Biol. J. Linn. Soc., 6: '89-96.With 1 figure
June 1974
A biological survey of St. Paul's Rocks in the
equatorial Atlantic Ocean
H. G. SMITH, P. HARDY, I. M. LEITH, V.W.SPAULL and E. L. TWELVES
Division o f Life Sciences, British Antarctic Survey,
Monks Wood Experimental Station, Abbots Ripton, Huntingdon, England
Accepted for publication November I973
In May 1971,an ornithological census was taken, and samples of soil and marine invertebrates
collected, on St. Paul's Rocks-an isolated group of small islands in the equatorial Atlantic
Ocean. Fish were caught nearby. Crabs (Crapsusgrapsus)were abundant on the Rocks and rock
pools contained anthozoa, polychaetes, crustacea and gastropods-a marine invertebrate fauna
apparently closely related to that of Brazil. Specimens of four species of fish were obtained
including one of Holocenmtm sanctipauli, a species endemic to the Rocks.
Protozoa, nematodes, bdelloid rotifen and cuticles of cryptostigmatid mites were found in
the soil; most of the species identified were microbial feeders with a cosmopolitan distribution.
The only terrestrial flora observed were green and blue-green algae and a nematode-predacious
fungus, continuous sea-spray upon the Rocks preventing the growth of higher plants. Breeding
populations of brown boobies and black and brown noddies were observed and counted. The
presence of all life-cycle stages of the booby suggested that its.breeding is seasonal.
CONTENTS
. . . . . . . . . . . . . .
. . . . . . . . .
. . . . . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . . . . . . . .
. . . . . . . . .
. . . . . . . . . . . .
Introduction
Results
. . . . . .
Marine biota
. . .
Terrestrial invertebrates
Terrestrial vegetation
Birds
Discussion
. . . . .
Acknowledgements
. . . . .
References
. . . . . . . .
. . . . . . . .
. . . . . . . .
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
. . . . .
. . . . .
. . . .
. . . .
. . . .
. . . . . . . . . . . . . . . . .
89
91
91
92
93
93
94
95
95
INTRODUCI'ION
St. Paul's Rocks (Penedos de Sio Pedro e Sio Paulo) are a small group of
islands in the equatorial Atlantic Ocean (0°56'N, 29'21'W). The group is
250 m across and the highest point is 19.5 m. The Rocks are pinnacles of a
steep-sided submarine mountain 4000 m high (Speiss, 1928),and are composed
of mylonitic peridotite (Tilley, 1966).They are more than 800 km from South
America, the nearest land mass.The terrestrial, littoral and benthic biota of the
Rocks are therefore extremely isolated and so are of considerable biogeographical and ecological interest.
I
89
90
H. G. SMITH ET AL.
Several scientific expeditions have made landings on the Rocks, including
those of Beagle (Darwin, 1860), Challenger (Wyville-Thomson, 1878), Quest
(Wild, 1923), Meteor (Speiss, 1928) and more recently Chain (Sachs, 1963) and
Atlantis II (Bowen, 1966). Most of the scientific work carried out by these was
geological, but they reported the presence of breeding birds (brown boobies
and noddies), crabs and abundant fish. Darwin (1860) found flies, ticks and
spiders epizoic on the birds. The Challenger expedition made observations on
the marine fauna.
The present paper reports the results of a survey of the Rocks carried out by
biologists from the British Antarctic Survey’s vessel R.R.S.Bransfield when she
was on her return voyage to the United Kingdom at the end of the 1970-71
summer season’s work in the Antarctic. The ship reached the vicinity of the
Rocks on the afternoon of 9 May 1971 and the biologists on board took the
opportunity to make observations and collect specimens of the biota of the
Rocks.
There was a heavy sea swell of 2 to 3 m amplitude around the Rocks so that,
although the wind was light (3.5 mhec), the Rocks were continuously beset by
strong surf and even the highest points subject to heavy spray. These conditions
made landing on the Rocks difficult; however access was gained by approaching
the Rocks from the north-west in rubber dingies and entering the lagoon from
where it was possible to land on Main Rock and East Rock (Fig. 1); the ship
m
t
North Rock
N
Lagoon
Rockpools
* * * * Sill
O
so
100
m
,
Figure 1. Sketch map of St. Paul’s Rocks (after Wild, 1923). The name “Booby Hill” follows
the usage of Wild (1923); the other names are used ad hoc for the present survey. 1,2. 3 , 4 and
5 are stations of marine hvertebrate collections. A is the station of soil sample collections.
