P o l a r Biol (1985) 4 : 8 9 - 9 4

© Springer-Verlag 1985

Biotic Zonation on Rocky Shores of Heard Island

J. M. B. Smith 1 and R. D. Simpson z

1 Department of Geography, 2Department of Zoology; University of New England, Armidale, NSW 2351, Australia

Received 21 May 1984; accepted 16 November 1984

S u m m a r y . The zonation of rocky shore biota on Heard Island is described for the first time, related to a univer- sal zonation scheme and compared with that recorded for other sub-Antarctic localities. The Kelp Zone of holdfasts of the giant kelp, Durvillea antarctica (Chamis- so) Hariot (one of the characteristic features of these re- gions) is confirmed as a sublittoral fringe. The occur- rence of a Bare Zone within the littoral zone on sub-Ant- arctic shores is discussed. The possible roles of submer- sion, spray, freezing and predation by gulls in influenc- ing the extent and composition of zones are discussed.

Introduct ion

Heard Island is a volcanic island measuring about 45 by 22 km and rising to 2745 m, located in the southern Indi- an Ocean at 73030 'E, 53°05'S. It is situated at approxi- mately the same latitude as many typically sub-Antarctic islands, yet lies south of the Antarctic convergence, and can be therefore regarded as intermediate between Ant- arctic and sub-Antarctic environments. This is reflected, for example, in the land vascular flora, which includes at most two species in Antarctic regions, between 18 and 163 on sub-Antarctic islands, and 7 or 8 on Heard Island. In a review of the biogeography of southern oceans with respect to littoral biota, Knox (1960) placed Heard Island in an Antarctic province, presumably because of the is- land's position south of the Antarctic convergence as Knox did not refer to any biota f rom Heard. In a study of marine molluscs, Dell (1964) noted that the relation- ships of the Heard Island species were overwhelmingly with those from Kerguelen Island.

The shore environment at Heard Island has cold Ant- arctic waters year-round and a colder climate than most sub-Antarctic islands, but without the extensive coastal sea ice typical of Antarctic shores. Air temperatures at Heard Island have a relatively small range, extremes re- corded over three years being only - 10.6 °C and 14.0 °C

(Law and Burstall, 1953; Table 1). Sea temperatures vary even less. During one year, average values in Atlas Cove ranged from about 0 °C in July-August to 3.0 °C in Feb- ruary-March, recorded extremes being - 1 . 8 ° C and 3.4°C (Chittleborough, 1956a). Mushy ice, sometimes forming pancakes, has been observed on several occa- sions to form and persist for several hours in sheltered parts of Atlas Cove during cold periods in winter. Ice- bergs have also occasionally been noted offshore. Ice boulders are abundant on beaches east of ice cliffs on Heard Island, but do not usually occur along the shores studied in the present project.

Both Antarctic and sub-Antarctic rocky seashores have been studied in several locations from the viewpoint of their biotic zonation: Antarctic - Knox (1960, 1968; Wohlschlag (1963); Dearborn (1967); Price and Redfearn (1968); Hedgpeth (1969, 1971); Dayton et al. (1970); Gruzov and Puskin (1970); sub-Antarctic - Knox (1960, 1968); Kenny and Haysom (1962); Delepine (1963); Ful- ler (1967); Bennet (1971); Grua (1971); Arnaud (1974); Simpson (1976a); de Villiers (1976); Bellido (1982). How- ever, those of Heard Island have not been reported upon previously, except in a mention of algal zones by Law and Burstall (1953).

Table 1. A i r t e m p e r a t u r e s , A t l a s C o v e , 1 9 4 8 - 50 (a f t e r L a w a n d Bur - stal l 1953)

M e a n t e m p e r a t u r e s E x t r e m e t e m p e r a t u r e s

M a x i m u m M i n i m u m M a x i m u m M i n i m u m

S u m m e r 4 .4 1 .0 10.7 - 1.8 (Dec - Feb)

A u t u m n 3.5 - 1.8 14.0 - 5.5 ( M a r - M a y )

W i n t e r 0 .6 - 3 .6 6.1 - 10.6 ( J u n - A u g )

S p r i n g 0 .9 - 2 .7 5.8 - 8 .9 (Sep - Nov)

