Microphytobenthos in Contrasting Coastal Ecosystems: Biology and Dynamics
107
the usefulness of the species concept for diatoms (Round et al. 1990; Mann
1999). Another major group are the cyanobacteria (StalI995) which are prokaryotic and members of the Eubacteria. Cyanobacteria are represented by
far fewer species than the diatoms but provide considerable taxonomic
difficulty due to their phenotypic plasticity (Palinska et al. 1996). Euglenoids
are often a significant component of microphytobenthic assemblages (Paterson et al. 1998) and form a bright green carpet on the sediment surface when
dominant (Fig. 5.1). In addition to the dominant forms, representatives of a
variety of other protistan groups are found including dinoflagellates and
flagellates (Patterson et al. 1989). The trophic position of many taxa is not
always clear, for example, dinoflagellates may be photosynthetic, mixotrophic
or heterotrophic depending on the species. Other mixotrophic taxa are more
cryptic or rare so that they are often overlooked, as is their contribution to the
productivity of the system. This group includes various forms of benthic
foraminifera (Fig. 5.1) represented by both testate and agglutinating forms.
The importance of mixotrophs to the general ecology of the system is poorly
understood and they may well contribute significantly to ecosystem turnover
through grazing and recycling of material at a microbial level. Ecological
studies of benthic forms such as foraminifera are few and far between (cf.
Moodley 1992) and it is clear that, even considering only the eukaryotic
microorganisms that inhabit sediments, our current knowledge is patchy. The
reason that we understand so little about the real nature and complexity of
sediment systems can be explained by a number of factors:
1. Small forms, meiofauna and microphytobenthos, often dominate,
2. Many organisms are delicate and are lost or damaged on sampling,
3. The protista that dominate are difficult to identify, and
4. Techniques that measure at an appropriate scale for the determination of
sediment properties have only recently been developed.
In addition, the diversity of form and the importance of the physical
environment mean that an interdisciplinary effort is required to investigate
the system.
5.3 Physical and Biological Sediment Properties
5.3.1 Sediment Types and Stability
Sediments are commonly described by reference to the Wentworth scale,
which divides sediments into size classes (e.g., Allen 1984). Sandy sediments
107
the usefulness of the species concept for diatoms (Round et al. 1990; Mann
1999). Another major group are the cyanobacteria (StalI995) which are prokaryotic and members of the Eubacteria. Cyanobacteria are represented by
far fewer species than the diatoms but provide considerable taxonomic
difficulty due to their phenotypic plasticity (Palinska et al. 1996). Euglenoids
are often a significant component of microphytobenthic assemblages (Paterson et al. 1998) and form a bright green carpet on the sediment surface when
dominant (Fig. 5.1). In addition to the dominant forms, representatives of a
variety of other protistan groups are found including dinoflagellates and
flagellates (Patterson et al. 1989). The trophic position of many taxa is not
always clear, for example, dinoflagellates may be photosynthetic, mixotrophic
or heterotrophic depending on the species. Other mixotrophic taxa are more
cryptic or rare so that they are often overlooked, as is their contribution to the
productivity of the system. This group includes various forms of benthic
foraminifera (Fig. 5.1) represented by both testate and agglutinating forms.
The importance of mixotrophs to the general ecology of the system is poorly
understood and they may well contribute significantly to ecosystem turnover
through grazing and recycling of material at a microbial level. Ecological
studies of benthic forms such as foraminifera are few and far between (cf.
Moodley 1992) and it is clear that, even considering only the eukaryotic
microorganisms that inhabit sediments, our current knowledge is patchy. The
reason that we understand so little about the real nature and complexity of
sediment systems can be explained by a number of factors:
1. Small forms, meiofauna and microphytobenthos, often dominate,
2. Many organisms are delicate and are lost or damaged on sampling,
3. The protista that dominate are difficult to identify, and
4. Techniques that measure at an appropriate scale for the determination of
sediment properties have only recently been developed.
In addition, the diversity of form and the importance of the physical
environment mean that an interdisciplinary effort is required to investigate
the system.
5.3 Physical and Biological Sediment Properties
5.3.1 Sediment Types and Stability
Sediments are commonly described by reference to the Wentworth scale,
which divides sediments into size classes (e.g., Allen 1984). Sandy sediments