A BIOLOGICAL SURVEY OF ST. PAUL'S ROCKS
91
meanwhile was hove to about 1 km to the south-west. Personnel involved
became drenched with sea-spray but, owing to the warm equatorial weather, no
special protective clothing was necessary. The landings were made at 15.30 hrs
(local time) and work was carried out until 18.30 hrs when failing light
prevented further work. Meteorological observations on board the Brunsfield
indicated that during this period the air temperature varied from 25' to 29OC;
the sea temperature was 28OC. Soil temperatures taken on Main Rock at
station A (Fig. l ) , using a right-angled soil thermometer, were 27OC at the
surface and 29OC at a depth of 30 mm.
An ornithological census of the Rocks was taken and soil samples and
specimens of marine invertebrates were collected ashore; concurrently the
ship's launch was used to catch fish just off-shore from the Rocks. Soil samples
were kept at 20' C in sealed polythene containers and marine specimens stored
in 5% formol saline during transport to the United Kingdom for laboratory
examinat ion.
RESULTS
Marine biota
The most obvious marine invertebrate inhabitants of the Rocks were the
numerous vividly coloured crabs, Grapsus grupsus L., which have been
extensively reported by previous expeditions (Wyville-Thomson, 1878; Wild,
1923). The 45 specimens collected showed considerable variation in size and
dimorphism in colour, one having more green in the carapace; the specimens
have been deposited with the British Museum (Natural History). Other
specimens were collected from one quadrat-station in the area of rock pools on
Main Rock and from four stations in an area of channels 20 m north of the
rock pools (Fig. 1). These areas were continuously flushed by sea-water which
broke over the south and west rim of the Rock onto the plateau of rock pools
about 3 m above MTL, then drained over a sill on the east side of the Rock
(Fig. 1). Loose pebbles and fauna attached to the sides of the pools and
channels were collected at each station, and one plankton-netted sample of
water was taken. Most of the loose rocks bore fine mats of green algae and a
strand of macro-alga was observed in one pool. The water in the lagoon was too
turbid to permit observation of the macro-algae reported by Moseley ( 1874)
and Wild (1923); nor were the corals reported by Masch (1966) observed.
Specimens collected from each station are listed below:
STATION 1: Shallow rock pools, 1 m2 in area, freely flushed.
Polychaeta: Spirorbinidae, Junuu (Junuu) pugensfechi (Quatrefages) (many)
Syllidae, Eusylinae sp. (1 specimen)
Copepoda: Nifocru uffinis uffinis Gurney (2 specimens)
Amphipoda: Hyalidae, Purhyule huwuiensis (Dana) ( 3 2 specimens)
Gastropoda: Fissurellu sp. Farfante (2 specimens)
Megagstropoda protospirals (many)
STATION 2: Long narrow rock pool up to 25 cm deep, freely flushed.
Pisces: Holocentrum suncti-pauli Gunther ( 1 specimen)
92
H. G. SMITH ET At.
STATION 3 : Narrow rock pool, 60 x 25 cm, up to 25 cm deep, continuously
filled with spray, occasionally swamped.
Polychaeta: Janua (Janual pagenstecheri (many)
Syllidae, Syllis (Syllisl sp. (Savigny) (2 specimens)
Amphipoda: Parhyale huwaiensis (1 3 specimens)
Gastropoda: Fissurella sp. (2 specimens)
Megagastropoda protospirals (3 specimens)
STATION 4: Narrow channel, 10 cm deep, continuously flushed, occasionally
swamped.
Anthozoa: Actinia sp. (new species?)
Polychaeta: Janua (Janua) pagenstecheri (many)
Amphipoda: Parhyale hawaiensis (10 specimens)
Gastropoda: Vermetidae sp. (1 specimen)
Megagastropoda protospirals ( 5 specimens)
STATION 5 : Vertical sided channel, 5-10 m deep, continuously damp with
spray or waves.
Brachyura: Plagusia depressa Fabricius (1 specimen)
The empty shells of two Serpulidae were found, one probably Protoleaospira
sp. (Station l), the other possibly Placostegus tridentutus Fabricius (Station 3 ) .