90

Fig. 1. Locations of transects on Heard Island

Sites and Methods

One of the authors (J. M. B. Smith) visited Heard Island in February 1983 as a member of the private "Heard Island DX Associat ion" expe- dition. On Feb. 6 t h - 8 t h five transects were described on rocky sea- shores on the Rogers Head peninsula, north of the former A N A R E Station on the northwest coast of Heard Island. Locations of transects are shown in Fig. 1. Transects 1, 2 and 5 were on bedrock on a west- facing shore, and transects 3 and 4 were on large boulders on a north- east-facing beach. The rock substrate in all cases was volcanic. Some higher parts of transect 5 were trampled and fouled by Rockhopper Penguins (Eudyptes chrysoeome (Forster)).

At each site a rope was anchored at the lowest accessible point, al- ternately exposed and washed by waves approximately 0.5 m high un- der the conditions then prevailing. The rope extended to a point beyond the highest limit of marine algae (or at transects 3 and 4 to the top of the boulder). Transect profiles are included in Fig. 2.

Using the rope as a centre-line, successive contiguous 1 m square quadrats were described. Slope and major topographic features were noted, and the estimated percentage cover of each plant species and the abundance of macroscopic animal species were recorded. Animals above the zone of kelp holdfasts were impossible to count under field conditions because of their small size and concealment beneath the al- gal ma t or in small rock crevices; relative estimates of abundance were therefore made. In the kelp holdfast zone, animals were counted and for these, more than 10 individuals per quadra t are described as "com- m o n / a b u n d a n t " , 2 - 9 as "occas ional / f requent" and a single individu- al as "rare" (Fig. 2).

Voucher specimens of all animal and most plant species were col- lected and preserved in 7% formalin for subsequent determination.

Results

Similar zonation patterns were recorded in all transects. Details of distributions are given in Fig. 2, and the zona- tion of the common plant species is summarized in Fig. 3.

The macroscopic fauna comprised 14 species, of which four were arthropods with terrestrial affinities. As well as the kelp Durvillea antarctica (Chamisso) Hariot and the encrusting coralline algae, nine macroscopic algae were found commonly. In addition Porphyra sp. cf. umbilicalis (L.) KUtzing was found once, on transect 5, and Bangiafuscopurpurea (Dillwyn) Lyngbye, Clado- phora sp., Endophyton sp., and Plumariopsis eatoni (Dickie) De Toni were later recorded as epiphytes or en- dophytes. An unidentified black encrusting lichen was common, though inconspicuous on the dark substrate, towards the top of the shore. The sublittoral kelp Macro- cystis is absent from Heard Island.

The lowest part of the shore sampled was dominated by Durvillea, between the holdfasts of which encrusting pink coralline algae form an almost complete cover. Some other small red algae also occurred, including Bal- lia callitricha (C. Agardh) Kt~tzing, Iridaea cordata (Turner) Bory and Palmaria georgica (Reinsch) Ricker (unpublished). The limpet Nacella kerguelenensis (Smith) was abundant, and the chiton Hemiarthrum setulosum Dall was common, both found mainly on rock surfaces but also on kelp holdfasts. A few specimens of the limpet Nacella (Patinigera) macquariensis Finlay were also collected from this area, all being found on rock surfaces. The amphipod, Hyale sp. (cf. H. hirtipalma) and the isopod, Cassidinopsis sp. (cf. C. emarginata) were associated more closely with the kelp. None of these animals occurred higher on the shore. Lower down, rock surfaces lacked kelp holdfasts and were mostly covered by encrusting coralline algae.

A clear demarcation occurred between the zone of kelp holdfasts and the higher community from which the kelp and its associated fauna were completely absent, and in which coralline algae only occurred locally in wide crevices. Above the demarcation, rock surfaces were mostly covered by filmy and filamentous algae, predomi- nantly red algae (especially Palmaria georgica, Porphyra columbina Montagne and Iridaea cordata) lower down, and green algae (especially Enteromorpha sp. cf. E. bul- bosa (Suhr) Montagne) higher up (Fig. 3). The littorinid, Laevilitorina (Corneolitorina) heardensis Dell, was found in crevices and rarely also in the kelp holdfast zone. The small bivalve mollusc, Kidderia bicolor (Mar- tens), occurred in similar well sheltered situations, some-

