and temporal patterns of the sediment-inhabiting diatoms were found, viz, an alternating dominance of Navjcula s a l~n a r u n~ and N. pygmaea. In 1993 this pattern had disappeared and A' phyllepta and N tlanatjca, specles with a lower tolerance to high ammonium and sulphide concentrations, were the d o n~i -nant species. This change could be attr~buted to a reduction of organic waste input. The declining abundance of N. pygmaea was probably also partly caused by the decreased abundance of the nematode Eudiplogastcr pararmatus, a n indicator of organic enrichment. In 1987 and 1993, the diatom populations on the mudflat showed density maxima in spring and late autumn, in contrast with the period 1976 to 1977, during which values were high (over 100 mg chlorophyll a m-2) during a large part of the year, not showing any spring 01-autumn bloon~. The d~fference in the development of microphytobenthos biomass was probably caused by the increasing numerical densities of the macrofaunal diatom grazers Nereis diversicolor and Corophium volutator, causcd by the reduction of the organic waste.

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

“…These values are within the range of published values (Underwood & Smith, 1998;Smith, 1999) and doubling times Peletier, 1996) for benthic marine diatoms. However, the species-specific growth rates did not vary significantly over the tested salinity range during short-term exposures.…”

“…However, the existence of seasonal and spatial patterns in species abundances within salt marsh, sand and mudflat habitats (Oppenheim, 1991;Laird & Edgar, 1992;Underwood, 1994;Saburova et al, 1995;Peletier, 1996) indicates that benthic diatom taxa may have niches to which they specifically adapt (Underwood, 2005). The adaptive potential of intertidal microphytobenthic diatom populations, however, is not well understood.…”

Grazing and UV radiation effects on an Antarctic intertidal microalgal assemblage: a long-term field study

“…However, the lack of UV effects found on biomass and abundance of benthic Antarctic diatoms confirmed former studies at different geographical sites (e.g., Hill et al 1997). Earlier field-studies on UV effects on benthic microalgae have mainly focussed on soft bottom communities where benthic diatoms seem to be very tolerant to UV-B radiation (Peletier 1996; and references therein). The main variable to some extent affected in these communities was primary productivity while structural variables such as the overall biomass and microalgal pigments appeared unaffected (Odmark et al 1998;Sundbäck et al 1997;Wulff et al 1999;Wulff et al 2000).…”

Satellite remote sensing reveals a positive impact of living oyster reefs on microalgal biofilm development

“…In some northwestern European flats, MPB maxima have been detected slightly later in spring and in September (van der Wal et al, 2010). The summer depression has been observed in some more southerly mudflats such as MarennesOléron Bay (France) (Cariou-Le Gall and Blanchard, 1995), the Tagus estuary (Portugal) (Brito et al, 2013), Cadiz Bay (Spain) (Garcia-Robledo et al, 2016), and in the Wadden Sea (The Netherlands) (van der Wal et al, 2010;Stief et al, 2013), and has been related to increased macrobenthos grazing in summer (Peletier, 1996;Weerman et al, 2011). Low NDVI values in summer may also be due to thermo-inhibition when sediment temperature exceeds 25 • C (Blanchard et al, 1997).…”