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laboratory observations are needed to confirm whether mature males relocate towards females, or vice versa, to confirm this. In conclusion, this study has shown the presence of aggregated distributions of a tube- building polychaete within small-scale (1-1.5m 2) patches of increased density. These patches were generally smaller than the sampling unit (3cm 2) and persisted all through the year. The presence of these patches support previous studies indicating that P. elegans are very tolerant of conspecific encounters. The process(es) generating these patterns were probably positive adult-juvenile interactions (passive and/or active), adult movement and/or sediment heterogeneity. However, since correlation analysis should not be used to imply causation, controlled laboratory experiments and observations, in addition to field observations, need to be carried out to test these hypotheses. 200
CHAPTER 8 THE FAUNAL COMMUNITIES OF PYGOSPIO ELEGANS PATCHES INTRODUCTION Epibenthic biogenic structures are conspicuous features of many marine soft-bottom habitats. Of these, the most widespread include seagrasses (e.g., Thistle et al., 1984), mussels (e.g., Ragnarsson, 1996), macroalgal mats (e.g., Hull, 1987, 1988; Everett, 1991, 1994; Raffaelli et al., 1999; Chapters 4 and 5 of this study) and high densities of tube-dwelling polychaetes, or 'tube-beds' (e.g., Fager 1964; Daro and Polk, 1973; Noji, 1994; Morgan, 1997). The ecological importance of the tube-beds of many polychaete species has been studied including the terebellids Lanice conchilega (Jones and Jago, 1993; Ragnarsson, 1996), Loimia sp. and Axionice sp. (Trueblood, 1991), the oweniid Owenia fusiformis (Fager, 1964), the maldanids Clymenella torquata (Sanders et al., 1962; Featherstone and Risk, 1977) and Axiothella rubrocincta (Weinberg, 1979) and the spionids Pygospio elegans (Dupont, 1975; Morgan, 1997), Polydora ciliata (Noji, 1994) and Spiophanes cf. wigleyi (Featherstone and Risk, 1977). The general inference arising from such studies is that tube-mats play a major role in determing soft-sediment community structure (Woodin, 1981; Gallagher et al., 1983). Both meio- and macrofaunal communities, together with many physical variables, of those sediments with biogenic structures have been found to differ from those of adjacent areas lacking such structures. The factors responsible for these differences are many and the effects of tube-beds on community composition and sediment structure ultimately result from the interaction of many complex and interrelated processes. Furthermore, since the fauna associated with tubes may have a marked effect on sediment structure and community composition themselves, quantifying the effects of tube-beds is inherently difficult since it involves both the direct alterations 201
- Page 166 and 167: Month Sample statistic (Global R) N
- Page 168 and 169: 2NP 3NP 4NP .•,, 6NP 5NP 6P 1NP i
- Page 170 and 171: Figure 6.8: Two-dimensional MDS ord
- Page 172 and 173: - - 5P ... 4P . 6P • .‘2NP 1NP
- Page 174 and 175: I 50. 1 60. 70. 80. 90. 100. BRAY-C
- Page 176 and 177: 'P2-AZ P3-AZ N2-AZ .- - - " .„ ..
- Page 178 and 179: o • o -o + 350 — 300 = 250 7 g
- Page 180 and 181: The importance of the ambient commu
- Page 182 and 183: In April, when P. elegans larval av
- Page 184 and 185: not only for errant polychaetes, bu
- Page 186 and 187: observed in this study. How crucial
- Page 188 and 189: Micro-scale spatial patterns of mac
- Page 190 and 191: METHODS Experimental design - A pre
- Page 192 and 193: study. These individuals would not
- Page 194 and 195: RESULTS Pilot survey - The pilot su
- Page 196 and 197: Transect survey - Micro-scale patte
- Page 198 and 199: Month v:m ratio pattern Id pattern
- Page 200 and 201: (i) March 1997, replicate 1 -iAlmiA
- Page 202 and 203: (xix) October 1997, replicate 1 (ra
- Page 204 and 205: The new recruits were only sufficie
- Page 206 and 207: The results of correlation analyses
- Page 208 and 209: cf.) . crt N ,—, Cr) C,1 ,—, Cr
- Page 210 and 211: 1.2 -0.4 "a 0.8 > (i) % Water conte
- Page 212 and 213: examine the micro-scale spatial pat
- Page 214 and 215: Invertebrate larvae, those of polyc
- Page 218 and 219: CHAPTER 8 THE FAUNAL COMMUNITIES OF
- Page 220 and 221: Other theories have been postulated
- Page 222 and 223: RESULTS Univariate analysis of spec
- Page 224 and 225: -T. g 80 g 50 40 30 20 10 (i) Adult
- Page 226 and 227: in significant differences in size
- Page 228 and 229: 8.2). This was mainly because of th
- Page 230 and 231: 120 100 80 60 - 40 20 0. cn1 c.n (i
- Page 232 and 233: 3NP 6NP 4NP 1 NP 5NP 2NP : 3P 1P 6P
- Page 234 and 235: 4P 3P 5P 5NP 6P 2P 1P Figure 8.8: T
- Page 236 and 237: Figure 8.10 shows the dendrogram pr
- Page 238 and 239: NP1 NP2 NP2 NP2 NP1 NP1 NP2 NP2 NP2
- Page 240 and 241: Sediment water, organic and silt/cl
- Page 242 and 243: 5 350 — 300 250 200 — ISO — 1
- Page 244 and 245: abundances of P. ciliata had more d
- Page 246 and 247: levels of silt/clay and organics. S
- Page 248 and 249: 1973; Noji and Noji, 1991). Competi
- Page 250 and 251: shown to consume up to 68% of a 0-g
- Page 252 and 253: In Chapter 7 the micro-scale spatia
- Page 254 and 255: and positions of patches. Consequen
- Page 256 and 257: epresent those found establishing i
- Page 258 and 259: distribution at the micro-scale. Ad
- Page 260 and 261: provide a rich food source for deme
- Page 262 and 263: Armonies W., 1988. Active emergence
- Page 264 and 265: Cha M.W., in prep. Macroalgal mats
laboratory observations are needed to confirm whether mature males relocate towards<br />
females, or vice versa, to confirm this.<br />
In conclusion, this study has shown the presence of aggregated distributions of a tube-<br />
building polychaete within small-scale (1-1.5m 2) patches of increased density. These<br />
patches were generally smaller than the sampling unit (3cm 2) and persisted all through<br />
the year. The presence of these patches support previous studies indicating that P.<br />
elegans are very tolerant of conspecific encounters. The process(es) generating these<br />
patterns were probably positive adult-juvenile interactions (passive and/or active),<br />
adult movement and/or sediment heterogeneity. However, since correlation analysis<br />
should not be used to imply causation, controlled laboratory experiments and<br />
observations, in addition to field observations, need to be carried out to test these<br />
hypotheses.<br />
200
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