Tane (1971) 17:67-74 67 WHALE ISLAND INTERTIDAL LIFE by Susan E. Beever*, Deborah DeB. Broadibot*, and Virginia L. Spencer* SUMMARY A preliminary investigation of the intertidal life on Whale Island was made with reference to shore mobility and exposure effects. INTRODUCTION An island such as W hale Island provides a unique opportunity to compare the effects of ocean swell exposure and shore mobility on the intertidal organisms, as a full range of exposure conditions and shore types is accessible within a small area. METHOD A brief survey was made of the island to give an idea of the range and distribution of substrate types (Fig. 1). Because the mainland is so close, the prevailing south-westerly winds have little effect on the swell. Consequently the main exposure is due to the ocean swell on the north side of the island. Observation sites were chosen in an attempt to give a generalised picture of the island by sampling as many types of shores and localities as possible. At A, B, D, G, H, and I, profiles and transects were taken using a five point abundance scale : - very numerous -, - occasional (local concentrations) - rare - absent Less detailed observations were taken at C, E, and the shoreline between F and G. RESULTS Transect A This transect was on a 1 in 4 slope of large rock slabs at the south-eastern end of the island. It faced the mainland, and was therefore sheltered from the effects of the ocean swell. Department of Zoology, University of Auckland.
68 TABLE 1: Abundance of organisms observed in transect A. 1 Melarapha oliveri occasional 2 Nerita melanotragus 3 Cellana radians 4 Lepsiella scobina occasional 5 Elminius modestus 6 Cellana ornata occasional 7 Balanus sp. rare 8 Perna sp. rare METRES 4 FIG. 2 Transect A; numbered as in Table 1. Transect B This transect was on a 1 in 4 slope of large rock slabs at the south-eastern tip of the island. Swell refracted around the point and caused an increase in exposure on a coast facing the mainland. TABLE 2: Abundance of organisms observed - transect B. 1 Melarapha oliveri 2 Chitons occasional 3 Limpets - in crevices rare 4 Chamaesipho brunnea rare 5 Elminius plicatus occasional 6 Chamaesipho columna 7 Siphonaria sp. rare 8 Lunella smaragda rare 9 Lepsiella scobina occasional 10 Pomatoceros coeruleus occasional 11 Corallina sp. 12 Perna sp. rare
69 2 13 METRES * 4 FIG. 3 Transect B; numbered as in Table 2. Transect D This transect was taken on the south coast, with angular boulders up to 2 metres in diameter, and a slope of 1 in 5. The area was sheltered from the ocean swell by the spit of transect G. TABLE 3: Abundance of organisms observed in transect D. 1 Melarapha oliveri 2 Nerita melanotragus 3 Chamaesipho columna 4 Notoacmea pileopsis 5 Elminius medestus 6 Corallina sp. rare occasional occasional very numerous FIG. 4 Transect D; numbered as in Table 3.
70 Transect G This was sited on the tip of a spit (slope of 1 in 7) of smooth, rounded boulders ranging from 0.2 to 1.0 metres in diameter. Exposure was predominantly from the north-western ocean swell. TABLE 4: Abundance of organisms observed in transect G. 1 Melarapha oliveri 2 Nerita melanotragus 3 Chamaesipho columna 4 Corallina sp. occasional 5 Melagraphia aethiops rare 6 Cellana radians occasional 7 Lepsiella scobina occasional 8 Lunella smaragda rare 9 Apophloea sinclairii rare FIG. 5 Transect G; numbered as in Table 4. Transect H This transect was sited on the south coast, facing the mainland, and hence protected from direct ocean swell. The slope of the shore was 1 in 3; the size of the boulders was up to 0.3 metres in diameter. TABLE 5 : Abundance of organisms observed in transect H. 1 Petrolisthes elongatus very numerous 2 Melarapha oliveri rare 3 Nerita melanotragus 4 Elminius modestus
71 PJBBH HHH HHH METRES 2 4 6 5 I 10 12 FIG. 6 Transect H; numbered as in Table 5. Transect I This transect was taken at the south-eastern end of the island where round boulders extend on to a sandy beach. The boulders were small and covered the sand to a depth of 10 cm. TABLE 6: Abundance of organisms observed in transect I. 1 Nerita melanotragus 2 Melarapha oliveri 3 Elminius modestus (on large boulders) 4 Plagusia capensis 5 Petrolisthes elongatus rare extremely numerous FIG. 7 Transect I; numbered as in Table 6. Transect C These observations were taken on a vertical rock face on the north side of the island receiving the full effects of the ocean swell. There were only three obvious species present, all in crevices : Notoacmea pileopsis (occasional) Nerita melanotragus (occasional) Cellana ornata (occasional)
