The benthic ecology and community structure in Lyttelton Harbour ...

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63. SECTION 5 DISCUSSION 5.1 The significance of the results I~ would appear from the results of both the recurrent groups analysis and, the multiple discriminal,t t function analysis that assemblages of animals do occuc in Lyttelton Ilarbour. It has been suggested in Section 4 that there is also a continuum composed of species that are not tied to one region but exist over a range of bottom types. Generally these have been found to show an affinity with one substrate, either muddy or sandy, where they are more successful. This type of study is investigating community structures on a small scale in a region that would norma~ly be classified as a muddy-bottomed harbour and the fauna present lumped into one community. The communities have been identified in relation to the substrate t~xture and organic carbon content. Towards these ends the substrate had to be categorized into sands, sandy muds, and muds. There are rather indefinite, and certainly arbitrary, distinctions but are necessary to reduce some of the variables and facilitate handling of the datao This type of approach· is very common among benthic ecologists and was used extensively by Sanders (1958) in stUdies in Buzzards Bay. He found a very marked correlation between the amount of fine material, the concentration of chemical nutrients and the density of faunae Fager (1968) found a strong relationship between a stable fine sand substrate 'and a well established epifaunal community off La Jolla, California. Rhoads and Young (1970) have gone further
than th in. their investigations. They looked at tl10 influ~nces of deposit-feeding organisms on community stability an~ found that wl1en the mud bottom was loosr~ned by the reworking of the material the material clogqerl the filtering apparatus of suspension feedi~g animals, blJr'ied newly settled larvae or discouraged further settling of larva~, and prevented the attachment of epifauna. The influence of fauna on the sediments varies with the distribution of animals and the trophic-group distribution. Animals that are heterotrophic either are suspension or deposit feeders. Rarely are both systems used. Often~ as has been shown in Lyttelton Harbour, there is a spacial d parity in the distribution of filter feeding and deposit feeding forms. The general rule in this respect appears that suspension feeders occupy regions of abundant water supply where currents provide a continual source of food particles. On the other hand, deposit feeders normally exist in areas of deposition where currents do not carry away the colloidal material, that composes most of the organic fraction. In this type of distribution individual tolerances play a great part in determining penetration, especially of filter feeders, into very fine sediment areas. 5.2 Lyttelton Harbour communities reviewed It is proposed to call the community that has been. identified in the muddy r~gions the Hemiplax hirtipes - Virqularia gracillimR community. This is in accordance with the ru+es for characterizing species pur forward in Thorson (1957) which require characterizing animals of the first order to occur in at least 50 percent of the samples taken and compose at least 5 percent of the living weight per standard unit. This
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THE BENTHIC ECOLOGY AND COM~UNITY S
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Figure LIST OF FIGURES 1 Lyttelton
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Figure 15~12 The distribution of Mi
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Table LIST OF TABLES Follo'V!ing Pa
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SECTION ,SECTION S8CTION ? • 9..
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1. SECTION 1 LYTTELTON HARBOUR; GEN
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FIGURE 1. Lyttelton Harbour relativ
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The,choppy seas produced by these t
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Mt. Evans 4
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FIGURE 3. Annual ranges of temperat
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, ::l", This contras ts sharply w
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1 MLW 0 1 2 3 4 5 transect 1. U) w
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MLWO - -.-- 1 2 3 4 5 transect 3. 6
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FIGURE 6. Map of Lyttelton Harbour
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very deep water studies where the s
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9. are shown in FigG 7. The numbers
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1000 100 CI:IJ epib. sl/ I 'orange
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11. boat was stopped and sled lower
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13. 1.9 Analysis of the data One of
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15. 2.2 Sediment sources Three majo
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17. is particularly apparent ar6und
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N ~ ~ MUDDY SAND PREDOMINANTLY MUD
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FIGURE 9. Directions and, speeds in
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FIGURE 10. Graphical representation
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eference to Fig.10 shows that a ~ur
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o = - L092 diameter. mm Phi (
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22. Where the range is small with a
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FIGURE 12. Regression relating mean
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of the sediment. and organic carbon
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100 80 I 12 60 40 20 o I- 100 Z W 8
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100 80 k14 k 8 60 40 20 0 ~ 100 Z W
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100 80 9 20 i 19 60 40 20 o I- 100
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100 80 h6 i4 60 40 20 b I- 100 Z w
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100 80 9 28 j 24 60 40 I-- 20 o I-
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100 80 100 9 22 80 h 21 60 60 40 40
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100 80 22 22 - 60 _ r-- 40 _ - 20 t
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26. 25 0 C are commqn. There is fre
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28. Crossaster iaponicus Al1ostich~
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10. t Pont Ius australis (Thompson,
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32. 2 or 3 animals thic~ with a bio
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FIGURE; 14. Composition of fauna in
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34. alga. disappears before the opp
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35. The normal inhabitants of the m
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Pontophilus austral is Vi rgularia
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37. (3) Chion~ stutchbutyi (Fig 15.
