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DISCUSSION
This study monitored the faunal and sediment conditions of P. elegans patches and
non-patch areas between April 1997 and August 1998. This discussion will firstly
address the faunal differences observed between the two habitat types, and secondly,
the differences observed in their sediment variables. Finally, since the results
obtained at the end of this study revealed the demise of the P. elegans patches, this
discussion will conclude with the faunal changes occurring within patches and the
possible processes causing their decline on Drum Sands.
Faunal differences between P. elegans patches and non-patch areas.
The results indicated that many species showed significant differences in abundance
between these two areas. C. capitata (April 1997), C. edule (April and August 1997,
August 1998), M. balthica (December 1997 and August 1998) and C. volutator (April
to December 1997) were all significantly more abundant in P. elegans patches
compared with non-patch areas while no species were significantly more abundant in
non-patch areas. The size distributions of certain species, i.e., P. elegans (April to
December 1997) and C. capitata (December 1997), were also significantly different
between the two habitat types. Multivariate analysis together with non-parametric
ANOSIIVI tests revealed that the community compositions were always significantly
different between the two habitat types and this was consistently due to several species
such as C. edule, C. cap itata and C. volutator.
The significant differences between the fauna of P. elegans patches compared with
those of non-patch areas in this study support the results of previous studies. Fager
(1964) noted that several species, the isopod Munna ubiquita, the pycnogonid
Oropallene heterodentata, the hermit crab Pa gurus sp. and the anemone Zaolitus
actius were only found in the stabilised sediments within the dense Owenia fusiformis
tube-beds in his study. Similarly, Sanders et al. (1962) found that the small amphipod
Listriella clymenella was only found within the tube arrays of the maldanid
Clymenella torquata in the intertidal flats of Barnstable Harbor, Massachusetts.
Woodin (1981) experimentally demonstrated that increases in the density of Diopatra
cuprea tubes resulted in increases in macroinvertebrate species richness and
abundances. Within the spionids, Noji (1994) noted that areas with moderate
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