S. Afr. J. Antarct. Res., Vol. 8., 1978 119
S ummary of the Symposium Proceedings
DISCUSSIO N SESSIONS
A list of all papers presented at the symposium is given her.e.
In cases where presentations have subsequently been published elsewhere, the references are given after the author's name(s).
Edited versions of pertinent questions and answers which followed the presentations arc included where applicabk This summary allows readers an insight into the proceedings of the symposium, as well as an overall view of the biologic:ll and geological research being undertaken at Marion Island.
KEYNOTE ADDRESS
Ecological Studjcs at South Georgia.
R. M. LAWS. Director. British Antarctic Survey, Cambridge, England.
REVIEW PAPERS
Origin and General Ecology of the Marion Island Ecosystem.
E. M. VAN ZINDEREN BAKKER (Sr), Director (retired).
I nstitutc for Environmental Sciences. University of the Orange Free State. Bloemfontein.
Plant Ecology of Mar ion Island: A Re,•iew.
V. R. SMITH. Institute for Environmental Sciences. Uni- versity of the Orange Free State, Bloemfontein.
Ornithological Research at the Prince Edward Islands: A Review of Progress.
W. R. SIEGFRIED. Director, Percy FitzPatrick Institute of African Ornithology. University of Cape Town.
The Mammals of Marion Island: A Review
J. D. SKINNER. Director. Mammal Research Jnstitute, University of Pretoria.
Marine Ecosystems of Marion Island.
J. R. GRINDLEY. School of Environmental Studies. Uni- versity of Cape Town.
SPECIAI.IST SESSIO~ I l\IAMMALOC\'
The Distribution, Abundance and Annual Cycle of Fur Seals (Arcwceplwlus spp.) on the Prince Ed\Htrd Islands
P. R. C'ONDY (S. A/r. J. Wild/. Res .. 8. 159-168. 1978)
A. E. Btll'j!er: Why did you regard the fur seal counts by De Villicr~
and Ros~ as unreliable "hi le those by Rand arc acceptable·?
Reply: The 1972,3 counts of De Villicrs and Ross arc unreliable for three m:1 in reasons: first, some counts were made too early to obtain a true rcllcction of 101:11 pUJ) production, •incc the birth season la~t~ into February: second. they did not censu~ parts of the
"estcrn coastline. ~uch as Triegaardt Ba). \\here significant number\
of seals occurred in 1974 and fimdly their 1973 pup CQunts we•·c, in some instances, less than 25 per cent of my counts in 1974.1 do not believe that pup production in some colonies could increase by
75 per cent in one )Car. Rand'\ 1951 2 data. \\hich ''ere based on bull and not pup counts, arc abo ~omc,,hat incomplete. Howc\cr, as he visited all parts of the coast where breeding occurred on about 11 different occasions between November 1951 and April 1952 and had conc;idcrable cwcrience at cen<;using \Cals.
r
con~idcr his data to be much more reliable.V R. Smirh: ln my opinion De Villiers and Ross did not cover the area a<; thoroughly as Rand or Condy. and De Villicrs' counts \\Crc on an opportunistic ba~is as he ''as primaril) concerned ''ith the island\ intertidal ecolog).
J. Vi.,.ler: Do you know how long the 1\\0 species of fur seals have been S) mpatric on Marion bland?
Reply: No. I ha\e no idea ho'' long thb situation has existed.
However. in the summer of 1951/2 Rand collected one 'pecimcn of A. ga:e/la, but whether this \\a~ a stray onimal or part of a small breeding population one cannot ~). In any e,·em, it \\Ould 'ieem that A.ya:ella ha~ occurred on Marion Island since at least 1951 2,
numhcr~ apparently having increased mainly during the past 10 years.
The Distribution and Abundance of Southern Eler>hant Seals Miro1111g(l leonina (Linn.), on the Prince Edwarcl Islands P. R. CON DY (in this volume)
V. R. Smirh: As~uming a the per cent per annum decline in ele- phant seals on Marion Island. how often would ccn·;;u~e.s have to be carried out and at what inten·als in order 10 confirm this figure with
~tatistical conlidencc '!
Reply: ldeall). ce1hu~es of the pup crop ~hould b.: carried out annuall) and these data could b~ smoothed over i\n1 or three year periods ~o that at least two such s~:ts of data were r~cquired. Alter- natively. a census could be carried out e\·cr) ~econd or third year until at least three ~et~ of data ''ere dc,clop<!J. Three consccuti\e annual censuse:. would give an indicatiQn of short-term c;1angc, but ideally data should span a longer period than that.
P. Fm.H: Do you ha'e an) information on the e'tcnt of co:11111Cr- cial fishing at or near Marion bland?
Reply: To the best of my knowledge there i~ no commercial 11shing at or near Marion bland. I belie'e that there is commercial fishing in the 'icinit~ of the French po~~e.>,ion, of the Cro£et and Ker- guelcn ;1rchipelago~. Since it -,cems that the \1 hole Kerguclen ele- phant 'cal stock, which includes the Marion Island population <h
defined by La\v~. i-. declining, thi~ commercial fi~h<!1 y may be im- plicated in the elephant seal decline.
