Microphytobenthos in Contrasting Coastal Ecosystems: Biology and Dynamics
113
rately. The influence of organisms can be "felt" long after their death or
relocation since the structures and secretions they have made may remain.
This is not confined to macrofauna but is also relevant to the micro biota
whose most famous relics are the laminated microbial mounds or stromatolites found in the fossil record (Riding and Awramik 2000). Far more subtle
remnants include polymeric material (Taylor et al. 1999), enzymes (Chrost
1991) and cellular remains. These phases do not only exist in isolation but
may overlap allowing for material transformations and transfers to occur between phases. For example, water can contribute to three phases: as structural
water with mineral particles (tightly bound and unavailable for chemical or
biological transformation); as free water; and as biologically bound water
where the molecules are associated with organic molecules such as cell walls,
membranes or with a wide variety of polymers (Decho 1990). The balance
between phases varies considerably between sediment types (Fig. 5.3).
Moreover, the biological influence on sediment characteristics and behaviour varies in space and time. The development of microbial assemblages
is patchy (Saburova et al. 1995; Serodio et al. 1997; Paterson et al. 1998) but
changes can be rapid with biofilms developing in days (Underwood and
Paterson 1993) with concomitant effects on sediment characteristics. The
rapid growth rate and ability to exploit conditions is a feature of the protista
and this has traditionally been exploited to examine ecological theory (Gause
1934; Petchey et al. 1999). Thus, the sediment matrix is a rapidly changing and
heterogeneous environment made more variable by the activity of the organisms themselves (Decho 2000).
5.5 Comparative Biodiversity
Although no direct comparison has been made between the diversity of
microphytobenthos on intertidal shores, assemblages on a sandy substratum
are usually much more sparse and distributed over a much greater depth than
for cohesive sediment (Round 1979; Yallop and Paterson 1994). The spatial
distribution of micro algae on the mesoscale depends mostly on the granulometric composition of sediments and on factors influencing particle size and
density (Oppenheim 1988; Saburova et al. 1995; Zong and Horton 1999). The
life style of the microphytobenthos varies between two extremes: cells are
attached to the grains or move through the interstitial spaces. The attached
forms are termed "epipsammon" while the motile forms are termed "epipelon" (Round 1981). While few epipsammic forms occur in cohesive sediment because small grains provide limited surface area for attachment, both
forms occur in mixed or sandy sediment, although epipelic forms are less
common as the energy intensifies.
113
rately. The influence of organisms can be "felt" long after their death or
relocation since the structures and secretions they have made may remain.
This is not confined to macrofauna but is also relevant to the micro biota
whose most famous relics are the laminated microbial mounds or stromatolites found in the fossil record (Riding and Awramik 2000). Far more subtle
remnants include polymeric material (Taylor et al. 1999), enzymes (Chrost
1991) and cellular remains. These phases do not only exist in isolation but
may overlap allowing for material transformations and transfers to occur between phases. For example, water can contribute to three phases: as structural
water with mineral particles (tightly bound and unavailable for chemical or
biological transformation); as free water; and as biologically bound water
where the molecules are associated with organic molecules such as cell walls,
membranes or with a wide variety of polymers (Decho 1990). The balance
between phases varies considerably between sediment types (Fig. 5.3).
Moreover, the biological influence on sediment characteristics and behaviour varies in space and time. The development of microbial assemblages
is patchy (Saburova et al. 1995; Serodio et al. 1997; Paterson et al. 1998) but
changes can be rapid with biofilms developing in days (Underwood and
Paterson 1993) with concomitant effects on sediment characteristics. The
rapid growth rate and ability to exploit conditions is a feature of the protista
and this has traditionally been exploited to examine ecological theory (Gause
1934; Petchey et al. 1999). Thus, the sediment matrix is a rapidly changing and
heterogeneous environment made more variable by the activity of the organisms themselves (Decho 2000).
5.5 Comparative Biodiversity
Although no direct comparison has been made between the diversity of
microphytobenthos on intertidal shores, assemblages on a sandy substratum
are usually much more sparse and distributed over a much greater depth than
for cohesive sediment (Round 1979; Yallop and Paterson 1994). The spatial
distribution of micro algae on the mesoscale depends mostly on the granulometric composition of sediments and on factors influencing particle size and
density (Oppenheim 1988; Saburova et al. 1995; Zong and Horton 1999). The
life style of the microphytobenthos varies between two extremes: cells are
attached to the grains or move through the interstitial spaces. The attached
forms are termed "epipsammon" while the motile forms are termed "epipelon" (Round 1981). While few epipsammic forms occur in cohesive sediment because small grains provide limited surface area for attachment, both
forms occur in mixed or sandy sediment, although epipelic forms are less
common as the energy intensifies.