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DISCUSSION
The present study explicitly addressed three questions with respect to disturbances on
intertidal sandflats. These were:
(i) do tube-bed communities have different early successional dynamics from non
tube-bed communities?;
(ii) does the successional stage of a community affect the colonisation mode of early
colonisers?;
(iii) can sediment disturbance lead to P. elegans patch formation on Drum Sands?
Do tube-bed communities have different early successional dynamics from non-
tube-bed communities?
These experiments compared the initial (3 week) communities colonising defaunated
sediments within P. elegans patches with those in non-patch areas. The results
indicated that some species colonised the two habitat types in significantly different
numbers, at least at certain times of the year. P. elegans larvae colonised in
significantly higher numbers in patch azoics than non-patch azoics during April 1997,
but showed the opposite trend in August 1997 when larval recruitment was relatively
low. Adult P. elegans colonised patch azoics in higher numbers than non-patch ones
during August and December, although this was not significant due to high replicate
variability. C. capitata consistently colonised in relatively high numbers in all three
experiments while C. edule and M. balthica colonised non-patch azoic sediments in
significantly higher numbers than patch azoics during April 1997. Multivariate
analyses, together with non-parametric ANOS1M tests, revealed that the community
composition of the azoic sediments was significantly different between the two habitat
types during April 1997 only. These analyses also indicated that there was a strong
temporal effect on initial community composition since the April community was
markedly different from those of August and December 1997. Sediment
measurements taken during December suggested that there were no significant
differences between the levels of water, organics or silt/clay in azoic sediments
between the two habitat types although the redox potentials at 2 and 4cm sediment
depths were significantly lower in non-patch azoics.
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