G. Nc•"·man: Commercial n~hing activitie:-. at MariPn Island arc negligible and a decline in fi-,h availabilit). due to li~hing. i.., not likel) w explain an) decline in elephant \Cal number-, at the io;land.
if foraging is confined to the' km it) of the i~land. Information on change> in the frequency of ~iller whale~ around the island could shed more light on the question. if such information is availabk.
Rep(!: During the ~ummcr months m(hl of the ,cal-,, cspeeiall) those aged bet\\een I and 5 months, probably hunt rca~onabl)
close to the island. From April to Sertcmbcr. mo;,t nre living pcla- gically ~omcwherc in the ocean, possibly on the Cro£et Platenu, wher.: apparent!) there i, a commercial !1-,hel). \\'ith regard to
killer '' hales, there arc no data on long-term change, in numbers and frequency of occun:nce. During my ~tudy from 1973 to 1975, they were being 'een oil' the base si<llion on a\eragc e'ery third da) from No' em her to Januar). and Rand commented that they were ·occa~ionall) · ~een during the summer of 1951 2. Ra-;cd on thi-..
then: M:cms to be 'ome indication that the frequency uf their vi~ih.
but not necess:.rily th.:ir numbers, has incr.::~sed but this is specula- lion.
120
1. Visser: What is the diei of ''caned elephant seals?
Reply: l do not kno'' \ince no ''caned elephant seal~ \\ere culled or $IOmach-pumped. However, since they appear to remain close irv;hore for the lirst momh al"ter weaning. I suspect they would feed on in~hore .,pccies of lhh and po~sibl) ~quid.
J. D. Skilllll!r: Do you have any idea \\hen the decline in elephant
~ea I number~ commenced?
Rep~r: Total pup production in 1975 ''a~ appro,imately 69 per cent lower than Rand\ estimate for 1951. Vnn Zinderen Bakkcr .lr.
counted birth~ at four beache; in 1965, and in 1975 numbers of birth> at the.,c beachc' ''ere do'' n b) approximately 48 per cent.
Rand ga'e pup numbers for only one of these beaches and by 1965 Van Zindercn Bakker"s estimate was down by approximately 16 per cent, so the decline was probably in progress by 1965.
Annual Food Consumption and Seasonal Fluctuations in the Biomass of Seals on Marion Island
P. R. CON DV (Mammalia, in press)
R. J\f. Laws: You slated that A.tropica/isconsumcd a ~mall amount of \..rill. What made :,ou conclude this and do )OU kno'' "hat species was being con~umed?
Reply: In some stomach> pinkish lluid and what appeared to be
e\O~I..eleton remain~ of a euphau~iid ''ere obsencd. and this led me to belie'c that atlea~t <;ome ·krill' "a~ beingconwmed.l do not know what species w<b involved and do not yet have enough evi- dence to implicate £uplwusia superba.
J. R. Griudley: In March-April 1976, J:l tooplankton ~mples
\\ere collected at ditrerent stations in the vicinity of Marion bland.
The Euphausncca were quite well represented in these samples, but
\\ere all ju,enile and the ~pecie~ ha'e not been determined. Some earlier work I did north of Marion Island indicated that Euplum- sia .1pinijern was the commone~t ~pecies there. £. supNhn was nor
prc~ent in any of the Jailer samples.
P. Fr11.11: In your anal)~es of the diet of the three :,eal species. how did you determine the percentage composition of the prey -by frequency of occurrence. by \Oiume or by mass?
Reply: The data presented here ''ere based on frequency of occur- rence. In about 30 per cent of cases stOmachs were entirely empty and about 40 per cent contained only stones. No stomnchs were full de~pite attempl' 10 collect rcccntl) hauled-out seals. With the fe"
remaining ~tomach~ containing ~ome recognisable prey rcmnins, J considered that mass and volume data were less m..:aningful than frequency of occurrence. However, mass but not 'olume wa!> al~o
recorded.
The Distribution and Density of the Feral House Cat (
re•
lis catus) on Marion IslandR . .1. VAN AARDr (S . . lji·. J. illltarct. Res .. in press)
Rc1Jroduction and Po1Julation Ecology in the Feral House Cat (Fe lis ea/us) on Mar ion Island
R. J. VAN AARDE (Carni1·. Cienet. i\'ews/1 .. 3. 288-316. 1978)
The Influence of Felin~ Panleucopaenia on the Feral House Cat Population on Marion Island
B. H. ERASMUS (unpublished)
R. 1\'. Pienaar: 1, there any likelihood that the cab would C\'Cntually
build up an immunit) to the' iru., '!
Reply: A partially in11nun.: population of cats mn) result in the
cour~e of time. Some indi\'iduab may ha'e a natural resistance and a degree of immunit) ma) be tran~mined from immune female, 10
their oll'spring. Up to 1)()\\, l\~O of the 96 carrier cat'> ha'e been captured and one re5ighted. Thi' represents about three per cent
~urvi\al rate a long time after infection. Serological test~ being
S. Afr. T. Antarkt. Nav .. Deel 8. 1978
conducted at present should :.hed further light on the presem c\lent of immunity in the population, but it appears to be very low.