72 FIG. 1 Map of Whale Island showing transect locations and distribution of intertidal substrate types.
73 Transect E This transect was taken on a smooth boulder beach on the north side of the island receiving the full ocean swell. On this beach the only animals observed were small amphipods, a few crabs and small flatworms which were able to tit into small cracks on the rocks. All these animals were well below the surface layers of rocks, amongst decaying algae. No sessile animals were found until well below low water mark, but even here the life was not abundant (C. J. Milligan, pers. comm.). Shoreline F to G This shoreline was a smooth boulder beach on the west coast of Whale Island. Any northwest winds would affect this area with direct ocean swell. Crabs, trochid gastropods and chitons were the most obvious animals apart from barnacles. Moving northwards away from the less exposed southerly point at G, the dominant barnacle Chaemaesipho brunnea increases as the number of Chamaesipho columna decreases. Also the C. brunnea zone becomes larger as the upper limit is raised in the presence of higher spray and its lower limit moves into the region of C. columna. In a similar way Elminius plicatus is more evident on the exposed stretch of shore than on the more southerly point. The number of mobile grastropods increases moving northwards from this point, both in numbers of species and population sizes. Lunella smaragda, Nerita melanotragus, Lepsiella scobina and Haustrum haustorium increase whil the numbers of Neothais scalaris decrease. Melarapha oliveri is concentrated in the crevices under rocks. Cellana ornata increases in relative proportion to Cellana radians towards the north. A few Notoacmea pileopsis were seen in the barnacle zone and a few Siphonaria zelandica in the Cellana ornata zone. DISCUSSIONS & CONCLUSIONS (1) Effects of Shore Mobility Melarapha oliveri becomes more abundant with increasing substrate stability; the crab Plagusia capensis also shows a preference for more stable boulder habitats. Chamaesipho brunnea is absent from transect E, the most mobile - and exposed - boulder beach studied. (2) Effects of Exposure Melarapha oliveri inhabits the splash zone of the shore and its abundance increases with exposure. Nerita melanotragus is in areas of low to moderate exposure but absent in very exposed localities. Neothais scalaris increases with exposure while Lepsiella scobina, Haustrum haustorium, and Lunella smaragda decrease with increasing exposure. Barnacle dominance changes with exposure; Chamaesipho brunnea - most exposed, Chaniaesipho columna - intermediate, and Elminius modestus in least exposed areas. The limpet Cellana ornata increases with exposure, while Cellana radians
74 decreases with increasing exposure. ACKNOWLEDGEMENTS The authors wish to thank Messrs G.R.V. Anderson, D.A. Francis and B. W. Hayward for assistance in the writing of this manuscript. REFERENCES CHAPMAN, V.J., 1968 "Rocky Shore Ecology of the Leigh Area, MORTON, J.E. North Auckland". Pelorus Press, Auckland. 44 pp. MORTON, J.E., 1965 "The New Zealand Sea Shore". Collins, MILLER, M.C. London. 638 pp. POWELL, A.W.U. 1961 "Shells of New Zealand". Whitcombe & Tombs Ltd., Auckland. 203 pp.