-17- AN INTRODUCTORY STUDY OF THE MARINE ALGAL ECOLOGY OF AN OPEN COAST AREA AT LEIGH. by W. B. Silvester

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1 -17- AN INTRODUCTORY STUDY OF THE MARINE ALGAL ECOLOGY OF AN OPEN COAST AREA AT LEIGH by W. B. Silvester The supra-littoral, littoral and sub-littoral zonation of the open coast in the Leigh area are discussed. The communities are recognised and related to tide heights and exposure. LOCALITY Leigh is situated immediately south of Cape Rodney on the east coast of New Zealand, forty miles north of Auckland. A list of the algae to be found in Leigh Cove is given by Dellow (1955). The open coast ecology of the area immediately south of the Leigh inlet is discussed in this survey. GEOLOGY The rocks exposed in the area provide a striking contrast to the usual type of shore line in the Hauraki Gulf, which is sandstones and mudstones of the Waitemata series. The strata exposed on the Leigh coast however, belong to the Waipapa Group of Mesozoic age, consisting of indurated greywackes, sandstones, arid argillites. They differ from the West Coast sandstones of a comparable age in being considerably contorted and folded. The greywackes of this group outcrop on about six miles of coastline from Cape Rodney to the Tawharanui peninsula and are overlain with a cover of tertiary beds of the Waitemata Group. (Although most of the offshore islands of the Gulf consist largely of these greywackes, they do not outcrop on the mainland in any large quantity between Orere Point and Whangarei, Hopgood (1959) ). The hard and well weathered nature of the substratum exposed on the Leigh coast has a marked effect on both the zonation and the flora.

2 HAURAKI GULP PIG. I LOCALITY MAP

3 S I I 5 1MESEMBRYANTHEMUMAUSTRALE 1 SAMOLUS gggfgj ZZZ [LICHINA PYGMAEA MELARAPHE OLIVERI" "2 BOSTRYCHIA ARBUSCULA CHAMAESIPHO BRUNNEA CHAMAESIPHO COLUMNA 1 APOPHLOEA SINCLAIRII SAXOSTREA GLOMERATA POMATOCEROS COERULEUS J HORMOSIRA BANKSII "1 CORALLINA OFFICINALIS XIPHOPHORA CHONDROPHYLLA ~") CYSTOPHORA TORULOSA ] CARPOPHYLLUM MASCHALOCARPUM ECKLONIA RADIATA C/* ~o m Q m c/> > O o < m n > 2 I CO C O z O -n SAXOSTREA < GLOMERATA POMATOCEROS COERULEUS

4 -20- OBSERVATIONS The Leigh coast because of its position and due to the nature of the substratum, provides a marked contrast with conditions to be found in more sheltered parts of the Gulf. For these reasons, wherever possible, - comparisons are made between the two. Three features of general contrast are at once apparent. 1. Although the exposure is not nearly as great as that to be found on the West coast, Leigh, lacking the shelter of the Hauraki Gulf is exposed to the full force of most of East or N. E. winds. These at times send spray 20 and 30 ft. up the cliff faces. 2. As a result of the broken coastline, the large boulders and the deeply weathered substratum, conditions of light, wave action and wind vary greatly over relatively short distances. These factors produce a complex and diverse zonation. 3. The rock substratum differing as it does from the softer, more porous sandstones and mudstones of the Waitemata series supports an algal flora more comparable with that found on basalt. This is displayed at Leigh by the great profusion of Apophloea sinclairii which is found very rarely on Waitemata rocks but grows well on the basalt of Rangitoto. TIDE LEVELS The tidal range at Leigh was calculated as being 79% that of Auckland. Thus the vertical range of extreme spring tides at Leigh was estimated as 9. 6'. The EHWS and ELWS marks roughly corresponding to the 10' and 0. 4' levels respectively as measured from the Auckland Harbour Board datum of 0. 00'. The area was visited in summer, autumn and winter and changes were noted over these periods. Sampling was confined to the exposed area immediately below Leigh township. At this point a narrow headland or stack protrudes some fifty feet into the sea in a S. E. N. W. direction. Most of the sampling was done in and around this stack as it provided all degrees of exposure and shelter. Three transects were studied in varying degrees of exposure and compared with similar adjacent areas along the beach. The species present were classified as follows: - - dominant (a) - abundant - frequent