Gene Frequencies in the Cat Population of Marion Island T. J. ROBINSON and R. J. VAN AARDE (unpublished)
P. Frost: You propo~ed a thermoregulatory advantage for black coat colour. Do you ha'e data to support this? Might there also be an advantage due 10 cryptic coloration, since the cats apparently hunt mostly at night?
Rl'ply: We ha,·e no direct e' idcnce to support this hypothesis.
which is an attempt to explain our results. As to whether cryptic coloration could be involved. it seems unimportant since cats hunt frequently during the day and frequently enter burrows to catch their prey. so little stalking is involved.
N. N. Pienaar: ls there any evidence that the mo~t likely kitlens to
~un ive "ould be the darker coloured ones?
Rep~r: There arc no data as yet on the selective monality of kiuens.
SPECIALIST SESSIO~ 2 J\1ARINE BIOLOGY
Littoral Zonation on Marion and Prince Edward Islands J. R. GRINDLEY and A. F. DE VILUERS (unpublished)
/t N. Pienaar: You mentioned the presence of Macrocy.rtis pyrifera and its epifauna in your re,·ie\\ of marine biological ~tudies.
but I did not :.ee it referred to in your diagrams of littoral zonation.
Why has it been omiucd?
Reply: Unlike the South African kelps. \\hich extend continuous!}
off\hore from the intcnidal zone. the Marion Island kelp species form two distinct bands. Dun-illea amanrica is intertidal, while f\1/acrocysris pyrifera occurs in deeper water ofl"shore and not in the lilloral zone~ shown in these diagrams.
J. D. Skinner: This may be too complicated to answer here, but
"hat factor~ cause speciation in liuoral organisms?
Rt•p~l·: I presume )OU are comparing the relati,ely low species
di~ersiiy and low endemism of the Jvtarion Island fauna to those of the Crozct Islands or Kcrguelen. I am sure that in addition to the gcologicall) younger age of Marion .Island, we arc concerned here
\\ ith limited habitat di,ersity and fc,\er opponuniuc~ for isolation.
The Crozcl and Kcrguclen island groups are both older and more complex. on·ering po~!>ibilities for separate isolation~ and for refuges from glaciation. Such features mu~t fa, our speciation and probably help to account for the greater diversity and endemism there.
R. \'. Pienaar: Could )OU gi'e me some idea of the abundance of corralinc red algae around Marion Island?
l?etlly: There arc several species of corallincs. including species of Corallirw. which arc common in the ~ub-littor~tl area, and pink
cncru~ting lithothamnia arc prominent.
R. N. Pienoar: What species of Porphyra occur on the island?
Rt•ply: The wecies of Porp!t)Tll ha> not yet been determined but it appears similar 10 Porphyra mpt•nsis.
1?. N. Pienaar: HO\\ stable are the boulder beds that you described"!
Rep~1·: The) arc not ~table during storm!> for boulders may be seen
\\ith cncru:.tations in abnormal position~ and the .. maller rounded bliUidcrs can be heard rattling in the surge of the surf. Nevertheless
llll.hl of the larger boulders appear to maintain their position~ for
~ub,tamial period~ and dc,·elop zonation panern~.
R. N. Pienaar: Do you find any member., of the Fucales around the i~land?
l?eply: The genus litm.> doe~ not occur on Marion Island. The kelp Dun•il/eu Ulllarctica is a member of the Fucalcs and plays a very important role on the shore., of the i~land.
S Afr. J. Antarct. Res .. Vol. 8., 1978
Zooplankton Around Marion and Prince Edward Islands J. R. GRINDLEY and SUE B. LANE (C.N.F.R.A .• 44.
111·125. 1979)
!?. Jvf. Laws: Your evidence for upwelling is related to the presence of Antarctic species in a sub·Antarctic area, but a number of Antarctic species. including Euphau~iacca and Chaetognatha amongst others. do occur in the sub-Antarctic.
Reply: Yes but the species of Copepoda involved here are rarely encountered in the sub·Antarctic, and then only in deep waters. so there appears to be clear e' idcnce for upwclling of Antarctic water.
B. Hwuley: Ts there any evidence of seasonal variation in the specie~
composition of zooplankton occurring around Marion l"sland? Reply: We do not have sufficie111 data as the sample~ on which thi~
study was based "ere all taken in one season. Howe,er, two addi·
tional samples which I took later in 1976 had the same group or species present.
V. R. Smi1h: Were there ob' ious difrerences in primary and secon- dary production rates of biomass between the waters of the east and west coasts of the island, indicating upwelling of the West \'Vind Drift due to the island shelf?
Reply: Due to the stormy nature of the sea '~est of the i)iand. it "a~
not possible to sample there, so comparison cannot be made at present.
SPECLALIST SESSION 3- ORNITHOLOGY
Mineral and Energy Contribution of Petrels (Procellariiformes) Killed by Cats to the Marion Island Terrestrial Ecosystem.
A.
J.
WILLLAMS (in this volume)Mineral and Energy Contributions of Carcasses of Selected Species of Sea birds to the Marion Island Terrestrial Ecosystem.
