338
D. Raffaelli and M. Emmerson
(Stephenson et al. 1971; Gray 1981), this comparative approach has been useful in generating hypotheses about likely animal-sediment interactions.
The comparison of biological patterns across different kinds of intertidal
and sublittoral sediments and similarities in patterns between biogeographical regions provide indirect evidence of common structuring processes
(Reise 1985; Brown and McLachlan 1990; Raffaelli and Hawkins 1996). However, similar patterns may be generated by a variety of alternative mechanisms and it is not always safe to assume causal links between pattern and
process. Direct, large-scale comparisons of the processes themselves are
preferable, but more difficult because much greater effort is usually required.
However, it is now possible to make such comparisons with respect to two
functional processes, energy flow and community dynamics.
Describing the flows of material between biological compartments in ecological systems was a major focus of research programmes in the 1960s and
1970s. Many of these were associated with the International Biological
Programme (IBP), one of the aims of which was to "ensure a world-wide study
of ... organic production on the land, in fresh waters, and in the seas ... "
(Worthington 1965). The approach adopted by the IBP provided a sensible
basis for the comparison of production (and hence food webs) in systems as
diverse as rain forests, taiga and, of course, sandy shores and mudflats.
Although the role of the IBP largely evaporated in the mid-1970s, the
programme did deliver many methodological handbooks (e. g. Vollenwider
1969; Holme and McIntyre 1971) and facilitated a great deal of research on
production and energy flow in shallow-water marine systems worldwide
(Raffaelli 2000a). This initiative provided the springboard for later detailed
studies at many other locations, such as in Gullmar fjord (Pihl 1985) and
South-west England (Warwick et al. 1975). The most significant feature of the
IBP is that it provided an agreed common methodological framework, mainly
through the standard protocols contained in the IBP manuals, and this greatly
facilitated the comparative approach.
These comparative studies identified the significance of allochthonous
imports of carbon for many sediment systems, where in situ primary production can often be of little importance, except perhaps at the local scale for
the most sheltered environments where macrophyte biomass is high (Raffaelli
and Hawkins 1996). A second feature to emerge from comparative energy flow
studies was the overriding importance of sediment particle size, and hence
the morpho dynamic state of the shore (Brown and McLachlan 1990), for the
retention and processing by heterotrophs of allochthonous organic matter on
which higher trophic levels ultimately depend.
In parallel with production studies, intertidal ecologists began to apply the
experimental manipulative approach to shores in an effort to identify the
important processes which might organise communities. However, in marked
contrast to the coordinated approach to energy flow facilitated by the IBP, the
D. Raffaelli and M. Emmerson
(Stephenson et al. 1971; Gray 1981), this comparative approach has been useful in generating hypotheses about likely animal-sediment interactions.
The comparison of biological patterns across different kinds of intertidal
and sublittoral sediments and similarities in patterns between biogeographical regions provide indirect evidence of common structuring processes
(Reise 1985; Brown and McLachlan 1990; Raffaelli and Hawkins 1996). However, similar patterns may be generated by a variety of alternative mechanisms and it is not always safe to assume causal links between pattern and
process. Direct, large-scale comparisons of the processes themselves are
preferable, but more difficult because much greater effort is usually required.
However, it is now possible to make such comparisons with respect to two
functional processes, energy flow and community dynamics.
Describing the flows of material between biological compartments in ecological systems was a major focus of research programmes in the 1960s and
1970s. Many of these were associated with the International Biological
Programme (IBP), one of the aims of which was to "ensure a world-wide study
of ... organic production on the land, in fresh waters, and in the seas ... "
(Worthington 1965). The approach adopted by the IBP provided a sensible
basis for the comparison of production (and hence food webs) in systems as
diverse as rain forests, taiga and, of course, sandy shores and mudflats.
Although the role of the IBP largely evaporated in the mid-1970s, the
programme did deliver many methodological handbooks (e. g. Vollenwider
1969; Holme and McIntyre 1971) and facilitated a great deal of research on
production and energy flow in shallow-water marine systems worldwide
(Raffaelli 2000a). This initiative provided the springboard for later detailed
studies at many other locations, such as in Gullmar fjord (Pihl 1985) and
South-west England (Warwick et al. 1975). The most significant feature of the
IBP is that it provided an agreed common methodological framework, mainly
through the standard protocols contained in the IBP manuals, and this greatly
facilitated the comparative approach.
These comparative studies identified the significance of allochthonous
imports of carbon for many sediment systems, where in situ primary production can often be of little importance, except perhaps at the local scale for
the most sheltered environments where macrophyte biomass is high (Raffaelli
and Hawkins 1996). A second feature to emerge from comparative energy flow
studies was the overriding importance of sediment particle size, and hence
the morpho dynamic state of the shore (Brown and McLachlan 1990), for the
retention and processing by heterotrophs of allochthonous organic matter on
which higher trophic levels ultimately depend.
In parallel with production studies, intertidal ecologists began to apply the
experimental manipulative approach to shores in an effort to identify the
important processes which might organise communities. However, in marked
contrast to the coordinated approach to energy flow facilitated by the IBP, the