5 -21- (0) - occasional (r) - rare (1) - local The broad vertical distribution of species at Leigh falls into the same four groups as described by Stephenson (1939) for the Coast of South Africa and employed by Dellow (1950) and Carnahan (1952) in describing zonation within the Hauraki Gulf. These four zones are termed: (1) Littorina zone (2) Barnacle zone (3) Mixed Algal zone (4) Sublittoral fringe. The supra-littoral area at Leigh is also discussed. SUPRA-LITTORAL ZONE In sheltered and shady places plants of this zone extend down to within two feet of EHWS. Two separate associations are recognisable: ME TROSIDEROS - STIPA COMMUNITY Range: In the upper splash zone Metrosideros excelsa Stipa teretifolia Scirpus nodosus Astelia solanderi Apium pro stratum Peperomia urvilleana Asplenium flaccidum Asplenium lucidum (a) (a) HALOPHYTE COMMUNITY Range: From within two feet of EHWS upwards. Salicornia australis Mesembryanthemum australe Samolus repens Coprosma repens

6 -22- This very compact community forms dense mats on almost bare rock, excluding any subordinate species. Individual plants of Salicornia and Samolus grow in fissures near EHWS mark while the trailing stems of the other two members of the community extend well down the cliff faces. In its lower limits this association is admixed with a grey and yellow lichen community which extends into the supra-littoral fringe. LITTORINA ZONE This zone is characteristic of the upper littoral and lower supra-littoral. positions of maximum exposure or in shaded areas the zone is extended upwards. In MELARAPHE - LICHINA COMMUNITY: Range: MHWM to upper heavy spray limit Melaraphe oliveri Lichina pygmaea Nerita melanotragus Bostrychia arbuscula (1) Chamaesipho brunnea (1) Melaraphe may move over a wide area retreating into fissures well up in the supra-littoral. Where the dual action of shade and high spray are acting on the south faces this zone may be extended 10' above EHWS. On the north and East facing sides - where exposure is greatest - the wide storm platform and the drying effect of the sun tend to depress the upper limit of this community. Quantitatively this may be as much as a 3' depression. The vertical elevation of Melaraphe is considerably less than on the west coast but appreciably greater than that within the Gulf. Bostrychia and Chamaesipho are affected to a lesser degree. BOSTRYCHIA ARBUSCULA Range: EHWS and above - MHWS COMMUNITY: Bostrychia arbuscula Caloglossa leprieurii Lomentaria umbellata Cent roc eras clavulatum Polysiphonia sp. Rhizoclonium riparium Chamaesipho brunnea (1, f) Oscillatoria nigroviridis (r)

7 -23- Bostrychia forms a dense mat especially in moist shaded crevices. In more sheltered but sunny areas Caloglossa and Rhizoclonium tend to become abundant. Here again the large barnacle Chamaesipho brunnea may have a swash zone through this community. Lomentaria forms frequent tufts in the felt of Bostrychia. The major development of this community occurs above the barnacle zone but the two communities merge at the interface. ROCK POOL COMMUNITY: Range: Above MHWS Lyngbya maiuscula Lophosiphonia macra Derbesia novae-zealandiae The small rock pools on the platform support large tufts of Lyngbya and lesser amounts of Derbesia on the bare rock. Lophosiphonia characteristically grows on firm sand and its abundance increases with sedimentation. BARNACLE ZONE The communities of this zone occupy a wide portion of the mid-littoral area. The whole of the mid-littoral area is dominated by the two barnacles, the oyster and Apophloea, the latter two giving the shore a distinct white and red banded appearance. CHAMAESIPHO BRUNNEA Range: EHWS - MHWS COMMUNITY: Chamaesipho brunnea Bostrychia arbuscula Chamaesipho columna Nerita melanotragus This rather compact community occurs from just above to just below the wave cut platform on the stack. It is present infrequently on isolated boulders. The barnacle formation at Leigh of C. brunnea n'orming a distinct zone above C. columna is characteristic of exposed coast oceanic conditions, e. g. Great Barrier Island. Below the C. brunnea community and sharply divided from it there is a very wide mid-littoral zone. Although not dominated in all places this zone is at least characterised throughout by the small barnacle C. columna. The other two species which co-dominate in this zone viz. Apophloea sinclairii and Saxostrea glomerata are