A. J. WILLIAMS, A. E. BURGER and A. BERRUTf (in this volume)
Mineral and Energy Contributions of Guano of Selected Species of Birds to the Marion Island Terrestrial Ecosystem.
A. E. BURGER, H. J. LINDEBOOM and A. J. WILLIAMS (in this volume)
P. R. Co/l(ly: Of what significance to the island's eco~ystem is the energy released from guano?
Reply: Solar energy b by far the most important source of energy for the Marion Island ecos)~tem. The energy in the guano i~
nevertheless an important source of energy for the large micro- organism and invertebrate detritivore populations in the soil and peat at penguin colonies. By ingesting guano and guano·derived
product~. these organisms can make use of much of the cnerg) in guano.
.!. R. Gri111fley: Is the llgure for energy conh:nt of guano nm mainly of academic intereM '? Surely the major importance of guano is it\
mineral content, '~hich. b) increasing primal) producti' ity. will result in the trapping of solar energy through photO~ynthesis far exceeding the energy release from guano?
Reply: The micro-organisms are important in metaboli-,ing certain mineral clcmems. notably nitrogen. into forms "hich can he assimilated by higher plants both on land and at sea. In the light of our present knowledge I agree that the mineral contributions from guano arc of greater importance than the energy comribution to the
island·~ ccO~)'~tem, hut the energy comribution ~hould not he ignored.
Mineral and Energ~ Contributions of Feathers Moulted b) Penguins. Gulls and Cormorants to the Marion Island Terres·
trial Ecosystem.
A. J. WILLIAMS and A. BERRUTJ (in this volume)
121
Mi.ncral and Energy Contributions of Eggs of Selected Species of Seabirds to the Marion Island Terrestrial Ecosystem.
W. R. SIEGFRI!::.D, A. J. WILLIAMS, A. E. BURGER and A. BERRUTJ (in this volume)
Terrestrial lm·ertebrates: A Food Resource for Birds on Mar ion Island.
A. E. BURGER (in this volume)
B. H. £rasmus: ln relation to soil aeration, what b the vertical distribution of earthworms in the soil?
Reply: Virtually all earthworms were found in the upper four centimetres of ~oil or peat. On Marion Island earthworms do not appear to make permanent burrows nor leave surface casting:. and they probably have very little aerating influence.
R. N. Pienaar: b it possible that Bledmum ferns have toxins which make them inedible 10 terrestrial invertebrates?
Reply: To my knowledge this has not been tested, but as some ferns do ha vc toxins. Blec/mum pen11a-marina may also contain toxins that have this efl'ect.
E. M. •·an ZinderM Bakker (Sr): How rapidly do the mires recover after being foraged upon by sheathbills and gulls?
Reply: Mires were foraged upon mainly during winter and by the follo"ing winter mo~t were rc,egetated. A longer rccO\ery period may be neces~ary to restore the original vegetation communities in full.
V. R. Smi1h: The information given in thi~ paper partially anS\\Crs the questions about the importance of energy in guano. The very high density of invertebrate detritivores found in vegetation com·
munitics influenced by guano deposition must surely be related to the increased energy available to these communities.
Ccphalopod Prey of the Sooty Albatrosses Pfloebetria fusca and P. palpebra/a on Marion Island.
A. BERRUTI and T. HARCUS (in this volume)
A. £. Burger: Is it possible tO sample remains of smaller squid beaks in the faecc~ of albatros~es, or arc they completely digested?
Reply: We round no squid beaks in the fa<.-ces of albatrosses.
P. R. Co11dy: What were the reasons for not taking any study specimens of sooty al b:~trosses?
Reply: The population of light-mantled ulbatrosse~ i~ too small to support \latistically adequate sampling for a comparathe anal)~is of stomach content~ of both species. Seven adult sooty albatrosses were collected for other research purposes, but most of the stomachs were empty or contained onl) a few cephalopod remain~.
P. R. C'11111~'·: In th.: absence of ~uch sample.;, how can you be ~urc
that the diet of ~OliiY albatro,,c., consist& mainly of squid, as you ha ,.e ~uggcsted?
Rep~•·: Onl) food' "ith hard pan~ "ere represented in casts, and the proportion of soft food~ in the diet i~ not known. Fish, krill and bird remains were found in the casts. but only rarely, nnd the cast~ consbted almost cmirely of cephalopod remains. An analysi~ of the stomach content~ of adult ~ooty and light-mantled albatro~~c~
by Mougin sho" ed that cephalopods were the most important food of both species. The few food remains that I found in sooty alba·
trosse'; ~tomach> were entirely of cephalopod origin.
./. R. Gri/1(/ley: Your data on ccphalopod prl.!) specie~ do not ~ecm 10 indicalc a marked d illerence in the diet of \OOty and I ight·mantlcd albatros,e>. Thi~ i~ remarkable in the light of their distribution.
which i~ apparent!) mainl) Antarctic for the light-mantled and sub-Antarctic for the ~ooty. bit the binh' temperaiUrc tolerance~, perhap~ during 1 he breeding season, rather than their food, which is producing this pattern?
12~
Reply: Yes, it is probable that this and other adaptive character- istics, such as nest site preference, influence the distribution of the species.