Three species of fish were obtained with lines from the ship's launch lying
off the Rocks:
Ballistes buniva Lac. (Triggerfish)
Carcharhinus limbatus Muller & Herle (Shark)
a r a n x ascensioni Forst. (Jack)
These species have been previously recorded by Gunther (1880). Difficulty was
experienced in obtaining these specimens as fish once hooked were frequently
taken by marauding sharks before they could be brought on board.
Terrestrial in vertebrates
Five samples of soil were taken from Station A, Main Rock (Fig. 1) total
weight 250 g. The soil was fine gritty material composed of weathered rock and
fragments of arthropod skeletons enriched by the excreta of sea-birds. It had a
mean pH of 6.6 f 0.5 and a loss on ignition (after ashing in a muffle furnace at
45OoC for 10 hours) of 13.5 k 0.4%dry weight.
Protozoa, nematodes, rotifers and cuticles of acari were observed in the
samples.
The presence of protozoa on the Rocks was recorded by Sandon & Cutler
(1924) wha analysed a sample of soil collected by the Quest expedition in
1921. They identified five flagellate, two rhizopod and one ciliate species. The
present samples were analysed for protozoa by inoculating 2 g portions onto an
agar base with Aerobacter aerogenes (NCIB 418) as food supply. Cultures,
moistened with sterile 0.5% NaCL, were incubated at 25'C and examined
periodically for protozoa. Slides of the soil material were prepared by
Couteaux' method (1967) and examined for testate amoebae. The following
protozoa species were observed:
A BIOLOGICAL SURVEY OF
ST. PAUL’S ROCKS
93
Mastigophora
(none observed)
Rhizopoda-Amoebida Astramoeba radiosa Ehrenberg
Rhizopoda-Testacida Corythion dubium Taranek
Euglypha laevis (Ehrenberg) Perty
Phryganella acropodia Hertwig 8c Lesser
Ciliata
Colpoda cucullus Muller
Cyclidium glaucoma Muller
Euplotes sp. Ehrenberg
Oxytricha fallax Stein
Four species of nematode belonging to the sub-order Rhabditina were
extracted from a soil sample of 150 g, using a modified Baerman funnel
(Whitehead & Hemming, 1965):
Number of nematodes in
150 g (74g dry weight)
Diploscapter cf. coronatus (Cobb, 1893)Cobb, 1913
3039
Acrob eloides sp.
1422
Butlerius sp.
628
Panagrolaimus sp.
109
The Diploscapter specimens agree fairly well with the original description of
D. coronatus (Cobb, 1893) and with the description given by Peters (1930);
they differ however in that the transverse striations on the cuticle are more
marked, especially on the tail just posterior to the anus. The specimens of
Butlerius do not correspond to any known species of this genus. Both males
and females were found in the populations of Butlerius and Panagrolaimus, but
in the Diploscapter and Acrobeloides populations only females were observed.
Numerous bdelloid rotifers were observed, but not identified.
The cuticles of five cryptostigmatid mites were observed. Although damaged,
four of them were provisionally identified as Scheloribates pallidus (Koch), and
the other as Scheloribates sp. (Wallwork, pers. comm.).
Terrestrial vegetation
In the cultures set up to determine protozoa, algae were also observed. A
sample of the culture fluid was inspected by B. A. Whitton, who identified a
filamentous bluegreen alga as Lyngbya sp. (trichomes 1.5 pm wide), and a
small green alga as Stichococcui bacillaris Nigeli. Three other species of green
alga, all with spherical or sub-spherical cells, were also observed.
A single specimen of nematode-predacious fungus was observed, a ring of
three cells constricting the anterior end of a juvenile Panagrolaimus.
No other plant life was observed; as reported by previous expeditions, the
Rocks appeared to be entirely devoid of vascular plants.
Birds
Three species of breeding birds were present on the Rocks:
Sula leucogaster Bodd. (Brown booby)
Anous stolidus Linn. (Brown or common noddy)
Anous minutus Mathews (Black or whitecapped noddy)
H. G . SMITH ET AL.
94
No vagrant species were observed. A census of the three species was taken on
Main Rock and East Rock (Fig. 1). Difficulty was experienced in counting
owing to the topography of the Rocks and human disturbance to the birds;
visibility was hampered by rain and sea-spray. The results of the census are
shown in Table 1.
