Abstract
Most wetted surfaces that are illuminated support a population of phototrophs. The marine sediment is no exception and there the major component of the microphytobenthic population is diatoms. These organisms are credited with stabilizing the sediment against physical disturbance by virtue of the extracellular carbohydrate polymers that they elaborate. However, diatoms synthesize and secrete several carbohydrate polymers and it is not certain which of them is involved in the stabilization process. In order to investigate this, we have constructed small glass bead-filled flow through bioreactors to mimic marine sediments. The flow rate through the bioreactors was found to reflect the physical stability of the bead bed. Thus flow rate was measured as a function of diatom growth and the production of three operationally-defined polymers, i.e., those soluble in the medium, those soluble in 0.5 M NaHCO3 at 90 °C and those not soluble in either solvent (matrix polymer). Growth of the diatoms did not change the hydraulic conductivity of the bioreactors. For Amphora coffeaeformis, neither did the production of medium-soluble nor NaHCO3-soluble polymers. However, matrix polymer accumulation was directly correlated with a reduction in flow (regression coefficient R2 = 0.96) and stabilization against physical disturbance. Results with species of Navicula were not as clear. Both NaHCO3-soluble and matrix polymers were involved in producing the flow reduction. In the same manner we also measured the effect of Pseudoalteromonas haloplanktis growth on bead bed hydraulic conductivity and bead bed stability. Growing alone, no effect was found, but in co-culture with a single diatom species, the bacteria reduced the diatom effect on flow through the bioreactors seen earlier, however did not reduce the extent of their growth. Confocal scanning laser microscopy of beads colonized with diatoms alone, or diatoms in co-culture with bacteria, revealed that P. haloplanktis was able to inhibit diatom adhesion to the beads. When the bacteria were present there was less matrix polymer evident. We speculate that this interference with diatom metabolic activity was either the result of less matrix polymer synthesis, or its hydrolysis by the bacteria. The results are applicable to mixed species biofilms of this type on surfaces other than sediments.
Highlights
Intertidal mudflats form an important part of an estuarine ecosystem.[1,2] Their position between the land and the open ocean is responsible for the fact that they bear much of the impact of human activities on the aquatic environment
There is a large body of literature on the physical stabilization of marine sediments[3,7,8,9,10,11,12,13,14,15,16,17,18] and most investigators agree that it is the activities of the microphytobenthic organisms, most likely those of the diatoms, that play a major role in the prevention of sediment movement by wave action
We found that the presence of bacteria in a diatom culture gave different results than those obtained with diatoms alone (Fig. 9)
Summary
Intertidal mudflats form an important part of an estuarine ecosystem.[1,2] Their position between the land and the open ocean is responsible for the fact that they bear much of the impact of human activities on the aquatic environment. It is well recognized that the microphytobenthic organisms inhabiting intertidal sediments are responsible for a large part of estuarine productivity[3,4] and that of sandy beaches.[5,6] Related to this is their involvement in the stabilization of estuarine sediment particles against physical disturbance. There is a large body of literature on the physical stabilization of marine sediments[3,7,8,9,10,11,12,13,14,15,16,17,18] and most investigators agree that it is the activities of the microphytobenthic organisms, most likely those of the diatoms, that play a major role in the prevention of sediment movement by wave action. It is not possible to exclude the activities of the benthic bacteria from this process,[20] but from a study of the correlation of the
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