J. Visser: Do albatrosses have preferred feeding times?
Reply: They apparently obtain most of their food at night. when their prey migrates to the sea surface.
P. R. Com(y: Considering the decline in numbers of sperm whales which feed mainly on squid, has there been any increase in the numbers of sooty albatrosses?
Reply: I do not have enough data to indicate whether recently there has been an increase or decrease in population numbers.
W. 1?. Siegj{·ied: What is the relevance of bioluminescence of squid in relation to the method of prey capture?
Reply: Many squids are bioluminescent, and many migrate ver- tically upwards to the sea surface at nighi. Therefore albatrosses, which apparently catch most of their prey on the surface at night, may make use of the luminescence to detect squid.
Seabird Distribution and the Transport of Nutrients to Ter- restrial Ecosystems.
P. G. H. FROST (S. Mr. I. Antarct. Res .. in press).
G. Newman: Estimates of biomass based on ship-board sightings could be biased by visibility, attraction to ships and the likelihood of duplicate counting. Can these problems be resolve:!?
Reply: Jt is diflkult to account for difterences in conspicuousness between species. Attempts have been made to develop visibility indices for different species, but in my opinion use of such correction factors contributes further uncertainty to the record~. However, one can distinguish between those birds seen closer to the ship than, say, 300 m from those seen farther away, up tO about I km from the ship. Biomass densities for the smaller, less conspicuous species can be calculated on the basis of the number of individuals seen within the 300 m wide search path. and for larger species on the basis of a I km wide search path.
The problem of birds following a ship can be partly overcome by making a distinction between birds Hying past the ship in an hour and the maximum number of individuals of habitual ship-following species recorded during the hour. The risk of counting the same birds twice can be reduced by shortening the sample periods. The internationally accepted method of ccnsusing scabirds is based on a 10 minute sampling period, which is probably short enough to ensure that relatively few birds are counted more than once in a
sample .. The problem is more acute when the ship is stationary and
most of my counts were made while the ship was moving. Hopefully, some degree of standardization will be achieved when the SCAR sub-committee on Bird Biology implements its seabird mapping scheme. Then at least biases are likely to be standardized throughout the data.
N. Faira/1: I would like to recommend that. with the increase in ships going down to the southern oceans. we get observers to collect regular data from them. If we could increase the volume of data collected then absolute accuracy may not be all that necessary.
Reply: I could not agree with you more. While I think that the problems of obtaining biomass data are very real. they should not deter us from making attempts at quamifying and comparing bird numbers and biomass. Providing that we state clearly the methods and assumptions used, I see quantification not as an end in itself but as a means to enable a better understanding of the factors aft'ecting seabird distribution and abundance. Seasonal and spatial changes in seabird distribution and abundance should also be monitored in a more systematic manner.
S. Afr. T. Antarkt. Nav., Deel 8. 1978
SPEClALIST SESSION 4- PLANT ECOLOGY AND GEO- MORPHOLOGY
Standing Crop and Production Estimates of Selected Marion Island Plant Communities
V. R. SMITH (in this volume)
R. N. Pienaar: The closed stands of Bledmum penna-nwrina and their relatively high primary productivity intrigue me. Is there any evidence that Blechnum produces some toxin which suppresses local growth of other plant species. as has been demonstrated for another fern (Pteridium)?
.Reply: No work has been done on this aspect but it is interesting that the younger Bfec/mwn leaves are very red, indicating the pre- sence of some interesting substances.
P. 1?. Condy: You mentioned that there was a seasonal peak in the growth of certain communities and you obtained relatively low productivity estimates for some of these. Were your measurements adjusted according to seasonality and do you have any idea what percentage of production occurred before and especially after the peak growing period when new growth is masked by dying tissue?
l?eply. Jn my discussion (see text) the first pan of the question i' partly answered where .1 discuss the limitations of the peak biomass method. My data suggest that about 80 per cent of total annual production occurs before the peak community biomass stage.
P. Frost: Rather than using the peak biomass technique, would it not have been better to sample at shorter intervals and integrate the area under a biomass versus time curve in order to obtain a pro- duction estimate of the communities?
Reply: We did, in fact sample at monthly intervals and the data are currently being treated in the manner you suggest. The problem is that we looked at seven communities, e1ch with about five species and these were divided into 3 to 6 organs. In addition, we sampled between 24 and 40 replic:ts per community and over the growing season this yielded a large body of data which, in view of the markedly dift'erent phenologies of the species concerned, is taking us some lime to reduce tO a meaningful form. In this account the totals of all the species were merely lumped together for the months when maximum biomass and maximum standing crop occurred.
Plant responses to Osmotic Stress in tlte Coastal Zone of Marion Island
V. R. SMITH (in this volume)
J. 1?. Grind/ey: In your work on water potential and osmoregu- lation, is it not possible to use micro-determinations of freezing- point depression as is done in studies of osmoregulation in small invertebrates?
l?epfy: We originally used a frcczing-poin t depression method but found that the results depended on the method of sap extraction.
We prefer to look at the water potential of the leaves rather than osmotic potential or osmotic pressure alone, and the psychrometric method enabled us to determine water potential on leaf discs.