8 -2Umuch more sensitive to exposure, and have narrower vertical ranges. For these reasons they are not found in every transect nor do they occur through the full range of Chamaesipho columna. The ranges for the three species are: C. columna MHWS - MLWN Apophloea MHWM - MLWN Saxostrea MHWN - E(H)LWN This community therefore occupies the wide vertical range of seven feet comprising 70% of the littoral zone at this station. The mid-littoral zone because of its position in the centre of the intertidal area, is exposed to wave action for more time than any other zone. Consequently, even though there are only three species occurring in abundance, a great diversity of zonation is found which does not allow them to be placed in circumscribed associations. At Leigh three grades of exposure can be observed both from observation of wind direction and exposure, and their correlation with the organisms. A. Very sheltered, in the lee of the stack among the boulders. B. Relatively sheltered, in the lee of the stack. C. Fully exposed, unsheltered by any rock formation. The barnacle zone is best studied under these three exposure conditions. A. Very sheltered. Apophloea sinclairii appears to demand the most sheltered environment of the three species and is therefore found to dominate at A. As Chamaesipho extends higher than Apophloea it forms a distinct band above it of about 6-9". Apophloea then dominates and forms a very compact consociation almost to the exclusion of the barnacle with which it obviously competes. On the sheltered but still sunny sides of the rocks Apophloea forms its characteristic erect portions. At about E(L)HWN the oyster Saxostrea begins to assume importance and below this at about MSL Apophloea and the oyster often form a compact association, but because of the very variable conditions among the rocks either may drop out. Below the lower limit of the oyster Apophloea and Chamaesipho are dominant according to conditions of light. Just below or partially obliterating this latter zone there may occur a thick mat of Pomatoceras coeruleus the spiny tube worm. These were found at A and C but not at B. B. Relatively sheltered As the exposure is increased Apophloea tends to be replaced at all heights by Chamaesipho. The amount of oyster coverage is diminished slightly but not to the same extent as the red alga. Consequently there appears a distinct Chamaesipho consociation above a Saxostrea - Chamaesipho association.

9 -25- C. Fully exposed At C, on the completely exposed side of the stack a further reduction in the oyster cover was noticed. This was correlated with a greater cover of barnacles which in this situation dominate throughout. Occasional molluscs found throughout the barnacle zone are Turbo (Lunella) smaragda, Nerita melanotragus, Cellana radians and Notoacmea pileopsis, and the white rock shell Neothais scalaris. The oyster borer Lepsiella scobina in places becomes quite frequent. Also found are Sypharochiton pelliserpentis, Onchidella patelloides, and Volsella neozealanicus. Occasional algae include Laurencia distichophylla, Gelidium caulacantheum and Scytothamnus australis. MIXED ALGAL ZONE This lower zone supports a wide variety of algae in the region from E(H)LWN to MLWS. The dominants of the area are also very sensitive to exposure effects and the composition of the zone varies greatly in the three degrees of exposure. Nevertheless four relatively distinct communities can be recognised. CORALLINA - HORMOSIRA Range: E(H)LWN - MLWS COMMUNITY: Corallina officinalis Hormosira banksii Jania hombroniana Ralfsia verrucosa Melobesia sp. Codium adhaerens Laurencia botrichioides Cellana radians Nerita melanotragus The two dominants are sensitive to exposure and occur in greatest abundance at A where Hormosira may grow quite large. At B there are small amounts of a stunted open coast form of Hormosira, while it is absent at C. Corallina with a smaller amount of Jania is able to survive exposure better and is found commonly at C. At A Ralfsia may form a definite zone just above the Hormosira and mixing in places with Apophloea. At B however it forms mats in positions that Hormosira would be expected to grow, while on smoother almost vertical rock both the Hormosira and Ralfsia are absent, leaving completely bare areas between the oyster zone above and Corallina below. The community is con-