Fig. 2. Profiles (a) and distributions of organisms (b) for transects 1 - 5. Plants: a black lichen, b Bostrychia vaga, e Porphyra columbina, d Entero- morpha sp. cf. E. bulbosa, e Chaetangium fastigiaturn (Bory) J. Agardh, f Iridaea cordata, g Ballia callitricha, h Palmaria georgica, i Durvillea antarctica, j encrusting coralline algae, k Xanthosiphonia austrogeorgica Skottsberg, 1 Microrhinus carnosus (Reinsch) Skottsberg. Animals: 1 mites, 2 Mesembriorhinus brevis (adult), 3 M. brevis (larva), 4 oligochaete, 5 small undetermined insect, 6 Nacella kerguelenensis, 7 Kidderia bicolor, 8 Laevilitorina (Corneolitorina) heardensis, 9 Gaimardia trapesina trapesina, 10 Hyale sp. cf. H. hirtipalma, 11 sea anemone, 12 Hemiarthrum setulosum, 13 Cassidinopsis sp. cf. C. emarginata, 14 Nacella (Patinigera) macquariensis. Lines indicate the limits of the eulittoral zone. Quadrats are 1 m in length; vertical and horizontal scales are the same in 1 - 5a

91

a b C d e

.~_ g h ~) .

{3. I j 1 2 3 4 5 6

Quadrats

4 1 D i

I ®

a

b C d h k e

~ f

7 4

CO

a

d C b h f

Q

a) I

4 14 6 13 12 10

a

b C d h

~ J (1) I

0') 4 7 3 5 8 I

12 6 11

I I

8 I 9 10. ~ 1 1 ~ •

6 I 1

Quadrats

Quadrats

11J 1 2 ~

5 6

5 6

1 4

Quadrats

I

I

L ~

I

4 5 6

L~.L 2

® I

1 ' 2 ~ 3 I 4 5 ' 6 ' 7 ' 8 J 9 10~ 11' 12 ' 1 3 ' 1 4 ' 1 5 ' 1 6 ~ 17 ' 18, 1 9 , 2 0 ,

Quadrats

Abundance Scale (1 b-5b) ALGAL COVER ANIMAL ABUNDANCE

<10% Rare 1 10-15% Occasional/Frequent 1 , 1 5 % Common/Abundant

92

100- r r LIJ > O O I-" 50- Z UJ L) rc LLI (3-

O

°o°o ° ' o ' o o°O o ~o oO~°oOo ;oo~oo~ ooo ooo

/ / / / / BLACK LICHEN SP. BOSTRYCHIA VAGA ENTEROMORPHA SP. CF. E. BULBOSA PORPHYRA COLUMBINA IRIDAEA CORDATA PALMARIA GEORGICA DURVILLEA ANTARCTICA HOLDFASTS ENCRUSTING CORALLINE ALGAE

Fig. 3. Proport ional cover by plant species of rocky shores at Heard Island, based on data f rom all transects. Top of the shore is to the right, the vertical lines indicating the limits of the eulittoral zone

times extending to higher levels than L. (C.) heardens&. Where the algal mat formed a porous spongy layer up to 1 cm thick containing silt, it was abundantly inhabited by oligochaetes. An occasional specimen of the red bivalve Gaimardia trapesina trapesina (Lamarck) was found im- mediately above the zone of kelp holdfasts. This is the first record from Heard Island for this species which is widely distributed in the sub-Antarctic (Dell 1964).

Further up the shore the algae became less diverse, and covered progressively less of the rock surface. Protu- berances became colonised by the black lichen, and ar- thropods of terrestrial affinity were found. Most abun- dant were two mites, Halozetes sp. and a less common, pale, undetermined species, and a beetle, Mesembriorhi- nus brevis (Waterhouse). Both inhabited vesicular holes in the rock surfaces and other similar small, dry crevices, although some mites were active and apparently feeding on dead filmy algae. The alga surviving at the highest lev- els was the red species Bostrychia vaga Hooker f. and Harvey.