Breakdown of Uric Acid by Micro-organisms and the Jnfiuence thereof on the Island Ecosystem
H. J. LINDEBOOM (unpublished. presented by D. F.
TOERIENl
The Limnology of Marion island. Southern Indian Ocean J. U. GROBBELAAR (in this volume)
Evidence for Three Glacial Episodes on Marion Island with a Reconstruction of the Wiirm-age Ice Cover and Climate K. HALL (unpublished)
S
Afr. J. Antarct. Res., Vol. 8 .. 1978J. R. Grindley: During our 'bit on the /1'/m·ion Du/resne in 1976 "e collected a series of sand samples from the sea bottom for you. t understand that you are able to obtain information relevant to the glacial history of the island from feature.-. of the sand. Could you explain whether an) interesting findings ha~e rc,uhed yet?
Reply: Unfortunately 11nancial limitations ha~c so far precluded scanning electron microscope analyses of the surface texture of
·;and grains from the sample) you collected for me. Kno" ing that the glaciers once extended ofl'shore, it is hoped that grain~ of sand from the bottom sediments, when analysed for mode of transport.
might tell if glacial or glaciofluvial deposits arc present and thereby aid delimitation of the former ice co,cr.
J. R. Grindley: During my stay on Prince Edward Island in 1973, I made some preliminai) observations of what appeared to be evidence of former high sea levels. Ha\e you been able to confirm the existence of marine erosion levels indicating raised sea levels, and if so. how have you interpreted your findings?
Reply: Marine erosion le,els ha\e certainly been recognised around the margins of Marion Island. Levels at c.
+
3,0 m and c. -r 6,0 m were observed around the whole island. whilst extrapolation from a river-long profile indicated the - 6.0 m level and an additional one at c . .; 10,8 m. Le,els of similar ahitudes ha\C been recognised on Crozet, Kerguelen, Livingston Island and in the South Shetlands.On Crozet and Kerguelen they have been attributed to the Climatic Optimum, whilst on the South Shetlands they have been dated within the recent past (c. AD 1200-1650). The levels cut across both the pre-glacial grey lavas and the post-glacial black lavas on Marion Island and thus they must post-date the black lava phase.
No dates are available for these la vas but I suspect that they origi- nated after 10 000 BP and before 4000 BP. 1t is unlikely that the levels are isostatically controlled as they are at a uniform height around the island and cut across se,eral different lavas from the black phase which arc from different emissions. Thus. I would suggest that they also relate to the Climatic Optimum. but this is
~peculation.
ABSTRACTS
Abstracts of papers presented at the symposium. but not published in this volume are listed here.
CONDY. P. R. 1978. The distribution, abundance and annual cycle of fur seals (Arctoceplwlus spp.) on the Prince Edward Islands.
S. Aji·. J. Wild/. Re.1., 8. 159-168.
Alwract: Two species of fur seals, Arcwt·eplwlus 1mpica/i.1' (Gray.
1872) and A. ga:e/la (Peters. J!l75) breed and appeared to hybridize on the Prince Edward i~land~. There \\ere about 7 000 A. 1ropicalis and 200-300 A. ~ta:elln on Marion bland. In A. lmpicali~ parturi- tion took f)lacc between November and February. For A. ~tnzella
birth season appeared to be 2 J weeks in advance of that for A .lropi- calis. On Marion Island O\er 90 per cem of birth~ took place on the windward west coast. There appeared to be some degree (If eco- logical separation on land between the two specie-; on account of difl"erent habitat preference and vocalbation. The population of A. 1ropica/i.l' on Marion Island increased by 10,5 per cent per annum between 1952 and 1975. In A. lmpicalis lactation lasts twice tiS long
<h in A. ga:ella and this. together \\ith the present ~tatus of tradi- tional food resource~. is con~idcred to be of particular significance in the diO'erent population growth rate~ of the two species.
CONDY. P. R. Annual food consumption and o;casonal fluctua- tions in the biomass of seals on Marion Island. Mammalia. in press.
Ab.,·fmcl: Recent population estimates fur the three specie;. of' seals occurring on Marion Island (/1/iroun).!ll /eoninu. Art/OI'f!fJiwlu.\ lropicali.l and A. ga:(•/la) arc a' ailablc. and their annual h;IUI-out cycles ha~e been investigated. These data have enabled estimation of the number of seals of each species that arc hauled-out each month on the island a~ \\ell as ~cat bioma~s hauled-out each month.
Total population biomass for M. leonina was 14 207 x 10' kg. for A. tropicali.1· 2 529 X I 0~ kg and for A. ga:ella 124 :x I 02 kg. Maxi- mum seal biomass occurred on the island in January ( 11 870 ' 102
12~
kg). and from November to April most elephant seal biomass was recorded inland in moulting areas. Annual food consumption for all species was estimated to be 346 353 x I 02 kg. of which M. leonina consumed 82 per cent. Of the total food consumed annually by all specie;. lish comprised approximately 29 per cent. squid 70 per cent, and krill one per cent.
