12 



LITTORAL PLANT AND ANIMAL COMMUNITIES OF COOK 



STRAIT. 



A weathered platform of greywacke rocks fronting the open ocean, 

 and with no large river discharging near-by, affords in the intertidal 

 belt solid foothold in clear water. Such ideal conditions for marine 

 life are found in Cook Strait, easily accessible by tram from the 

 City of Wellington. Good collecting- ground may be found near the 

 Island Bay, Lyall Bay, and Seatoun termini. Being an open coast, 

 there is no heaping up of tides, so that the moderate range of about 

 5 ft. at ordinary springs is the rule. This allows for the development 

 of only two or three distinct belts of plant and animal life in vertical 

 sequence at any point. Situated as Wellington is near the middle 

 of the Dominion, samples of the typical marine algal communities 

 of both the northern and southern portions of New Zealand may be 

 seen, though some especially characteristic cold- and warm-water 

 associations are absent, such as the small moss-weed (Bostrychia} 

 association of Otago and the mangrove and tunicate communities of 

 Auckland. 



Durvillea Association. On the most exposed portions of the rocky 

 coast outside the harbour the large kelp-weed (Durvillea antarctica] 

 forms a miniature marine forest. On the shore the maximum amount 

 of light and supply of water occur in that strip between the level of 

 low tide at neaps and springs. Here, where the waves beat hardest 

 and the waters are consequently most aerated, the kelp loves to grow. 

 Its large discoidal holdfasts are fixed to the rock high up in this belt, 

 and its large palmate leathery fronds hang down, covering the rock- 

 face while the tide is out, and, when covered with water, stand 

 upright by virtue of their natural buoyancy. This buoyancy is 

 brought about not, as in many kinds of brown algae, by special air- 

 vesicles, but by the large polygonal cells which make up the bulk 

 of the tissue of the thallus. The upper margin of the Durvillea 

 association is usually defined by a fringe of Laurencia, a dark-purple 

 species forming tufts 2 in. to 3 in. high. Following on this is a narrow 

 belt of the common brown alga Xiphophora chondrophylla, easily 

 recognized by its branching flat thalli. Below these algae the bulk 

 of the formation lies, and consists principally of a mixture of Lessonia 

 variegata, Carpophyllum maschalocarpum, Marginaria boryana, Sargas- 

 sum Sinclair i, and Cystophora dumosa extending some distance below 

 low-tide mark. Beneath these large species is an undergrowth com- 

 prised of smaller red, green, and brown algae, such as Pterocladia 

 lucida, Caulerpa sedoides, C. Brownii, Lychaete Dart&ini, Zonaria Tur- 

 neriana, Glossophora Harveyi, Stypocaulon paniculatum, and others, 

 while the rock-face itself is covered with the crustaceous corrallines 

 Melobesia and Lithothamnion, and the branching corallines Amphiroa* 

 Corallina, and Jania. The animals associated with the large brown 

 algae include the herbivorous gastropods Cantharidus opalus, C. 

 purpurata, and Turbo smaragdus, feeding on the larger algae ; the 

 large sedentary chitons, such as Endoxochiton nobilis, Plaxiphora 

 biramosa, and Sypharochiton Sinclairi ; the mussels Mytilus canali- 

 culus and M. maorianus ; and the large ear shells Haliotis iris and 

 H. australis. Shore fishes include various blennies and the sucker-fish 

 Diplocrepis puniceus, the former usually taking protection in rock. 



