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D.M. Paterson and S.E. Hagerthey
However, where cyanobacteria become dominant, they not only dramatically
affect sediment stability but also reduce diversity since the mats tend to be
dominated by few species. Thus, beginning with a coarse high-energy sandy
system, diversity is expected to increase as sediment characteristics change
(non-cohesive »mixed flat) then decline again (mixed flat »cohesive) as
sediment grain size decreases.
Superimposed on the relationships between microphytobenthic diversity,
EPS production, sediment stability, and sediment characteristics are three
important factors. First, microphytobenthic production is dependent on
nutrients. The supply rate of resources (e. g., nitrogen and phosphorus) affects
microphytobenthic biomass and species composition (Tilman 1982; Grover
1997). Here low nutrient supply rates and interspecific competition limit
diversity. Second, sediment dwelling fauna can affect sediment stability in
three ways:
l. Regulation of microphytobenthic biomass and species composition
through direct consumption,
2. Bioturbation of the sediments, and
3. Secretion of EPS or mucilage
In natural environments, nutrient supply rates and herbivory work in
concert to structure microphytobenthic algal assemblages. Whereas grazers
increase diversity and perhaps decrease sediment stability under nutrientlimited conditions, it is unclear what influence grazers have on microbial
assemblages at intermediate and high resource supply rates (Proulx and
Mazumder 1998). Third, the development of a microbial mat establishes a
feedback mechanism by which EPS traps finer particles, thus changing the
nature of the sediment and potentially the diversity (Daborn et al. 1993;
Underwood and Paterson 1993).
The complex interactions between the physical and biological properties
that regulate and maintain microbial assemblages are just beginning to be
understood. However, the primary factors controlling diversity are not well
known and areas requiring study are the influence of mixtures of sediment
types; successional changes, interaction between nutrients and grazing
pressure; biostabilisation, and bioturbation. The nature of trophic interactions and how infauna affect microphytobenthic structure and function are
particularly interesting in terms of the ecosystem dynamics, Although these
have still to be elucidated, some initial studies have described trophic cascades with direct physical effects (Daborn et al. 1993). While a great deal of
work is required in these areas, conversely, intertidal sediments may provide a
valuable model and an experimental system in which to investigate ecological
theory (see Chap. 16).
D.M. Paterson and S.E. Hagerthey
However, where cyanobacteria become dominant, they not only dramatically
affect sediment stability but also reduce diversity since the mats tend to be
dominated by few species. Thus, beginning with a coarse high-energy sandy
system, diversity is expected to increase as sediment characteristics change
(non-cohesive »mixed flat) then decline again (mixed flat »cohesive) as
sediment grain size decreases.
Superimposed on the relationships between microphytobenthic diversity,
EPS production, sediment stability, and sediment characteristics are three
important factors. First, microphytobenthic production is dependent on
nutrients. The supply rate of resources (e. g., nitrogen and phosphorus) affects
microphytobenthic biomass and species composition (Tilman 1982; Grover
1997). Here low nutrient supply rates and interspecific competition limit
diversity. Second, sediment dwelling fauna can affect sediment stability in
three ways:
l. Regulation of microphytobenthic biomass and species composition
through direct consumption,
2. Bioturbation of the sediments, and
3. Secretion of EPS or mucilage
In natural environments, nutrient supply rates and herbivory work in
concert to structure microphytobenthic algal assemblages. Whereas grazers
increase diversity and perhaps decrease sediment stability under nutrientlimited conditions, it is unclear what influence grazers have on microbial
assemblages at intermediate and high resource supply rates (Proulx and
Mazumder 1998). Third, the development of a microbial mat establishes a
feedback mechanism by which EPS traps finer particles, thus changing the
nature of the sediment and potentially the diversity (Daborn et al. 1993;
Underwood and Paterson 1993).
The complex interactions between the physical and biological properties
that regulate and maintain microbial assemblages are just beginning to be
understood. However, the primary factors controlling diversity are not well
known and areas requiring study are the influence of mixtures of sediment
types; successional changes, interaction between nutrients and grazing
pressure; biostabilisation, and bioturbation. The nature of trophic interactions and how infauna affect microphytobenthic structure and function are
particularly interesting in terms of the ecosystem dynamics, Although these
have still to be elucidated, some initial studies have described trophic cascades with direct physical effects (Daborn et al. 1993). While a great deal of
work is required in these areas, conversely, intertidal sediments may provide a
valuable model and an experimental system in which to investigate ecological
theory (see Chap. 16).