Table 1. Results of the ornithological census at St. Paul's Rocks
Numbers observed on:
Main Rock
East Rock
S.leucogaster
Occupied nests
Incubating adults
Chicks in down
Fledglings
Egg clutches
32
14
7
11
6 with 1 egg
1
1
0
0
1 with 2 eggs
2 with 2 eggs
A . stolidus
Nest sites
Egg clutches
Chicks
27
0
19
1 with 1 egg
0
0
19
13 (+ 3 uncertain)
A. minutus
Nest sites
Estimates of total populations
on all the Rocks:
c. 200
S.leucogaster
> 200
> 150
A . stolidus
A. minutus
In addition to the eggs and chicks of S.Zeucoguster counted, many juveniles
were observed. Five dead individuals were found: two adults and three
fledglings. It appeared that eggs were lost to the crabs and occasionally to the
wash of the sea. Nests were disturbed as little as possible during counting, so
the relative numbers of different stages in the breeding cycles of the noddies
could not be determined. It is clear from previous expeditions (Mosely, 1879;
Nicoll, 1904) that breeding goes on throughout the year, but its intensity may
vary with the seasons.
DISCUSSION
The biota of St. Paul's Rocks constitute an interdependent community
whose species composition appears to be determined largely by local ecological
conditions. The absence of higher plants is certainly due to continuous
sea-spray on the Rocks. The soil fauna by contrast is surprisingly diverse. This
is probably a result of the substratum, being nutrient-rich from spray and from
guano deposits of sea-birds at temperatures approaching 30"C, supporting
abundant growth of bacteria and algae, which in turn support a diverse
community of protozoa, rotifers and nematodes. The algae identified are
ubiquitous and occur in many soils except the most acid (Whitton, pers.
comm.). The protozoa are all cosmopolitan; they are species typically found in
soil and thrive on a diet of bacteria or algae or both. The nematode genera
A BIOLOGICAL SURVEY OF ST. PAUL’S ROCKS
95
Acrobeloides, Diploscapter and Panagrolaimus are commonly found in
decaying organic debris and are thought to be microbial feeders (Goodey,
1963). At least six of the eleven described species of Bublerius feed on other
nematodes (Pillai & Taylor, 1968; Russell, 1968); Pillai & Taylor found that
one of these predacious species could also be maintained on a mixed culture of
a bacterium and an amoeba. The mite Scheloribates has a cosmopolitan
distribution-including Argentina and Bolivia (Wallwork, pers. comm.).
Of the marine life observed, the jack and shark are active pelagic fish, widely
distributed through the tropical Atlantic Ocean; The trigger-fish, a benthic
species usually associated with rock outcrops is similarly widespread in the
tropics; Holocentrum sancti-pauli is an endemic species of a widespread genus.
The marine invertebrate fauna appears t o be related to that of Brazil, which is
described by Ekman (1953) as “a pauperisation of the rich profusion of the
West Indian species”. The spirorbinid, Janua (Janual pugenstecheri is regarded
as one of the most temperature-tolerant species of Junua, ranging from Norway
to Australia. Some of the specimens collected more closely match the
description of the West Indian form Spirobis epichysis Bailey, but this is now
regarded as indistinctly separate from J. (J.) pagenstecheri (E. W. Knight-Jones,
pers. comm.). The copepod Nitocra affinis uffinis is almost entirely confined to
tropical waters and the amphipod Purhyale hawaiensis is widespread in the
tropical Pacific and has been found in the Caribbean; the brachyuran Plagusia
depressa Fabricius is common in the Caribbean. The limpet Fissurella sp.
closely resembles the Brazilian species F. chenchi Farfante. Ekman’s observation was based mainly on fish studies by Gunther (1880)but it appears to be
true also of the marine invertebrates.
The breeding birds are all fisheating species of the tropical and sub-tropical
Atlantic, St. Paul’s Rocks being in the middle of their ranges (Watson, 1966).
Darwin (1860) recorded that he saw “a vast multitude of sea-fowl” at St. Paul’s
Rocks and Moseley (1879) refers to “birds hovering in thousands”-expressions
which are not consistent with our observations (Table l), so it is possible that
the bird populations have declined; this was the opinion formed by Bowen
(1966). The reasons for a decline are not clear, but it may be owing t o human
disturbance and the gradual erosion of the Rocks by the sea.