Discussion

The zonation of biota down the rocky shores of Heard Island was identified as, in descending order: Lichen Zone, Mixed Algal Zone, Kelp Zone, Encrusting Coral- line Algal Zone. This local zonation pattern can be aligned with the universal zonation scheme of Lewis (1964) - Table 2. The Lichen Zone has universal recog- nition as corresponding to the littoral fringe where or- ganisms are alternately exposed to air and wetting (prin- cipally by splash and /o r spray), but the exposure is pre- dominantly to aerial conditions. Typically for the sub- Antarctic region, there were no littorinid molluscs form- ing a zone high on the shore to delineate the littoral

Table 2. Rocky shore zonation of Heard Island applied to a universal scheme

Universal scheme zone Heard Island zones

Littoral fringe Eulittoral zone

Sublittoral fringe Sublittoral zone

Lichen zone Mixed Algal Zone - comprising mainly Enteromorpha, Por-

phyra and Palmaria, with cover as shown in Fig. 1. Kelp Zone Encrusting Coralline Algal Zone

fringe either totally or in part. Encrusting coralline algae identify the upper limit of organisms that are truly mar- ine - the sublittoral zone. The Kelp Zone (the zone of holdfasts of Durvillea antarctica) can be regarded as a sublittoral fringe (see later). This leaves a region of mixed algal species (Mixed Algal Zone) for the eulittoral zone where the shore is alternately emersed and sub- mersed, but the conditions are predominantly wet and the region is occupied by the majority of littoral organ- isms.

In the absence of barnacles which are normally used to define the littoral zone - littoral fringe boundary (Lewis 1964), the littoral fringe or Lichen Zone was char- acterized by the presence of terrestrial arthropods as well as of lichen. Local occurrences of lichen were recorded lower down in transect 5. The mites (Halozetes sp. and another species) and beetles (Mesembriorhinus brevis) had essentially the same vertical range. A small, undeter- mined insect and larvae of Mesembriorhinus brevis were found sporadically with algae near the lowest mite occur- rences. The lower level of these arthropods also approxi- mated to the upper level of Porphyra eolumbina. The up- per limit of the Porphyra Zone was used by Simpson (1976a) to define the top of the eulittoral zone on Mac- quarie Island.

Across the eulittoral zone there was a mixture of filmy and filamentous algae. No plant or animal species recorded in the eulittoral zone had a distribution in clear horizontal belts. The animals were encountered mainly in crevices. Quadrats of rock surface in the transects fre- quently included lichen as well as mixed algae of the eu- littoral zone. However, the two zones did not intergrade. Lichens with their associated arthropods occurred on higher rocks, while macroscopic algae were mainly re- stricted to depressions and overhangs. Apart from mites being found sometimes on desiccated algae the two com- munities were discrete, lichens and filmy algae being sep- arated by several centimetres of bare rock. However this was on too small a scale to be easily compared with the high "Bare Zone" recorded on Marion Island by Fuller (1967).

The existence of a Bare Zone on sub-Antarctic rocky shores presents some curious questions. Kenny and Hay- sore (1962) suggested that on Macquarie Island, such a zone resulted from abrasion by kelp fronds. However,

Simpson (1976a) showed that, when the rocky substrate was not favourable to occupation by siphonariid limpets (Kerouelenella lateralis (Smith)) the position of the Bare Zone was overgrown by algae. This indicated that the Bare Zone resulted from grazing pressure by the siphona- riid limpets - the dominant organism of the zone. The lack of siphonariid limpets and the lack of a distinctive Bare Zone on Heard Island support this view. On Mari- on and Prince Edward Islands, Fuller (1967) reported a Bare Zone immediately below the Lichen Zone - that is, higher than that on Macquarie Island. However, in a more comprehensive study of the littoral zone of these is- lands (particularly Marion Island), de Villiers (1976) did not recognise a Bare Zone and made a general statement that the limited information available to Fuller led to misinterpretation of the zonation pattern on Marion's shores. K. lateralis is abundant in the littoral zone on Marion Island, as it is on the Kerguelen Islands where a Bare Zone has also not been recorded (Delepine 1963; Arnaud 1974; Bellido 1982). Thus, the Bare Zone ap- pears to be a feature peculiar to Macquarie Island.

During transect observations waves were generally small. The shore above the uppermost parts of the Kelp Zone was continually emersed and received little or no spray. In spite of persistently cool, moist weather with little sunshine (though less cold than usual February con- ditions), mortality by desiccation was apparent in some filmy algae, and even the stunted plants of Durvillea near the top of their range were becoming shrunken and flac- cid. A week after the transects were described the weather changed, and during a gale, spray was seen to be continually flung over and beyond the western shore of Rogers Head peninsula. As would be expected for this latitude, high winds are typical of Heard Island weather (Law and Burstall 1953), so wetting by spray must be fre- quent, and no doubt is responsible for the wide extent of the eulittoral zone and the littoral fringe far above tidal reach.