10 -26- siderably compressed at C by a Melobesia community above and a fine algal turf below. The small amounts of Hormosira at B may be due to the almost vertical slope of the rock as well as to exposure. At C however, its absence is due purely to the greater exposure. In general Corallina assumes full dominance below Hormosira, but in some cases they may form two distinct zones. ENCRUSTING CORALLINE COMMUNITY: Range: E(H)LWN - ELWS Basal Corallina officinalis Melobesia sp. This community occurs only sparsely in the shelter at C, but it assumes an important position at B where the rock may be vertical and too steep for colonisation of other algae. On the exposed side of the stack it is important in depressing the zone of erect Corallina. In certain situations the community may extend down into the sub-littoral fringe. MIXED ALGAL TURF COMMUNITY: Range: MLWN - MLW Gelidium caulacantheum Caulacanthus spinellus Ulva lactuca Dictyota ocellata Champia novae-zealandiae Corallina officinalis Leathesia difformis Polysiphonia sp. Laurencia distichophylla Centroceras clavulatum (a) seasonal This community assumes importance only on the exposed side of the stack where it forms a distinct band mainly on the flatter rock immediately above the brown algal zone. It merges with Corallina above and Xiphophora below. Many subordinate species occur epiphytically in this turf, e. g. Pterosiphonia pinnata, Herposiphonia cerratoclada and Calithamnion sp. XIPHOPHORA - CYST OPHORA COMMUNITY: Range: MLWM - ELWS Xiphophora chondrophylla Cystophora torulosa

11 -27- These two brown algae form a distinct belt immediately above the sub-littoral fringe. They merge with the algal turf and Corallina zones above and with the Carpophyllums beneath-. Xiphophora is found growing in all transects while a distinct belt but it is hard to know whether the community lies in the sub-littoral fringe or in the mixed algal zone. They resemble the turf in being upright and relatively small compared with the large flaccid Carpophyllums and Ecklonia. On the other hand they are larger than all of the species of the turf and they are brown, giving them strong affinities with the sub-littoral fringe. Because of precedent I have included them in the mixed algal zone. SUB-LITTORAL FRINGE Again considerable variety within the one clearly defined zone can be seen. CARPOPHYLLUM - ECKLONIA COMMUNITY: Range: MLWS - below reach of all tides. Carpophyllum maschalocarpum Carpophyllum plumosum Ecklonia radiata Melanthalia abscissa Zonaria angustata Laurencia botrychioides Pterocladia capillacea Champia novae-zealandiae Liagora harveyana Laurencia distichophylla Lomentaria umbellata Tethya fissurata Rhodymenia leptophylla Glossophora kunthii (a) (a) (1, a) seasonal Epiphytic Metamorphe colensoi (a) Abroteia suborbicularis (a) Hymenena variolosa Strebocladia (a) Melobesia sp. Of the dominants C. maschalocarpum and Ecklonia occur at all points but C. plumosum is found only in shallow sheltered areas. At A and B C. plumosum forms

12 -23- a dense mat with C. maschalocarpum, it may go above it in transect A. The water. Zonaria is found sheltering among the mat of Carpophyllums at all points but Melanthalia is only found at C. Champia may grow epiphytically or terrestrially. The small orange sponge Tethya and the iridescent alga Rhodymenia are frequent in deep water. The five common epiphytes may form a very dense mat on the Carpophyllums, Metamorphe and Abroteia often forming a complete cover on the basal, more sheltered parts. SEASONAL CHANGES Liagora harveyana and Leathesia difformis form a thick turf on sheltered rocks during the summer but quickly disappear in autumn. The latter is commonly found at about MLWM while the former is at about ELWS in the summer months. FRESH WATER SEEPAGE In a region of fresh water seepage two species dominated, Chaetamorpha aerea and Enteromorpha intestinalis. EXPOSURE The three exposure transects studied reveal the following distributions: Species Transect A B C Apophloea sinclairii d o absent Saxostrea glomerata d f - d o Chamaesipho columna f - d d d Hormosira banksii d o absent Cystophora torulosa d d " Carpophyllum plumosum d d " Melanthalia abscissa absent absent f These results may reflect variations in the slope of the rock, sun and shade as