ACKNOWLEDGEMENTS
We wish to thank C. M. Bell, H. J. Blackley, 0. H. S. Darling, A. Feenan,
A. C. Skinner, G. J. Soar, R. F. Stocks, R. Tiffin, R. J. Wells and the Master
and ship’s company of the R.R.S.Brunsfield for assistance with the field work.
W e thank also Dr N. P. Ashmole, Dr V. T. Bowen, Capt. K. England, Dr J. D.
George, Dr R. W. Ingle, Prof. E. W. and Phyllis Knight-Jones, Dr K. Thomas,
Dr M. H. Thurston, P. J. Tilbrook, Dr J. A. Wallwork, Dr J. B. J. Wells and
Dr B. A. Whitton for assistance with the identification of specimens and
information on the literature.
REFERENCES
BOWEN, V. T., 1966. St. Paul’s on the subway. Oceanus, 12: 2-4.
COBB, N. A., 1893. Nematodes, mostly Australian and Fijian. Dept Agr. N.S. Wdes, Misc. Publ., 13.
H. G. SMITH ET AL.
96
DARWIN, C.. 1860. Journal of Researches into the Naiuml History and Geology of the Countries Visited
during the voyage of H.M.S. Beagle round the World,519 pp., 2nd ed. London: Murray.
COUTEAUX, M. M., 1967. Une technique d’observation des Thecamoebiens du sol pour I’estimation d e
leur densite absolute. Rev. Ecol. Biol. Sol, 4: 593-6.
EKMAN, F., 1953. Zoogeography of the seas, 416 pp. London: Sedgwick & Jackson.
GOODEY, T., 1963. Soil and freshwater nematodes, 544 pp. 2nd ed. revised and rewritten by J. B.
Goodey. London: Methuen.
GUNTHER, A., 1880. Report on the shore fishes procured during the voyage of H.M.S. Challenger
1873076. Report on the scientific research of the explomtory voyage of H.M.S. Challenger 1873-76.
Zoology,1: part vi, section B.
MASCH, D.,1966. Life on the Rocks. Oceanus. 12: 5 8 .
MOSELEY, H. N., 1874. Notes on the plants at St. Paul’s Rocks. J. Linn. SOC.,(Bot.), 14: 354-5.
MOSELEY, H. N., 1879. Notes by a naturalist on the “Challenger”, 606 pp. London: Macmillan.
NICOLL, M. J., 1904. Ornithological journal of a voyage round the world in the “Valhalla”. Ibis, 4:
32-66.
PETERS, B. G.,1930. Some nematodes met with in a biological investigation of sewage. J. Helminth., 8:
165-84.
PILLAI, J. K. & TAYLOR, D. P., 1968. Butlerius micans n. sp. (Nematoda: Diplogasterinae) from Illinois
with observations on its feeding habits and a key to the species of Butlerius Goodey. 1929.
Nematologica. 14: 89-93.
RUSSELL, C. C., 1968. Taxonomy and bionomics of the nematode genus Burlerfus. Dbs. Abstr., 29: 232.
SACHS, P. L., 1963. A visit to St. Peter and St. Paul’s Rocks. Oceanus, 9: 2-5.
SANDON, H. & CUTLER, D. W., 1924. Some protozoa from the soils collected by the “Quest”
expedition (1921-22). J. Linn. SOC.,(Zool.), 36: 1-12.
SPEISS. F., 1928. Die “Meteor”, 630 pp. Berlin: Fahrt. Reimer.
TILLEY, C. E., 1966. A note on the dunite (peridotite) Mylonites of St. Paul’s Rocks (Atlantic). Geol.
Mag., 103: 120-3.
WATSON, G. E., 1966. Sea-birds of the tropical Atlantic Ocean, Smithsonian identification manual,
120 pp. Washington, D.C.: Smithsonian Press.
WHITEHEAD, A. G . & HEMMING, J. R., 1965. A comparison of some quantitative methods of
extracting small veriform nematodes from soil. Ann. appl. Biol.. 55: 25-38.
WILD, F., 1923. The Voyage of the “Quest”. Ceogrl. J., 61: 73-108.
WYVILLE-THOMSON, C., 1878. Report on the scientific research of the exploratory voyage of H.M.S.
Challenger 1873-76. Narrative, I : 201-9.