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CHAPTER 5
THE EFFECTS OF MACROALGAL COVER ON THE SPATIAL
DISTRIBUTION OF MACROBENTHIC INVERTEBRATES: A
INTRODUCTION
SURVEY APPROACH
The effects of macroalgal cover on the sediments and invertebrate faunal assemblages
of intertidal estuaries and sheltered bays have been investigated by two contrasting
approaches (see Chapter 4). Compared to surveys, controlled manipulation
experiments allow a more mechanistic approach and the study of the cause and effect
of weed cover. These have tended to be small-scale experiments, usually of just a few
square metres in area (Raffaelli et al., 1999). Descriptive surveys, although having an
intrinsic problem of spatial confounding, allow the investigation of large-scale effects
of weed cover.
The results of surveys investigating the effect of weed cover on the faunal
communities of intertidal sediments have helped to form the basis for management of
these areas with respect to nutrient inputs (e.g., Mathieson and Atkins, 1995).
However, this outcome has been problematical because of the different results from
surveys. Although many studies have reported increases in opportunists such as C.
capitata and M. fuliginosus and in epibenthic invertebrates such as H. ulvae, along
with decreases in the numbers of some spionid polychaetes and bivalve molluscs
(Perkins and Abbott, 1972; Nicholls et al., 1981), there have been several studies
which have not shown significant changes in species composition or diversity (e.g.,
Soulsby et al., 1982). It has been noted that the responses of invertebrates to weed
cover are complex and result from the interplay between many factors (Hull, 1988)
associated with both the weed (Sundback et al., 1990; Everett, 1994) and the receiving
system (Soulsby et al., 1982). Therefore, as with controlled experiments, the
responses of most invertebrate species to weed cover ascertained by any survey within
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