13 -29- well as exposure. LEVELLING SURVEY A levelling survey was carried out for the dominant and physiognomically important species occurring in the area. As has been previously demonstrated for other areas Dellow (1950), Beveridge and Chapman (1950) and Carnahan (1952) four critical levels are seen. I II m IV Between MHWS and MHW Between E(H)LWN and MLWN At approximately MLW, this is perhaps not a valid critical level. Between MLWS and ELWS. These limits show graphically the basis on which the littoral area is divided into its four zones. SUMMARY The communities are described as far as possible for the open coast at Leigh and their tide heights in relation to the A. H. BJD. are given. Comparisons are drawn with stations deeper in the Hauraki Gulf as to exposure and rock type and their subsequent effects on zonation. Three transects were made and from these, three types of exposure are discussed in relation to the zonation of particular communities and species. It is recognised that to gain a fuller picture of the area a deeper and more concentrated study should be made over a wider period of time. The Leigh coast provides an ideal area in which the differential effects of exposure, shade, rock type and slope can be studied. Further work on these lines should prove very rewarding. ACKNOWLEDGEMENTS The writer wishes to acknowledge the help given by Mr D. J. Chapman in identifying many of the algal specimens, to Professor V. J. Chapman under whom the study was made and to Miss J. Wheeler for the use of her unpublished notes on Apophloea sinclairii.

14 -30- APPENDIX I Algal species found in the area and not listed in the text are given below. Ulva parva Enteromorpha bulbosa Cladophora crinalis Cladophoropsis herpestica Bryopsis plumosa Lola tortuosa Chaetamorpha melargonium Notheia anomala Bangia fusco-purpurea Porphyra columbina Gelidium pusillum Antithamnion sp. Callithamnion sp. Laurencia virgata Herposiphonia cerratoclada Pterosiphonia pinnata Euzoniella sp. REFERENCES Batham, E. J Ecology of Southern New Zealand Sheltered Rocky Shore. Trans. Roy. Soc. N. Z. Vol. 84, Pt. 2, Ecology of Southern New Zealand Exposed Rocky Shore at Little Papanui, Otago Peninsula. Ibid. Vol. 85, Pt. 4, pp Beveridge, W. A. & Chapman, V. J The Zonation of Marine Algae at Piha, in relation to the Tidal Factor. Pacific Science, Vol. 4, pp Carnahan, J. A. Chapman, V. J Intertidal Zonation at Rangitoto Island, New Zealand. Pacific Science, Vol. 6, pp The Marine Algal Communities of Stanmore, Bay, New Zealand. Pacific Science, Vol. 4, pp

15 -31- Chapman, V. J. Dellow, V. Dell, R. K. Hopgood, A. M. Lindauer, V. W. Moore, L. B., Stephenson, T. A. Trevarthan, C. B The Marine Alga of N. Z. Pt. 1, Myxophyceae and Chlorophyceae. Journ. of the Linn. Soc. Lond. Botany. Vol. LV. No pp Intertidal Ecology at Narrow Neck Reef, New Zealand. Pacific Science, Vol. 4, pp Marine Algal Ecology of the Hauraki Gulf, New Zealand. Trans. Roy. Soc. N. Z., Vol. 83, Pt. I, pp Native Shells Notes on the Structure of Greywackes and Argillites at Tawharanui Peninsula, Auckland. N. Z. Journ. of Geo, and Geophysics, Vol. 3, No. 2, pp A Descriptive Review of the Phaeophyceae of N. Z. Trans. Roy. Soc. N. Z., Vol. 85, Pt. 1, pp Some intertidal Sessile Barnacles of N. Z. Soc. N. Z., Vol. 73, pp Trans. Rov "Our Living Environment" - Seaweeds. Post Primary Schools Bulletin, Vol. 2, No. 13, Wellington The Constitution of the Intertidal Fauna and Flora of South Africa, Pt. 1, Linn. Soc. Lond. Journ. Zool., Vol. 40, pp The Use of A Zonation Diagram in Intertidal Ecology Science Record, Dunedin, Vol. 3, pp