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Chione stutchburyi ) Myodora st ri~
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FIG 15.5 The distribut~on Lyttelton
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39. ex~ent of"2 or 3 ~er square met
Page 98 and 99: Ha lie arc i nus w hit e i Austromi
Page 100 and 101: The distribution of LytteltonHarbou
Page 102 and 103: 41. channel and a very dense growth
Page 104 and 105: Sepiola pacifica M icrelenchus hut
Page 106 and 107: 43. (13)' Zege~erus tenuis (Fi~ 15.
Page 108 and 109: Zegelerus tenuis Maoricol pus roseu
Page 110 and 111: FIG 15.15 The distribution of Achel
Page 112 and 113: I}S. (18) Hemiplax hirtipes (Pig 15
Page 114 and 115: Xymene plebejus Hemiplax hirtipes
Page 116 and 117: Trochus tiaratus Aste rina regul ar
Page 118 and 119: FIG 15.21 The distribution of Nucul
Page 120 and 121: to the more normal figure of 3 to 4
Page 122 and 123: Ostrea heffordi Nectocarcinus a nt
Page 124 and 125: 49. have been found packed with Pon
Page 126 and 127: 51. SECTION 4 COMMUNITIES 4.1 Intro
Page 128 and 129: 53. communities. among workers The
Page 130 and 131: 55. 4.4- . Fager'~ recurrent groups
Page 132 and 133: FIGURE 16 A trell diagram drawn fro
Page 134 and 135: FIGURE 17 A schematic representatio
Page 136 and 137: 57. their ranges were not en~irely
Page 138 and 139: 59. analysis had shown that there w
Page 140 and 141: 60. mud and mudd~ regions and basic
Page 142 and 143: 61. difference in the discrirrinati
Page 144 and 145: 30 ,- o Z 20 T=" o o ~ . 10 ...J o
Page 146 and 147: 30 M. 20 o Z -,... o )( - . 10 ..J
Page 150 and 151: 65. situation must extent over the
Page 152 and 153: 67. The third grouping as disclosed
Page 154 and 155: 69. lY1aor:icolpus being filled by
Page 156 and 157: Atrina zelandica. There is some r~s
Page 158 and 159: 73. 5.4 The continuum related to th
Page 160 and 161: 75. 5.5 Human activities influencin
Page 162 and 163: 77. sed iments I.rJcre explained an
Page 164 and 165: 7f) REFcnENCES Braun Blanquet'J J o
Page 166 and 167: 81 of San Pedro Basin, Southern Cal
Page 168 and 169: 83 Piper, C .. S., 1947: Soil pIa n
Page 170 and 171: Wiesser, W., 1960: Benthic studies
Page 172 and 173: APPENDIX (1) Sediment analysis (1)
Page 174 and 175: iii APPENDIX (2) Organic Analysis T
Page 176 and 177: v l~rroL"s Present In many sediment
Page 178 and 179: ,: i \ SITE DISrt~RSION S l\ F." J
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The benthic ecology and community structure in Lyttelton Harbour ...

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