On Macquarie Island, the line of Durvillea holdfasts closely followed the pattern of wave wash over rock sur- faces (Simpson 1976a). Also, Arnaud (1974) remarked how the height of attachment of Durvillea antarctica on different parts of the shore on the Kerguelen Islands was determined by the degree of wave action. Since this belt therefore appears to be dependent on being frequently awash rather than continually submersed, it could be considered to be the lowest part of the eulittoral zone as defined by Lewis (1964). However, there is biological justification for designating the Kelp Zone as a sublitto- ral fringe. The Kelp Zone is clearly and sharply demar- cated, in both biotic composition and vegetative struc- ture, f rom the adjacent part of the eulittoral zone. Al- though the Durvillea holdfasts themselves are not contin- uously submersed, the proximal stipes and fronds provide a canopy for biota that are normally found in the sublittoral zone. Simpson (1976a, b) showed that, on re- moval of areas of Durvillea at Macquarie Island, the typ- ically sublittoral fauna and flora beneath were either

93

killed or disappeared. In particular, the numbers of the small chiton Hemiarthrum setulosum (also present at Heard Island in the same region of the shore) were dras- tically reduced on removal of Durvillea. Conversely, the density of a limpet (Nacella (P.) macquariensis), which had a range extending above the Kelp Zone, increased in the denuded areas. Thus, the underlying biota of the Kelp Zone is dependent on the presence of the kelp itself - a biological justification for the special description of

"sublit toral fringe". Previously, Arnaud (1974) designat- ed the Kelp Zone on the Kerguelen Islands as an upper fringe of the sublittoral (infralittoral) zone because the Kelp Zone was constantly wetted and its associated fauna was essentially sublittoral.

The sharp change at the top of the Kelp Zone is prob- ably due to factors associated with emersion during peri- ods of lesser wave action. In addition to desiccation these factors may include predation of molluscs by the Kelp or Dominican Gull (Larus dominicanus Lichtenstein) and winter freezing. A number of gull middens consisting of shells of the limpet Nacella kerguelenensis were observed on the shores. Nacella limpets form a prominent part of the diet of these gulls which have been reported as prey- ing heavily on N. kerouelenensis on the Kerguelen Is- lands (Arnaud 1974), Nacella (P.) macquariensis on Macquarie Island (Simpson 1976b) and Nacella (P.) de- lesserti (Philippi) on Marion Island (Blankley 1981). Most of the limpets on Heard Island occupy submersed habitats yet gulls have been observed capturing limpets from shallow depths at both Marion (Blankley 1981) and Macquarie Islands. It is possible that gull predation on Heard Island prevents colonisation of the eulittoral zone in summer by N. kerguelenensis.

Air temperature remains mostly below freezing point for much of the year (Table 1). Seashore rocks have been reported to become glazed by ice from freezing sea spray in winter (Scholes 1951). Freezing may kill most organ- isms on exposed surfaces above the level of frequent wetting at this season. This may explain the restriction of Laevilitorina (Corneolitorina) heardensis and Kidderia bicolor to crevices, and may also bring about an annual cycle of algal growth, the rich cover of which in February might only be the ephemeral result of brief summer col- onization and growth. Even below water, Chittle- borough (1956b) found that fouling of ground glass plates submerged in Atlas Cove by algae, including dia- toms, was about ten times as fast in early summer as in winter. It would be of great interest to examine seashore biota and zonation at different seasons, to confirm whether such an extreme annual cycle occurs as postulat- ed here.

Acknowledgements. Some financial assistance for this work was sup- plied by internal research grant from the University of New England. Ms Dominique Ward assisted during the fieldwork. We would like to thank the following for identifications of specimens: Dr R. W. Ricker (algae), Dr J. Lowry (crustaceans), Dr W. Ponder (molluscs), Dr C. N. Smithers (insects) and M. Gray (mites).