ERAS M US, B. H. The influence of feline panleucopaenia on the feral house cat population on Marion Island. Unpublished manu- script.
Ab.mact: Quantitative data on population siLe. intrinsic growth rate and seasonal fluctuation~ "ere a'ailablc for the Marion Island cat population before feline panleucopaenia (FPL) was introduced.
By assuming that the rate of increase in seasonal population size was exponential, it "as possible to calculate a hypothetical population size for any season. The relationship between number of cats sighted per hour and the hypothetical value gave a straight line equation with the form y I 137x-+ I 610. Thi~ equation was used to calculate a series of expected population sizes, assuming that the influence of FPL was zero. After its introduction, the observed population size was significantly lower than the expected population size. The number of individuals sighted per unit time was 136 per cent les~ than that obser'ved in the pre-FPL sample periods. Litter size remained the same, but IJJ per cent more kittens were sighted before the introduction of FPL. and sightings of groups of cats also decreased after its introduction.
FROST. P. G. H. Sea bird distribution nnd the transport of nutrients to terrestrial ecosystems. S. A/r. J. AIIUirclic Res .. 9, in press.
Abslracl: The di;tribution and abundance of seabirds was studied in the southwest Indian Ocean during March-April 1976. A total of 17 200 birds of 46 ~pecies was counted during the survey. Generally.
birds \\ere sparse!) distributed o"er the ~ubtropical water~ but "ere more abundant and widespread in the sub-Antarctic.: zone. Peak~
in abundance occurred near the islands and in the vicinity or the subtropical convergence (40 S). The estimated bioma~~ density of the sea birds bcmeen 20 and JO S wJs 0.2 kgtkm': betll een JO and 40 S. 1.6 kg/km" and between 40 and 50S. 7.7-10.3 kg/km".
Different species were encountered at dilferent distances from land.
~upporting the hypothesis that closely related ~pecies tend to occur over different water 1.0nes. The distance from land that a seabird must fly to feed during the breeding season is a major determinant of foraging pattern. feeding behaviour. breeding strateg) and social
organi~ation. The hypothesis i~ advanced that these features in turn have an important hearing on the contrihuiion made by each species to the import of nutrients from the marine to the terre~trial eco- 'YStem. principall) through determining the frcquenc) <ll which food i~ brought to the island, the growth rate and energy require- ments or chicks and the duration of the breeding season.
GRINDLEY. J. R. & DE VILLIERS. A. F. Littoral zonation on Marion and Prince Edward !~lands. Unpublished manuscript.
Ab~mu·t: Basic zonation on plane sloping rocky faces c.:on,isted or a black lichen (I ·errucaria) tone in the ~upra-liuoral. a Porphym Lone in the mid and upper I ittoral. a kelp wne of Durvillea nmorc·
1ica in the lower littoral. and a lower red .wne of delicate rhodo-
phyte~ in the upper sub-littoral zone~. Departure from this basic pauern occurred as a result of increa~ed shelter. increa~ed shade
<Jnd decreased stability of substrate. The shallow sub-littoral was characterbed by abundant corallines and other rhodophytcs as well as phaophytes of the genera Desmore.\lia and Dunillea. In part~.
large aggrcgations of the patellid Nacella delesserti "ere found. Pools were infrequent and biota in them vuried with salinity. A wide variet) of invertebrates \\Crc a~sociated with the t..clps Mm·mcys1i1 and Dul'l'illea. Zon<llion conformed "ith the pauern noted on other
~ub-Antarctic islands except Tristan d<1 Cunha. The young age of the island and relatively recent gl;tcial and volcanic activity may account for the paucit) of species and Jm, endemicity.
GRINDLEY. J. R. & LANE, SUE B. 1979. Zooplankton around Marion and Prince Edward !~lands. C.N.F.R.A., 44, 111-125.
124
Abstract: Samples of zooplankton taken at 12 stations around Marion and Prince Edward Islands in March 1976 from the M(IJ·ion Duji-esne and at two stations in the same area in November 1976 from !he RSA have bee:1 studied. Twenty species of Copepoda and a number of other organisms were recorded. The copep.:>d community was Antarctic rather than sub-Antarctic in character. Antarctic species such as Calwws propinqt111.1-, Ca/anoide.1 oculus. Rhincolanu;
gigas, Scolecithricella J.:iaciali.l and Oirhmw frigido were present. while characteristic sub-Antarctic species were scarce. It is suggested that this peculiar species composition results from upwelling in the lee of the islands. The greatest number of organisms per cubic metre of water occurred at depths of between 100 and 175 metres. Some species showed evidence of vertical migration. Zooplankton biomass ranged from 8,7 to 34,9 mgfm3 with a mean of 18,3 mg/ms for vertical hauls ranging from 30-0 m to 300-0 m with a 50 c.n diameter WP If net.
HALL, K. Evidence for three glacial episodes on Marion lsland with a reconstruction of the WOrm-age ice cover and climate. Un- published manuscript.