94

References

Arnaud PM (1974) Contribution a la bionome marine benthique des r6- gions antarctiques et subantarctiques. Tethys 6:456-656

Bellido A (1982) Les biocenoses du littoral rocheux aux IlesKerguelen. Colloque sur les ecosyst6mes subantarctiques. CNFRA No 51, pp 81 - 92

Bennett I (1971) Shores of Macquarie Island. Rigby, Adelaide, 69 pp Blankley WO (1981) Marine food of kelp gulls, lesser sheathbills and

imperial cormorants at Marion Island (Subantarctic). Cormorant 9:77 - 84

Chittleborough RG (1956a) Hydrology at Heard Island, 1949. In: Ealey EHM, Chittleborough RG (eds) Plankton, hydrology and marine fouling at Heard Island. ANARE Interim Report 15 Publication 30, pp 46 - 66

Chittleborough RG (1956b) The settlement of marine organisms on submerged surfaces at Heard Island, 1949. In: Ealey EHM, Chittle- borough RG (eds) Plankton, hydrology and marine fouling at Heard Island. ANARE Interim Report 15 Publication 30, pp 67 - 81

Dayton PK, Robilliard GA, Paine RT (1970) Benthic faunal zonation as a result of anchor ice at McMurdo Sound, Antarctica. In: Hold- gate MV (ed) Antarctic ecology, vol 1. Academic Press, London, pp 244 - 258

Dearborn JH (1967) The fauna of the Ross Sea. 5. Stanford University invertebrate studies in the Ross Sea 1958- 61: General account and station list. NZ Dep Sci Ind Res, Bull 176:31- 47

Delepine R (1963) Un aspect des ~tudes de biologie marine dans les ~les Australes frangaises. 1. La zonation marine. CNFRA 3:3 - 12

Dell RK (1964) Marine Mollusca from Macquarie and Heard Islands. Rec Dom Mus Wellington 4:267 - 301

Fuller NR (1967) A preliminary report on the littoral ecology of the Marion and Prince Edward Islands. S Afr J Sci 63:248- 253

Grua P (1971) Introduction 6cologique. In: Invert6br6s de l'infralit- toral rocheux dans l'Archipel de Kerguelen. CNFRA 30:1- 66

Gruzov EN, Puskin AF (1970) Bottom communities of the upper sub- littoral of Enderby Land and the South Shetland Islands. In: Hold- gate MV (ed) Antarctic ecology, vol 1. Academic Press, London, pp 235 - 238

Hedgpeth JW (1969) Preliminary observations of life between tide- marks at Palmer Station, 64°,45'S. 64°45'W. Antarct J US 4:106 - 107

Hedgpeth JW (1971) Perspectives of benthic ecology in Antarctica. In: Research in the Antarctic. Am Assoc Adv Sci, pp 93 - 136

Kenny R, Haysom N (1962) Ecology of rocky shore organisms of Mac- quarie Island. Pacif Sci 16:245 - 263

Knox GA (1960) Littoral ecology and biogeography of the Southern Oceans. Proc R Soc London, Ser B 152:577-624

Knox GA (1968) Tides and intertidal zones. In: Symposium on Antarc- tic oceanography. Scott Polar Research Institute, Cambridge, pp 131 - 146

Law PG, Burstall T (1953) Heard Island. ANARE Interim Report 7 Publication 12, 32 pp

Lewis JR (1964) The ecology of rocky shores, English Universities Press, London, 323 pp

Price JH, Redfearn P (1968) The marine ecology of Signy Island, South Orkney Islands. In: Symposium on Antarctic Oceanography. Scott Polar Research Institute, Cambridge, pp 163 - 164

Scholes WA (1951) Fourteen men. Allen and Unwin, London, 273 pp Simpson RD (1976a) The shore environment of Macquarie Island. Rep.

ANARE Set B(I) Publ No 125, 41 pp Simpson RD (1976b) Physical and biotic factors limiting the distribu-

tion and abundance of littoral molluscs on Macquarie Island (sub- Antarctic). J Exp Mar Biol Ecol 21:11- 49

de Villiers AF (1976) Littoral ecology of Marion and Prince Edward Is- lands (Southern Ocean). S Afr J Antarct Res, Suppl 1:1 - 4 0

Wohlschlag DE (1963) Research program on the ecological and physio- logical characteristics of McMurdo Sound animals. US Antarct Proj Off Bull 5:12-16