Absrract: Investigations around the coast of Marion lsland showed that three ti 11 sequences of difrerent ages were present. At locations where thick interglacial deposits of intercalated pyroclasts and lavas did not cover the till, palae.>ols were found. DJtcs from inter- glacial lavas showed that glaciations equate with the cycles D. C and B of Kukla rather than classic Northern Hemisphere classifica- tions. Consideration of the stratigraphic sequences enabled deter- mination oft he succession of stades and inter-stades f ..)reach glacial.
For the last (cycle B) glacial the variation in ice cover is known for the complete time span. Utilising moraine sequences, the former equilibrium line altitude (ELA) was established for numerous glaciers on the eastern side of the island. Using the ELA both snowline and AAR approximations were made. Assigning a range of temperature values lO the snow line, the palaeotemperature of the present-day sea level could be calculated for the cycle 8 glacial maxima. The range of values agreed with those fr..)l11 pollen and deep-sea core analyses.
LINDEBOOM. H. J. Breakdown of uric acid by micro-org:111i3m3 and the influence thereof on the island ecosystem. Unpublished manuscript.
Ahstracr: Uric acid in fresh penguin guano added 10 samples of surface deposits from penguin rookeries is rapidly and completely convened to ammonia by micro-organisms. The rate of this process is sulllc::ient to account for all the guano produced by the penguins.
The seasonal variation in uric acid and ammonium-nitrogen concentrations and of count' of uric acid-metabolizing bacteria in the king ancl macaroni peaguin colonic.> of Kildalkey Bay arc presented. The fate of the ammonia produced is (;onsidered and a.
nitrogen-cycle model of the macaroni penguin colony constructed.
Some conclusions on the effect of the presence of penguins on rates of peat development arc presented.
ROBINSON. T. J. & VAN AARDE. R. J. Gene frequencie~ in the cat population of Marion Island. Unpublished manuscript.
Abstract: The domestic cat Fe/is tarus is p.:Jiymorphic for a number of coat colour. texture and pattern characteristics. of which the mode of inheritance is well known. The cat population on Marioru Island originated in isolation from a limited stock (five animals) ..
S. Afr. T. Antarkt. Nav .. Deel 8. 1978
for which the phenological composition is known. To establish whether selective environmental forces have resulted in selection for a specilic coat colour or pattern. mutants were scored for the autosomal loci controlling agouti and non-agouti, striped and blotched tabby, piebald white spotting and non-spotting, intense and dilute, and short or long hair. Two loci for which adequate data were available for comparative purpascs were the agouti and non- agouti and piebald spotting and non-spotting. Tests between the observed and expected incidence of non-agouti and piebald spotting in the grouped sample, based on the founder frequencies, were significa.nt (P
<
0,05). 1t appears that there has been a significant positive selection for non-agouti and a signilkant negative selection for white spatting. rt is proposed that the extreme environmental conditions experienced on the island have directed these changes.VAN AARDE, R. J. 197S. Reproduction and population ecology in the feral house cat. Felis tarus, on Marion Island. Carniv. Gene/.
Newslt., 3, 288-316.
Abstract: The population and reproductive ecology of the feral house cat was studied using information obtained from direct observations, and from material sampled from animals collected over 18 months. Although primarily asocial. groups consisting of 2-5 (mean 2,65
±
0,95; n=79) individuals were observed. Age- specific sex ratio deviated significantly from unity (in favour of males) in the adult (X2 11 ,59) and subadult (x2=5,54) age classes ( P< 0,05), but juvenile and prenatal sex ratios did not deviate significantly from unity. The sex ratio of animals that died from natural causes did not deviate significantly from unity (x•=2,46).Seasonal differences in daylight length and prey abundance are probably the major factors causing seasonal breeding. Extrapolation of foetal age from foetal mass indicated that mating occurred mainly from July to January. and parturition from September to March. Pregnant and/or lactating females were collected from July to April. Tl:e se:~sonal reproductive pattern of the adult male.
indicated by highly significant seasonal changes in mean teste:; mass, epididymide> mass and tubuli seminiferi diameter, coincided with that observed for adult females. Sexual maturity was attaineJ during the fir5t breding sea30n following birth. Adult fe:nales produced on average two liners per season, with a mean pre:~atal litter size of 4,63 1,07 (n= 14) and at weaning 2,66±0,76 (n=41), indicating a neonatal mortality of 42 per cent. Intrinsic rate of natural increase was calculated as 23,3 per cent per year over a period of 26 years.
VAN AARDE, R. J. The distrihution and dc:-~sity of the feral house cat (Felis cattts) on Marion Island. S. Afr. J. Amartt. R~s., 9, in press.
Abstracr: Feral cats were found lO be well established all round Mar·ion Island, and over an area of 234 km" up to the 450 m contour line. Estimated crude and ecological densities for the coastal and interior regions were 9.75. 13,85 and I ,31 and 4,98 cats per km\
respectively. Cat distribution and habitat preference were influenced by the distribution of their avian prey species. the distribution of the latter being strongly influenced by the availability of soft soil to burrow in. The majority of cats inhabited the coastal region. with the highest densities occurring in grey lava slopes, followed by Cotula hillocks. and areas of vegetated black lava. No cats were observed on barren black lava flows. Extrapolaiion of region- specific density data gave a p::>rulation estimate of 2 137 individuals at the onset of the 1975 breeding season.
